SECTION 6

ENGINE ASSEMBLY

CONTENTS OF THIS SECTION

Figure Index
Six Cylinder Engine
Eight Cylinder Engine
Troubles and Remedies
Six Cylinder Engine Specifications
Eight Cylinder Engine Specifications
Assembly Manual

Figure Index

Engine

Index

The six-cylinder engines (fig. 1) used in 1955 Chevrolet Passenger Cars are available in two models. Of similar construction, the differences are in the valve lifters and camshafts. The engine used in standard transmission and overdrive models is equipped with solid valve lifters while Powerglide models are equipped with hydraulic type lifters. The lift of the camshaft is such that in standard transmission models, the gross horsepower is 123 while Powerglide equipped models have 136 horsepower. The engines have a displacement of 235.5 cubic inches, a 3 9/16" bore, 3 15/16" stroke and 7.5:1 compression ratio. The standard shift engines develop 207 ft. lbs. torque at 2000 RPM, and the Powerglide engines develop 209 ft. lbs. at 2200 RPM.

The cylinder head assembly, as installed on the engine, includes the valve guides, valves, valve springs, rocker arm and shaft assemblies, spark plugs, temperature indicator fitting, water outlet, exhaust and intake manifolds and other assembling parts.

The carburetor and air cleaner assembly is bolted to the top of the intake manifold. The rocker arm cover is attached to the top of the cylinder head by four screws and encloses the valve mechanism.

The cylinder block and crankcase assembly is the major section of the engine as it is fitted with the camshaft, crankshaft, timing gear plate, timing gears, pistons, piston rings, piston pins, connecting rods and miscellaneous parts. In addition to the above parts which are part of a cylinder block assembly, the following units are attached to this assembly when in the vehicle-water pumps oil pump, distributor, starter, generator, flywheel, clutch and transmission or Powerglide transmission, harmonic balancer, fuel pump and other miscellaneous parts.

A "V" type fan belt operating from a combined harmonic balancer and pulley on the front of the crankshaft drives the generator, water pump and fan.

The distributor, mounted on the right side of the engine, is gear driven from the camshaft. The oil pump connects to the lower end of the distributor shaft and is driven at distributor speed. The fuel pump mounts on the right side of the engine and is operated by a special cam on the camshaft.

Pistons, of cast alloy aluminum, are cam ground to provide slightly greater diameter at right angles to the piston pin. Pistons have three piston ring grooves above the piston pin bosses. The piston pin bosses are bored 5/64" off-center, a type of construction that reduces the severity of piston slap such as might be encountered in cold engines.

One oil control ring and two compression rings are used on each piston. The oil control ring is composed of four units, an upper rail, a lower rail, a separator and an expander of zig zag type construction. All compression rings are of t e deep section twist type.

The exhaust valves on both models are aldipped on the seat portion to insure long valve life. All valves are of solid alloy steel.

Camshaft bearings are steel backed and babbitt lined, providing uniform expansion and long life. The bearings are installed in the cylinder block and finish bored for precise alignment.

Main bearings are precision interchangeable, thin wall babbitt type with dual advantages of longer life and simplified installation. Babbitt thickness is .003" to .007". This type of bearing gives increased bearing life and at the same time provides satisfactory embedability, or the ability of the babbitt to absorb foreign particles and so prevent scoring.

The precision interchangeability features of the bearings facilitate engine repair as well as engine assembly because the bearings are accurately machined to close tolerances and are ready for installation as received.

The crankshaft has four large bearing journals. It is heavily counterbalanced and weighs approximately 78 pounds, contributing to Chevrolet's smooth engine performance.

The four bearing cast iron camshaft is designed to provide accurate, quiet valve action and hold the valves open long enough to provide complete discharge of the exhaust gases and allow entry of a full charge of fuel mixture. The cams have a wear resisting treatment, which combined with off-center lifters, provide unusually long life and quiet operation, The camshaft is a hi-lift cam design in the Powerglide model.

Connecting rods are of large section, drop forged "I" beam construction for rigidity and strength. The upper end is fitted with a clamp bolt for securely attaching the rod to the piston pin. All connecting rod bearings are of the precision interchangeable insert type.

On standard transmission vehicles, a heavy cast iron flywheel bolts to a flange at the rear end of the crankshaft and a steel ring gear is shrunk on the outer diameter of the flywheel. On Powerglide transmission vehicles, a reinforced steel stamping with a welded ring gear is used. The starting motor drive pinion engages this ring gear when cranking the engine. Flywheel and crankshaft are accurately balanced to minimize engine vibration and the rear flywheel face on standard shift models is accurately machined for clutch mounting.

The front end of the crankshaft is fitted with a harmonic balancer. This balancer consists of a hub pressed onto the crankshaft and a small inertia weight riveted to the hub, interspaced by two rubber gromments. This rubber mounted weight is tuned to resist quick changes in crankshaft speed caused by the power impulses, and thereby dampens out or absorbs crankshaft vibration.

The same cylinder head is used on both engines and is designed to provide 7.5:1 compression ratio. Large water passages in the head provide adequate coolant capacity for efficient engine operation. The valve rocker cover attachment is provided at the gasket ledge through four screws, located midway between the center and/or front and rear of the cylinder head. This attachment provides excellent gasket sealing and valve operating noise suppression.

The intake manifolds are circular in cross section and are mounted to the engine with the main passage parallel to the ground.

The exhaust manifolds are designed to reduce back pressure to a minimum. Located on the inside of the exhaust manifold is the thermostatically operated heat control valve. This valve directs the hot exhaust gases against the center of the intake manifold when the engine is cold as shown at the left of Figure 2. As the engine warms up and engine speed increases, the thermostatic spring closes the valve and directs the exhaust gases away from the intake manifold as shown at the right of Figure 2. This thermostatic control results in the proper temperature of the incoming gases under all operating conditions.

A full pressure lubrication system is used on all engines. A gear driven oil pump maintains 35 psi pressure lubrication; it is equipped with a spring loaded by-pass valve to control maximum pressure at high speeds and when engine oil is cold and sluggish during cold weather starting. The engine pressure oil system is designed to provide positive lubrication of all moving parts ( fig. 3). Full pressure lubrication to the main and camshaft bearings is provided by oil flow from the oil pan through the floating pump screen to the oil pump to a block fitting and then to the oil gallery. From the oil gallery the oil passes through drilled passages in the main bearing support webs of the cylinder block to the four main bearings. The oil then passes through grooves in the bearings to passages drilled in the other side of the cylinder block webs and on to the camshaft bearings. The crankshaft also contains drilled oil passages connecting the main bearing journals with the crank-pins which provide positive pressure lubrication for the connecting rod bearings.

Timing gear lubrication is supplied by conducting oil through a milled slot in the rear surface of the engine front plate from the front camshaft bearing to a nozzle extending out from the front and so aimed that an oil stream effectively lubricates the timing gears.

Pistons and cylinder walls are lubricated by the oil spray thrown out through spurt holes in the connecting rods and bearings. Piston pin lubrication is maintained through two drilled passages in the top surface of the recessed piston pin bosses.

Lubrication of the valve mechanism is supplied by a drilled passage from the rear camshaft bearing to the pipe located under the push rod cover to a fitting at the top of the cylinder block. The oil then flows through a passage drilled in the cylinder block and head to the valve mechanism oil connector pipe between the two hollow rocker arm shafts, then distributed to all rocker arm bearings. A bleeder hole in each rocker arm supplies oil for lubrication of the valve stems and push rod sockets.

Lubrication control of the inlet and exhaust valve stems is provided by an oil seal. A synthetic rubber seal is assembled between the valve stem and the valve spring cap. An extra groove is provided on the valve stem to accommodate this rubber seal. Both seal and cap are interchangeable between intake and exhaust valves. Valve stem tips are hardened and finished to reduce wear and noise from contact with the rocker arms.

The engines used in models equipped with Powerglide transmission have hydraulic valve lifters that provide a means of automatically maintaining zero valve lash or tappet clearance at all times.

A direct oil feed is maintained to the lifters at all times through a 9/16" oil gallery which runs the full length of the engine. This gallery goes through the center of each valve lifter bore and intersects an oil passage drilled in the block from the rear camshaft bearing. Whenever lash tends to be present, the plunger spring expands, pushing the plunger until solid contact is made with the push rod and linkage. This creates a difference in oil pressure on either side of the ball check valve, the lower pressure being below the plunger. The higher pressure above then forces the oil to flow to the chamber below the plunger until the pressure is equalized. When the lifter is raised by the cam, the oil pressure is increased below the plunger, and forces the ball check valve against its seat. The oil space then becomes a hydraulic ram and is effectively a solid link in the mechanism to lift the valve. There is a certain controlled amount of oil leakage between the plunger and lifter body while the engine valve is open. This controlled clearance is necessary to the operation of the valve train. It permits positive valve closing even though the valve train effectively changes length during warm-up and operation.

Care, Maintenance and Adjustments

Engine or under hood maintenance is divided into three categories, routine inspection, periodic maintenance and tune-up. Each category serves to insure the maximum in performance, economy and long life built in to the Chevrolet engines.

ROUTINE INSPECTION

The routine inspection operations are those items which should be checked at regular intervals, determined by the service condition of the vehicle and varying from daily to semi-monthly. The engine oil level should be maintained between the "Full" and "Add" marks on the dipstick. The battery electrolyte level should be maintained at the bottom of the split rings in the battery filler openings, by the addition of distilled or demineralized water. The cooling system fluid level should be maintained one inch below the bottom of the filler neck on the radiators with a cold cooling system or at the bottom of the filler neck when the system is warm. These three checks are important to prevent damage to the battery and engine and should be made as frequently as driving conditions demand.

Periodic Maintenance

The periodic maintenance includes those items requiring service at the regular 1000 mile lubrication operations. As called out in the Lubrication Section of this manual, these items are the starter solenoid, crankcase breather, generator and distributor. In addition, an engine crankcase oil change and air cleaner element cleaning is recommended every 2000 to 3000 miles as discussed in the Lubrication Section of this manual.

ENGINE TUNE-UP

One of the most important duties to perform on modern high compression engines is proper engine tune-up. This operation more than any other determines whether or not the vehicle will produce the maximum amount of performance with the greatest amount of economy. Only by performing these operations and staying within limits, clearances and specifications, is it possible to obtain the performance and economy built into the Chevrolet engine.

Tune-up operations should follow a definite procedure. A process of elimination by checking each individual component one by one is costly and time consuming. A fast, high-quality tune-up can be performed, using a group of test instruments designed specifically for tune-up work. By combining tune-up operations with testing operations, only the necessary items need be serviced and top performance will be assured with a minimum of time and cost.

Before making any checks on an engine, it should be run for several minutes and allowed to warm up and normalize. This assures proper lubricant vicosity at each engine component and that engine components will be at their operating temperature and size.

In each of the following tests and operations, a visual inspection should always be made for unusual or out-of-line conditions.

Cranking Voltage Test

The cranking voltage test checks the starting mechanism and circuit as well as the ignition primary circuit to the coil and will check to see that the coil resistor is shorted out during cranking.

1. Connect a voltmeter of approximately 16 volts capacity with the positive lead to the positive or battery terminal of the ignition coil and the negative lead to a good ground.
2. Remove coil wire from distributor cap.
3. Turn ignition switch to on position, note meter reading and then turn switch to start position. Check engine for 15 seconds and read voltmeter while still cranking.

With the switch in the ON position, the meter should indicate 5 to 7 volts. If it does not, refer to the Engine Electrical Section of this manual for further checks. With the switch in the START position, the meter should read 9.0 volts or better with a good rate of cranking speed. If the reading is below 9.0 volts or the engine cranks slowly, further tests must be made to determine the cause. The Engine Electrical Section of this manual outlines the battery testing, starter circuit testing and ignition primary circuit testing procedures.

Battery Hydrometer Test

In normal operation, a charging system in good condition should maintain the battery in at least a 3/4 charge condition. A hydrometer test should show a specific gravity of at least 1.215 or better and a maximum variation between cells of 0.025 gravity points. If either of these two specifications are not met, the battery and charging system should be thoroughly checked and tested as outlined in the Engine Electrical Section of this manual.

After the hydrometer check, the electrolyte level should be brought up to the bottom of the split-rings in the filler openings. If there is evidence of acid, dirt or resultant corrosion on the top of the battery, the top should be cleaned with ammonia or soda water and flushed with water. Exercise care not to get solution in the filler holes through vent holes. If the terminals show corrosion, they should be removed and the terminal and posts thoroughly cleaned. The posts and terminals should be completely coated with petrolatum and then reassembled and tightened securely.

Compression

The compression of each cylinder should be checked, because an engine with uneven compression cannot be tuned successfully to give peak performance.

1. Remove any foreign matter from around the spark plugs, and then loosen them about one turn to break free any accumulation of carbon.
2. Start engine and accelerate to 1000 RPM to blow out the carbon. (Starting and accelerating the engine after the plugs are loosened is extremely important in preventing false compression readings due to chips of carbon being lodged under the valves.)
3. Stop engine and remove spark plugs, placing them in order that they were removed.
4. Block throttle in wide open position.
5. Insert compression tester in a spark plug hole.
6. Crank engine with the starting motor until the cylinder being tested passes through four compression strokes.
7. Repeat this test on all cylinders and record the compression reading of each cylinder.
8. Compression on all cylinders should be 130 pounds or better and all cylinders should read alike within 10 pounds for satisfactory engine performance.

Should a low compression reading be obtained on two adjacent cylinders, it indicates the possibility of a leak from one cylinder to the other, usually caused by a leak at the cylinder lead gasket. If the compression readings are low, or vary widely, the cause of the trouble may be determined by injecting a liberal amount of engine oil on top of the pistons of the low reading cylinders. Crank the engine over several times, then take the second compression test. If there is practically no difference in the readings when compared with the first test, it indicates sticky or poorly seating valves. However, if the compression on the low reading cylinders is higher and about uniform with the other cylinders, it indicates compression loss past the pistons and rings. The cause of low or uneven compression should be corrected before proceeding with an engine tune-up.

Spark Plugs

Spark plug life is governed to a large extent by operating conditions. To insure peak performance, spark plugs should be checked and tested frequently and replacement of spark plugs should be made as necessary.

The spark plugs used as standard equipment on all Chevrolet Passenger Car Engines are AC 44-5. If plug fouling is being experienced in a vehicle because of continuous low speed operation, AC 46-5 plugs are available to combat this situation. If excessive electrode wear is experienced in a vehicle because of continuous heavy duty or high speed operation, AC 43-5 COM plugs are available for better spark plug life.

Worn and dirty plugs may give satisfactory operation at idling speed, but under operating conditions they frequently fail. Faulty plugs are evident in a number of ways such as, wasting gas(in extreme cases one gallon in every ten), loss of speed and power, hard starting and general poor engine performance.

Spark plug failure, in addition to normal wear, may be due to dirty or leaded plugs, excessive gap or broken insulator.

Dirty or leaded plugs may be evident by black carbon deposits, or red, brown, yellow or blistered oxide deposits on the plugs. The black deposits are usually the result of slow speed driving and short runs where sufficient engine operating temperature is seldom reached. Worn pistons, rings, faulty ignition, over-rich carbonization and spark plugs which are too "cold" will also result in carbon deposits. These deposits, a consequence of the use of leaded fuel, usually result in spark plug failure under severe operating conditions. The oxides have no adverse effect on plug operation as long as they remain in a powdery state. But, under high speed or hard pull, the powder oxide deposits melt and form a heavy glaze coating on the insulator which, when hot, acts as a good electrical conductor, allowing current to follow the deposits and short out the plug.

Excessive gap wear on plugs of low mileage, usually indicates the engine is operating at speeds or loads that are consistently greater than normal or that a plug which is too "hot" is being used. In addition, electrode wear may be the result of plug overheating, caused by combustion gases leaking past the threads and gaskets, due to insufficient compression of the spark plug gaskets, or dirt under the gasket seat. Too-lean carburetion will also result in excessive electrode wear.

Broken insulators are usually the result of improper installation or carelessness when regapping the plug. Broken upper insulators usually resulting from a poor fitting wrench or an outside blow. The cracked insulator may not make itself evident immediately, but will as soon as oil or moisture penetrates the fracture. The fracture is usually just below the crimped part of the shell and may not be visible. Broken lower insulators usually result from carelessness when regapping and generally are visible. In fairly rare instances, this type of a break may result from the plug operating too "hot" such as encountered in sustained periods of high speed operation or under extremely heavy loads. When regapping a spark plug, to avoid lower insulator breakage, always make the gap adjustment by bending the ground or side electrode. Never bend the center wire. Spark plugs with broken insulators should always be replaced.

Clean the spark plugs thoroughly, using an abrasive-type cleaner. If the porcelains are badly glazed or blistered, the spark plugs should be replaced. All spark plugs must be of the same make and number or heat range. Use a round feeler gauge to adjust the spark plug gaps to .035".

CAUTION: In adjusting the spark plug gap, never bend the center electrode -V which extends through the porcelain center. Always make adjustment by bending the ground or side electrode.

Install the spark plugs in the engine with new gaskets and tighten to 20-25 ft. lbs. torque. If torque wrench is not available, tighten plugs finger tight and 1/2 turn more. Plugs are of a 14 millimeter size and care must be exercised when installing or the gap setting may be changed.

Air Cleaner

1. Remove wing nut, cover and filter element.
2. Wash filter element thoroughly in cleaning solvent.
3. Let element dry and dip in engine oil and allow excess oil to drain.
4. Install element and cover and secure with wing nut.

NOTE: If oil bath air cleaner is used, see instructions under Engine-Fuel.

Manifold Heat Valve

The tension of the thermostatic spring is very important. When too tight, the heat will not be turned off the intake heat riser as the engine warms and speeds up, with the result that the incoming gases will be expanded several times greater than normal and it will be impossible to get a normal fuel charge into the cylinders. This condition will reduce power and maximum speed. Therefore, it is important that the thermostatic spring be wound up just enough to slip its outer end over the anchor pin (fig. 4) and no more. This is approximately 1/2 turn of the spring from its position when unhooked. Sometimes the heat control valve shaft seizes in the manifold; when this condition occurs the valve may stick in either the "heat on" or "heat off" position. If it sticks in the "heat on" position, it will result in poor engine performance, overheating and detonation. On the other hand, if it should stick in the "heat off" position, the heat will be turned off the intake heat riser at all times and result in poor performance, particularly while the engine is warming up and driving at lower speeds. On all engine tune-up jobs and also on complaints of poor performance, overheating and detonation, the operation and adjustment of the manifold heat control valve should be closely checked and any necessary corrections made.

1. Unhook the thermostat spring from its anchor pin and check the adjustment.
2. Proper adjustment requires only 1/2 turn of the spring from its unhooked position to slip it over the anchor pin. NOTE: Should this spring be distorted in any way it should be replaced.
3. Check valve shaft to make sure it is free in the manifold. If shaft is sticking, free it up with kerosene or alcohol containing a small amount of baking soda.

Ignition Distributor

1. Visually check the spark plug wires for damaged insulation and oil soaked condition.
2. Remove the distributor cap. Check the cap and distributor rotor for cracks or carbon tracks and burned or pitted contacts.
3. Check the distributor automatic advance mechanism by turning the distributor cam in a clockwise direction as far as possible, then release the cam and see if the springs return it to the retarded position. If the cam does not return readily, the distributor must be disassembled and the cause of the trouble corrected. See Engine Electrical Section for "Distributor Repair."
4. Check to see that the vacuum spark control operates freely by turning the distributor body counterclockwise and see that the spring returns it to the retarded position. Any stiffness in the operation of the vacuum spark control will affect the ignition timing.
5. Examine the distributor points. Dirty points should be cleaned with a clean point file. Normal point condition is an overall gray color. If a test instrument for checking resistance is available, check the point resistance. The criteria for point quality should be a combination of visual inspection and a resistance or voltage drop check. If the points are badly worn, pitted or misaligned, replacement is recommended. If, with the points closed and the ignition switch in the On position, there is less than a 0.125 volt drop across the points, the points may be considered satisfactory for further use. This check may be made with a sensitive voltmeter or one of the various point resistance meters available for this purpose. For point replacement procedure, see the Engine Electrical Section in this manual.
6. Check the contact point alignment and align the points if they have been cleaned or replaced. Align by bending the stationary point only.
7. Crank the engine until the cam follower is located between the cams. Hook the end of a distributor point scale over the movable point and pull steadily on the spring scale until the points just start to open. At this point the reading on the scale should be between 17-21 ounces. Adjust the tension by bending the breaker arm spring as required.
8. Crank the engine until the distributor point cam follower rests on the peak of the cam. Adjust the point gap to .016" for old points, .019" for new points, (fig. 5) using a feeler gauge or dial indicator. This operation must be performed very accurately because it affects point dwell or length of time the points remain closed in operation and, in turn, ignition coil performance.
9. If a dwell or cam angle meter is available, start the engine and check the dwell, which should be 26° to 33°. If the cam angle or dwell is outside the specified limits, recheck gap and check for defective or misaligned points, or worn distributor cam lobes. Proper point gap should produce a dwell angle within the specified limits.
10. If a dwell or cam angle meter is available, note dwell variation between idle and 1750 engine R.P.M. This should not exceed 3°. Excessive variation indicates wear in the distributor.

NOTE: Do not make dwell or cam angle readings above 1750 engine RPM

Ignition Timing

1. Set the octane selector at "0" on the scale (fig. 6) and attach a timing light to the No. 1 spark plug and spark plug wire, using an extension to make contact, and to a good ground. Start the engine and run it at idling speed with light aimed at flywheel housing opening.
2. Loosen distributor clamp and rotate distributor body until the steel ball in the flywheel lines up with the pointer on the flywheel housing.
3. Tighten distributor clamp screw and remove timing light.

Ignition Performance

If ignition performance test equipment is available, the ignition system performance should be tested in accordance with the equipment manufacturers procedures. If such equipment is not available, the ignition coil and distributor condenser should be checked on available equipment, and the ignition circuit wiring and terminals thoroughly inspected.

Carburetor

1. Inspect carburetor for loose body screws, damaged linkage, loose mounting, fuel leaks or excessive dirt accumulations.
2. Start and operate engine for a sufficient period of time for engine to reach normal operating temperature.
3. Set idling speed by adjusting stop screw on carburetor throttle lever, 450-500 RPM with Standard Transmission, 400-450 RPM with Powerglide Transmission in Drive range.
4. Turn idle screw gradually to right or left to give peak RPM and highest steady reading on vacuum gauge.
5. If engine idles too fast after this adjustment, readjust throttle stop screw until correct idle speed is obtained. Recheck idle mixture adjustment.

If any fault was found during visual inspection or it is impossible to obtain proper idle adjustment, remove carburetor from engine, disassemble, clean, inspect and reassemble carburetor as outlined under Engine-Fuel. Install carburetor and repeat idle adjustment.

Valve Adjustment

With the engine warmed up and normalized, torque the cylinder head and manifold bolts as outlined under Cylinder Head Service Operations in this section. On models equipped with standard or overdrive transmissions, adjust the valves as outlined under Cylinder Head Service Operations in this section. Correct valve lash is .006" on intake valves, .013"' on exhaust valves. Engines equipped with hydraulic valve lifters do not normally require valve adjustment on tune-up operations.

Cooling System

1. Check all hoses and connections for evidence of leakage or decay. Make certain that the spring-type clamps are positioned squarely on the hoses and are over the pipe or casting that the hose is attached to.
2. Check the coolant level in the radiator, level with bottom of filler neck with a warm engine.
3. Check the fan belt condition and adjustment and adjust if necessary. Correct adjustment will produce 5/16" deflection with a light force applied midway between the fan pulley and generator pulley.

Operating Voltage

The operating voltage test serves as a check on the charging system in general. If the findings are not within limits, the entire charging system check should be made as outlined in the Engine Electrical Section of this manual before any adjustments are made.

1. Attach voltmeter leads to the battery terminal of the voltage regulator and ground.
2. Attach a tachometer to measure engine speed.
3. With a normalized engine, and regulator, start engine and run at 1750 RPM.
4. When voltmeter needle stabilizes, note reading. The reading should normally be 14.0 to 15.0 volts. The reading should be correlated with the battery hydrometer check and electrolyte level check if over-charging or under-charging is suspected. See the Engine Electrical Section of this manual for a more complete discussion on voltage regulator settings and charging system checks.

Road Test

After the completion of the tune-up, the vehicle should be road tested to check out the job and add insurance to the value of the tune-up.

VALVE ADJUSTMENT

Solid Valve Lifters

Before adjusting the valve stem to rocker arm clearance, it is extremely important that the engine be thoroughly warmed up to normalize the expansion of all parts. This is very important because during the warm-up period, the valve clearances will change considerably. To adjust the valves during or before this warm-up period will produce clearances which will be far from correct after the engine reaches normal operating temperature.

Tests have shown that valve clearances will vary as much as .005" from a cold check through the normalizing range; consequently the engine should be run approximately 30 minutes to properly normalize all parts.

Covering the radiator will not materially hasten this normalizing process because even with the water temperature quickly raised, it does not change the rate at which the oil temperature increases or the engine parts become normalized.

The actual temperature of the oil is not as important as stabilizing the oil temperature. The expansion or contraction of the valves, rocker arm supports, push rods, cylinder head and cylinder block are relative to this oil temperature. Therefor, only after the oil temperature is stabilized, do these parts stop expanding and valve clearance changes cease to take place.

1. Remove rocker arm cover attaching screws, cover and gasket.
2. Normalize engine.
3. Tighten all manifold bolts, valve rocker shaft support bolts and cylinder head bolts. NOTE: Cylinder head bolts should be tightened to 90-95 ft. lbs. tension in the order shown (fig. 7), rocker shaft support bolts to 25-30 ft. lbs., manifold center clamp bolts to 15-20 ft. lbs. and manifold end clamp bolts to 25-30 ft. lbs.
4. Lubricate valve stems with engine oil to insure free movement of valves in their guides.
5. Adjust valve clearances on intake valves to .006" and on exhaust valves to .013".
6. Install rocker arm cover using a new gasket and check for oil leaks.

Hydraulic Valve Lifters

The hydraulic valve lifters used in models having the Powerglide transmission very seldom require attention. The lifters are extremely simple in design, readjustments are not necessary, and servicing of the lifters requires only that care and cleanliness be exercised in the handling of parts.

The easiest method for locating a noisy valve lifter is by use of a piece of garden hose approximately four feet in length. Place one end of the hose near the end of each intake and exhaust valve with the other end of the hose to the ear.

In this manner, the sound is localized making it easy to determine which lifter is at fault.

Another method is to place a finger on the face of the valve spring retainer. If the lifter is not functioning properly, a distinct shock will be felt when the valve returns to its seat.

The general types of valve lifter noise are as follows:

1. Hard Rapping Noise-Usually caused by the plunger becoming tight in the bore of the lifter body to such an extent that the return spring can no longer push the plunger back up to working position. Probable causes are:
   • Excessive varnish or carbon deposit causing abnormal stickiness.
   • Galling or "pick-up" between plunger and bore of lifter body, usually caused by an abrasive piece of dirt or metal wedging between plunger and lifter body.
2. Moderate Rapping Noise-Probable cause is:
   • Excessively high leakdown rate or leaky check valve seat.
3. General Noise throughout the Train This will, in almost all cases, be a definite indication of insufficient oil supply.
4. Intermittent Clicking Probable causes are:
   • A microscopic piece of dirt momentarily caught between ball seat and check valve ball.
   • In rare cases, the ball itself may be out-of-round or have a flat spot.

In most cases where noise exists in one or more lifters, all lifter units should be removed, cleaned in a solvent, reassembled, and reinstalled in the engine. If dirt, varnish, carbon, etc. is shown to exist in one unit, it more than likely exists in all the units.

In instances where parts are damaged, particularly the plunger or lifter body, the complete lifter unit should be replaced. However, in rare or emergency cases an Arkansas hard stone may be used to remove metal scratches or humps; and if after correcting, the plunger will operate freely in the lifter body, the parts may be thoroughly cleaned and the unit reassembled and reinstalled.

A few precautions to follow when servicing the valve lifters are:

1. Plungers are not interchangeable, they are a selective fit at the factory. Should a plunger or lifter body become damaged, it is necessary to replace the whole unit.
2. The plunger must be free in the lifter body. A simple test for this is to be sure the plunger will drop of its own weight in the body.
3. There must be no excessive leakdown and there must be no ball check valve leakage.

Removal

1. Remove rocker arm cover attaching screws and remove cover and gasket.
2. Disconnect spark plug wires and disconnect high tension wire from coil. Remove push rod cover attaching screws and remove cover and gasket.
3. Remove bolts and nuts which retain valve rocker arm assembly to cylinder head 'and remove rocker arm assembly.
4. Remove the twelve push rods and twelve valve lifters.

NOTE: Valve lifters and push rods should be placed in a rack in their proper sequence so they can be reinstalled in their same positions in the cylinder block.

Disassembly and Assembly

1. Hold plunger down with a push rod and using a small screwdriver or pointed awl, remove plunger retainer.
2. Remove push rod seat, plunger, ball check valve, ball retainer and spring. Figure 8 shows a layout of the parts.
3. Thoroughly clean all parts in cleaning solvent, then inspect them carefully. If any parts are damaged, the entire lifter assembly should be replaced.
4. To reassemble, invert the plunger and set the ball into hole in plunger and place the ball check valve retainer over the ball and on the plunger.
5. Place check valve retainer spring over retainer.
6. Assemble valve lifter body over the complete assembly being careful to line up the feed holes in the lifter body and plunger.
7. Turn assembly over and fill with SAE 10 oil, then insert end of tool J-4274 through ball seat hole in bottom of plunger and press down solid, at which point holes in lifter body and plunger will be aligned.
8. Insert pin which is part of J-4274 through both holes to hold plunger down against spring tension. Remove tool from top of lifter.
9. Fill assembly with SAE 10 oil, install push rod seat and spring retainer.
10. Press down on push rod seat and remove pin. The hydraulic lifter is now completely assembled, loaded with oil and ready for installation in the engine.

Installation

1. Install valve lifters in cylinder block.
2. Install push rods and valve rocker arm assembly, and install push rod cover and gasket.
3. Replace high tension wire to coil and connect spark plug wires.

Adjustment

Any time the rocker arm assemblies or valve lifters are removed from the engine it is necessary to make an initial adjustment for each valve lifter. This adjustment must be made when the lifter is on the base circle of the cam according to the following procedure.

1. Remove distributor cap and crank engine until distributor rotor points to number one (1) cylinder position with the breaker points open. In this position the piston in number one cylinder is at top center on compression stroke with both lifters on the base circle of the cam and both valves can then be adjusted.
2. Turn adjusting screw down until all lash is removed from lifter to valve. This can be determined by checking push rod side play at adjusting screw end while turning the adjusting screw. At the point where no side play of push rod can be felt, continue turning adjusting screw down 1 1/2 turns and tighten lock nut securely. This places the lifter plunger in center of its travel and no further adjustment is required.
3. Crank engine until the distributor is pointing to number five (5) cylinder position. Then adjust both valves for number five (5) cylinder in the manner described above.
4. The other valves may be adjusted by setting the engine with the distributor as described above. It should be noted that we are following the firing order of the engine which is 1, 5, 3, 6, 2, 4; therefore, both intake and exhaust valves for each cylinder should be adjusted in this order.

The condition of the cylinder head and valve mechanism, more than anything else, determines the power, performance and economy of a valve-in-head engine. Extreme care should be exercised when conditioning the cylinder head and valves to maintain correct valve stem to guide clearance, correctly ground valves, valve seats of correct width and correct valve adjustment.

Removal and Disassembly

1. Drain radiator, raise hood, loosen air cleaner clamp, remove support bolts and remove air cleaner.
2. Remove cotter pin at lower end of throttle rod and disconnect rod from bell crank and disconnect throttle return spring.
3. Disconnect gas and vacuum lines from carburetor.
4. Remove gas and vacuum line retaining clip from water outlet.
5. Remove capscrews and clamps that attach manifold assembly to cylinder head and pull manifold assembly off the manifold studs. Remove intake manifold pilot sleeves.
6. Disconnect radiator hose from water outlet, remove outlet to cylinder head bolts and remove outlet and thermostat.
7. Remove rocker arm cover attaching screws and remove cover and gasket.
8. Disconnect wires and remove all spark plugs.
9. Remove high tension wire from coil, remove coil attaching screws and lay coil down out of the way.
10. Remove push rod cover attaching screws and remove cover and gasket.
11. Remove temperature indicator element from cylinder head.
12. Remove four bolts and two nuts which retain rocker arm assembly to cylinder head and remove rocker arm assembly.
13. Remove twelve push rods and twelve valve lifters. NOTE: Valve lifters and push rods should be placed in a rack in their proper sequence so they may be reinstalled in the same positions in the cylinder block at assembly.
14. Remove the cylinder head bolts, cylinder head and gasket.
15. Place cylinder head assembly on its side on a bench then, using Valve Lifter Tool KMO-642, compress valve spring and remove valve lock, seal, spring cup and spring. Repeat this operation on each valve (fig. 9).
16. Remove valves from cylinder head and keep them in their proper sequence for inspection and assembly.

Cleaning

1. Clean all carbon from combustion chambers and valve ports using Carbon Removing Brush KMO-7004.
2. Thoroughly clean the valve guides, using Valve Guide Cleaner KMO-122.
3. Clean all carbon from push rods and valve lifters, disassemble, clean and reassemble hydraulic valve lifters on models where used.
4. Clean valve stems and heads on a buffing wheel.
5. Clean carbon deposits from pistons and cylinders.
6. Wash all parts in cleaning solvent and dry them thoroughly.

Inspection

1. Inspect the cylinder head for cracks in the exhaust ports, combustion chambers, or external cracks to the water chamber.
2. Inspect the valves for burned heads, cracked faces or damaged stems.
3. Check fit of valve stems in their respective guides. This check may be made with a Last Word Indicator, so arranged that a side movement (crosswise to the head) of the valve stem will cause a direct indicator reading. The indicator stem must contact valve stem just above top of guide. With the valve head slightly (1/32") off its seat, move the valve stem from side to side and read the clearance. This should be .001" to .003" on intake valves, and on exhaust valves. By trying new valves in old guides, it can be determined whether the valves, guides or both should be replaced. NOTE: Excessive valve to guide clearance will cause lack of power, rough idling and noisy valves. Insufficient clearance will result in noisy and sticky functioning of the valve and disturb engine smoothness of operation.
4. Check valve spring tension with KMO-607 Valve Spring Tester (fig. 10). NOTE: On standard shift models, spring should be compressed to 1 1/2", at which height it should check 155 to 165 pounds. On Powerglide models, springs should be compressed to 1 29/64" at which height it should check 194 to 210 pounds. Weak springs affect power and economy and should be replaced if not within the above limits.
5. Check valve lifters for free fit in block. The end that contacts the camshaft should be smooth. If this surface is worn or rough the lifter should be replaced.
6. Check push rods for bent condition.

REPAIRS

Replace Valve Guides

1. Place the cylinder head on the table of an arbor press and press the old valve guides out using remover J-267 (fig. 11).
2. Press new precision exhaust (short) guides into the cylinder head using replacer J-5734.
3. Press new precision intake (long) guides into the cylinder head using replacer J-5599. NOTE: Replacer tools have stop collars for proper positioning of the guides.
4. The exhaust guides are installed in the head so they will extend 7/8"' above the head and the intake guides extend 15/16" above the head (fig. 12).
5. Finish ream all guides with a .343" hand reamer.

Reseating Valve Seats

Reconditioning the valve seats is very important, because the seating of the valves must be perfect for the engine to deliver the power and performance built into it.

Another important factor is the cooling of the valve heads. Good contact between each valve and its seat in the head is imperative to insure that the heat in the valve head will be properly carried away.

Several different types of equipment are available for resealing valve seats; the recommendations of the manufacturer of the equipment being used should be carefully followed to attain proper results.

Valve reseater set KMO-105-B and J-4387 contains all necessary valve seat reconditioning equipment necessary for proper renewing of valve seats. Regardless of what type of equipment is used, however, it is essential that valve guides are free from carbon or dirt to insure proper centering of pilot in the guide.

1. Install proper expanding pilot in the valve guide and expand pilot by tightening nut.
2. Place roughing or forming cutter over pilot and just clean up the valve seat. Use a 31° cutter for intake and a 46° cutter for exhaust valve seats.
3. Remove roughing or forming cutter from pilot, install finishing cutter on pilot and cut just enough metal from the seat to provide a smooth finish.
4. Narrow down the valve seats to the proper width of 3/64" to 1/16" for the intake and 1/16" to 3/32" for the exhaust. NOTE: This operation is done by machining both port and top of valve seat.
5. A form cutter must be used to thin down the intake seats from the top. This cutter also machines the edge of the valve recess in the head smoothing this passage for the free flow of incoming gases.
6. Remove expanding pilot and clean head carefully to remove all chips from above operations. NOTE: Valve seats should be concentric to within .002" total indicator reading (fig. 13).

Refacing Valves

Valves that are pitted can be refaced to the proper angle, insuring correct relation between the head and stem on a valve refacing machine. Valve stems which show excessive wear, or valves that are warped excessively should be replaced. When a valve head which is warped excessively is refaced, a knife edge will be ground on part or all of the valve head due to the amount of metal that must be removed to completely reface. Knife edges lead to breakage, burning or pre-ignition due to heat localizing on this knife edge. If the edge of the valve head is less than 1/32" thick after grinding, replace the valve.

1. If necessary, dress the valve refacing machine grinding wheel to make sure it is smooth and true. Set the chuck at the 30 mark for grinding 30 intake valves. Set chuck at 45 mark for grinding exhaust valves (fig. 14).
2. Clamp the valve stem in the chuck of the machine.
3. Start the grinder and move the valve head out in line with the grinder wheel by moving the lever to the left.
4. Turn the feed screw until the valve head just contacts wheel. Move valve back and forth across the wheel and regulate the feed screw to provide light valve contact.
5. Continue grinding until the valve face is true and smooth all around valve. If this makes the valve head thin the valve must be replaced as the valve will overheat and burn.
6. Remove valve from chuck and place stem in "V" block. Feed valve squarely against grinding wheel to grind any pit from rocker arm end of stem. NOTE: Only the extreme end of the valve stem is hardened to resist wear. Do not grind end of stem excessively.
7. Make pencil marks about 1/4" apart across the valve face, place the valve in cylinder head and give the valve 1/2 turn in each direction while exerting firm pressure on face of valve.
8. Remove valve and check face carefully. If all pencil marks have not been removed at the point of contact with the valve seat, it will be necessary to repeat the refacing operation and again recheck for proper seating.
9. Grind and check the remaining valves in the same manner.

Rocker Arms and Shafts

Sludge and gum formation in the rocker arm shafts and rocker arm shafts restrict the normal flow of oil to the rocker arms and valves. Each time the rocker arm and shaft assemblies are removed they should be disassembled and thoroughly cleaned.

1. Remove the support bolts, hairpin locks, springs, rocker arms and supports.
2. Clean all sludge or gum formation from the inside and outside of the shafts and from valve rocker shaft tube.
3. Clean oil holes and passages in the shafts and rocker arms.
4. Clean the rocker arm shaft oil connector assembly.
5. Inspect the shafts for wear. Check the fit of rocker arms on the shafts and check the valve end of rocker arms for excessive wear. Replace all worn parts.
6. There are three each of four different type rocker arms used-right and left hand exhaust and right and left hand intake. They must be installed on the shafts in correct position. For identification each type rocker arm carries a different number stamped on the side.
7. The proper location of the rocker arms according to number are as follows:

                                   STANDARD SHIFT ENGINE 
No. on Rocker Arm                  Type Rocker Arm                   For Cylinder No.

9                                  L.H. Exhaust                      1-3-5 Exhaust
0                                  R.H. Exhaust                      2-4-6 Exhaust
3                                  L.H  Intake                       2-4-6 Intake
4                                  R.H. Intake                       1-3-5 Intake

POWERGLIDE ENGINE
No. on Rocker Arm                  TYPE Rocker Arm                   For Cylinder No.
7                                  L.H. Exhaust                      1-3-5 Exhaust
8                                  R.H. Exhaust                      2-4-6 Exhaust
3                                  L.H  Intake                       2-4-6 Intake
4                                  R.H. Intake                       1-3-5 Intake

1. One end of each rocker arm shaft is plugged; the open end of each shaft must be toward the center.
2. Install the rocker arms, springs, supports, support bolts and locks in their correct position by referring t6 the above chart and Figure 15.

Assembly

1. Clean valves, valve seats, valve guides and cylinder head thoroughly.
2. Starting with No. 1 cylinder, place the exhaust valve in the port and place the valve spring and cap in position. Then using Valve Spring Compressor KMO-642, compress the spring and install the oil seal and valve keys (fig. 16). See that the seal is flat and not twisted in the valve stem groove and that the keys seat properly in the valve stem groove. NOTE: Place valve springs in position with the closed coil end toward the cylinder head.
3. Assemble the remaining valves, valve springs, spring caps, oil seals and valve keys in the cylinder head using tool KMO-642.
4. Check the installed height of each spring, measuring from the top of the spring to the spring seat on the cylinder head. If this is found in excess of 1 55/64", install valve spring seat shim, approximately 1/6" thick. At no time should the spring be shimmed to give an installed height of less than 1 51/64".

Installation

1. Thoroughly clean out cylinder head bolt holes in block and clean cylinder bolt threads. Place a new cylinder head gasket in position on the cylinder block following the instructions stamped on the gasket. This assures alignment of water passages and bolt holes in the block and head with openings in the gasket.
2. Place two cylinder head guide pins through the gasket and screw them into the cylinder block front and rear holes on the manifold side to hold the gasket in position and guide the cylinder head into place.
3. Place the cylinder head in position over the guide pins, and lower the head into position.
4. Oil threads of cylinder bolts and install cylinder head bolts finger tight. Remove guide pins and install two remaining bolts.
5. Tighten the cylinder head bolts a little at a time in the order shown in Figure 7. The final tightening should be to 90-95 ft. lbs.
6. Install 12 valve lifters in right side of block and drop the 12 valve push rods down through the openings in the cylinder head and seat them in the lifters.
7. Place the oil connector over open ends of the two rocker shaft assemblies, install rocker arm assembly retaining bolts in assembly and place shaft assembly on the cylinder head. Align oil return tube with drain hole in cylinder head.
8. Tighten retaining bolts evenly to 25-30 ft. lbs. torque. Figure 17 shows rocker arm and shaft assemblies correctly installed on head.
9. Install temperature indicator fitting and tighten securely.
10. Install thermostat and thermostat housing using a new gasket and connect radiator hose.
11. Place coil in position and install attaching screws, tighten screws to 5-8 ft. lbs. torque.
12. Clean all spark plugs with abrasive type cleaner, inspect for damage and using a round feeler gauge, set the spark gap at .035".
13. Place new gaskets on plugs and install. Tighten to 20-25 ft. lbs. If torque wrench is not available, tighten finger tight and 1/2 turn more.
14. Connect spark plug wires to their respective terminals and the high tension wire to the coil.
15. Clean gasket flanges on cylinder head and manifold, and install new gaskets, intake manifold pilot sleeves, and the four cap screws with clamps loosely to hold gaskets in place. Position the manifold and slide it into place over the end studs and pilot sleeves, making sure it seats against the gaskets.
16. Install the two end cap screws with clamps and turn the center clamps into position against manifold. Tighten the center clamp bolts to 15-20 ft. lbs. torque and the two end clamp bolts to 25-30 ft. lbs. torque.
17. Connect lower end of throttle rod and install a new cotter pin.
18. Connect gas and vacuum lines to carburetor, and vacuum lines to manifold fitting.
19. Attach gas and vacuum line retaining clip to water outlet.
20. Fill cooling system and check for water leaks.
21. Clean air cleaner and install.
22. Roughly set all valve clearances to make sure that all valves have clearance.
23. Normalize engine and adjust valves as instructed under Care, Maintenance and Adjustments, Valve Adjustment.

Effective crankcase ventilation is provided on all engines by a road-draft tube type of system. A ventilator tube, leading from the crankcase, is exposed to the air moving underneath the vehicle. The shape and position of the end of the tube is such that a differential of pressure is created between the ends of the tube. Thus, in addition to providing a ready exhaust for any crankcase pressure due to vapor formation, heat expansion or piston blowby, a draft is created through the engine. The path of the draft is from a breather filter in the sealed valve rocker cover on top of the engine, through the valve train section of the engine to the crankcase to the ventilator tube. In this manner, crankcase vapors are drawn from the engine as they are formed, reducing the possibility of harmful acid or sludge formation in the lubricating oil.

The only service required for this system is the cleaning of the breather intake filter and road-draft tube.

The breather filter should be cleaned with a solvent every 2000 miles. After cleaning, oil the mesh with light engine oil.

The road-draft tube seldom requires service. Driving conditions determine the length of time required to build up a sludge formation in the tube. If there is evidence of crankcase pressure, such as leaking seals on the crankshaft above and beyond normal conditions, -the tube should be checked as a possible source of trouble. The tube should be removed from the vehicle for cleaning, which may be done with solvents or by burning out the sludge formation. This is a good precaution on high mileage engine overhauls.

Crankcase Ventilation-Positive

Positive crankcase ventilating units are available as an option. Installation of this unit will serve:

1. To prevent entrance of dust or dirt into the crankcase on vehicles that are operated in dusty areas. Dust and dirt in the crankcase and oiling system will result in rapid wear of main and connecting rod bearings, piston rings, cylinder walls and other moving parts. NOTE: An oil bath air cleaner should also be used in dusty areas.
2. To provide adequately controlled crankcase ventilation on vehicles used continuously in slow speed, door to door delivery and similar type operations by effectively removing harmful vapors which contaminate the oil, also to prevent corrosion and sludge formation in the crankcase.

Operation

Positive crankcase ventilation is accomplished by utilizing the vacuum created in the intake manifold and the system features controlled circulation of clean air through the crankcase and valve chamber at all engine speeds and loads. Clean air is drawn into the engine from the carburetor air cleaner through a ventilation valve which regulates the amount of ventilation to meet changing operating conditions. To assure proper operation of positive crankcase ventilation system it is important that the crankcase oil level be correctly maintained and not over filled.

When the positive crankcase ventilation system is installed on a Chevrolet engine an extra quantity of air is permitted to enter the intake manifold below the carburetor. This may in some instances result in a leaner air-fuel ratio in the engine than is desirable. No change in carburetion should be made unless definite evidence of lean mixture is experienced. If this condition is experienced, one step rich main metering jet may be used in the carburetor.

Maintenance

The positive crankcase ventilation system will operate effectively as long as normal maintenance is applied. Due to the nature of the materials carried by the ventilating system, the valve and pipe are subject to fouling with sludge and carbon formation.

At regular intervals of 10,000 miles or less, depending on operating conditions, the metering valve, the pipe running from the valve to the intake manifold and manifold fitting should be removed from the engine, disassembled and cleaned thoroughly.

NOTE: Under cold weather operating conditions, when vehicles are operated at slow speeds with low engine temperatures, more rapid accumulations of harmful fumes may be present in the engine. Under these conditions of operation the valve and tube must be cleaned more frequently than specified above. However, no specific mileage recommendation can be made under these conditions. Frequency of cleaning must be dictated by experience.

Disassemble the valve (fig. 18) and clean the valve parts with any good solvent cleaner and the. v blow dry with compressed air. The jiggle pin, which floats in the center orifice of the valve, may be snapped out of position by pressing on the end of the pin so that the center orifice of the valve may be cleaned. The pin may then be snapped back into position.

When reassembling the valve parts, be sure to attach the spring on the valve by pushing the end coil over the tapered end of the valve, over the ridge and into the groove machined just under the head of the valve. This is very important. Unless the spring is properly assembled, the valve will not contact the valve seat squarely and will not close properly. Consequently, the engine will not idle properly due to the entrance of too much air into the intake manifold. If the spring has been stretched the same trouble may occur.

If improper action of the spring is suspected due to spring being distorted, bent or etched from corrosive action, the valve assembly should be replaced. Clean the steel ventilator connection tube and intake manifold connector with solvent and blow dry with compressed air.

Remove oil filler tube and inspect for sludge accumulation, if necessary burn clean, make sure all holes in baffle inside of oil filler tube are open. Inspect oil filler cap and gasket for sealing. If necessary replace gasket as ventilating system efficiency depends on a sealed cap at this point. Inspect for and correct any air leaks at valve rocker cover gasket, valve side cover gasket and ventilator connecting tube and fitting to prevent entrance of air.

Oil Pan

OIL PAN

Removal

1. Raise front of vehicle and place on stand jacks.
2. Remove oil pan drain plug and drain crankcase oil.
3. Disconnect steering idler arm bracket from right hand frame side rail and drop for clearance.
4. Remove oil pan retaining bolts and screws and remove oil pan. NOTE: Crankshaft may have to be repositioned to allow clearance at front cross member.

Installation

1. Thoroughly clean all gasket sealing surfaces.
2. Install pan side gaskets on cylinder block, using grease as a retainer.
3. Install oil pan end gaskets in grooves in front and rear main bearing caps.
4. Reverse the removal procedure to complete the installation. Corner bolts should be tightened to 12 1/2 to 15 ft. lbs., and side rail screws to 6-71/2 ft. lbs.

The oil pump (fig. 19) consists of two gears and a pressure relief valve enclosed in a two-piece housing and driven from the distributor drive shaft which in turn is driven by a helical gear on the camshaft.

The pump cover is equipped with the pressure regulator valve that limits oil pressure to approximately 35 psi.

The pump intake is of the floating type. It floats on the crankcase oil level, picking up only the cleanest oil in the sump. A mesh screen filters out small particles of dirt and sludge which may be present. In the event that the screen becomes clogged, a valve in the center of the float will allow the pump to pick up oil, by-passing the screen.

Inasmuch as the oil pump is serviced on an exchange basis, no repair operations other than disassembly and inspection operations are covered in this manual.

Removal and Disassembly

1. Remove oil pan.
2. Disconnect oil pump to block oil line at the block.
3. Remove oil pump retaining sleeve lock screw and remove oil pump and pump to block oil line.
4. Remove pressure oil line from pump and remove pump cover attaching screws, cover, gasket, idler gear and drive gear and shaft.
5. Remove regulator valve pin and valve parts.
6. Remove floating intake screen from pipe by bending tang on float travel control and sliding float assembly off pipe. CAUTION: Do not disturb pick-up pipe. This pipe is located at assembly and controls controls level.
7. Wash all parts in cleaning solvent and dry by using compressed air, if available.

Inspection

Should any of the following conditions be found during inspection operations, it is advisable to replace pump assembly.

1. Inspect pump body for cracks or excessive wear.
2. Inspect oil pump gears for excessive wear or damage.
3. Check shaft for looseness in the housing.
4. Check inside of cover for wear that would permit oil to leak past the ends of gear.
5. Check the oil pick-up screen for damage to screen, by-pass valve or body. Check for oil in the air chamber.
6. Check pressure regulator valve plunger for fit in cover.

Assembly and Installation

1. Should it be necessary to replace the oil pump pipe to case fitting, caution should be exercised. The fitting should be installed finger tight plus one turn to avoid cracking the block.
2. Place drive gear and shaft in pump body.
3. Install idler gear so that smooth side of gear will be toward the cover.
4. Install a new GENUINE Chevrolet gasket to assure correct end clearance of the gears.
5. Install cover and attaching screws. Tighten screws securely and check to see that shaft turns freely.
6. Install regulator valve plunger, spring retainer and pin.
7. Install oil line to pump body loosely.
8. Install pick-up screen on pipe and bend float travel control tang back in place.
9. Place oil pump in block fitting, aligning oil lines and install oil pump retaining sleeve lock screw and tighten it securely. NOTE: Make sure that tapered end of lock screw draws 'down into hole in oil pump body. Tighten lock nut securely.
10. Tighten oil pump to block oil line connector nuts securely. CAUTION: Make sure oil lines are property fitted so as to eliminate the possibility of shaft seizure when tightened.
11. Install oil pan.

Removal

1. Drain radiator and disconnect upper and lower radiator hoses. On Powerglide models, remove oil cooler lines.
2. Remove radiator core to radiator core support bolts and remove radiator core. Note number of spacer shims removed.
3. Remove fan belt.
4. Install Harmonic Balancer Puller J-1287-B to harmonic balancer and turn puller screw to remove balancer and pulley assembly (fig. 20).
5. Remove oil pan.
6. Remove timing gear cover attaching screws and two bolts that are installed from the back through the front main bearing cap and remove cover and gasket.

Repairs

Timing Gear Cover Oil Seal-Replace

1. Pry old seal out of cover from the front with a large screwdriver.
2. Install new seal so that open end of the seal is toward the inside of cover and drive it into position with Oil Seal Driver J-995 (fig. 21).

Installation

1. Make certain that cover mounting face and cylinder block front end plate face are clean.
2. Install Timing Gear Cover Centering Gauge J-966 over end of crankshaft.
3. Coat the oil seal with light grease and using a new cover gasket install cover and gasket over centering gauge (fig. 22).
4. Install cover screws and two bolts through bearing cap and tighten 6-71/2 foot pounds torque. Remove centering gauge. NOTE: It is important that the centering gauge be used to align the timing gear cover so that the harmonic balancer installation will not damage the seal and to provide uniform seal tension on the hub of the balancer.
5. Install new oil pan gaskets and end corks. Carefully place the oil pan in position and tighten pan bolts securely. NOTE: Tighten oil pan corner bolts to 12 1/2 -15 foot pounds. Tighten flange bolts to 6-7 1/2 foot pounds.
6. Install relay rod idler arm bracket to frame side rail bolts and tighten securely.
7. Remove puller screw from harmonic balancer. Install two 3/8"-16 x 1" capscrews in balancer to support wheel portion during installation.
8. Position balancer on crankshaft so that keyway aligns with key in crankshaft and drive balancer onto shaft until it bottoms against crankshaft gear, using a heavy hammer and a long bar through the grille. Use care to obtain a straight installation. Remove two 3/8"-16 bolts previously installed.
9. Adjust the fan belt to give 5/16" deflection midway between pulleys.
10. Replace radiator core, spacer shims as required, and attaching bolts and tighten securely.
11. Replace upper and lower radiator hoses and refill cooling system.

Front and rear engine mountings are of the non-adjustable type. Because of this, service is seldom required. Broken or deteriorated mounts should be replaced immediately because of the added strain thrown on other mounts and drive line components.

Front Mounts-Replace

1. Remove top and bottom stud nuts and remove washer and cushion between each nut and the cross member or engine bracket.
2. Raise front of engine and remove studs with cushions, washers and retainers. CAUTION: Raise only for enough for clearance. Check for interference between rocker cover and body.
3. Replace necessary cushions (fig. 23).
4. On each end of studs, install washer, cushion with step and retainer.
5. Install stud and cushion assemblies in front cross member and lower engine into place.
6. Install cushion and washer over each end of each stud, install nut and tighten securely.

Rear Mounts-Replace

1. Support engine weight to relieve rear mounts.
2. Remove mount attaching bolts from frame outrigger and flywheel housing and remove mount.
3. Install new mount and bolts.
4. Remove engine support.
5. Tighten bolts securely with normal engine weight resting on mounts.

When making main bearing shim adjustments to take up excessive clearances, all shims may be removed if necessary to obtain the proper running clearances, providing there is no excessive fatigue, distress, abrasion, erosion, nicks or damage from handling, excessive scratches, etc., in the bearings or crankshaft journals.

In general, the lower half of the bearing shows the greater wear and the most distress from fatigue. If upon inspection the lower half is suitable for use, it can safely be assumed that the upper half is also satisfactory. If the lower half is fatigue cracked to the point of near failure, both upper and lower halves should be replaced. Never should one-half bearing be replaced without replacing the other half.

If the running clearance of a bearing is still too great with all of the shims removed, it will be necessary to install both upper and lower bearing halves. Should this become necessary the crankshaft bearing journal should be checked with a micrometer for out-of-round, taper or underside. Experience has shown that clearance increase from wear in main bearings is not only due to bearing wear but is also due in part to crankshaft journal wear. If the journal exceeds .001" out-of-round or taper, the crankshaft should be replaced or reconditioned to an underside figure that will enable the installation of underside precision type bearings.

Adjustment of main bearings with the engine in the vehicle, is extremely difficult due to the mechanic's inability to find adequate means of turning the engine over by hand so as to get a definite feel of bearing drag during adjustment.

In view of this fact, and also in an effort to eliminate the human element involved in this type of adjustment, the ammeter method of main bearing adjustment is recommended to eliminate all of these factors and at the same time provide a quick and accurate method of adjustment.

In preparing a unit for adjustment by the ammeter method, it is imperative that the battery be in good condition and each cell should show a minimum hydrometer reading of 1.260. Hydrometer readings below this figure will permit discrepancies of ammeter readings.

After determining that battery gravity reading is within proper working limit (minimum 1.260) proceed with the bearing adjusting as follows:

1. Remove spark plugs and disconnect positive cable from battery. Drain oil from oil pan and remove pan.
2. With control handle on Battery Capacity Tester in the "Off" position, connect positive ammeter lead to the positive terminal of battery and negative ammeter lead to the positive battery cable previously disconnected from battery terminal. CAUTION: Wrap negative ammeter lead and positive battery cable where connected together to prevent shorting.
3. Attach remote control switch to starter and then turn control handle of Battery Capacity Tester to starter position and check stabilized cranking load. Record this reading as it will be the base for the bearing adjustment.
4. Remove bearing cap and remove one shim from bearing, replace cap and torque bolts to 100-110 ft. lb. and then recheck cranking load. If cranking load is the same as the initial check, remove another shim and recheck. When cranking load increases, replace one .002" shim to bring cranking load back down to original reading.
5. Repeat this procedure on remaining bearings. When using the above procedure it is not necessary to loosen the bearing cap bolts after the bearing has been adjusted before proceeding with the adjustment of the next bearing; this saves time in the complete main bearing adjustment. NOTE: It must be remembered that the base amperage demand (load) must be established for the engine being worked on, because there will be differences in engines, starting motors and batteries which will affect the initial base reading of the ammeter. However, once the base reading has been established the procedure for adjustment is the same; namely, remove shims until the ammeter reading increases, then replace one .002" shim.

By following the foregoing procedure the serviceman can be sure the main bearings will be properly adjusted-neither too tight or too loose.

Rear Main Bearing Oil Seal - Replace

Sealing at the crankshaft rear bearing is made very effective due to machining the rear bearing cap and cylinder block to receive a wick type seal (fig. 24).

To install a new wick seal in the rear main bearing cap proceed as outlined below.

1. Remove rear bearing cap.
2. Remove old seal from groove and make sure groove is clean.
3. Insert new seal in groove with the fingers.
4. Using a rounded tool, roll the seal into the groove. NOTE: When rolling the seal start at one end and roll it to the center of the groove. Then starting from the other end, again roll toward the center (fig. 25).
5. Cut the small portion of the seal that protrudes from the groove flush with the surface of the bearing cap. NOTE: To prevent possibility of pulling seal out of groove a round block of wood the same diameter as the crankshaft flange may be used to hold packing firmly in place while the ends are being cut off.
6. If it should be necessary to replace the upper half of the seal, it will be necessary to remove the engine from the chassis and remove the crankshaft as outlined under Major Service Operations in this section.
7. Replace cap and adjust bearing.

Engine Removal

1. Drain cooling system, crankcase and transmission.
2. Scribe alignment marks on hood around hood hinges and remove hood from hinges.
3. Disconnect R.H. headlamp, parking lamp, and horn wires and remove wires from radiator core support brace.
4. Remove both horns.
5. Remove radiator hoses and heater hoses on models so equipped. On Powerglide, remove and plug oil cooler lines.
6. Remove radiator core support to fender bolts, core support to fender side baffle bolts and core support to front cross-member bolts. Remove radiator core and core support.
7. Remove battery, battery support and battery cables.
8. Disconnect starter and generator wires, engine to body ground strap, oil pressure indicator wire at switch on block and coil primary lead at coil.
9. Remove windshield wiper motor. Remove temperature indicator element from cylinder head.
10. Remove air cleaner.
11. Disconnect gasoline feed pipe from fuel pump and disconnect vacuum lines from intake manifold.
12. Remove exhaust pipe to manifold bolts.
13. Disconnect carburetor control rod from dash panel bell crank.
14. Remove transmission control rods.
15. Remove clutch control bell crank and control rods on conventional transmission models. On overdrive models, disconnect overdrive wires and cables. On Powerglide models, remove oil filler tube and plug opening.
16. Disconnect speedometer cable at transmission.
17. Split rear universal joint. Remove propeller shaft.
18. Remove rocker arm cover and install lifting hooks from Kit J-4536 in cylinder head bolt holes.
19. Raise engine slightly and remove all four engine mounts. Remove the engine and transmission from the vehicle as a unit.

1. Mount engine in stand and clamp it securely so that the engine can be turned over when necessary. Remove the lifting attachment.
2. On conventional transmission models:
   • Remove bolts attaching transmission to clutch housing. Remove transmission. NOTE: Support the transmission as the last mounting bolt is removed and as it is being pulled away from the engine to prevent damage to clutch disc.
   • Remove flywheel underpan extension and clutch release link from clutch fork.
   • Remove throwout bearing from clutch fork and remove fork.
   • Install Clutch Pilot J-5824 to support clutch during disassembly. Loosen clutch to flywheel bolts a turn at a time (to prevent distortion of clutch cover) until the diaphragm spring pressure is released. Remove all bolts, pilot tool, cover assembly and disc.
   • Remove starter assembly and engine ground strap.
   • Remove the flywheel and clutch housing.
3. On all models equipped with a Powerglide transmission, proceed as follows:
   • Remove two upper transmission to converter housing bolts, install lift sling J-4262 and attach chain hoist to lift sling.
   • Remove spark plugs and wires, and remove flywheel cover and flywheel underpan extension.
   • Remove three flywheel to converter bolts, working through bolt access hole on left side of flywheel housing adjacent to cylinder block drain cock. NOTE: Do not remove converter cover bolts which extend through holes in flywheel.
   • Remove converter housing to flywheel housing bolts and separate transmission assembly from engine. Install Converter Assembly Holding Tool J-5384.
4. Remove octane selector retaining screw and disconnect vacuum line from vacuum spark control. Disconnect spark plug wires from spark plugs and lift the distributor up out of engine.
5. Disconnect gas line from fuel pump, remove fuel pump bolts and fuel pump.
6. Disconnect fuel and vacuum lines from clip at water outlet and from carburetor and remove lines.
7. Remove spark plugs, push rod cover, and oil gauge rod. Remove two bolts attaching water outlet to thermostat housing and remove water outlet and thermostat.
8. Remove two bolts attaching thermostat housing and remove water outlet and thermostat.
9. Remove two bolts attaching thermostat housing to cylinder head and remove housing.
10. Remove water pump retaining bolts and remove generator brace and pump.
11. Attach Harmonic Balancer Puller J-1287-A to balancer and turn puller screw to remove balancer and pulley assembly.
12. Disconnect throttle rod from throttle and accelerator lever and remove throttle rod.
13. Remove throttle and accelerator lever, and accelerator rod from cylinder block.
14. Remove carburetor attaching nuts and carburetor.
15. Remove nuts and cap screws attaching manifold to cylinder head and remove manifold assembly and gaskets.
16. Disconnect rocker arm shaft oil line at cylinder block and remove oil line.
17. Remove valve lifters.
18. Remove rocker shaft assembly and push rods.
19. Remove the cylinder head attaching bolts, cylinder head and gasket,
20. Using Valve Lifter KMO-642, compress the valve springs and remove valve keys, spring caps, oil seals, springs and valves (fig. 9).
21. Remove the timing gear cover attaching screws and the two bolts that are installed from the back through the front main bearing cap and remove cover and gasket.
22. Pull the crankshaft gear with Gear Puller T-126-R by attaching it to the gear and turning the puller handle (fig. 26).
23. Remove the two camshaft thrust plate screws by working through holes in the camshaft gear (fig. 27).
24. Remove the camshaft and gear assembly by pulling it out through the front of the block. NOTE: Support shaft carefully when removing so as not to damage camshaft bearings.
25. Remove the engine front mounting plate attaching screws and remove plate and gasket.
26. Disconnect oil pump to block oil line from pump and block fitting and remove oil line.
27. Remove oil pump retaining screw and remove oil pump.
28. Remove oil pump cover attaching screws, cover, gasket, idler gear and drive gear and shaft.
29. Check the connecting rods and pistons for cylinder number identification and, if necessary, mark them.
30. Remove connecting nuts and rod caps. Push the rods away from the crankshaft and install caps and nuts loosely to their respective rods.
31. Push piston and rod assemblies away from crankshaft and out of the cylinders. Remove ridge at top of cylinder bore if necessary. NOTE: It will be necessary to turn the crankshaft slightly to disconnect some of the rods and to push them out of the cylinder.
32. Remove piston rings by expanding them and sliding them off the ends of the pistons.
33. Clamp the piston in Piston Vise J-1218 (fig. 28), remove the connecting rod to piston pin clamp bolt and push the piston pin out (all pistons).
34. Remove main bearing cap bolts and remove the bearing caps and shims.
35. Lift the crankshaft out of the block and place it where it will not get damaged.
36. Lift bearing shells from block and bearing cap.

1. Wash all parts thoroughly in cleaning solvent.
2. Remove oil gallery plugs, located one at front and one at rear face of cylinder block. These plugs may be removed with a sharp punch or they may be drilled and pried out. This oil passage should be thoroughly cleaned either by using compressed air or wire brush.
3. Clean all oil passages in the cylinder block and crankshaft by blowing them out with compressed air. It is good practice to blow them out separately. On the block this can be done by plugging the holes in three of the bearings and placing the nozzle of the air gun in the oil inlet of the cylinder block and blowing through the remaining bearing oil passages. Continue this until all passages are clean. Blow through the passage to the camshaft bearings.
4. Run a fine wire through the cylinder wall lubrication holes in each connecting rod.
5. Blow out the rocker arm shaft oil line, and the passage up from the rear camshaft bearing.
6. Clean carbon from piston heads, ring grooves and inside of piston head. Clean carbon from cylinder head combustion chambers and valve ports with Carbon Removing Brush KMO-7004. Clean valve guides with Valve Guide Cleaner KMO-122. Clean valve stems and heads on a buffing wheel.
7. Check the cylinder block for cracks in the cylinder walls, water jacket and main bearing webs.
8. Check the cylinder walls for taper, out-of-round or excessive ridge at top of ring travel. This should be done with a dial indicator (fig. 29). Set the gauge so that the thrust pin must be forced in about 1/4" to enter gauge in cylinder bore. Center gauge in cylinder and turn dial to "0." Carefully work gauge up and down cylinder to determine taper and turn it to different points around cylinder wall to determine the out-of-round condition.
9. Set the indicator to the standard cylinder size using a pair of micrometers. Then, by checking the cylinders, the oversize pistons required and the amount necessary to be removed from the cylinders can be determined.
10. Inspect the main bearing shells for wear or damage that would make replacement necessary.
11. Inspect camshaft bearings for wear or damage.
12. Inspect the camshaft for damaged cams or bearing journals. If the journals are out-of-round more than .001" the shaft should be replaced. Check the fit of the camshaft in the bearings.
13. Inspect the crankshaft journals and crank pins for roughness and scores. Check them with a micrometer of out-of-round or taper. If out-of-round more than .001" or tapered, the shaft should be replaced or reconditioned.
14. Inspect the connecting rod bearings for damage that would make replacement necessary.
15. Determine whether or not pistons are to be replaced. New piston assemblies and rings are required when the cylinders are to be honed or rebored. If the pistons are to be used again, check the piston pin fit in the pin bores.
16. Inspect the timing gears for excessive tooth wear and for loose hub in camshaft gear. Inspect the camshaft thrust plate for excessive wear.
17. Check the cylinder head for being warped, for having clogged water passages, cracked valve seats or worn valve guides.
18. Inspect the manifolds for excessive carbon in the ports. Check the operation of the heat control valve and make sure that the gasket between the manifolds is in good condition.
19. Inspect the oil pump gears for wear, check the shaft for looseness in the loosen and the inside of cover for wear that would permit oil to leak past end of gears. Check screen for damage.
20. Instructions for inspection and repair of the fuel pump, carburetor, air cleaner, generator, starting motor, distributor, clutch and water pump will be found in their respective sections of this manual.

Some of the following repair operations may not be required on all engine overhauls, depending upon the result of the inspections made. In making some of the repairs, certain engine assembling operations must be performed; therefore, the assembling operations will start with the engine partly assembled as covered under repair operations.

Cylinder Conditioning

If the cylinder block inspection indicated that the block was suitable for continued use except for out-of-round or tapered cylinders, they can be conditioned by honing or boring and honing.

High limit standard size pistons are available for service use so that proper clearances can be obtained for slightly worn cylinder bores and blocks requiring only light honing to clean up the bores. There are four standard size pistons available for service under two part numbers. These aluminum pistons are selected by size and are unitized in groups of six for service usage. In addition, aluminum pistons are serviced in .020", .030" and .040" oversizes. If the cylinders were found to have less than .005" taper or wear they can be conditioned with a hone and fitted with the high limit standard size pistons. A cylinder bore of less than .005" wear or taper may not entirely clean up when fitted to a high limit position. If it is desired to entirely clean up the bore in these cases, it will be necessary to rebore for an oversize piston. If more than .005" taper or wear they should be bored and honed to the smallest oversize that will permit complete resurfacing of all cylinders. The use of a dial gauge set up with a pair of micrometers to the standard cylinder bore size as outlined under "Cleaning and Inspection," will aid in determining the size pistons for which the cylinders must be bored.

Cylinder Boring

1. Before using any type boring bar, the top of the cylinder block should be filed off to remove any dirt or burrs. This is very important. Otherwise, the boring bar may be tilted which would result in the rebored cylinder wall not being at right angles to the crankshaft.
2. In Chevrolet engines, the piston clearance is provided for on the piston and this must be taken into consideration when setting the cutter in the boring bar. The piston to be fitted should be checked with a micrometer, measuring just below the lower ring groove and at right angles to the piston pin. The cylinder should be bored to the same diameter as the piston.
3. If a micrometer is not available to measure the piston, the cylinder should be bored .002" less than the oversize piston to be fitted. For example, when fitting a .020" oversize piston, the cylinder should be bored .018" over standard.
4. The instructions furnished by the manufacturer of the. equipment being used should be carefully followed.

Cylinder Honing and Piston Fitting

1. When the cylinders are to be honed only for use of standard high limit piston or for final finishing after they have been rebored to within .002" of the desired size, they should be finish honed and polished with a hone. Rough stones may be used at first and fine stones for the polishing operation.
2. Place the hone into a cylinder bore and expand the stones until the hone can just be turned by hand. Connect a 3/4" electric drill to the hone and drive hone at drill speed while slowly moving hone up and down entire length of cylinder until hone begins to run free. During this operation a liberal amount of kerosene should be used as a cutting fluid to keep the stones of the hone clean.
3. Expand the stones against the cylinder bore and repeat the honing operation until the desired bore diameter is obtained.
4. Occasionally during the honing operation, the cylinder bore should be thoroughly cleaned and the piston selected for the individual cylinder checked for correct fit.
5. Check fit of the aluminum pistons in the following manner:
   • Invert the piston, skirt end up, and place a .0015" by 1/2" wide feeler ribbon, part of Piston Fitting Gauge and Scale Tool, J-5513 on the side of the piston 9' from the piston pin holes.
   • Insert the feeler ribbon and inverted piston into the cylinder bore so that the center of the piston pin is flush with the top surface of the cylinder block. Keep the feeler ribbon straight up and down and keep the piston pin parallel with the crankshaft axis.
   • Pull the feeler gauge straight up and out, noting at the same time the scale reading which should be between 7 and 18 pounds (fig. 30).
   • If the scale reading is greater than the maximum allowable pull, try another piston or lightly hone the cylinder bore to obtain the proper fit.
   • Should the scale reading be less than the minimum allowable pull, try another piston, or if standard size, try a standard high limit piston. If proper fit cannot be obtained, it will be necessary to rebore the cylinder to the next oversize piston.
   • Mark each piston after fitting to correspond with the cylinder to which it has been fitted. This will assure proper installation.
6. Permanently mark the piston for the cylinder to which it has been fitted and proceed to hone cylinders and fit the remaining pistons. CAUTION: Handle the pistons with care and do not attempt to force them through the cylinder until the cylinder has been bored to correct size as this type piston can be distorted through careless handling.
7. Thoroughly clean the cylinder bores. It is extremely essential that a good cleaning operation be performed. If any of the abrasive material is allowed to remain in the cylinder bores, it will rapidly wear the new rings and cylinder bores in addition to the bearings lubricated by the contaminated oil. The bores should be swabbed several times with light engine oil and a clean cloth and then wiped with a clean dry cloth. Cylinder should not be cleaned with kerosene or gasoline. Clean the remainder of the cylinder block to remove the excess material spread during the honing operation.

Piston Pin Fitting

All new Chevrolet pistons are serviced with properly fitted piston pins, therefore, pin fitting is unnecessary when new pistons are installed. Where cylinder condition and piston fit justify the use of old pistons, it may be desirable to install new piston pins which are available in .0015", .003" and .005" oversize. Correct alignment of the pin bores is essential; therefore, the following procedure should be carefully followed.

1. Adjust the expansion reamer for a light cut and clamp square end in bench vise.
2. Place piston over reamer and start reamer pilot in piston pin bores (fig. 31).
3. Turn the piston until the reamer has passed through both bores.
4. Expand the reamer by easy stages and repeat the reamer operation until the piston pin is fitted.
5. Stabilize the temperature of the piston and piston pin by immersion in oil at 70F.
6. Wipe the piston and pin dry, and lightly coat the pin with an oil film.
7. Place one end of the pin in either boss.
8. The fit must be such that the pin will hold its own weight in either boss and yet permit movement under thumb pressure in its final position (fig. 32).
9. If pin is too tight, lightly hone pin hole.
10. If pin is too loose, ream to next oversize pin. After fitting the first piston pin, the other bores may be reamed quickly by reducing the diameter of the reamer approximately .0005" (half a thousandth) by backing off the expansion screw. This permits quick roughing out of all bores leaving about half a thousandth for the finish cut.
11. It is good practice to check the diameter of all piston pins with a micrometer. In case there should be a slight variation in diameter, consideration must be taken when adjusting the reamer for the finish cut.

The camshafts are of cast alloy iron with the following bearing journal sizes: front 2.1537" - 2.1547"; front intermediate 2.0912"-2.0922"; rear intermediate 2.0287"-2.0297"; rear 1.9662"-1.9672".

These dimensions should be checked with a micrometer for an out-of-round condition. If the journals exceed .001" out-of-round, the camshaft should be replaced.

The camshaft should also be checked for alignment. The best method is by use of "V" blocks and a dial indicator (fig. 33). The dial indicator will indicate the exact amount the camshaft is out of true. If it is out more than .002" dial indicator reading, the camshaft should be straightened. When checking, the high reading of the dial indicator indicates the high point of the shaft. This point should be chalk marked to tell exactly where to apply pressure when straightening.

NOTE: During the straightening operation, care should be taken to protect the bearing journals and prevent damage of their surfaces. Use care to avoid breakage of the cast iron camshaft.

After the camshaft has been straightened, it should be rechecked to be sure it is within .002" dial indicator reading for alignment.

Rear Main Bearing Oil Seal

The upper half of the rear bearing cap oil seal, located in the cylinder block, can only be replaced with the crankshaft removed from the block. See Oil Seal-Rear Bearing Cap under Care, Maintenance and Adjustments for replacing oil seal in bearing cap.

1. Remove old wick seal from groove in block and make sure groove is thoroughly cleaned.
2. Install new wick seal in groove with the fingers.
3. Use a rounded tool and roll the seal into the groove starting at one end and roll it to the center. Then starting from the other end again roll to the center.
4. Cut the small portion of the seal that protrudes from the groove off flush with surface of the bearing. NOTE: A round block of wood the same diameter as the crankshaft flange should be used to hold the packing firmly in position in the groove while the ends are being cut off.

Precision type main bearings used as service replacement are of high quality with close tolerances of fit and do not require line reaming on installation. The close dimensional tolerances assure an equalized bearing surface at all points on the crankshaft when replaced in sets. Bearings are available in standard sizes and undersizes of .002", .010", .020" and .030".

Precision type main bearings may be replaced either with the engine in the vehicle or with the engine removed. With the engine in the vehicle, proceed as outlined below.

1. Remove harmonic balancer and timing gear cover as previously outlined.
2. Remove rocker arm cover and loosen all rocker arm screws to relieve tension on camshaft.
3. Remove spark plugs.
4. Remove transmission from vehicle (see Section 7 of this manual).
5. Drain the oil, remove the oil pan and oil pump.
6. Rotate crankshaft to best possible position for removal of all bearing caps and mark the meshing teeth of the timing gears so that they can be remeshed in the same position.
7. Loosen all four main bearing cap bolts evenly until the crankshaft is lowered approximately 3/8".
8. Remove front intermediate and rear bearing caps and remove upper and lower bearing shells. If upper bearing shells do not come away with the crankshaft, tap lightly to loosen. NOTE: Always replace bearings in pairs. In this way two bearings are supporting the crankshaft while you are working on the other two.
9. Install new upper half bearing shells in rear and front intermediate bearing bores by rolling into position, centering, and pressing up into place. If the bearings have the correct spread, they will snap into place and stay there. NOTE: Be sure to install all upper bearing halves so the smaller of the two oil holes will be toward the camshaft when the bearing halves are rolled into place.
10. Install new lower half bearing shells in rear and front intermediate bearing caps and replace caps, using three .002" shims on each side of bearing as a starting point for adjustment. Lubricate bearings with light engine oil. Draw bolts up until caps are snug to crankshaft bearing journals.
11. Remove front and rear intermediate bearing caps and remove upper and lower bearing shells. If upper bearing shells do not come away with the crankshaft, tap lightly to loosen.
12. Install new upper half bearing shells in front and rear intermediate bearing bores by rolling into position, centering, and pressing up into place. NOTE: Due to close side fit, the upper half of the rear intermediate bearing may not go all the way into place. Start it evenly and it will go all the way into place when the crankshaft is raised.
13. Install new lower half bearing shells in front and rear intermediate bearing caps and replace caps using three .002" shims on each side of bearing. Draw bolts up until caps are snug to crankshaft bearing journals.
14. After all main bearings have been replaced, raise the crankshaft by tightening the bearing cap bolts alternately and evenly. NOTE: At the some time, check the meshing of the timing gears, turning the camshaft gear as necessary so that the gears engage with the previously installed marks (step 6) aligned.
15. With the crankshaft up in place, force it all the way fore or aft and check the end clearance at the rear intermediate bearing (fig. 34).This should be .003" to .009".
16. Adjust main bearings as outlined under Minor Service Operations, Main Bearings Adjust.
17. Replace oil pump and lines.
18. Install transmission (see Section 7 in this manual).
19. Adjust and replace spark plugs.
20. Replace harmonic balancer and timing gear cover as previously outlined.
21. Tighten rocker arm screws, start the engine and after it has normalized, adjust the valve clearances. Install the valve cover.

Main Bearings-Adjust

Plastigage consists of a wax-like plastic material which will compress evenly between the bearing and journal surfaces without damaging either surface. To obtain the most accurate results with Plastigage, certain precautions should be observed. If the engine is out of the chassis and upside down, the crankshaft will rest on the upper bearings and it can be assumed that the total clearance can be measured between the cap bearing and journal.

NOTE: To assure the proper seating of the crankshaft, remove rear main bearing oil seal. In addition, preparatory to checking fit of bearings the surface of the crankshaft journal and bearing should be wiped clean of oil. If the Plastigage check is to be made on engine in the chassis, the crankshaft must be supported by a jack or blocks, up against the upper bearings.

1. Starting with the rear main bearing, remove bearing cap and wipe oil from journal and bearing cap. NOTE: The other bearings must be left at their specified torque.
2. Place a piece of Plastigage the full width of the bearing (parallel to the crankshaft) on the journal (fig. 35).
3. Install the bearing cap and shims removed and evenly tighten the retaining bolts to 100-110 ft. lbs. torque. CAUTION: Do not rotate the crankshaft while the Plastigage is between the bearing and journal.
4. Remove bearing cap, the flattened Plastigage will be found adhering to either the bearing shell or journal. On the edge of Plastigage packing envelope there is a graduated scale which is correlated in thousandths of an inch.
5. Without removing the Plastigage, check its compressed width (at the widest point) with the graduations on the Plastigage envelope (fig. 36). NOTE: Normally, main bearing journals wear evenly and are not out-of-round. However, if a bearing is being fitted to an out-of-round journal be sure to fit to the maximum diameter of the journal. If the bearing is fitted to the minimum diameter of the journal and the journal is out-of-round .001' or more, interference between the bearing and journal will result in rapid bearing failure. If the flattened Plastigage tapers toward the middle ends, there is a difference in clearance indicating a taper, low spot or other irregularity of the bearing or journal. Be sure to check the journal with a micrometer if the flattened Plastigage indicates more than .001" difference.
6. If the bearing clearance is not over .004" old, .003" new or less than .001" the bearing insert is satisfactory. If the clearance is not within these limits, selective fit bearing by removing or inserting. NOTE: When adjusting main bearings if is a good practice to remove the shims evenly. However, should it be necessary to use an uneven number of shims, the greater number of shims should be on the same side of all bearings.
7. If removal of shims does not bring the clearance below .004" it will be necessary to regrind the crankshaft journal for use with the next undersize bearing. NOTE: Bearings are available in standard sizes and .002", .010", and .020' and .030" undersize.
8. New bearing shell clearance should be .003" maximum and .001" minimum.
9. After adjusting rear main to specifications, proceed to next bearing. After all bearings have been adjusted, check to see that there is no excessive drag on the crankshaft. NOTE: When installing front main bearing cap, timing gear cover through-bolts should be tightened before bearing cap bolts to assure seal between cap and front end plate.
10. Install new rear bearing oil seal.
11. Install front end plate and gasket and crankshaft gear.

Examine the tin-timing gear oil nozzle, which is of tubular construction, and pressed and flared in place in the cylinder block front end plate.

In the event the oil nozzle is damaged it will be necessary to replace the front end plate assembly as it is not practical to replace the nozzle only without the use of special equipment.

Cylinder Block Front End Plate

1. Install new oil gallery plugs at front and rear face of block making sure they seat properly.
2. Install new front end plate gasket and end plate, and hold in position with three screws and two hex head bolts. Tighten screws to 15-20 ft. lbs. and stake securely at bottom of slot.

NOTE: Make sure gasket surfaces on block and on end plate are thoroughly cleaned.

Crankshaft Gear-Install

1. Place the two woodruff keys in their respective keyways in the crankshaft.
2. Place the crankshaft gear on the end of crankshaft with keyway in line with key.
3. Drive the gear onto the shaft, using a suitable driver until gear bottoms against shoulder on shaft.

Camshaft Gear and Thrust Plate

1. If the inspection indicated that the camshaft, gear and thrust plate were in good condition, the camshaft end play should be checked (fig. 37). This clearance should be .001" to .005"".
2. If the inspection indicated that the shaft, gear or plate should be replaced, the gear must be removed from the shaft. This operation requires the use of Camshaft Gear Remover J-971-A.
3. Place the camshaft through the gear remover, place end of remover on table of a press and press shaft out of gear (fig. 38). CAUTION: Thrust plate must be so positioned that woodruff key in shaft does not damage it when the shaft is pressed out of gear. Also, support on the hub of the gear or the gear will be seriously damaged.
4. To assemble camshaft gear, thrust plate and gear spacer ring to camshaft, proceed as follows:
   • Firmly support shaft at back of the front journal in an arbor press.
   • Place gear spacer ring and thrust plate over end of shaft, and install woodruff key in shaft keyway.
   • Install camshaft gear and press it onto the shaft until it bottoms against the gear spacer ring. The end clearance of the thrust plate should be .001" to .005".
5. Install the camshaft assembly in the engine block, being careful not to damage bearings or cams.
6. Turn crankshaft and camshaft so that the valve timing marks on the gear teeth will line up and push camshaft into position. Install camshaft thrust plate to block screws and tighten them securely.
7. Check camshaft and crankshaft gear runout with a dial indicator (fig. 39). The camshaft gear runout should not exceed .004" and the crankshaft gear runout should not exceed .003".
8. If gear runout is excessive, the gear will have to be removed and any burrs cleaned from the shaft or the gear replaced.
9. Check the backlash between the timing gear teeth with a narrow feeler gauge (fig. 40). The backlash should not be less than .004" nor more than .006".

Timing Gear Cover

1. A spring loaded oil seal is pressed into the crankshaft opening of the timing gear cover to prevent oil leakage around the hub of the harmonic balancer.
2. If this seal shows signs of wear or damage, it should be replaced by prying it out of the cover from the front with a large screwdriver.
3. Install new seal so that open end of the seal is toward the inside of the cover and drive in place with Oil Seal Driver J-995 (fig. 21).
4. Make certain that cover mounting face and cylinder block front end plate face are clean.
5. Install Timing Gear Cover Centering Gauge J-966 over end of crankshaft.
6. Coat the oil seal with light grease and using a new cover gasket install cover and gasket over centering gauge.
7. Install cover screws and two bolts through bearing cap and tighten to 6-7 1/2 foot pounds torque using a torque wrench. Remove centering gauge. NOTE: It Is important that the centering gauge used to align the timing gear cover so that the harmonic balancer installation will not damage the seal and to provide uniform seal tension on the hub of the balancer.

1. Remove puller screw from harmonic balancer.
2. Install two 3/8"-16 x 1" bolts in harmonic balancer.
3. Line up keyway in balancer with key on crankshaft and drive balancer onto shaft until it bottoms against crankshaft gear using J-5590, Transmission Front Bearing Installer (fig. 41).
4. Remove two 3/8"-16 bolts.

Models with Standard Transmissions or Overdrive

1. Install clutch housing and attaching bolts and tighten to 45-55 foot pounds with a torque wrench.
2. Install indicator extension in a crankshaft stud hole, attach indicator to extension and check pilot hole runout (fig. 42). This runout should not exceed .008".
3. Should runout exceed .008" the clutch housing should be aligned as outlined for flywheel housing, Powerglide models.
4. Remove indicator and indicator extension.

Flywheel Housing-Powerglide Models

The flywheel housing used on Powerglide models differs from the regular production clutch housing in both design and tolerances. Parallelism of the face must be within .007" and total bore runout must not exceed .005". Special oversize dowel pins are to be used to obtain proper bore runout with respect to the crankshaft bearings.

Procedure for installing this flywheel housing and checking alignment correction is as follows. In addition, this method of alignment correction may be applied to correct bore n-misalignment, where found, of the clutch housing on standard or overdrive transmission models.

1. Remove old flywheel housing from cylinder block.
2. Carefully clean mating surfaces of block and new housing of dirt, burrs, nicks, etc.
3. Install new flywheel housing to block, install attaching bolts and tighten evenly to 45-55 ft. lbs. torque,
4. Install indicator post J-2494 in one of the crankshaft flange stud holes. Attach swivel J-4656-1, swivel sleeve J-4656-3 to indicator post. NOTE: Swivel, swivel sleeve and indicator extension rod are part of swivel set J-4656 designed for this alignment check.
5. Install indicator KMO 30-B to indicator extension rod and set indicator to read zero at the six o'clock position on the flywheel housing face (fig. 43).
6. Indicate face of housing and take readings at the 9, 12 and 3 o'clock positions. The runout limit is .007". NOTE: Care should be exercised so that the indicator button is not on the edge of a bolt hole when the readings are taken.
7. Reset the indicator to read zero at the six o'clock position on the machined inside diameter of the flywheel housing bore, being careful that the indicator button is centered on the narrow machined flange and does not touch flange step.
8. Take readings at the 9, 12, and 3 o'clock positions, carefully lifting indicator button over each cutaway section of flange. The runout should not exceed .005" (fig. 44).

Alignment Correction

NOTE: When applying this alignment correction to clutch housing of a standard or overdrive transmission engine, face parallelism should be disregarded as this alignment check must be made with the transmission case assembled to housing in the normal manner. This alignment correction is covered in the transmission section.

1. If bore runout is in excess of .005" or if housing face parallelism exceeds .007", remove indicator and the flywheel housing from the engine block.
2. Remove the lower left hand dowel by driving it out, using a drift punch through hole in cylinder block flange.
3. Center punch the other two dowels and then drill through the dowels using a 7/32" drill.
4. Run a 1/4"-28 tap through drilled holes in dowels.
5. Install a 1/4"-28x2 capscrew into each dowel. Tighten capscrew to push dowels out of block.
6. Clean mating faces of flywheel housing and engine block and make certain there are no burrs or metal extrusion around dowel or bolt holes.
7. Install flywheel housing and tighten attaching bolts evenly to 4