[Report on Engine Bearings]
[From the U.S. Government Publishing Office, www.gpo.gov]

REPORT ON ENGINE BEARINGS:
REPLACEMENT TECHNIQUE FOR
INSTALLATION OR FITTING
Submitted to vehicle maintenance section. OFFICE OF DEFENSE TRANSPORTATION
by MAINTENANCE METHODS COORDINATING COMMITTEE OF TRANSPORTATION AND MAINTENANCE ACTIVITY SOCIETY OF AUTOMOTIVE ENGINEERS, INC.
GOVERNMENT PRINTING OFFICE - WASHINGTON - 1943
SAE Maintenance Methods Coordinating Committee
W. J. Cumming, Chairman, Chief, Maintenance Section Office of Defense Transportation
E. P. Gohn, Test Engineer The Atlantic Refining Company
M. E. Nuttila, Superintendent, Motor Vehicles Cities Service Oil Company
G. W. Laurie, Manager, Automobile Transportation Dept. The Atlantic Refining Company
T. L. Preble, Colonel, War Department Office of Chief of Ordnance
J. Y. Ray, Supervisor, Automobile Equipment Virginia Electric & Power Company
S. B. Shaw, Automotive Engineer Pacific Gas & Electric Company
W. A. Taussig, Automotive Engineer Burlington Transportation Company
E. W. Templin, Automotive Engineer Los Angeles Department of Water & Power
D.	K. Wilson, Superintendent, Automobile Equipment New York Power and Light Corporation
A. M. Wolf, Automotive Consultant
Subcommittee on
“Engine Bearings: Replacement Technique For Installation or Fitting”
A. B. Willi, Chairman, Chief Engineer, Federal-Mogul Corporation
R. Creter, Service Manager Cummins Diesel Engine Corp, of New York
Ray F. Crom, Manager McQuay-Norris Manufacturing Company
G. L. Ferguson, Engineer Monmouth Products Company
Earl Ginn, Vice President Continental Motors Corp.
Charles R. Lynch, Branch Manager Clawson & Bals, Inc.
W. R. Waddell, Service Manager Federal-Mogul Corporation
E.	P. Gohn
Project Chairman
A Report on Engine Bearings: Replacement Technique for Installation or Fitting
SECTION 1
TYPES OF BEARINGS AND MATERIALS OF ENGINE BEARING CONSTRUCTION
There are three types of engine main and connection-rod bearings in common use, classified according to their mechanical features. A description of these types, together with associated material combinations, follows:
Types of Engine Main and Connecting-Rod Bearings
Type 1
Precision insert (interchangeable) bearings.—No boring, reaming or otherwise fitting required to prepare bearings for shaft.
Advantages.—Ease of replacement and lower assembly cost. Not necessary to remove piston and rod assembly to replace connecting-rod bearings. Not necessary to completely remove crankshaft to replace the main bearings. Installation can be made by a mechanic with limited training. No special machine or tool equipment is required to make an emergency repair in the field.
Disadvantages.—Inaccuracies in dimensions and out of roundness of bearing saddle bores in connecting rod and crankcase will be closely duplicated by bearings after assembly. Misalinement, warpage and bow in crankcase cannot be corrected by installation of new bearings.
Material.—Tin base babbitt applied to a steel of bronze back. Lead base babbitt applied to a steel or bronze back. Cadmium alloy bearing metal applied to a steel back. Copper-lead bearing metal applied to a steel back.
Type 2
Removable beari/ngs.—Bored or reamed to exact size after preassembly in crankcase or connecting rod.
Advantages.—More accurate replacement job. Dimensional inaccuracies and crank-bearing saddle bore misalinement, warpage and bow are automati-• cally corrected during the final boring or reaming operation.
Disadvantages.—Replacement is more difficult. Piston and rod assemblies must be removed to replace connecting rod bearings. Engine must be removed from chassis to replace main bearings. A
more or less extensive set of boring or reaming equipment is necessary. A skilled operator is required to set-up and operate the boring or reaming equipment.
Material.—Same as for type 1.
Type 3
Direct babbitted bearings.—As applied to connecting rods or bearing caps. Bored or reamed to exact size at assembly.
Advantages.—Same as for type 2.
Disadvantages.—Same as for type 2 .
Material.—Tin base or lead base babbitt directly applied to connecting rod or, in a few cases, to the bearing cap forging.
Note.—Direct-babbitted caps must be used with align-bored (or reamed) upper bearing shells.
RANGE OF UNDERSIZE REPLACEMENT BEARINGS
A large percentage of engine models have been produced with precision insert (interchangeable) main and connecting-rod bearings. When the same precision insert bearing has been used in production during a period of years, a wide range of undersize replacement bearings has been demanded so as to match crankshaft wear and successive re-grindings. In the table below is shown the record of the connecting-rod bearings used in two popular medium-sized truck engines with respect to range of sizes furnished, and the percentage sold of each size. Data is taken from the records of one manufacturer for the year of 1941 and 4 months of 1942.
SIZE RANGE AND SALES DEMAND OF SELECTED REPLACEMENT CONNECTING ROD BEARINGS
Rod bearing “A” —1934 to 1942		Rod bearing “B”—1937 to 1942	
Size	Demand	Size	Demand
Standard			Percent 42. 81	Standard __	Percent 48. 75 20. 42 12. 96
. 001 under		24. 31	. 001 under	
. 002 under________	12.43	. 002 under __	
. 003 under				3. 99		
. 005 under		2.30	. 005 under			. 22
. 010 under		4. 95	. 010 under. _ 		5. 28
. 012 under		. 75		
. 015 under ___ _	. 25		
. 020 under 		4. 74	. 020 under			7. 40
. 030 under			2. 36	. 030 under __ 			3. 12
. 040 under _			. 44	. 040 under			. 12
. 060 semifinished		. 67	. 060 semifinished		1. 73
			
505643°—43
(1)
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The range of undersizes does not represent standard practice on all engines, as the size range is variable and, in commercial vehicle engines particularly, it depends largely on local conditions^
Many replacement precision insert bearings are supplied only as standards, 0.002 undersize and 0.060 or 0.090 undersize; the latter being semifinished on the inside diameter. These are either finished to size at assembly or are bored to the desired size in special bearing sizing machines in local facilities.
One builder (Chrysler) has regularly produced engines with two conneCting-rod bore sizes ; standard ana 0.005 oversize. The use of the 0.005 oversize has been a means of salvaging rods which would otherwise have been scrapped. Another manufacturer (Ford) rebuilds many engines as a production proposition using connecting rods which have been refinished undersize in the crankpin bore, in combination with undersize crankshafts.
After long service, many connecting rods originally fitted with precision insert bearings become warped and out-of-round in the bearing saddle bore. Correction to restore true bore roundness is often made locally by regrinding or honing to 0.005 or 0.010 oversize.
A condition thus exists whereby certain replacement bearings have been required which are not only undersize on the inside diameter but also oversize on the outside diameter.
CONSTRUCTION FEATURES OF UNDERSIZE BEARINGS
Materials used for bearing linings (tin and lead base babbitts, cadmium alloys and copper-lead mixtures) are low in certain physical properties and they are used in combination with a higher strength back structure of steel or bronze (fig. 1). Until comparatively recently, the back thickness (“A” in fig. 1) remained the same for standard size bearings and all associated undersizes. The lining thickness (“2?” in fig. 1) was a variable and changed with the different
bearing sizes. This arrangement made it possible more economically to manufacture relatively small quantities of assorted undersize bearings for replacement along with large quantities of standard size original equipment bearings, since no separation for final size was made prior to the final bore sizing operation. Another important advantage of this
construction is availability, since a 0.060 undersize semi-finished bearing can be bored to standard or any intermediate undersize. Similarly, any undersize bearing can be rebored to standard or smaller undersize.
A late development in engine bearing design has been a rather drastic reduction in bearing lining thickness (to a range of approximately 0.002 to 0.010), primarily to improve bearing mileage. To carry the benefits of this development as far as possible, many undersize bearings are now made with variable back thicknesses so that the lining thickness can be held more closely in accord with the thickness used in the standard shaft size bearing.
For example, certain manufacturers supply 0.060 undersize bearings with a steel back thickness which will allow machining to a 0.030 undersize. For undersizes between 0.030 and standard, a 0.030 undersize bearing is furnished which can be machined to standard.
Due to uncertainties in the availability of steel and bronze used for bearing backs, additional variations in back thicknesses are not improbable. Realizing the hazards of this condition, most replacement bearing manufacturers are packing a suitable notice in bearing cartons stating the minimum undersize or range of undersizes to which the bearing can safely be bored. In some cases this information is rubber-stamped on the bearing back surface, or on the outside of the earton. When any undersize bearing is rebored to another size, it is important to make sure that the desired size can be obtained from the bearing selected.
The use of very thin linings has not been extended to the type 2 “removable align bored” bearing and relatively few engine models are currently built with this type of bearing. It can be safely assumed that stock bearings of this type can be bored to standard or any undersize within their rated range.
The lining in direct babbitted connecting rods and bearing caps is cast in sufficient thickness to bore to any desired size.
RECOMMENDED RANGE OF STOCK REPLACEMENT BEARINGS
Precision insert (interchangeable) bearings — Standard:
0.002 undersize (to lengthen time before first crankshaft regrind).
0.010 undersize.
0.020 undersize.
0.030 or 0.040 undersize.
0.060 or 0.090 undersize semifinished. Rebore as required for intermediate undersizes.
Note.—In certain cases, the above undersizes are required with a 0.005 or 0.010 oversize outside diameter.
Removable bearings—Aline bored:
0.060 or 0.090 undersize.
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BEARING MATERIAL SUBSTITUTIONS
Copper-lead and cadmium-alloy bearings are commonly used in heavy-duty engines where the loads and operating conditions are too severe for conventional tin base or lead base babbitts.
Copper, cadmium, and tin are obtainable only on high priorities and the availability of these metals for replacement bearings in commercial operations is questionable at this time. The alternative is a lining of lead base babbitt.
No lead base babbitt bearing can be expected to show mileage which is equivalent to that of copperlead or a cadmium alloy bearing in an engine originally built with the heavy duty bearings. If this substitution is necessary, the operator must expect reduced bearing mileage or he must reduce the severity of his operation.
Lead base babbitts, as used by the several specialist engine bearing manufacturers, can be expected to show mileage which is superior to that of tin base babbitt bearings PROVIDING the babbitt thickness does not exceed 0.035. If the babbitt thickness ranges between 0.035 and 0.060. the performance of lead base and tin base babbitt can be expected to be on a par. If the thickness of a lead base babbitt is in excess of 0.060, its performance will probably be inferior to that of tin base babbitt unless the severity of the operation is reduced.
RESTORATION OF STANDARD CRANKSHAFT DIAMETERS
When crankshafts have been reground to the limits established by available undersize bearings, it is obvious that any further reduction in diameter is impractical because of lack of suitable bearings, and what is perhaps of greater importance, the shaft may be dangerously weakened by additional regrinding.
Since it is improbable that new shafts will be freely available for replacement purposes, it may be possible to restore the crankpins and journals to their original diameters by available methods of applying a coating or build-up by metal spray (metallizing). The term “may be possible” is used because of possible limitations in the availability of metal spray equipment and materials. It is not within the scope of this article to describe the details of metal spraying but it is in order to point out that this work must not be carelessly done. The surface to be built up must be properly prepared by turning or grinding to clean up. Do not cut sharply into the end fillets; round into them so as to not impair the strength of the shaft at these points. This surface is further prepared by blasting with sand or steel grit or by special knurling or grooving tools. Oil holes are plugged with carbon or chalk.
The prepared surface must be clean and free from oxides, oil, dirt, and water. The sprayed metal must
be finely atomized to insure that the molten particles are small enough to penetrate the finest openings in the prepared shaft surface. Obviously, the correct metal must be applied.
SECTION 2
OPERATIONAL GUIDE FOR ENGINE BEARING REPLACEMENT
STOCK STORAGE
Replacement bearings are protected against rust and deterioration by suitable treatment and are packed in sturdy cartons. A stock of bearings should not be abused by storage in a room which may be excessively humid, damp, or contaminated by acid fumes. Arrange the stock so that the older bearings are used 'first. When bearings are issued for any job, do not remove them from their cartons to lay around on a dirty work bench. Protect them until ready to install.
Figure 2.—Connecting rod blade and cap steel stamped with cylinder number.
CONNECTING ROD AND MAIN BEARING CAPS MUST BE STAMPED TO IDENTIFY THEIR LOCATION AND POSITION
During the removal of the connecting rod and main bearing caps in the engine tear down; apply or find previously applied steel stamped numerals which indicate their location in the engine, and the end which faces the front (or the rear). Connecting rods and caps are stamped to correspond with the cylinder in which they are assembled (fig. 2). The crankcase and main bearing caps are logically stamped to correspond to their numerical location in the line ; No. 1 for the front, 2 for the next in line, etc.
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If the caps are mixed or reversed end to end at assembly, the effects will certainly be damaging to the bearings.
Particular care must be used to assemble “offset” connecting rods in their correct position. If the rod is assembled in reverse, the wrist pin end will ride against the piston boss, and early engine failure will result.
OBTAIN THE CORRECT BEARINGS
When ordering replacement bearings, be sure that the correct crankshaft sizes are known (figs. 5 and 6).
Compare the new bearings with the old to insure that the proper bearings have been obtained. As a general thing, oil grooves, oil holes, etc., should be tne same on both. This is not always the case, however, since the replacement bearings were probably made at a later date than those removed from the engine and certain alterations to improve performance may have been applied to them.
CRANKSHAFT THRUST BEARINGS—FLANGED
Flanged crankshaft thrust bearings in heavy undersizes are often made with extra stock on the thrust faces (fig. 3) to permit fitting for correct crankshaft end clearance. Undersize bearings are always used with reground crankshafts and in regrinding, it is often necessary to touch up or true up the thrust collars on the crankshaft journal. The length of the journal is thus increased and it is to compensate for this greater length, which increases with the number of regrinds, that the bearings are made with fitting stock on the thrust faces.
Figure 3.—Undersize crankshaft thrust bearing with fitting stock on flange faces.
In ordering undersize flanged thrust bearings or standard diameter thrust bearings which are used in locations other than the front or No. 1 and which are to be rebored from semifinished stock, it is necessary to specify the length (in inches and thousandths of an inch) between the crankshaft thrust collars as shown in fig. 4.
Local conditions may sometimes make it impossible to furnish bearings to the exact length required. In this event, the bearing flange faces must be scrapped to fit at assembly.
When the thrust bearing is located at the front of the engine, means of end clearance adjustment are always provided; and it is not necessary to hold the bearing length to close limits required in location where no adjustment is possible.
RECOMMENDED CRANKSHAFT END-CLEARANCE AT THRUST BEARING
Diameter crankshaft journal (inches)
Recommended crankshaft end-clearance (inch)
2 to 2%_______________________________
2x%6 to 3^____________________________
Over 3^_______________________________
0. 004 to 0. 006
. 006 to . 008
. 008 to . 010
FAULTY MAIN BEARINGS MAY CAUSE ROD BEARING FAILURE
When a connecting-rod bearing failure occurs, do not stop with its replacement. Investigate the conditions of its adjacent main bearings. The main bearings which supplies the rod bearing with oil may be so badly worn or broken up that it cannot retain oil and the rod is starved of lubrication.
CRANKSHAFT
Replacement main bearings are frequently installed without removing the crankshaft from the engine and since it is impossible in most engines to reach the crankshaft journals with a conventional micrometer, the determination of the journal size and bearing diameter has often been largely a matter of guesswork. Guesswork can be eliminated by the use of a special crankshaft caliper (fig. 5) which is suitable
5
for use in all engines in which the main bearings can be removed and replaced without dis-assembling the crankshaft. With the old bearings rolled out, it is possible to reach in with the caliper and obtain the journal size as shown in figure 6.
Figubh 6.—Obtaining size of crankshaft journal.
The actual dimension is finally taken with an inside micrometer as shown in figure 7. Take measurements at enough points on each j’ournal to find the largest diameter and to establish the amount of wear and associated out-of-roundness.
Crankpin sizes can easily be obtained with the crankshaft caliper or with outside micrometers. It is absolutely necessary that the crankshaft journal and crankpin sizes be accurately established so that replacement bearings can be supplied which will have the correct oil and clearance. If the crankshaft is out-of-round, bearings must be obtained which will have proper clearance over the largest diameter.
However, as a general rule, if the main journals are more than 0.003-inch out-of-round and the crankpins more than 0.002-inch, the shaft is unfit for
Figure 7.—Measuring distance between contact pads on crankshaft caliper with inside micrometer.
further use and must be reground. These out-of-roundness values are selected as a compromise between the ideal condition of true roundness with associated maximum bearing mileage. Certain engine manufacturers recommend regrinding when out-of-roundness of 0.0015-inch exists. Bearing will last longer with truly round journals and crankpins than if out-of-roundness in any amount exists.
The installation of new hearings with an out-ofround crankshaft must he considered as an emergency repair and full mileage car/not he expected from the hearings.
A crankshaft which is worn to the extent that the bearing surfaces are ridged and scored is unfit for use and must be reground. After regrinding, the ground surfaces must be finally lapped and polished to obtain a satisfactory smooth finish. A ground finish only is considered too rough and will result in a high rate of both shaft and bearing wear.
A number of different polishing cloths have given satisfaction—viz: Electro-Coated Lightning Metalite Cloth (Behr-Manning) in No. 240 grit for roughing and No. 320 for polishing, Three-Mite No. 120 grit (Minnesota Mining Co.) and others. The polishing cloth must be thoroughly wetted with engine oil.
The lapped surfaces are sufficiently smooth if a piece of sheet copper (or a copper penny) can be scraped back and forth across the surface to be tested parallel with the centerline of the shaft without leaving traces of copper on the steel surface. The crankshaft surfaces must be completely dry and free from oil when this test is made.
After grinding and polishing, the crankshaft must be washed and all internal oilways thoroughly cleaned out.
The crankshaft must be in true alinement and free from warpage and distortion. The journals are readily checked for alinement in V blocks and a dial
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indicator is used for determining if the shaft is true.
With the set-up as shown, the center or intermediate bearings should show an indicator reading of not more than 0.003. For testing either front or rear main journals, one of the V blocks is moved to the center. The same error is permissible for either of the end bearings as is allowed for the center. The shaft should be protected from scratches while being turned in the blocks by a strip of paper laid in the V’s.
CRANKCASE AND BEARING CAP ASSEMBLY
For use with precision insert (interchangeable) main bearings, the crankcase bearing saddle bores must be round within 0.002 and in true alinement
Avoid cap misalinement sidewise by using wrench sockets of the proper diameter.
CONNECTING RODS
Accurate engine reconditioning demands careful alining of the connecting rods. As defined in figure 9 the crankpin bearing bore and the piston pin bushing bore must be parallel with each other within 0.001 in 6 inches and the twist between these bores must not exceed 0.001 in 6 inches.
In maintaining correct connecting-rod alinement, the object is to have the piston gliding surface truly square with the connecting-rod bore. Misalined connecting rods with pistons out-of-square with respect to the rod bore imposes high false loads not only on the connecting-rod bearings but on the
Figure 8.—Diagram
of a bowed crankcase.
lengthwise. If the crankcase has become bowed so that the centerline of the main bearing saddle bores corresponds to the warped centerline B, figure 8 (which is shown exaggerated), a straight crankshaft will be thrown out of alinement and heavy and false loads imposed upon the main bearings, particularly toward the center of the crankcase. The crankcase bearing saddle bores are in correct alinement when an “aiming bar” (which extends the full length of the case) ground 0.00075-inch under the case bore diameter can be turned by hand with the aid of a 15-inch pipe extension (or wrench) after the caps are tightened down over the bar.
If the saddle bores are out-of-round in excess of 0.002-inch and the crankcase is excessively bowed as described, precision insert (interchangeable) bearings should not be used if maximum bearing mileage is expected. The main hearings should aline hored in the crankcase so that the discrepancies can he compensated for.
The aline bored finish must be smooth as obtained with a 0.002-inch feed per revolution using a tool bit having a 90° nose with the sharp point stoned off.
Tighten all main bearing bolts and nuts with a torque wrench to uniform settings—as specified by the engine manufacturer or torque wrench manufacturer.
Figure 9.—Recommended limits for connecting rod alignment.
piston skirts and cylinder walls. They cause engine knocks, oil pumping and blow-by because the faces of the piston rings are held at an angle to the cylinder bore.
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A number of fixtures for checking rod and piston alinement are commercially available. Corrections are usually made by twisting or bending the rod with a notched bar. Heavy rods seldom remain alined after this operation. The steel is not permanently set and the rod soon returns to its warped condition. It is better to accurately bore the piston pin bushing to size and in true alinement with the connecting rod bore, thus eliminating any bending or twisting of the rod.
undersize bearing installed which is bored to size in the rod so as to obtain a truly round bearing bore.
INSPECT THE COMPLETE COOLING SYSTEM
Excessive engine temperatures are damaging, not only to the bearings, but to many other engine parts. The radiator and engine water jackets must be clean and free from deposits of lime and scale which will impede free flow of the cooling water.
Figure 10.—Checking roundness of connecting rod bore with a special indicator.
For use with precision insert (interchangeable) • bearings, the connecting-rod bore must be round within 0.002 inch.
Connecting-rod bores are quickly and accurately checked for roundness with a special indicator of the type illustrated in figure 10.
If out-of-roundness in excess of 0.002 inch exists, the rod should be reconditioned or replaced or an 505643°—43-------2
Inspect all water hose connections. Badly deteriorated water hose connections in which the water passage is almost closed off will cause an engine to run too hot and detonate (spark knock) badly.
Inspect all thermostats in the cooling system. It is particularly dangerous if they are inoperative from the closed position—a cracked block or head will almost certainly result.
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It is obvious that leakage at the water pump packings must be corrected.
CHECK THE CONDITION OF THE INTAKE VALVE STEMS AND GUIDES
Excessive clearance of the intake-valve stems in their guides will induce heavy oil loss (fig. 11). If intake-valve stems or guides are worn, the vacuum created on the intake stroke of the piston draws excessive amounts of oil and air through this channel into the combustion chamber.
Figure 11.—Oil is drawn through worn intake valve guides into the combustion chamber on intake stroke of piston.
Oil passing the intake-valve guides can easily be detected because inspection of the intake valve will reveal a heavy deposit of carbon or soot on the underside of the head. This condition can be corrected by the installation of valve stem packing or the replacement of intake valves and their guides.
Excessive air drawn through worn intake-valve guides disturbs carburetion of the engine and affects its idling.
THE PISTONS, RINGS, AND CYLINDER BORES
It is obviously necessary that pistons, rings, cylinder bores or liners, valves and valve seats must be in good condition if maximum engine performance is to be obtained. It is not within the scope of this work to go into greater detail concerning these parts.
However, it is well to note that if cylinder bores or liners have been reground, they must be true and square with the axis of the crackcase bearing saddle bores. Out-of-squareness of the cylinder bores is just as harmful to the connecting rod bearings and pistons as a bent connecting rod.
ENGINES MUST BE KEPT CLEAN
Dirt is the No. 1 enemy of bearings and engines. A satisfactorily clean engine cannot be obtained by passing flushing oil through it after the job is completely and finally assembled. Engine cleanliness must start with a clean shop and orderly surroundings.
In a complete tear down and overhaul, all metal parts, such as cylinder blocks, crackcases, gears, connecting rods, oil pans, etc., must be thoroughly washed. Clean parts are more convenient to handle and possible defects, such as cracked valve seats, water jackets, etc., are easier to detect. If dirty parts are assembled into an engine, trouble will surely follow.
A number of efficient cleaning methods and materials are offered by specialists in the mechanical cleaning field. Included in these methods are immersion of the parts in tanks containing hot water solutions of suitable solvents, the use of vapor degreaser equipment, steam jets, etc.
Clean surfaces are readily obtained. It is usually necessary to apply a coating of oil to bright finished parts just as soon as they are dry, to prevent rusting.
It is not sufficient that the cylinder block was thoroughly cleaned before the operations of valve grinding and cylinder grinding. It must be thoroughly cleaned afterward as well, to remove all abrasive residue from these operations.
Crankshaft oilways and drilled oil passages within the cylinder and crankcase must be carefully swabbed and flushed out, preferably with kerosene or a special flushing oil.
If blown out with an air hose, watch that the dirt does not befoul and contaminate adjacent clean parts which are ready for assembly. An air hose, carelessly used, can be a dangerous implement by blasting filth over everything within range.
Obviously, work benches and machine equipment must be kept clean and orderly.
The use of an oil pressure loss-indicator tank as a final check for bearing clearance provides added insurance against dirty bearings, as the flow of oil under pressure will flush out all oilways and bearings before the crankshaft turns over under power.
It is often necessary to clean out the interior of an engine independently of a complete tear down and overhaul. Efficient flushing compounds and flushing oils are readily available and their use can be recommended—if proper care and judgment are used.
A part of the flushing procedure usually is to run the engine at idling speed for 45 to 60 minutes or more, so that the flushing agent can penetrate and loosen the deposits.
If the engine interior is badly sludged and dirty, * large quantities of loosened deposits will be collected in the oil pan.
These settlings, in excessive quantity, may tangle themselves in the oil suction screen to the extent of partially or completely clogging it. Watch the oil gauge pressure carefully at this time. If the pres
9
sure drops off, it is an indication that the suction screen is clogged and oil is not getting through the system. Stop the engine, remove the oil pan, clean things up and start over.
Drain while the engine is still warm as the mixture will flow more freely. Remember that the location of the drain in most oil pans is such that approximately one pint of old oil always remains to contaminate the new.
If the engine interior has been choked up with filth, remove the oil pan after the fbashing operation so that it can be thoroughly cleaned out. Inspect and thoroughly clean the oil suction screen, make sure that the interior of the oil filter is clean and install a fresh oil filter cartridge. Then hook up an oil pressure loss indicator tank and finally flush out the system, using the flushing oil selected with the detector tank set for 30 pounds or more gauge pressure.
Don’t wait until an engine interior is choked up with sludge and wall deposits. There are many hazards connected with trying to clean it out without complete dismantling.
Oil changes at suitable intervals, depending on the type of operation, will usually keep an engine clean.
Interior flushing at 15,000- to 20,000-mile intervals is desirable and this should start after the first 15,000 or 20,000 miles.
ATTEND TO THE OIL FILTER
Thoroughly clean the oil filter, replacing the filter cartridge and attend to whatever other points of maintenance are required for the particular type of unit used.
A clean and efficient oil filter is a necessity if maximum bearing life is to be obtained.
ATTEND TO THE AIR CLEANER
Thoroughly cleanse the carburetor air cleaner. At high speeds, several hundred cubic feet of air per minute is drawn into the engine and may be contaminated with heavy quantities of abrasive dust which causes excessive wear of all moving engine parts. This air must be purified. A clean and efficient air cleaner is of real help in obtaining long bearing and engine life.
INSPECT THE VACUUM BOOSTER PUMP
Certain engines are equipped with a vacuum booster pump to provide sufficient vacuum (power) to operate the windshield wiper when the throttle is open.
If the diaphragm in this pump is cracked, punctured, or porous, oil may be drawn direct from the pump into the intake manifold causing a smoky exhaust and excessive oil consumption.
To check the condition of the booster pump, accelerate the engine and watch the action of the wiper
blade. If the blade stops, it is an indication of a defection diaphragm.
A positive check is to disconnect the vacuum line and run the engine several minutes. If smoke at the exhaust ceases, it indicates a defective diaphragm which must be replaced.
BEARING SPREAD
Most split main and connecting-rod bearings are purposely made with the “spread” (width across the open ends) slightly greater than the diameter of the crankcase or connecting-rod bore in which they are assembled. (See figure 12.)
The amount by which the spread dimension exceeds the case or rod bore diameter will range between 0.005 and 0.020 inch depending on the thickness and structural stiffness of the bearing. The bearing must thus be snapped or lightly forced into its seat at assembly, and it will remain in place during subsequent assembly operations when the caps are handled upside down.
Figure 12.—Diagram showing “spread” in a split bearing.
The Ford V8 floating connecting-rod bearings (all models) are exceptions to the general rule that the width across the open ends should be greater than the rod bore diameter.
Any split bearing is relatively fragile and unstable structurally, and it sometimes happens that due to rough handling in shipment for storage and certain other natural phenomena, these bearings increase in width across the open ends so that they are slightly wider than the rod bore.
In the Ford rod bearings, it is preferable that they be truly round and smaller at every point in the circumference than the rod bore, but nevertheless a certain amount of excess width is permissible without damage, even though the rods may feel somewhat tight when assembled over the bearing.
The correct distance across the open ends of the various Ford connecting-rod bearings as taken from original equipment specifications is shown in figure 13.
Excessive “spread” in any bearing is readily cor* rected as follows:
Hold bearing on a smooth block as shown in figure 14 and strike the side lightly with a soft mallet. Continue until the correct width is obtained.
If, during this operation, the width is decreased to a point less than it should be, it can be increased again by laying the bearing on the wood block as shown in
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figure 15 and striking the back lightly with the soft mallet.
The spread of any bearing can be safely adjusted by this method.
therefore, be provided between shaft and bearing in which this film can form.
Since the rotating shaft creates a considerable amount of frictional heat, this clearance space must ®
be sufficient to allow oil flow through the bearings so that cool oil is constantly replacing that which has been heated.
Oil not only lubricates, it cools the bearing as well, and one function is just about as important as the other.
If the oil clearance is too small, many troubles arise, such as wiped bearings, worn crankshafts, excessive cylinder wear, scuffed piston rings, worn pistons, etc.
If the oil clearance is too great, another series of ailments will develop.
The increasing use of precision insert main and connecting-rod bearings considerably reduces the difficulty of obtaining correct oil clearance if the crank-shaft is finished to proper decimal dimensions and the crankcase and connecting-rod bores are round and true to dimensions as originally manufactured.
• However, many bearings must be locally align bored or otherwise sized to fit the crankshaft and the accuracy of the oil clearance must be carefully attended to.
RECOMMENDED OIL CLEARANCES FOR VARIOUS TYPES OF
ENGINE MAIN AND CONNECTING-ROD BEARINGS
CHECK THE CONDITION OF THE CAMSHAFT BEARINGS
Worn camshaft bearings, if pressure lubricated, are often responsible for puzzling cases of lack of oil pressure and high oil consumption. Excessive oil leakage can occur at worn camshaft bearings just the same as at worn mains and rods. Cam bearing wear is considerably slower, but after an engine has used up two sets of main ana connecting rod bearings, the cam bearings are a potential source of trouble due to wear.
Worn camshaft bearings are easily located by the use of an oil pressure loss indicator tank.
CORRECT OIL CLEARANCE AT THE MAIN AND
CONNECTING-ROD BEARINGS MUST BE PROVIDED
Any heavily loaded engine bearing must be separated from its shaft by an oil film. Space must,
[For pressure (force-feed) lubrication]
Diameter crankshaft journal or crankpin (inches)	Clearance in inches		
	Tin base babbitt or bermax high lead babbitt	Genuine cadmium silver copper	Federaloy B.30 copper lead
2 to 2%		0. 0015 . 0025 . 0030	0. 0020 . 0030 . 0035	0. 0025 . 0035 . 0040
2% to 3%				
3%6 to 4 		 _ _			
			
Note a. A tolerance of 0.001 inch is allowable on the clearances specified.	f
Note 6.—Oil clearance as shown in this chart is the difference in the diameter of the crankshift journal or crankpin and the bore diameter of the bearing.
To obtain the clearances specified, it is assumed that the crankshaft diameters will be accurately obtained by micrometer measurement and the bear
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ings accurately bored to suit, also by micrometer measurement. However, it is necessary to check the ♦ clearance after the various machining operations and for this purpose the use of brass shim stock of the correct thickness has been very successful.
In using this material, care must be exercised to avoid damaging the bearing. The length of the
Repeat the operation next at the rear bearing— then at the intermediates.
Make sure that ends of bearings do not ride the crankshaft journal fillets.
If desired, the feeler may be made from cigarette papers which measure from 0.0008 to 0.0016 in thickness. Use one or more to obtain required thickness.
Connecting rod end clearance
Figure
Crankshaft journal
Connecting rod
RECOMMENDED CRANKSHAFT END CLEARANCE AT THRUST BEARING AND CONNECTING ROD END CLEARANCE	
Diameter Crankshaft Journal in Inches	Recommended End Clearance
2 to 2%	.004toOOSìn.
2I3/IS to 3'/g	. OO6to.OO8 in.
Over 31/g	,OO8to.O1Oin.
-•j*- Cronkshoft end clearance
shim stock gage should be approximately one-fourth-inch less than the length of the bearing and one-fourth inch wide. It is desirable that the edges be smoothed down on an oil stove so that no sharp, turned-over corners will remain to embed themselves in the soft bearing material.
Place cylinder block in an inverted position. Start at center bearing or one of the intermediates, in a four-bearing engine. Coat feeler lightly with engine oil on both sides.
Place feeler of correct thickness, and made as previously described, on crankshaft journal, assemble and tighten down cap and lower half of bearing, rotate the crankshaft by hand through an arc of , e 2 inches; 1 inch each way. With the feeler in place, the shaft should be movable with a fairly heavy drag. Without the feeler it should be possible to turn the shaft without bind or drag.
. Remove feeler, replace cap, BUT DO NOT TIGHTEN; this check must be made with the cap and bearing over the feeler only, tightened down. The remaining caps should be loosely in place.
CORRECT CRANKSHAFT AND CONNECTING-ROD END CLEARANCE MUST BE PROVIDED
It is important that proper crankshaft and clearance (end play) be provided at the thrust bearing.
End clearances are recommended as shown in figure 16.
End play should be checked with a feeler and with the crankshaft pried as far as possible either to the front or the rear—whichever is the most convenient on the particular engine, since the thrust may be taken at the front, center, or rear bearing—depending on the make of engine. With the thrust collar on the crankshaft in contact with the thrust surface of the bearing at one end, the total clearance is readily measured with a feeler at the other end. Check the clearance at several points around the bearing flange. Remember that one bearing only in the line should take thrust of the crankshaft, and the other bearings should have ample clearance at each end.
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USE A TORQUE-INDICATING WRENCH FOR TIGHTENING ALL BEARING STUDS, NUTS, AND CAP SCREWS
The excessive tightening of studs, nuts, and cap screws in an engine will harmfully distort cylinder heads, cylinder blocks, connecting rod bores, crankcase main bearing bores and many other parts. Studs and cap screws may be strained and stretched to the point that failure will occur in service.
In all engine manufacturing plants, torqueindicating wrenches are used to insure that nuts and cap screws are correctly and uniformly tightened.
Thus, when the crankcase bearing saddle bores and the connecting rod bores are originally machined, the cap bolts or nuts have been tightened to a specified reading on a torque-indicating wrench. The bores are exactly round under the specified condition of bolt tightness, but if the bolts are drawn down tighter or if they are not as tight as the original setting, the crankcase and rod bores will not be truly round, and bearing life will suffer.
Accurate bearing replacement cannot be made without the use of similar “measuring” wrench which will make it possible to duplicate factory assembly conditions.
SPECIAL POINTS TO BE WATCHED IN BEARING ASSEMBLY
1.	Wipe backs of bearings, also the crankcase, bearing cap, and rod bores to remove dirt particles at the time each individual bearing shell is placed in its seat. If shims are used, wipe off each one individually.
2.	Inspect for burrs in crankcase, caps, rod, and on bearings, which would interfere with proper seating of the bearings.
3.	Light wall steel back bearings are located endwise and retained against turning by a lip stamped out from the steel back. At assembly these lips must be carefully and completely nested in the slots provided for them in the crankcase, bearing caps, and connecting rod.
4.	Make sure the main bearing and connecting rod caps are not misplaced endwise or sidewise at assembly.
5.	Bolt the caps on lightly. Tap them at the crown to centralize; then tighten.
6.	Never place shim stock between the back of the bearing shell and its seat to obtain greater bearing height or to close in a worn bearing for a better fit over the shaft.
Air spaces are formed which retard the transfer of heat to cooler parts of the engine; this heat at the bearing lining builds up and early failure results.
7.	Many mechanics have attempted to make adjustments with precision (interchangeable) bearings by filing the contact surface of the bearing cap. This is
poor practice. Bearings are short-lived, the roundness of the crankcase and bearing cap bore is destroyed and the installation of new bearings, when • this is finally done, is greatly complicated.
SPECIAL POINTS TO BE WATCHED IN ALIGN BORING OF MAIN BEARINGS
1.	After bearings, shims (if used), and caps are properly assembled, plug all oil ways with small but substantial pieces of clean rag to prevent chips and borings from getting into the lubricating system.
2.	In locating the boring bar, great care must be exercised to insure that the centerline of the finished bearings will be the correct distance from the top of the cylinder block, parallel with it and at right angles to the cylinder bores. In an engine built with a gear drive to the camshaft the distance between the centerline of the camshaft and its bearings and the bore of the main bearings must be very accurately maintained so that the crankshaft and camshaft drive gears will mesh properly. A little more leeway is permissible if the camshaft is driven by a chain.
3.	After all boring and thrust bearing facing operations are completed, be sure to remove all plugs from the oilways and ALL chips from the interior of the crankcase.
ASSEMBLING PRECISION INSERT MAIN BEARINGS WITHOUT REMOVING CRANKSHAFT
In certain engines employing precision insert bearings, it is possible in an emergency to remove and replace an upper main bearing shell without removing the crankshaft. The bearing may be light wall steel back with the locking lip on one side or heavy wall steel or bronze back, in which no dowel is used in the upper shell.
To remove a bearing of this character from the engine, remove the cap at the bearing involved and back off all the other caps slightly so that the shaft is entirely free from the upper bearings. A special headed plug of steel or bronze of the general design shown in figure 17 is then inserted in the crankshaft oilway and the shaft rotated until the extended end of the plug is in contact with the bearing on the side opposite the locking lip. Turning the crankshaft carefully in a direction towards the locking lip will rotate the bearing from its position in the crankcase.
To install a new upper bearing, the crankshaft must be turned in the opposite direction to that used when the old bearing was removed. Place the new * bearing on the crankshaft journal with the plain edge ready to enter the space between shaft and crankcase bore on the side of the crankcase bore which is milled to receive the bearing locking lip. Make a careful visual alinement of the bearing locking lip and its slot in the crankcase when the bearing is placed on the shaft so that as the bearing is
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rotated into position, the lip will nest properly in its slot without binding. If the lip binds on the side ♦ of the crankcase slot, the bearing surface will probably be harmfully distorted and disturbed.
Head extended to prevent plug from dropping thru oi!*oy
Figure 17.—Removing upper main bearing shell by means of a special headed plug inserted in crankshaft oilway.
If the bearing to be removed is a heavy wall type without a dowell, turn the crankshaft in a clockwise direction (looking from front of engine). To install the new bearing, turn the crankshaft counterclockwise.
As explained previously, all bearings are made with a certain amount of spread across the open ends. In heavy wall bearings this spread may cause some difficulty when it is attempted to make a bearing installation as described without removing the crankshaft. In this event, round up the bearing as shown in figure 14.
This type of bearing replacement is an emergency measure only. The work is done “blind” and there are many chances for error. Be sure that the crankshaft journal, crankcase bore, and bearing back are wiped clean.
REPLACE GASKETS AND CHECK FRONT AND REAR MAIN-BEARING OIL SEALS
, t To prevent unnecessary oil loss, replace the gaskets at all parts which have been removed; oil pan, valve chamber cover, gear or chain case cover, etc.
Front main bearing oil seals must be in perfect • condition.
Rear main bearing oil seals and the surrounding gaskets must be in perfect condition. Oil leakage at the rear main bearing is a fairly common ailment-
Oil often has a tendency to work past this bearing and through the sealing mechanism because of a “sucking” action of the rotating flywheel at high engine speeds.
Leakage is aggravated if abnormal “blow-by” of compression and explosion past the piston rings exists as this creates a certain amount of pressure within the crankcase which forces oil and oil-laden vapors out of all openings in the crankcase.
The construction at the adjacent to a typical rear main bearing basically follows figure 18.
Figure 18.—Typical construction at a rear main bearing.
Oil enters the bearing through drilled oilway A. When it reaches the crankshaft, the flow is toward both ends of the bearings following arrows & and c. Oil flows toward the rear (arrows &), is stopped at the interrupter groove or channel at D in the crankcase and bearing cap. Oil which reaches groove D is supposed to drain back into the oil pan through orifice E in the bearing cap.
When blow-by pressure exists within the crankcase, the opening to outside atmosphere through the rear main is one of the most natural avenues of escape. This pressure acts upward through the oil drain orifice E into the groove at D and escapes into the flywheel or clutch housing through the clearance space between the crankcase (and bearing cap) and the crankshaft at F. Since orifice E and groove D are partially filled with oil, the escaping crankcase pressure carries oil along with it.
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High crankcase pressure causing front and rear main bearing oil leakage will be built up if the oil filler cap and ventilator tube are clogged or obstructed.
Excessive clearance at the bearing will allow more oil to flow through the bearing than can be controlled by the sealing construction.
USES OF THE BEARING OIL PRESSURE LOSS INDICATOR TANK
These devices consist of a tank holding several quarts of clean oil under air pressure obtained from a convenient source. The air pressure within the tank is uniformly controlled by a pressure regulator which can be adjusted to match the engine oil pressure. In operation, the dash oil gauge line is disconnected at the engine and the hose leading to the tank is connected up.
With the oil pan removed, oil under pressure is admitted to the engine and leakage at the main bearings can be observed. It is usually necessary to reposition the crankshaft for each bearing so that the leakage from the bearing under observation can be properly segregated and not confused with the leakage from another point.
Instructions are furnished with the various tanks to enable the operator to determine if the oil flow through the bearing as observed in the form of end leakage is correct.
In general, if there is no oil leakage at the ends of a bearing, that bearing is fitted too lightly or there is an obstruction in its oil supply. If the leakage exists in the form of a large solid stream, there is excessive clearance or the bearing is badly worn.
These devices are most valuable for locating faulty main, connecting rod and camshaft bearings m pressure lubricated engine (Pontiac excepted) also points of leakage due to breaks or cracks in main oil header or other internal oil lines BEFORE the engine is dismantled. They are of equal value in obtaining a final check on a bearing replacement job.
When used as the final check for oil flow through newly installed bearings, a further advantage is obtained in that the bearings are completely pre-lubri-cated before the engine turns over under its own power, and dirt or other foreign particles which may have remained in the oil passages or bearings will be flushed out.
CORRECT OIL PRESSURE MUST BE MAINTAINED
The amount of engine oil pressure is shown by the oil gage and must be maintained at the point recommended and built in by the engine manufacturer. Oil pressure which is higher than the engine builder’s recommendation is seldom harmful (and also seldom encountered) but low oil pressure is likely to result in inadequate lubrication and early failure of new connecting rod bearings, especially during highspeed operation.
Assuming that all bearings have the correct amount of oil clearance, low oil pressure is usually caused by wear in the oil pump gears or oil pump 1 housing, a faulty oil pump cover gasket and a weakened oil pressure relief valve spring. Leakage at breaks or cracks in main oil headers or other internal oil lines are also responsible for reduced oil pressure, but trouble at these points is easily located by the use of a bearing oil loss indicator.
CORRECT OIL GAGE PRESSURE DOES NOT AL-
WAYS INDICATE A SATISFACTORY BEARING CONDITION
With full pressure engine lubricating system, an oil pressure gage is always connected up with the system. It has been stated previously that badly worn main, rod and cam bearings will promote high oil consumption and oil loss because of excessive oil throw off or leakage from the ends of the bearings. The question has been frequently asked, “How can there be excessive oil leakage from worn bearings and subsequent oil pumping from this source if the oil pressure gage registers the normal pressure ?”
Another common question has been, “If the car or truck showed, when new, a gage pressure of 40 pounds at a given speed and if that same pressure is retained later on when high oil consumption has developed, does it indicate that the bearings are not worn and are therefore not involved as a cause of high oil consumption, and do worn bearings lower the oil pressure?”
Any engine will require a definite amount of oil flow per minute at a given pressure to provide adequate lubrication to all moving parts.
If the delivery capacity of the oil pump used on any given engine was exactly equal to the requirements of the engine when new, all of the oil pumped would be delivered to the bearings and other points requiring lubrication.
With such a pump, any increase in bearing clearance due to wear would result in a reduced pressure at the bearings, which would be indicated by a reduced pressure reading on the gage, although exactly the same quantity of oil would be pumped through the engine.
Obviously, an installation of this kind would provide no safety factor, as the reduced pressure might starve the bearings which had not worn excessively and provide excess oil to the bady worn bearings.
To provide an adequate factor of safety, the oil pump is usually made big enough to supply a great deal more oil than a new engine needs so that when < wear occurs there will be oil and pressure in reserve. To prevent the excess oil thus provided from being forced through the bearings, a bypass relief valve is installed in the system as shown at A in figure 19.
This relief valve is spring-loaded so as to remain closed until a predetermined desired pressure is reached. At this pressure, the excess oil delivered by
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the pump through the pipe B will be bypassed to the oil pan through hole G without going through the * bearings. Thus, if the oil pump has 100 percent greater capacity than is normally required by the engine, one-half of the oil delivered by the pump will be returned to the oil pan through the relief valve. In such an engine, bearing wear up to a certain point results in more oil being pumped through the bearings and less being bypassed through the relief valve.
The gage pressure, however, will remain the same. As soon as a point is reached when the bearing wear is so great that the full pump delivery is forced through the bearing with none being bypassed, then any additional bearing wear will cause a reduction in the gage pressure.
It is thus evident that when the usual large capacity pump is used, considerable bearing wear may result in excess oil being forced through the bearings and thrown out at the ends without any reduction in the gage pressure. This will obviously induce oil pumping and high oil consumption.
On the other hand, if the pump capacity is very ‘ * close to the normal requirements of the engine, sometimes a relatively small amount of bearing wear will result in reduced oil pressure gage readings.
‘	ENGINE BREAK-IN
If the instructions for installing bearings as given in this treatise are followed, there will be no tight
bearings which will require “running-in.” However, the natural antagonism of new raw metal surfaces (such as a newly ground shaft and new bearings) working against each other should be overcome by deep and thorough wetting with lubricating oil.
To obtain this oil wettedness and otherwise condition the bearing surface, use an oil a grade or two lighter for the first 500 miles than the engine builder and oil producer specify for regular operation.
New piston rings, pistons, and refinished cylinder bores will be more sensitive to break-in abuse than the main and connecting rod bearings. Any break-in procedure recommended for standard or special types of pistons or piston rings will be agreeable to . the bearings, if installed as directed.
A DETONATING ENGINE WILL PREMATURELY DESTROY ITS BEARINGS
A “detonating” engine (spark knock, ping) will prematurely destroy its main and connecting-rod bearings. Detonation may be caused by an early spark, a lean carburetor, unsuitable fuel, a hot running engine (caused by a clogged radiator or water jackets or a late spark), or heavy carbon deposits in the combusion chambers or on the piston heads. An engine must not labor, lug, and detonate at low speed. Shift gears to use a higher engine speed and relieve the strain.
OIL AND LUBRICATION
The life blood of an engine is its oil.
Select a good lubricating oil on the basis of competent advice which takes into consideration all features of the engine construction and its type of operation and MAINTAIN that oil properly.
It is not a sufficient safeguard that the original filling of oil was of the proper specification and the level maintained by additions of the same oil. The oil must be changed at the intervals recommended by the oil manufacturer in order that it be kept free from harmful contaminents, the most active being those acids which attack certain heavy-duty types of copper lead and cadmium alloy bearings.
Keep the oil level up to the “full” mark on the gage. A full oil pan means cooler oil.
CHECK LIST FOR A BEARING REPLACEMENT JOB
1.	Was the work done by careful mechanics in a clean and orderly shop?
2.	Were the correct bearings to suit the engine model installed?
3.	Were the crankshaft journals and crankpins round within the required limits?
4.	Were the crankshaft journal and crankpin diameters accurately obtained?
5.	Were the crankshaft journal and crankpin surfaces smooth and correctly finished?
16
6.	Was the crankshaft in correct alinement and free from bow and disorder?
7.	Were the crankshaft oil ways clean?
8.	Were the crankcase bearing saddle bores round within the required limits and in correct alinement?
9.	Were the connecting rod bores round within the required limits?
10.	Were the connecting rod bores and piston pin bushing bores parallel and free from twist within the required limits?
11.	Were the radiator, water jackets, water hose connections, thermostats, water pump packing and the cooling system in general, inspected and is it in good condition?
12.	Were the intake valve stems and guides in good condition to prevent oil loss?
13.	Was the engine interior including all oil passages thoroughly cleaned before reassembling?
14.	Was the oil filter attended to?
15.	Was the air cleaner attended to?
16.	Was the vacuum booster pump diaphragm inspected?
17.	Was the condition of the cam bearings checked for wear?
18.	Did all main and connecting rod bearings have correct radial oil clearance?
19.	Did the crankshaft and connecting rod bearings have the correct end clearance?
20.	Was the torque indicating wrench with the correct settings used in tightening all bolts and nuts and were the wrench sockets of the proper diameter to avoid pushing caps sidewise?
21.	Were all caps assembled in their proper positions and locations?
22.	Was the bearing installation finally checked and prelubricated with a suitable bearing oil pressure loss indicator tank?
23.	Were all disturbed gaskets replaced?
24.	Was a lighter grade of oil used for the first charge after reassembling?
25.	Was the oil pressure normal?
26.	Was the engine free from detonation and spark knock?
o