1957 - 1965 Corvette: Service Bulletin: Diagnosis and Fitting Main and Rod Bearings
1957 - 1965 Corvettes built with either a 283 or 327 cu. in. engine fall under this factory service bulletin. This information of fitting main and rod bearings to factory specs should be helpful to anyone performing a restoration on one of these Corvettes.
Subject: Diagnosis and Fitting Main and Rod Bearings
Model and Year: NA
Source: Chevrolet Technical Service Bulletin
Bulletin No: DR #742
Date: May 27, 1965
TO: ALL CHEVROLET DEALERS
Diagnosing connecting rod and main bearing problems by visual observation of the bearings requires experience and familiarity with bearing wear patterns.
The information on the following pages is intended to be helpful in analyzing rod and main bearing problems.
In addition, a newly designed front main bearing for 283-327 engines is discussed, as well as methods of selectively fitting bearings.
Normal Bearing Wear Patterns
In some cases, main and/or connecting rod bearings are being replaced due to a misunderstanding of normal bearing wear patterns.
The babbitt overlay on the bearing faces (See Fig. 1) can be as thin as .0005 and in normal short mileage this can be removed from limited areas. This can cause a difference in color or appearance in the bearing face which is sometimes mistaken for being defective bearings.
The bearings shown in Figure 2 have been operated for a short period of time, fitted within specified clearances and show initial wear patterns. This includes examples of minor scratches resulting from minute particles being circulated with the lubricant into the bearing clearance space. This type of wear is considered acceptable and has no detrimental effect on the function of the bearing. Extended operation will complete the wear pattern over the entire surface of the bearings.
When servicing crankshaft bearings, it is essential to use plastigage as outlined in the 1965 Shop Manuals to determine the actual clearance of the bearings. Also, it is important to understand and properly diagnose bearing wear patterns.