As gearhead says, the main bearing installation is a little convoluted. The
1955 second series service manual does not mention the use of shims. As expected, the
1954 shop manual does describe the need for main bearing cap shims. The
master parts catalog shows a part number for shims for all 1937-57 six cylinder engines, as I read it.
For further confusion, I have two early (1954 or first series 1955) 261s that have the tang-type of main bearings with no shims. To the best of my knowledge, both of these engines were purchased as replacement engines; Chevrolet must have upgraded the engines when the replacements were assembled.
In any event, I agree with gearhead's advice.
Does everyone use the
terrific website that Keith Hardy has assembled?
