I have only rebuilt one post-1954 engine (a 1960 261, on which I used no shims - the engine is still running strong 38 years later), so my experience is quite limited.
The 1958 Chevrolet Truck Shop Manual states:
(page 8-22)
Main Bearings
.
.
Replacement (Engine Installed)
NOTE: If, for any reason, main bearing caps are replaced, shimming may be necessary.
(top of page 8-24)
NOTE: If new bearings cap is being installed and clearance is less than .001", install shims as required.
Maybe I am just not not finding the mention of using shims when installing main bearings, except in cases where the original bearing cap is not being used?
On page 8-28, the 1958 Shop Manual states that shims are not even used on rod bearings?
I do understand why/when someone might want to use shims to avoid having to get the crankshaft bearing-journals ground; but, I do not see this use of shims described in the 1958 Shop Manual (except for when a main bearing cap has been replaced).
I have been known to mis-read things, so I apologize in advance if I am missing something in the Shop Manual.
