Inliners International Forums General Discussion Engines Shims on Chevy Mains?

OK. I have done a search on this question and am still confused.

I scored a 1952 Chevy Truck 235 motor in pretty good condition. On a complete tear-down it shows only light wear in the cylinders, the valve head did need a new head gasket --- here what my question is.
Each main bearing only has a single shim installed opposite the cam side of the main bearing caps. These are NOT laminated "stock" Chevy shims.

This motor has .010 under-size mains, so prior crankshaft work was definitely done (and the crank still looked pretty good).

IF I bolt the main bearing caps back on WITHOUT the bearing inserts in place , without any "shims", torque to spec : should the measurements I get show the main bearing housing bores (saddle bores) to be concentric (round) . OR should those main saddle bores show eccentric (more or less at crown than parting line)?

I can't figure if I am working with 1952 "stock" main bearing bores , or some latter machine shop align boring on them?

Hi Dinky . . .

Shims are not unusual:


But shims on just one side are . . . they are typically fitted in pairs.

Not sure why the previous builder decided to do that. It seems doubtful that any align boring was involved. More likely they didn't have a thin enough shim set so they opted for one side only.

I guess eccentric at the crown is eccentric . . .balanced or not . . . in this case the crown/crest is oblique to the cam side of the caps.

My understanding is that shims were designed to cope with minor differences in crank tolerances - not the basic machining of the block and caps.

regards,
stock49

stock49; Thanks for the reply!

I have been mic'ing the shims and I am getting the sneaky suspicion that they were just part of some standard "shim pack" that was sent with the main bearings. (my shim set is approximately .006"-.008" each, only 4 shims, no laminations -thus maybe they were made for latter 1953+ Full_pressure 235's ?).
Looks like over the many years since that engine was made, all kinds of aftermarket bearings were produced to fit those crankshafts. I think the last re-builder just put the shim pack in that was sent with the main bearings: or maybe they were the precise shims needed to get the proper oil clearance?

Oh well, I found a cheap (but really dirty) set of NOS Clevite .010 main bearings that need a good cleaning, but the babbitt lining looks good and they match all the old shells. Replacing these bearing should let me start over with any new "shimming".

I wonder if I should get some .002" shim stock ,cut my own shims, then use the shop manual method of setting the "feel" of the crankshaft to bearing fit.
Anyone know if Brass 260 shim stock (like at McMaster Carr) is better or worse than the modern plastics, bronze, etc shim stock offered ? http://www.mcmaster.com/#shim-stock/=hs3niz
If the Brass shimstock is fine ... is "1/2 Hard Temper" correct ?