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shims on main caps


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The 36 V12 I'm working on has shims underneath the main brg. caps. In my reading on the engine I didn't find any mention of them. Could they have been used to allow extra clearan ce for the crankshaft brgs? The crank will be reground to clean it up on this rebuild.

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  • 2 weeks later...

Some shops used shims like this for a number of reasons, for example, to make extra clearance if the only available bearings were too much undersize for the crankshaft journal. The idea is to provide clearance. The problem is that the "hole" is no longer round. As soon as shims are used, the hole is oblong. Sometimes the shims are put between the bearing cap and the bearing insert to make the hole smaller, but the same problem occurs -- it becomes an oval rather than a circle. Some manufacturers made tapered shim material that was a ribbon, thicker in the middle and thinner on the sides, to try and correct this problem. In any event, it's not a good practice to use shims, even though it was often done in the past. A properly ground shaft riding in properly sized and correctly aligned bearings is the right way to build (or rebuild) an engine.

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