I'm assembling a '55 261 that's 10 under on the mains. The chevy shop manual says to use shims on both sides of the main caps and remove shims to get the right bearing clearance. I've also been told that the block and caps were factory line bored and shims should not be used. If I tighten the caps with no shims, the crank is locked in place. The counter-bores mic slightly oblong (wider than tall) shims may correct it I haven't tried any. If the caps are torqued without the bearings, the parting lines can be felt, but these caps and this block were a running engine to start with. I've got conflicting advice on shim vrs line-bore. Have you had this sitution and what did you do. Shims are cheap next to the line-bore, but I want to be right. Thanks. joe
