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Old 02-26-2006, 02:58 AM
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Main Cap Problem SBC

Hi everyone,

I'm assembling a 4 bolt 350 SBC (entire engine kit) I bought from Larry's Performance in Montebello, California (TERRIBLE company by the way). I am having problems with the front main cap.

I'm installing ARP studs and it is unusually difficult to install one of the studs with the cap in place. It will screw all the way in but requires a significant amount of torque on an allen wrench to do so, even with lubricant. Without the cap in place the stud will screw in freely by hand just like the others. I noticed a slight resistance above normal for the other stud, but nothing like the stud I just mentioned. I made sure the cap is facing the correct direction. I took out the studs and left the cap in place and looked down the holes with a headlight. The holes in the cap appear to be not perfectly centered with the holes in the block, theyre both offset to the side in the same direction - possibly a cap from from a different block?

Sure I can install the cap and the crank spins freely (with what I think to be a reasonable amount of resistance from friction) but the fact that the stud is stressed such a way worries me. You can actually see how it is deflected to the side of the bolt hole in the cap. I don't think the stud is actually bending, I think its just shifting in its threads.

Could/Should I bother drilling the bolt holes in the cap to a larger size so they dont touch the studs? The registers would still keep the cap centered in the critical direction.

Then again, if that interference is eliminated, might it actually put the bore out of alignment? - assuming the mains were assembled and bored/honed with the interference present.

Thanks ahead for any advice!

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Old 02-27-2006, 10:52 AM
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Check the bore with a dail bore guage.

Your No 1 cap might be from a different block. You may need a align hone.

Where did you buy the block from?

If the block has already been align honed, I wouldn't worry about it. I've seen it before as long as the cap will go on with the stud installed.
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Old 02-27-2006, 07:24 PM
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Ok, supposedly everything was checked on the block by the shop I bought the assembly kit from, including the main bores, and maybe they thought this interference was nothing to worry about, but we're dealing with a cheap shop. Sure I can install the cap and the crank spins freely but the fact that the stud is stressed such a way worries me. You can actually see how it is deflected to the side of the bolt hole in the cap. I don't think the stud is actually bending, i think its just shifting in its threads.

Maybe the safe thing to do would be to just enlargen the cap holes at a local shop?

Then again, if that interference is eliminated, it might actually put the bore out of alignment, since the mains might have been assembled and bored/honed with that interference present.
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Old 02-27-2006, 08:08 PM
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Your main caps fit snuggly into a recessed 'saddle', I don't think you'd change the alignment enlarging the holes slightly.
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