4 bolt main caps on a 2 bolt main 454? - Chevelle Tech
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post #1 of 3 (permalink) Old May 3rd, 05, 10:22 AM Thread Starter
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4 bolt main caps on a 2 bolt main 454?

Just pulled the pan on the 454 I got for the Barbie Elky, The engine came out of a 81 pick-up. It has 4 bolt main caps but only two of the holes are being used and the block has not been drilled or tapped for 4 bolt. Was this a common thing for GM?

When I asked my engine guru he said that the caps must have been replaced and the prior rebuilder didn't bother to have the block drilled & tapped. I always thought that if you replace the caps you have to line bore the engine to make it match the new caps. So why not drill & tap at the same time?

Checked the archives.....nothing there.

Thanks,

Ron
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post #2 of 3 (permalink) Old May 3rd, 05, 12:33 PM
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Re: 4 bolt main caps on a 2 bolt main 454?

I've seen a small-block 400 where the block was drilled but not tapped for the outer bolts, and then GM installed two-bolt caps on it.

I'll believe 'most anything when it comes to production line screwups.
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post #3 of 3 (permalink) Old May 3rd, 05, 12:36 PM
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Smile Re: 4 bolt main caps on a 2 bolt main 454?

Quote:
Originally Posted by freakinbarbie69
Just pulled the pan on the 454 I got for the Barbie Elky, The engine came out of a 81 pick-up. It has 4 bolt main caps but only two of the holes are being used and the block has not been drilled or tapped for 4 bolt. Was this a common thing for GM?

When I asked my engine guru he said that the caps must have been replaced and the prior rebuilder didn't bother to have the block drilled & tapped. I always thought that if you replace the caps you have to line bore the engine to make it match the new caps. So why not drill & tap at the same time?

Checked the archives.....nothing there.

Thanks,
Well, the short answer is he was lazy, but they maynot have had the necessary tooling to do the job right. You just don't drill some holes and tap them. There's counter bore to deal with, the depth is critical as you can crash out at the bottom. Then the taps are a whole different ball game, and last but not least, a nice big narly vertical mill with enough room under the milling head to do the job.
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