4 bolt main conversion.
Burning Brakes
Joined: May 2004
Posts: 996
Likes: 13
From: Dallas TX
The upper untapped hole doesn't appear to be on the same axis as the original threaded hole. It looks shifted right vs the original hole. Is this just an optical illusion or is there a purpose for that?
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Instructor
Joined: Dec 2017
Posts: 239
Likes: 17
very well could be off center, I didn’t locate center of block casting, I bolted the cap on with the center bolts and aligned to the bottom then tightened and then found center of outside hole of cap and drilled in that spot. Seems gm’s tolerance were pretty dang loose when it came to hole placement.
Racer
Joined: Aug 2011
Posts: 493
Likes: 217
When the center 3 caps are replaced with billet caps the boring bar is registered off the original front and rear cap, not sure how you would bore that will all the caps replaced. After thinking about it, you could replace the center 3 then located off them after they were cut, then cut the front cap, then located off number 1 and 4 and cut the rear cap and then of course line honed it
Last edited by Vortecpro; Feb 26, 2018 at 08:27 AM.
Thread Starter
Instructor
Joined: Dec 2017
Posts: 239
Likes: 17
When the center 3 caps are replaced with billet caps the boring bar is registered off the original front and rear cap, not sure how you would bore that will all the caps replaced. After thinking about it, you could replace the center 3 then located off them after they were cut, then cut the front cap, then located off number 1 and 4 and cut the rear cap and then of course line honed it
Heel & Toe
Joined: Feb 2018
Posts: 23
Likes: 1
When the center 3 caps are replaced with billet caps the boring bar is registered off the original front and rear cap, not sure how you would bore that will all the caps replaced. After thinking about it, you could replace the center 3 then located off them after they were cut, then cut the front cap, then located off number 1 and 4 and cut the rear cap and then of course line honed it
I have the same set up and thats what I would do. I actually have some junk caps that have been cut down and narrowed for line boring I use them on 1 & 4 when cutting the 3 center caps in and front and rear 2 & 4 journals seems to work fine. Always finish with an align hone. The PLB-100
Last edited by BROKEN RODS; Feb 26, 2018 at 11:24 AM.
Thread Starter
Instructor
Joined: Dec 2017
Posts: 239
Likes: 17
Thread Starter
Instructor
Joined: Dec 2017
Posts: 239
Likes: 17
When the center 3 caps are replaced with billet caps the boring bar is registered off the original front and rear cap, not sure how you would bore that will all the caps replaced. After thinking about it, you could replace the center 3 then located off them after they were cut, then cut the front cap, then located off number 1 and 4 and cut the rear cap and then of course line honed it
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Instructor
Joined: Dec 2017
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i got it to the machine shop and he said it looked very good but yes i think it’s all in the caps. If you have the right equipment and basic knowledge then it’s easy but if the caps aren’t dang close to your last ones you just opened a can o worms
Melting Slicks
Joined: Oct 2008
Posts: 2,154
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From: Regina Sk Canada
I picked up a nice std bore 4 bolt main block for $250.00 Planning a 7200 rpm 331Ci build for a 64 Chevy II i am looking at. Local guy here has close to 25 four bolt main block that he has collected
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Instructor
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