I had a spare 4.1 291 block sitting around that was supposed to be standard bore, but was actually .030 over. It also had small cracks in the deck on the center bolts. I honed it out to 4" and had it decked .005 to see how deep the cracks were. They were deep enough to cause concern. I put Time Sert thread inserts in the 4 bolt holes affected by the cracks. Attached is a photo of the finished inserts. I used steel inserts and used a big flat whetstone to bring them down flat to the deck. I countersunk the holes to within .015 of the full depth the countersink tool goes to. I modified a Time Sert fixture I bought cheap on E Bay to bolt it flat to the deck with a drill bushing to drill the holes straight, then used the tap and tap guide in the 7/16-14 Big Block Chevy kit to tap the holes for the inserts. I will have another .005 taken off the deck if I ever use this block. The biggest problem is getting the inserts in perfectly square to the deck. I first tried this on a junk block and got them crooked before I used the plate type fixture I modified. Having the inserts even with the deck, instead of recessed as the inserts are intended to be, should keep water away from the studs.
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