I was looking to buy a used 350 to rebuild. I found one and it all looked good until I felt a scratch in one of the cylinders. I haven't bought it yet. The deepest part of the scratch is about 1/8 of and inch. I was wondering if a .30 overbore would make it ok or if I should just look for a different engine.

 

.030" overbore = remove .015" of metal

1/8" = .125" (more than 8 times as much as a .030" overbore)

A 1/8" deep scratch would probably hit water, it would be so deep. Odds are, it isn't that deep.

It can be real hard to evaluate a block for boring even when you'er standing there looking at it with a micrometer in your hand. It's impossible to make that judgement without seeing it. Who knows, sight unseen, if the block has already been bored (did you measure it?); how worn the metal is around the scratch, if it's worn .010" and has a .010" deep scratch, that's a .040" bore to clean it up if all else is perfect; whether the cylinders are centered or not, if that .010" scratch was on a side of the cylinder that was already .010" to the side of where it's supposed to be, that's .040" boring to clean it up; etc. etc.

Either get a better measurement of the damage, or pass on it and keep looking. There's millions and millions of 350 blocks in the world, it's not like you'll never find one again. Even a block that looks perfect carries some risk so dont think you can ever eliminate the chance of buying a useless one. It happens to everybody once in a while.

My personal favorite was a 4-bolt 350 block, looked perfect to the eye, no cracks, etc. Had it bored and various other machine work done to it; but when we put it together, it seemed really hard to turn. Upon closer inspection, it turned out that the block had so much core shift that the cylinders were nearly 1/16" to the rear of where the crank was; the factory pistons had enough space for the small end of the rod to be that far off center and not cause a problem, but better ones didn't, so the rods would bind from being forced to the side. We scrapped about $400 worth of paid-for machine work, basically took all that money out of our pocket and threw it in the garbage. Who would ever think to check a block for something like that???

Good luck!

 

Thanks for your help. I was also wondering around how much it would be to get a machine shop to bore a 350 .30 over?