Chevy and GMC Duramax Diesel Forum - View Single Post - LB7 Rebuild-Nitride Crank?
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post #4 of (permalink) Old 06-20-2019, 04:30 PM
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Originally Posted by palamesa View Post
I'm doing a rebuild on my 2002 DMAX. My local machine shop (who I've been using forever for gas engines) did the machining and short block assembly for me. This was their first DMAX. The motor had 250K miles and cylinder wall damage from a blown head gasket. We went .10 on the crank mains and rods and .30 over on the cylinders. I came across some older threads about the need to re-harden the crank after machining. I've seen some say it's required and others say it's not. I'm also interested in opinions about the cylinder walls too. Do they need anything done after going .30 over.
I'm hoping now that these engines are being rebuilt in large numbers I could get updated information. It currently is on my engine stand with all new ARP bolts and I really don't want to take it back apart.
I think your hardening question would depend on how hot the crank got during machining as well as if the crank was surface hardened or through hardened, which i do not know the answer to. if it was kept cool and through hardened, then there should not be any change in the hardness, though heat treating it again would likely relieve any internal stresses that may have changed as metal was removed. If it was surface hardened, then depending on how deep that hardening process goes into the metal, you could have ground your way into the softer steel. my guess would be they come from the factory with a surface hardening on them so they are strong and resistant to cracking, yet wear resistant, however i do not know this to be true. Your machine shop can probably answer this question for you though. I'm not a machinist, hopefully one of them comes along and can correct me if im wrong, i know we have a few on this forum. As for the cylinder, assuming the machine shop honed them so you have the factory hatching, you should be good there. I am not aware of any special requirements for the cylinders unless you have so much damage you have to sleeve them, but that doesn't sound like your situation.

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