Crankshaft Hardness

[n2omike]

Took my crank to ShaftTech in Ohio to get cut 0.010" on the mains. Very high end place that does amazing work. They are cutting it to half a thou below low limit, which is great. Turn around was only a few days! They came HIGHLY recommended, and are supposed to be almost magic. Northwest Ohio, about 40 miles north of Toledo.

Anyway, They offer Nitriding. They said the rods had a hardness in the low 50's, and after cutting the mains they he said they were around 42 I believe. He said Nitriding would take another 2-3 weeks and cost an extra $100. But, he was very straight up and honest, and said that the crank still had some hardness to it, and old factory cranks generally came out in the low 30's. The last crank I used was an old Boss 302 that was cut 0.030"/0.040" on the main/rods, and it was never hardened. Worked just fine.

I told him not to bother, and to just send it. He said it would be just as strong, it would just have a slightly shorter service life. Last crank lasted over 10 years, and still looks fine, even after breaking a rod bolt! lol

Anyway, enough rambling. For future reference, anyone care to provide an education on crank hardness, and hardening procedures? Its benefits?

Thanks!

[modok]

I personaly believe hardness is more important with harder bearings.
You can run a very soft crank on tri-metal bearings, if oil stays clean, it'll outlive you.

Also a fan of relatively mild steel tuftrided cranks, aka carbo-nitiriding.
Still used by honda sometimes, and in Duramax, just lovely cranks.
It's not very deep hardness but far less likely to crack.

[MadBill]

Yes, an added benefit of processes such as nitriding that infuse material into the crank surface is that they produce a compressive layer that increases fatigue life by ~50%.

[pamotorman]

i offset ground 350 chevy cranks to make 3.562 strokers for short track engines and never had a crank or bearing failures