My question is if you crank has had a case hardening procedure done, such as nitriding, if you ground .010 on the mains would that affect the overall strength of the crank?

A process such as that only hardens the outer surface of the crank and is only about .007 thick, so if you take that surface off, would you have to re-heat treat it to return the crank to it's original strength.

Thanks,
Brett

 

Yes, you would remove most of the nitrided case (.005 per side on a -.010 grind). Depending on the crank material and other heat treatment that might have been done to it, if you wanted the hard journals you'd need to re-heat treat it. The case hardening is mostly for wear resistance on the journal, but the total heat treating process could easily change the overall or "core" hardness of the crank which certainly changed the strength.

A thought: Assuming the whole crank was case hardened (nitrided), and you just ground the journals, and then re-cased it, most of the crank would have additional case depth, although probably not twice as much as initially. Would this be beneficial?
Again, it will depend on the original crank mat'l and heat treatment. Perhaps you might want to anneal the whole thing first, then go thru the case hardening all over again. This would be safer, IMO.

I would suggest contacting the crank manufacturer and ask for advice. If it is an OEM crank that's a problem. If it's a cast nodular iron crank it's even more of a problem.

Cooking the crank at nitirding temps will probably bend it a little, so straightening is in order, as is polishing the journals to assure size and surface finish.

Sorry if I opened a can of worms.

Did you have a particular crank in mind?

 

I had just seen some eagle cranks for sale for a pretty cheap price because they needed to be ground down from the factory because of "bad journal sizing". I was just wondering how this would affect the crank.

If it doesn't lower the strength of the crank too much, I don't think it would be worth it to get it re-nitrided and straightened. That would sort of off set the deal.

Just considering this as one of many possibilities.

Thanks for the input,
Brett

 

As the old man said it's going to cause excessive bearing wear, and the lowered bearing life alone will off set it.

You can always call Eagle and ask them how thick the case is.

Nitriting was a common practice of race preped stock GM forged cranks back in the day. You would do all of this after you did all the previous prep to the crank.

We were looking into offset grinding a aftermarket 4340 forged crank and using smaller journal rods to get the stroke we were looking for in a competiton engine. It was going to envolve re-heatreating and nitriting the crank after all the work was done. The 4340 core was needed because of the strength and durability.

Bret