Nitride on crank question

[83Blzr62]

I took my block to the machine shop to get it machined today. He said that he would probably grind the crank and that it would be fine without that nitride coating after they grinded it. I told him everything I have heard on this website said I should not have it turned or ground. He then said I could just get it recoated if I really wanted to because it was important that he ground it to get correct clearences.

Would it be fine to get it recoated and is there any important information I should know if I do?

[Kennedy]

I don't think the OE cranks were nitrided. I could be wrong. I had my 6.5 crank index ground and nitrided.

[83Blzr62]

What specifications did you get it nitrided to? I got my crank ground and I want to know how I hould get it nitrided.
Thanks,
Kyle

[ronniejoe]

I had my crank index ground but didn't nitride it. Be careful with the nitriding. If they do not remove the compound layer by mechanical or chemical means after nitriding, you actually increase your risk of fatigue failure.

I've attached a photomicrograph of a nitrided surface with the compound layer still on the part after running in a wear test machine for 8,000 revolutions (test conducted by Molinari). Notice the microfragmentation of the surface with a network of microcracks. Each of these little cracks is a potential initiation site for a major fatigue crack that could propagate into the diffusion layer and into the core of the part.

[83Blzr62]

What is index ground and what do you mean by compound layer? They took .010" off of my crank.

[ronniejoe]

Index grinding is a process that ensures that the crank journals are exactly where they are supposed to be in angular orientation and that the stroke lengths are all the same.

The compound layer is a very thin layer of various iron nitrides left on the surface of nitrided parts. It is often referred to as "white layer" because it is white in appearance. You can see it in the photomicrograph that I attached to my previous post.

[83Blzr62]

Well I think that since you got yours ground and not nitrided, I do not need to get mine nitrided because yours was the 6.5 power project.
Thanks,
Kyle