I have been looking at some irons which I am considering using for an engine build. Basically planning to be just stock, probably not even ported and running simplified sequential twins at 10 - 12psi max. I have been reading all of the threads I can find regarding lapping, re-nitriding, and/or just breaking the glaze on the surface. Fortunately the plates I am considering have minimal step wear (<0.0015) so lapping and re-nitriding isn't really a consideration.

But it brings me to a question. From what I have found there seems to be some uncertainties regarding the depth of the original Mazda nitride layer. I have seen numbers ranging from basically just on the surface to a depth of .006" or .007". One of the most common thoughts is approximately .004". If you look at the FSM Mazda says the plate can be re-used if step wear doesn't exceed .0039". Is that a clue on what the nitride depth could be. It would seem that Mazda wouldn't say a plate can be re-used if the corner seal pathway is through or nearly through the nitride layer.

Anyway any thoughts from people who know much more about this than myself would be appreciated.

 

Even pre-nitrided irons have a wear limit of .004 so the limit has nothing to do with nitriding thinkness, but rather the side seals ability to seal a plate with excessive step wear.