Nitriding isn't a coating it's a heat treatment. Nitriding penetrates anywhere from .020 to .080" into the crank. Even if you took out all the nitrided steel when you grind the crank .010" over you could still have it nitrided again. And if you needed to take more out you can have the crank welded, reground, and nitrided.

 

I know it's not a coating, but I consider it a coating because only a measurable amount of surface depth is nitrited.

Mitsubishi themselves say the cranks are not serviceable, and 99% of the time the cranks are cut and never re-nitrided. If you want to go through the work of welding grinding nitriding and balancing go right ahead but most shops won't tackle the job, it'll cost somewhat similar to a new crank and who knows if it's nearly as reliable as a new crank. I sure as hell don't want a welded crank..............

 

Yeah I was listing that as a last case scenario. If you cut .010'' off a crank you wont have to have it nitrided again. Mitsubishi wants to sell you cranks. I don't trust their opinion. There are cars running cut cranks that run just fine. I wouldn't do it on a 1000hp car, but for most it's fine.

 

Fair enough conclusion.

 

+1, i didnt know the oem cranks were nitrided... learn something new everyday

 

For most it continues to spin bearings. If it cant be micro polished it destined to be a mailbox post or table leg. 10/10 cranks were cool 40 years ago when my Grampa started his shop building budget motors for circle track cars.

I have NEVER seen a 10/10 crank last any appreciable amount of time in anything, if it needs cut you need a new crank.

To answer your question about bearings-

Torque not horsepower is the issue, 550 ft lbs (typically somewhere around 650-700whp) is the normal limit before steel rods regardless of brand or type start imparting damaging harmonics to the bearings. RPM is the next cause of issues and this seems to be anything over 9400. That being said we have a customer who on his steel rod motor was turning 94-9500 and went 10k on one set of bearings. They were not completely damaged when pulled, no noises we were just doing a check pre-season. The car is raced every chance he gets whether its on pump gas (580whp) or Q16 (40psi and 708+). It does not live an easy life but what can you expect when it runs 140+mph traps

 

I'll have to disagree with you Aaron. I have a friend who's seen a BJ's crank out of one of shep's motors that was cut .040" on the rod journals. He says nitriding has no effect on surface action, is only a case hardening process, so it wouldn't effect your bearings anyway.

I'm searching now for a thread where a guy at a metal lab analyzed a cross section of our cranks and found nitriding to be more than sufficiently deep.

I'd say more often than not the crank grinder doesn't know what they're doing, and the customer didn't check it after.

 

What'd the bearings look like? And what type were they?

 

That depends upon the H-beam rod in question.

Carrillo, Arrow, Wossner? - Yes.

Eagle, Manley, K1, Brian Crower, and similar rebranded Chinese rods? - Given the torque loads that typically accompany 600+whp, I wouldn't recommend it.


AFAIK, the factory crankshafts are induction hardened, not nitrided. Induction hardening is a surface treatment - not like nitriding. They should not be turned.

Don't equate the factory crankshaft to aftermarket nitrided billet cranks. The latter are salvageable.

 

That depends upon the actual construction of the OEM bearings, and I can't tell you anything about that, simply because I don't consider using them.

What I can tell you is that a real 'race' bearing usually differs from OEM parts in several ways. For starters, race bearings typically have a harder backing that improves their structural rigidity. Also, race bearings typically have a harder surface material, which although less forgiving to dust and dirt in the oil (which OEMs must consider), is less likely to wear unusually under severe service. Likewise, race bearings are sometimes deliberately configured to channel oil more rapidly away from the edges of the bearing, which is just as important as is feeding oil to the bearing.

With a motor of only 4-cyl that is expected to bear such high torque loads, I am a believer in buying bearings best suited for the job (e.g. ACL Race, Clevite 77, etc.). I even have them sent off for an additional surface treatment before using them.