OK Engine Builders what about nitriding cast cranks?

[Tim Corcoran]

This question is related to the bennifits or negative aspects if any of nitriding an aftermarket cast crank. Does the process make the crank stronger, last longer and less prone to cracking?

Tim C

[Tim Corcoran]

This question is related to the bennifits or negative aspects if any of nitriding an aftermarket cast crank. Does the process make the crank stronger, last longer and less prone to cracking?

Tim C

[Tom Vaught]

Nitriding a cast crank is a common process from
Moldex. Makes the crank surface harder so better
bearing life with Hard bearings.

A very smart bearing engineer from Federal Mogal
told me last week that Aluminum bearings will
show no wear if properly set-up but will not eat
foreign material well.

I need to pick his brain more before he retires
at the end of the year. He understands the Nitride process very well too.

Any questions you want to ask him before he retires? I will create a new post on that, sorry Tim.

Tom Vaught

[Brian Baker]

Ask him about any benefits of it in a racing application, particularly if some "foreign" material does get between the crank and the bearing? Any benefits on a forged crank?

[Robert C.]

When nitriding a casting or crank shaft you are hardening the surface area. Most times no more then .010 deep below the surface. You must have it put .020 deep per side and regrind the surface down .010. The heat treat process is done in an oven. The Nitriding is a carbon gas that is injected in to the oven under pressure. The crank is suspended in the oven on it end to keep it from warping. The crank is heated to around 1000 degrees for a length of time that will determine the depth. Then it is quenched for hardening in oil or water. Then it may have to be annealed to the proper hardness. The longer it is in the oven the deeper it will go. Cost is based on how deep it is done. To check if a crank is Nitrided take a file and file a surface lightly. If the file bounces off it is nitrided. You stop filing metal around 38 to 40 Rockwell hard on the C scale.

Cnc machine beds have there moving ways harden in this way to help with ware.

If you have a hard surface and flexing involved you my cause a crack to start sooner then if it was soft. They will start in the corners first. This is why there are radii on each side of the crank main and rod journals. Remember it is still a casting that is soft in the middle. This will let the casting flex with out braking. It is just for ware and will not add strength to the cast crank. It will polish to a finer finish and rotate with less surface tension in an oiled bearing. If you change the crank shaft before you have used it to its service life your motor will last. The cast crank will do a good job in a high horse power motor, but for how long. Buying a cast crank and trash it after a season and replace it may be an answer to buying a $2,200.00 crank. Most racers use up the life of their parts and they brake the motor. They blame it on that damn cast crank. But if you do preventive maintenance and change the high risk parts out you will be better off in the end and cheaper too. I plan to trash my crank after 125 runs. Most races are on a budget and will run until something brakes. Would you pay $250.00 dollars and your time to save your motor that you may have 10k in? This is just 2.5% of the total cost. Cheap insurance is it not? Same goes on the block. $2,200.00 or 3k and plus the casting surcharge of $107.00 as of the last pour. And don’t forget the tax if you live in Va.

I agree with Tom statement: if the block does not move, then less stress is past to the crank. Less movement the longer it will last.

[SupergasDil]

I've had my last 3 cranks nitrided and so far with great results. One in my current engine, one in a race engine and one in a street engine. Also nitrided cranks will have a flat black appearance.

[Mr. P-Body]

Nitriding is a "low temperature" heat treat. According to Moore & McMillan (in Sevierville, TN, where we get ours done), it's done at 900 degrees (F). They charge based on weight. It costs $1 per pound, with a 250 lb. minimum. This is a crankshaft company, not a heat treating company. They are intimately familiar with the problems associated with crankshafts. They hang the cranks from the snout. We had a heat treating company try one, locally. They turned a nice 302 Ford crank into a doorstop...
All machining must be complete before nitriding, including balance. Once the crank comes back, a quick polish of the journals will remove any residuals. We have seen no more than a .0005" change in diameter, and never a warp.
In one 400, the man revved a cold engine too hard, and hung the relief valve in the pump. It began knocking almost immediately. We took it apart, and found two rod bearings starting to melt. Peeled the material off the journal, polished it again, threw in new bearings and a new pump, and he got about 200 more passes out of it before we lost touch. Nitriding saved that crank!
FWIW

[4mula71]

I use a shop in Richmond, VA that primarily manufactures gears but also performs their own nitriding and heat treating processes. They Ion nitride which is virtually distortion free because it operates at a lower temperature than conventional nitriding. Heat can relax or induce stress, which can create cracks (micro or otherwise).
I have had 21" diameter gears made of 4150 steel, hardened to 52 Rc, and have seen less than .0003 distortion or growth in diameter. The typical penetration is .050 deep.
My recommendation would be to first have the crankshaft stress relieved, then mag particle tested for cracks, then grind, nitrided, then finish grind if necessary.

[Tim Corcoran]

I appreciate all the responses. My primary question is, does the nitriding process make the crank stronger. What I mean by stronger is will the crank provide longer service before stress cracks develope. We know that cast cranks will eventually crack if it is ran in a high performance or racing application. I understand that the nitride process will harden the journal surface, and it seems that some people believe that the hardened surface does give some bennifit as far as bearing and journal wear. This is a little off my main point though. Although the surface hardening may reduce wear of the journals, I don't believe that it strengthens the crank at all. My theory is that a nitrided surface will excellerate stress cracks. The reason I believe this is, since the hardened surface will resist flexing at a different rate than the parent material, the transition of the hardened surface and the parent material in the journal radius area will create a stress riser. This is just my opinnion though. I talked with a guy from Ohio Crankshaft yesterday on this subject. He told me that he does not have any data that would support that nitriding a cast or even a steel crank extends the service life of the part. He also made the same statement about stress relieving using cryogenitcs. I personally am not convinced that a stress relief using cryo after all machining would not lead to extended service life. Ohio Crankshaft is no small outfit and they are involed in racing so I find it hard to discount their opinnion on this subject.

Tim C

[Mr. P-Body]

Nastiac, I'm very interested in the shop in Richmond. Who is it? I live in Chesterfield and do a lot of business in Richmond. If I could find someone that could do it locally, it would be a big help.

[Robert C.]

Call me at 804-349-0014 I deal with them ever week or so. Midlothian, VA.

[4mula71]

Tim
Stress relieving aids grain flow of the material, which reduces cracks and adds more structural integrity, so I believe it is stronger. I am not a metalurgist to tell you how much stronger. And I was referring to a heat type process to stress relieve, not the cryo method, although I hear the cryo method is better (and more costly).
Bob
Contact Mel Belcher at Progressive Engineering 804-648-7221. He should be able to help you out with any hardening process that you need.