The Crankshaft Co.'s take on Nitride treated cranks.

[packinkimber45]

Hello everyone. Recently I have had the misfortune of having to either find a used/new or debate having my nitride coated dsm crank reground. I have heard many say it is okay to grind the crank including known vendors on this site, and handful of people say not to. Browsing through the internet tonight I found this article on crankshaft company. They state...

Recently, we have received quite a few questions regarding crankshaft journal hardening processes and concerns about machining steel crankshafts that have been hardened. Since a solid explanation will take longer then a paragraph, we have left this answer out of our frequently asked questions page so that we could devote more time to a detailed answer.

There are three common types of hardening processes used on steel crankshafts, and they are induction hardening, tuftriding, and nitriding. Below I will explain these hardening processes in more detail.

Most stock OEM steel crankshafts have been induction hardened. This is a low cost process in which the surface is heated by a high frequency alternating magnetic field that generates heat in the crank's surface quickly before being quenched. The depth of this hardening process is around .060 - .080. Because of uneven heating and cooling, this crankshaft hardening process creates stress within the crankshaft. While it is an ideal hardening process for stock applications, it is less then favorable for high performance racing applications.

Tuftriding was a process used by some OEM's on special high-performance crankshafts, primarily to avoid the stresses imposed by induction hardening. In Tuftriding, the crankshaft is immersed in hot cyanide compounds, creating a tough, resistant surface that improves fatigue resistance. The hard layer in a Tuftrided crank is usually very shallow, only penetrating around .005. One drawback of Tuftriding is the potential for warpage of the crank.

Nitriding is a chemical hardening process in which the part is heated in a furnace, the oxygen is vacuumed out, and nitrogen is introduced which penetrates the entire surface. The depth of hardness is dependent upon the time the crankshaft is exposed to the gas. Typically, a nitrided crankshaft will have a hardness depth of about .010 - .030. Nitriding is a low heat process compared to Tuftriding, but it shares the advantage of avoiding the introduction of localized stress zones as in induction hardening.

In most cases, a stock OEM steel forged crankshaft can be welded and/or ground then installed without concern. The induction hardening process has a significant depth, and on non welded journals will remain after being ground.

Tuftrided crankshafts can be welded and ground without concern. However, the shallow depth of the hardness would be lost after the grind. Therefore, it is recommended to have the crankshaft hardened again.

Nitrided crankshafts can easily be welded and ground without concern. A .010 undersize grind will cause some of the benefits of nitriding to be lost. At .030+ undersize, nearly all of the nitriding benefits are lost. Therefore, it is recommended to have the crankshaft hardened again after grinding.

It is important to discuss crankshaft hardening with the machinist which will be grinding your crankshaft prior to the weld and/or grind. These hardening processes can add to the size of the journals, so the crankshaft needs to be finish ground in such a way that allows for the expansion caused by hardening. I have personally ground new aftermarket crankshafts that were shipped out of tolerance. Trust me, as a machinist it is time consuming to setup and grind off .001 of an inch. So please let your local machinist know if you plan to have the crankshaft hardened!

There are some automotive machine shops that will not weld a steel crankshaft because it has been hardened. As a machinist, I have never turned away a crankshaft weld because of hardening. If you note my explanation of the hardening processes above, hardening is generally restricted to the surface. To weld a tuftrided or nitrided crankshaft, the journal or thrust needs to be underground first to remove this surface hardening. Then the weld can be applied. In cases where induction hardened crankshafts have been severely damaged, normally pre-grinding the crankshaft for a weld removes this hardening.

What about cast iron crankshafts? Do they need to be hardened? The answer is no. During the machining process, cast iron crankshafts become work hardened. If a more durable crankshaft is desirable for your application, it would be a good idea to look into purchasing an aftermarket steel crankshaft.

I want to see how everyone feels about this known issue and the following info. Anyone with lots of machining and motor building experiences feel free to chime in.

 

[tkelly27]

It never made sense to me that these crankshafts were always considered time bombs when they are cut. Even if you get rid of all the hardening, you can get it re-done! Mine has been ground and I haven't broken it... yet. I think it does say in the FSM somewhere that you must replace the crank, and I think that's where everyone got the idea that you have to throw them away.

"Do not attempt an undersize machining on the crankshaft with special surface treatment. This crankshaft can be identified by its dull gray appearance."

Anyway, doing a search you find one person who blames his spun rod bearing on a machined crank, and another guy running 11's in a DD on a .010" under crank. I probably wouldn't put one into a 1000hp machine, but I don't think I could ever afford a top end that would break the crank I have right now.

 

[interex]

I don't see why anyone fears running a .010 under crank. You have to understand that is only 0.25 millimeters. You won't hurt anything using a .010 under crank. SBR and quite a few other places sell them and I'm sure most anyone who has bought a reman crank can swear by them. Cranks are hard, they are the backbone of the engine, they are tough already. Good Luck.

 

[Defiant]

It's not a matter of anyone's feelings. Mitsubishi say the crankshafts used in DSMs are a non-serviceable item, and are to be replaced if they measure out of spec, and are not to be reconditioned.
Many ignore, or aren't aware of this, and continue on blissfully. So far as I am aware (or, would ever tell), the hit teams from Mitsubishi have never killed anyone for not following their admonitions.

That anyone has ever found out about.

 

[packinkimber45]

Thanks for clarifying that defiant. As far as what the manual states I know that it states not to do it. My fault for wording it wrong. How about based on everyone's experiences and have gone this route. Share your experiences and results. How many horsepower, how much was it undercut, what bearings were used if not oem, how many miles the crank has surpassed w/ no ill effects and such. Then off course those who have gone this route that had a crankshaft failure or spun bearings that could have been from getting the crank reground. Not looking to change my route or anything as I am going to be ordering a new crank. Just want to see how many are going this route with success or failures. I'm sure there are other variables that can cause spun bearings and crank failures. But ones I am talking about are one's that had high contribution to the failure due to reground cranks.

 

[interex]

Sure, quite a few engine manufactures state that exact same thing. It's one way of doing two things... Cause the consumer to spend more money, and help keep the engine in spec. It isn't just a mitsubishi thing, and it isnt that the crankshaft cant, and wont handle it but just a statement they like to put in the "manual" to protect theirself.

 

[SnowBird]

I used a cut crank in my first talon 2 years ago. Crank was cut 10 under and I had it balanced and polished. I also had my block line honed, and my pistons and rods weight matched.

I spun rod bearing number 3 after 1200 miles, the knock came out of nowhere one day and was undriveable right away. Was it the crank? I dont know, but Ill never use one again.

 

[packinkimber45]

That sucks man! I bit the bullet today and ordered a new crank through sanrafael mitsu. Steve was great to deal with not too mention they have really good prices. Cheapest I found the crank online was $750, and locally at my mitsu dealership was $730 plus tax. He was able to sell me one for $648.75 plus shipping which should not be more than $35-40.

This was the type of answers I was looking for. Looking good. Let's keep it coming everyone.

 

[freeman 188]

mine was regrinded to .10 under and is still working great ,1000 km,s at 20psi of boost ,I used clevite bearing and all is good