Nitriding and crank grinding

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needsaresto

needsaresto

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Quick question or two here. When grinding a cast crank (say for example a 360 crank to 340 mains) and removing lots of material, can it be nitrided?
Or is that just for forged cranks?
Is it necessary if possible?
He doesn't feel grinding a 360 crank down this far will affect strength, but it will remove all surface hardening?

What are your feelings on cutting down a 360 crank to fit 340 mains? I realise the scat cast crank is $289 bucks,but I might have scored a FREE 360 crank. So I could potentially have a 3.58 340 main crank for the cost of grinding it. Acourse balancing costs might make a stock crank a bad idea.

Local machinist wants $150 for grinding a crank,no matter what crank or how much material removed. That's canuck bucks in a remote area.

Also wants $25 per hole for boring/honing. So $200 will get you a hot tank,cam bearings and bore/hone. $150 to deck a block. Not bad prices for here. He's the only guy available locally. More of a G.M guy...but a good machinist. Dealt with him before.

Im determined to pursue the 349 build for my M. Need torque for that heavy pig. Thanks BJR!
 
If your in the sticks, so to speak, I can't see nitriding and having a factory oe turned is cost effective. You will still not have the rolled fillets (the radius on the journals). Turnign the journals down is one thing, but for a quench build engine, you should have it indexed and stroke corrected, because a varience on either of those of .005-.010 can create problems and wont be found until the assembly phase. Nitriding gives some strength but is primarily a surface treatment. Done properly it can go deep enough to not worry about it if you are turning the journals down .010. If you are truly looking to make a factory crank better, I would first cryogenically treat it, then machine it, then nitride it. Cryo goes completely thru the material, and changes it's structure, making it much stonger. However like heat treating, it will change shape, so you have to do it prior to machining. (and yes, machining it gets much harder...lol)
 
moper said:
If your in the sticks, so to speak, I can't see nitriding and having a factory oe turned is cost effective. You will still not have the rolled fillets (the radius on the journals). Turnign the journals down is one thing, but for a quench build engine, you should have it indexed and stroke corrected, because a varience on either of those of .005-.010 can create problems and wont be found until the assembly phase. Nitriding gives some strength but is primarily a surface treatment. Done properly it can go deep enough to not worry about it if you are turning the journals down .010. If you are truly looking to make a factory crank better, I would first cryogenically treat it, then machine it, then nitride it. Cryo goes completely thru the material, and changes it's structure, making it much stonger. However like heat treating, it will change shape, so you have to do it prior to machining. (and yes, machining it gets much harder...lol)
Click to expand...

I assumed he was talking about a factory stroker. Mp's are full radius.......
 
That's what I meant... no matter how you "cut it". the stock 3.58 stroke isnt going to be as strong as the MP part. For $300, it's really a no brainer.
 
Cryogenics ? Like what ? dipping it in Liquid Nitrogen. I don't see how this will harden the material, and for that matter, this is a "cast" crank we are talking about here, not a forged crank.

Cast steel is stable and will NOT distort anywhere near what a forged steel crank would, when put under these conditions (or heat treat).

This is why forged cranks should be stress relieved after machining/prior grinding.

Either way (forged or cast) Nitiding it will not hurt.

I do have to agree with the removing a large part of the rads, you will for sure loose way to much strength, and the cast cranks are already weak.

Nitride is surface hardening only, will only help slow down wear factor.

I strongly feel that machining your crank in this manner, however inexpensive it may be...it's a timebomb ticking.

Don't do it.

My ramble.
 
Cryo treating is not just dipping it. I'm not positive on the minute details of the process. But all cast iron and steel gets significantly more dense and stable. I've seen the difference and it has amazing affects. But it also
distorts like mad regardless of what the people say...lol
http://www.300below.com/cryo-processing/motorsports.html
 
340butterduster said:
Cryogenics ? Like what ? dipping it in Liquid Nitrogen. I don't see how this will harden the material, and for that matter, this is a "cast" crank we are talking about here, not a forged crank.

Cast steel is stable and will NOT distort anywhere near what a forged steel crank would, when put under these conditions (or heat treat).

This is why forged cranks should be stress relieved after machining/prior grinding.

Either way (forged or cast) Nitiding it will not hurt.

I do have to agree with the removing a large part of the rads, you will for sure loose way to much strength, and the cast cranks are already weak.

Nitride is surface hardening only, will only help slow down wear factor.

I strongly feel that machining your crank in this manner, however inexpensive it may be...it's a timebomb ticking.

Don't do it.

My ramble.
Click to expand...

I dunno. It ends up being the same as a 318/340 cast crank at the mains. Could be ground with a full radius too.

Are you saying mopar cast cranks are weak? NOT! Among the strongest of factory cranks!

My concern (and why I asked about nitriding) has more to do with almost a 1/3 inch of material removed from the mains,what about the factory induction hardening? Is it gone when this much is removed?
 
I dont know the exact amount to remove... But, if it's .150" from each side you could have a radius made on it. Again, lots more cash tho as it's not really easy to do without being setup for it. The MP cast cranks are good. And again, the one designed to to that exact job and be 100% strong is cheap. There is no value in it, even with import duties you may have to pay. Any cast crank gets less strong by cutting. You're reducing the diameter by .333? I dont know the sizes off the top of my head. The factory specs a max of .040 to retain factory strength. You're only exceeding that by 800%. Why not :D?
 
moper said:
Cryo treating is not just dipping it. I'm not positive on the minute details of the process. But all cast iron and steel gets significantly more dense and stable. I've seen the difference and it has amazing affects. But it also
distorts like mad regardless of what the people say...lol
http://www.300below.com/cryo-processing/motorsports.html
Click to expand...
.

Very interesting stuff, I'll be doing some more exploring on the subject.
Thanks, for the info.
 
needsaresto said:
I dunno. It ends up being the same as a 318/340 cast crank at the mains. Could be ground with a full radius too.

Are you saying mopar cast cranks are weak? NOT! Among the strongest of factory cranks!

My concern (and why I asked about nitriding) has more to do with almost a 1/3 inch of material removed from the mains,what about the factory induction hardening? Is it gone when this much is removed?
Click to expand...

I wasn't comparing a Mopar crank to any other make cast crank, did I ?

What I said is a cast crank is weak, as in much weaker then a forged crank.

Cast cranks (ductile iron) have a 100,000 psi tensile strenght @ 50rc (temper hardness).

A forged steel crank has a 140,000 psi tensile strength.

Only 40% better.


Now a 360 main Journal dia. is 2.810", and 273/318/340 main journal dia. is 2.500" dia.

You will be removing .310" dia. (11.5 %) .

Now you do the math, your cast crank is 40% weaker then a forged and you want to take another 11.5 % away from it!

Now do you see were I'm coming from, just trying to save you some grief.
But by all means, it's your crank, your engine, it's your choice.

As far as the factory induction hardening, with this amount of material removed, I would have to say I don't know, but I would not risk it.

Try and sell that crank, and get yourself the one you need.

All the best
 
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