Crank Grinding and Nitriding

[Ishiftem]

For some back story look here: viewtopic.php?f=1&t=65232&start=15
Eagle bbc (409) crank. It was ground .010 and he screwed up so he agreed to grind it another .01 N/C. Well the guy needs to step away from the grinder. Very poor finish, some radii have flat spots (not even sure how that is even possible) and the journals grow .001-.002 in diameter befor the radius starts. I have found a competent person to do the grinding but here is my question. It will have to go another .01 under so that would make it .03 under. I would imagine that the nitriding would be gone at that point. Plus the rod side clearance is now .033 which I imagine will grow a touch after grinding again. Would it be ok to run with the nitride treated surface gone? Or should I have it ground and sell the thing and get a new crank? Maybe 750 hp and 6800-7000 rpm drag application.

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[ProPower engines]

The surface hardening may only be a few thou deep so now that its been ground its a mute point.
But in a perfect world the bearings should never touch the journal anyway when running with a oil wedge between the crank and bearings.

Have you asked the shop to compensate you for the screw up?? I would be doing that since its their mistake in the 1st place and to touch up the journals will be impossible to correct the radius lip issue you have now.

You can always get it reground correctly and sell it and just but a new crank if they are available.

[MotionMachine]

Flat spots in the radius is chatter, a result of radius forming with a hand held stick and not a proper diamond dresser.

[Truckedup]

I have been told that that nitriding increases fatigue resistence

[gregsdart]

There is another option. For the rod journals you can go down to a 2.100 size sbc bearing. Molnar sells bbc h beams in 6.135 and 6.385 lengths. If there is room on the main journals (additional undersize choices) it may be worth goin this way.

[Ishiftem]

The surface hardening may only be a few thou deep so now that its been ground its a mute point.
But in a perfect world the bearings should never touch the journal anyway when running with a oil wedge between the crank and bearings.

Have you asked the shop to compensate you for the screw up?? I would be doing that since its their mistake in the 1st place and to touch up the journals will be impossible to correct the radius lip issue you have now.

You can always get it reground correctly and sell it and just but a new crank if they are available.

It's just not worth it. He really thinks he did an awesome job. If he didn't want to do anything the first time I would of went after him. The fact that he did it a second time no charge shows me his intentions are good but he just isn't capable so I'm just going to write it off. It definitely need to be ground. I'm just not sure if I want to run it if I do.

[Ishiftem]

There is another option. For the rod journals you can go down to a 2.100 size sbc bearing. Molnar sells bbc h beams in 6.135 and 6.385 lengths. If there is room on the main journals (additional undersize choices) it may be worth goin this way.

I didn't think of that but if I have to get rods and grind the crank and have it balanced, I might just as well get a new crank. This time I would get one with center counter weights. But, I don't have the budget this year for another crank. The car would need to be parked till next year. The nitride is gone and the radius is now .100 instead of .125. If there is going to be a durability issue, I'll get a new crank. If not, I'll run this one after having it ground correctly. That's the question.

[In-Tech]

The nitride is handy if you have soft bearings, otherwise if anything touches you have other issues. Where do you stop? Your decision.
Check/Set the clearances and run the biatch, if she's too tight I'll marry her, that only happened ONCE

[rebelyell]

Does the machine operator Own the shop? Is there another person (Not necessarily In the shop) who has a financial interest in the shop? ...
.... this is kinda touchy ... even a family member w/ a financial interest? Any investor /silent partner in the shop?

I do think you should begin with another crank ... but, sadly understand having to make do until next year with what you have now.

[SchmidtMotorWorks]

I guess he doesn't have a good radius dresser and doesn't know how to feed the face dresser according to the sharpness of the diamond.

May also be some travel issues with the table feed along the length.

If it is an old Storm grinder, the slide under the grinding head can wear out to the point that it rocks.
It is an easy fix though at a good surface grinding shop.

Our old mains roughing grinder at Bryants had that problem, I think the grinder fixed if for 200$ but that was in the 80's

[Ishiftem]

Well, I think I’ll go with another crank. Even a stock crank is induction hardened and GM performance cranks were tufftrided. The cost of shipping, grinding, and nitriding is not worth it for a China crank. That and it will be .030 under so if anything happens to it in the future, it’s junk. I don’t want to spend the money but I think it will be a wise investment in the long run.

[Dave Koehler]

Flat spots in the radius is chatter, a result of radius forming with a hand held stick and not a proper diamond dresser.

interesting. I can't say I ever had the radius flat issue.
I had a radius grinder but did a lot of hand radiusing with a hard stick. Boron I think.
However the stick came after machine dressing. Maybe that is why I didn't have issues.
Seems like I did a fair amount of stick dressing due to having to blend into whatever was there.

I remember one 6 cyl. diesel crank that was a mystery. It had a different radius on each rod journal.
After some historical research I found that at the factory minion 1 ground one journal only. It then moved to a different machine with minion 2 and so on.
I suppose there was a bean counter reason but it was weird.
Cost was adjusted for the next one that showed up.

Why didn't I grind them all to the smallest radius?
Fear that some twit would point out that it was wrong as the oem knew better. Go with the flow.

[MotionMachine]

When I started out grinding on an old 465 VN, I noticed the radius chatter right away, using just a very coarse hand held stick. I figured out to use a much finer grit stick as a final dress to reduce the chatter. My 2nd machine had a diamond radius dresser and it was a huge improvement, no more chatter at all.

[enginepieces]

So let me get this straight the man buggered the crank the first time. You sent it back expecting a better job he buggered it. I think I would stopped and looked for another shop. His talent with the grinder had not changed. The bearings on the spindle have not changed the slack in the machine has not changed. I wish I could help the hp and rpm you want to run this engine at I would look for a new crank.
Just my 2 cents

[Dave Koehler]

It's probably not near the issue it was in the past and I would hope it's a non issue on performance cranks these days.
The older stuff, 70s on back to dirt and in particular industrial cranks varied fairly often.
EX. I would run into one that was .130 radius. OK, easy to clean up.
Ex. I would run into one that was supposed to be .125 but was actually .120. Have to hand blend the radius for that one.
There were also the metric versions that needed a bit of a touch to match.
Oh, the joys of job shops. Never a dull moment. Not always profitable. Just never dull.

There is a shop within driving distance that only does cranks. Some would buy exchange from them.
Really Dirt cheap they were in the day when things were actually cheap.
I used to cringe when one came in for balancing. Sizing, finish, radius were all god awful.
I noticed in the last 10 years that either they got a new machine and/or a machinist that that knows his stuff.
I can't grumble about what I have seen lately.