re-using a crank that had .50 taken off

[7M4EVR]

So my machine shop had to remove .50 from the rod journals (because of spun rod) and .25 from the mains. Has anyone had any actual success or the more probable failure from running the 6m crank with that much taken off?

Some say it will be fine and some say no way.

 

[Dan_Gyoba]

Best I can tell, it's a crapshoot at that much.

I have one that's had 0.75 and 0.5 taken off of it, which I got from a working pull, and it just polished up. It was apparently just fine, but I opted not to use it, and instead got one that's had 0.25 taken off cranks and mains.

If mine had been 0.50 and 0.25, I'd probably have used it. The 0.75 made me nervous though.

 

[7M4EVR]

Yeah that .75 would scare me, but then again .50 does too..someone has to be running with this much taken off.

 

[IJ.]

The induction hardening is a shallow process, about 10 thou....

I wouldn't use it like that.

 

[Quin]

Paper weight find another one.

 

[7M4EVR]

Well what .50 and .25 translates into is 20 thou, and 10 thou off my crank. Is it the hardening of the crank that I ought to be worried about or does it come down to affecting the bearings and clearances more?

I just can't imagine at my goals being able to throw enough at this crank to make it break. I want to think that they wouldn't make bearings that size if they didn't think the crank would handle it, but then again, if people buy them why not.

 

[Dan_Gyoba]

You buy bearings to fit what was taken off of your crank (And if they had to do more than a polish to the block for the mains and whatever they had to resize your rods to.) So for clearances, so long as you can buy bearings, that part is okay. If you've still got the hardness on the surfaces, you're okay, but if not, then the crank is too soft, and any contact at all with the bearings is far more likely to spin it. The bearings are deliberately soft to prevent damage to the crank in the event of contact, and the crank is hard to prevent deformation of the journal surface, which can grab the bearing and spin it.

As stated the hardening process is shallow, but your machine shop SHOULD be able to tell if it's useable. One of the larger problems for the crank with 0.75mm taken off is that it was really difficult to find bearings, though it is possible.

How much power are you shooting for? If it's more than 300 WHP, then it's worth finding another crank (Though this can be difficult ) If you're looking for stock power, maybe with a bit of boost control, but keeping under stock fuel cut, (Which is what I'll be looking for from the currently rod knocking 7M in my '89, where I'll use that crank that I have, unless a better one lands in my lap) then I would probably use it, though I would do so knowing that there's some risk attached.