How well will a turned 6 bolt crank hold up???

[1990TSIAWDTALON]

Hello and please be honest as this is a very important decision, but virgin 6 bolt cranks are very hard to find these days. I am posed with a decision. I am having a motor built ( I usually do these myself but am too busy to do it at the this time so I am farming it out to a reputable shop). I can't find a crank that has good factory size journals so how good would a cut 6 bolt crank work in a 10:1 motor that will see 7500, maybe 8000 at the most. I have heard both stories. I build Small Block Chevy's all the time and a turned crank in those works just fine and I have never ever broken a crank because of turning one .010 and those motors would see 7000, sometimes 8000...no problems in 30 some years but because I am new to these little monsters I am wondering how well they would hold up if one had to be turned. Please chime in and give me reliable answers so I can make an informed decision. Results from experience would be good to hear also. Thanks very much.

 

[curt-s]

It has more to do with how bad was the crank before being cut (bent, microfractures, etc.) and how skilled is the machinist that does it on a good core.

Many full blown quarter mile queens run cut cranks. Some get them treated, some don't. Nobody can give you a reliable answer because it's all a witchcraft art, and a crank can fail for any number of reasons. Aftermarket cranks can fail.

Yes, Mitsubishi says the crank can't be cut and should be replaced. They also say a lot of other things that shouldn't be done, yet we do them gleefully anyway. It's for different reasons than most think.

Besides, somebody runs a cut crank and pops it, they'll immediately blame the crank cracking in half on the fact that they had it turned... not because the machinist was drunk, their tune was messed and running 13:1 at 20psi with a deaf knock sensor, meanwhile chattering their clutch and hopping on launch.

That being said, I decided to run a 0.010 cut and polished crank and I've been going for almost 10k km now. I was mindful of it for the first couple months and then totally forgot about it.

10:1 though, better make sure you have everything dialed really, really well. That's sound advice for any crank, new, aftermarket, or cut

 

[1990TSIAWDTALON]

I appreciate the information. I run them in my SBC's and never worry about them, but needed to ask about these since I am new to the crowd. I did go with a new Eagle crank since it was a pretty radical build, but have a crank that could be cut if needed in the future and didn't want to discard it for trash. Appreciate the candidness, that is what I was looking for and I agree that any crank can fail for any number of reasons so my hunch was right that under normal rebuild conditions I could use one with correct machining which my machinist has done for over 35 years. Appreciate it!!!