On Turning Stock Cranks

[Raptor]

Originally posted by JET@Feb 12 2004, 09:19 PM
You have to use the correct bearing size Jacek.

Raptor, I agree with Lightning, you are going to increase the pressure on the oil between the bearings if you decrease the diameter of the crank. Just like smaller diameter tires have a smaller contact patch. I would think that is a bigger possibility of squeezing the oil out than the extra speed.
Actually, this isn't something that is just me guessing, it is proven theory. Decreasing diameter does reduce bearing surface speed. Consider it like this, in the same revolution, a larger bearing journal is going to have a larger circumfrence to cover which means higher speed on the bearing surface causing more friction at higher RPM.

As far as squeezing oil out, there would be no issues if the correct oil viscosity, preasure and bearing clearances are used.

As Vicious pointed out, on this small of a reduction in diameter, the benefit would be negligible. My main point on that was that it isn't necessarily a bad thing if the nitriding isn't affected.

And yes I am getting old, but you are still older Mike and from what I hear, Shane too! :razz2:

[1ViciousGSX]

Originally posted by Raptor@Feb 12 2004, 10:06 PM
And yes I am getting old, but you are still older Mike and from what I hear, Shane too! :razz2:
Yeha I heard Shane's been holding out on the old age :razz2:

[FORSFED]

As long as my physics are up to par, I'm about 99.9% sure that you are correct Mike. After taking all of this information in, I'm thinking that the main issue on turning dsm cranks is the nitride layer. I need to find out how thick it is from the factory to determine whether or not it's still there or not. If it's there or I have the crank re-nitrided, either way I can't really see that there could be anything bad coming from reducing the crank journals by .010"...

[JET]

Originally posted by Raptor@Feb 12 2004, 10:06 PM
Actually, this isn't something that is just me guessing, it is proven theory. Decreasing diameter does reduce bearing surface speed. Consider it like this, in the same revolution, a larger bearing journal is going to have a larger circumfrence to cover which means higher speed on the bearing surface causing more friction at higher RPM.

As far as squeezing oil out, there would be no issues if the correct oil viscosity, preasure and bearing clearances are used.

I agree with the speed being lower, that is simple physics. I just don't think it outweighs the smaller contact patch. I too agree that it would be negligable with this small change.

The nitride thickness on a DSM is supposed to be .012", so turning one .010" is asking for trouble if you ask me.

[LightningGSX]

Forget I said that(the speed thing), I was thinking about it the wrong way.I did a little math and now I feel dumb.

[FORSFED]

Hey JET, are you pretty sure about that thickness then? If that's the case I may have to do some rethinking.

[Raptor]

The physics on the small contact patch are accurate, there is less area to absorb load, but still not a problem. The formula 1 circuit and bikes should be adequate proof of that. As with anything else, if you arn't turning extremely high RPMs there is no reason to ever consider reducing journal diameter other than getting past blemishes on the journals.

If the nitriding is only .012" I definately would have it re-nitrided.

Last note on the journal size thing, with a large shot of N20, I would probably opt for the larger journal just due to the more violent immediate load on them that nitrous can cause which would make the contact patch theory more important.

Any other thoughts or comments on this? I love this kind of thread just for the mental exercise it causes. At my age that sort of thing is good for ya.

[1ViciousGSX]

:idea: Here's one for you Raptor. :idea: With the power levels the 4g63/64 are reaching these days, the blocks are starting to twist. How would you go about trying to stop it from twisting?

Time for bed, I'll check with you in the morning. ;)

[Raptor]

Hahahaha, Hey Mike, we already have that covered. If you want to find out how, send your motor back to Magnus, and we will hook ya up ;)

[Jacek]

you have to use the correct bearing size Jacek.

sorry i should have known that im dumb this week.. it started on monday when i killed my finger on a cutting wheel on a handheld grinder at work :headache: