How well balanced is the stock crank?

[RoadWarrior222]

Hi folks,

Just wondering what the balance is like on a stock crankshaft, usually pretty good or usually some way off? Just curious, having some dumb idea about rounding off some edges when I have the oil pan off sometime, and wondering how badly I could screw it up.

thanks,

RW222

[DustyR/T]

not a good idea. Stock crank is balanced pretty well, but a good machinist improves. Mine was balanced perfectly from my machinist. If you want a knife edged crank, either purchase a used one and pay for it at a machinist or yank yours all together and have it done. It's definitely not a DIY thing. A well balanced engine vs. a poorly balanced engine will definitely make the difference in reliability and longevity.

[m90daytona]

+1...i wouldnt shave anything off w/ out having it balanced.

[Ondonti]

i dont know how you can knife edge the crank cause My crank had to have weight added to help balance things (slightly heavier/larger pistons).

I would think you will then be permanently "imbalanced"

There is power to be had in a simple balance. Like dusty said, talk to your machinist about what he thinks can be done without messing things up.
Its probably not worth the investment though to do anything beyond balancing.

[Shadow24V]

now where would you take the crank to be balanced? or even the whole rotating assembly?

[Ondonti]

take the whole rotating assembly......they balance the counterweights to your piston/rods and then i dont really know what else they do.

Some shops will do a better job then others as its a labor intensive process and people like to skip steps.

The guy who built my motor said that their worker (a kid) who usually balances is a lot better then he was. He said he was never quite able to get a perfect balance and that kid could.

[RoadWarrior222]

Hmmm I guess that means leave it the hell alone if you don't wanna splash da cash. Yeah, I was thinking about trying to find some of the benefits of knife edging thru' just radiusing the edges of things slightly. Even just slightly rounded corners are way better aerodynamically than any sharper edges. Dunno exactly how "sharp" everything is in there though, haven't seen one up close and personal yet. I was wondering if the material removed would be kind of insignificant compared to stock rods and pistons generally being +/- a couple of ounces I've heard. So ideally, if everything was in perfect balance, and I just randomly hacked at it, I'd screw it up. I'm thinking though that I'm would be removing about half an ounce of metal per journal offset piece, so presuming I got within 30% of the same weight removed anywhere by eyeball, I think it would work out that I probably wouldn't put the balance out more than an ounce of what it was in the worst case. (3x 30% high on one half 3x 30% low on the other)

So, the best way to do it ain't in question, I'm just wondering if an extra ounce out of balance is all that much worse than stock balance for the whole shebang. Just trying to find out all the stupid little extra low dollar things I might be able to do, that might add up to a couple of ponies when it's all back together.

RW222

[DustyR/T]

some parts of the crank need mallory added to balance it as well, which is the expensive part of the balancing process because mallory is expensive from what my machinist tells me.
Knive edging is more about deminishing resistance on the crank from impacting with the oil as well as keeping the foaming and oil temps down caused by friction. So it's improving on the efficiency of the engine and longevity of your oil on a small scale which will assure a reliable race engine. Kinda along the lines of what Brent said, if you're looking for EVERY hp possible, knife edge it proffessionally, but mallory may needed to be added to prevent countering the weight of the rotating assembly.