750 twin balance shafts help

I just got off the phone with the guy in Canada that races the 750 twin. He's having trouble with the balance shafts and wants to know if anyone has ever heard of running a 750 twin without them.
The plan is to cut the balance weights off the front shaft and keep it (since it runs the oil pump), and remove the rear balance shaft completely.

Anyone ever done something similar or heard of anyone that has?

My opinion is that the shafts are there for dynamic balance, to counteract the imbalance caused by the firing impulses, not to have any effect on the static balance (counteract the weight of the pistons and rods), and it will have more vibration after removing the shafts, but not enough that he can't live with it or effect reliability. Anyone disagree?

I might start another thread someday on how to build a 90 rwhp 750 twin motor

Hint: It involves lot's of money


He also said that if anyone has any questions about the motor or the bike, that they can e-mail him directly and he'll be happy to reply (it may take awhile though).
Contact me for his e-mail address, I'm not going to post it here.

Post edited by: steell, at: 2008/02/26 11:01

steell wrote:

My opinion is that the shafts are there for dynamic balance, to counteract the imbalance caused by the firing impulses, not to have any effect on the static balance (counteract the weight of the pistons and rods),

The factory manual says the opposite. The rotating balancers are there specifically to counter the side shaking force which occurs when the crankshaft is moving through the horiziontal plane, as well as oppose the up-down force of the pistons and crank.

I don't know how bad the thing will shake without the balancers. I'd wager it will loosen your back teeth.

Sounds to me like he is trying to turn it into a Norton. Might be a good question for T.C. Christiansen. I'm sure it couldn't vibrate any worse than this did.

bountyhunter, now that you mention it I do recall reading that in the FSM :blush:

The problem is he's breaking the front balancer drive sprocket, and that leaves the chain with a whole lot of slack and not much room to move without breaking other things.

I suggested that he go ahead and remove the rear balancer and cut the weights off the front, then take the crank, rods, and pistons, somewhere to have the crank balanced. I know there has been at least one other 750 twin manufactured without balancers (Triumph 750 Bonneville), and the vibration didn't bother me (it was noticeable though), so it should work on the KZ750 twin.

Odd Ivar (Ibsen22000) told me about someone else that had removed the balancers and rebalanced the crank, but that was a couple of years ago and I don't remember any details, and he's no longer around to ask, unfortunately

Post edited by: steell, at: 2008/02/26 14:41