Hello DaBeechMan. I guess I learn something everyday. I would like to understand this more. A YZ450 is a dirt bike engine that has a balancer shaft. Why did Yamaha put a balancer on that bike engine? Next, isn't a quad heavier than a dirt bike? If so, wouldn't it be affected less not more by the vibration? I noticed that the cr500 has a massive crankshaft and a short stroke. Wouldn't that tend to reduce the requirements for a balancer shaft? Is it possible that traditionally ATVs had relatively low hp, high torque, low RPM motors so they didn't require balance shafts?
I am just looking to understand, thanks DaBeechMan
BryceGTX

 

There is a renowned engine builder building a dirtbike motor that bumps the cc's way up w/ a counter balancer and is going to be put in an all new quad that will weigh less then anything ever produced.. It will be for the desert and dune crowd.. It's not the quad that has the Maico motor from Florida they sell for 17k..

 

I took mine out. It vibrates a little, but having the crank trued really helps.

 

That seems to make sense Sandgod. It seems if you want the ultimate accelertion, removing the balance shaft would reduce the rotating inertia, thereby allowing the engine to rev quicker. Kind of like shaving weight off the flywheel. Shav0 points this out in his first post. As far as I understand, removing the balancer only affects vibration. So it may be a good tradeoff to get the faster acceleration.

Shav0, you have an excellent point about a trued crank. I have heard that since cranks are pressed together, they can often be slightly off which will affect vibration. And as you suggest in you first post, balancing has to be a plus. I have also seen the trued cranks welded to keep the pressed joints from moving. It seems to be quite common with the modified multi-cylinder 2-stroke jetski engines.