Why dont dirt bikes have couneter balencers like an atv does?

 

If your crank is balanced you don't need the counterbalancer. They can be removed on any quad, but you have to have your crank balanced and trued. Doing this and lightening the flywheel can remove a pound of the recipracating mass, which is instant power.

 

I wonder why they just dont balence the crank right from the factory.

 

good question
That has somthing to do with why dirtbikes have way more power then quads. And also because of the power to weigh ratio.

 

Hello ThreeWRacer. What I have seen is that counter balance shafts are put in when the engine reaches a certain size per cylinder. Once a single cylinder gets to about 400cc or a twin gets to 800cc, you start to see counter balance shafts. Four cylinder car engines often have counter balance shafts. The primary reason for a counter balance shaft is to reduce vibration. It could be that some engine designs require it to balance the crank as Shav0 says. Hope this Helps. Have a good day.

 

It is standard in most ATV's even the smaller cc ones such as the blaster.

 

Yea just about all atv's ive taken apart all have counter balencer. And all dirt bikes I have, dont have one.

 

If you get the chance to have your crank trued and balanced then do it. You can remove the CB and have alot more power from your motor in smaller RPM's. Expecially on 2 strokes it makes for a world of difference.

 

The following ATVs do not have balance shafts:
Kawasaki 80, yamaha 80, Honda 250, Polaris 330, Polaris 250, Polaris 90, Honda 90, Kawasaki 80.

The following Yamaha bikes have balance shafts:
YZ450, YZ250

The numbers I have given for balance shafts are general rules. Four strokes may have balance shafts for smaller engines and two strokes may put balance shafts on larger engines. Four strokes have higher torsional vibrations because they fire only half as often. Maximum engine speed also comes into effect. At higher engine speeds, the tortional vibrations increase because inertial forces due to reciprocating masses increases to an amplitude that exceeds even the combustion torque pulse. So it is quite often that you will find balance shafts on high RPM engines. In general, the balance shafts are used to reduce engine vibration.
Have a great day.

 

actually the reason why dirtbikes dont have counterbalancers and quads do has little to do with engine size, but rather how many wheels are touching the ground. For example, if you were to take a kx500 or a cr500, cr250, ect and put it in a quad frame it would vibrate very bad. Even though a dirtbike crank may be built with tighter tolerances the motor is still going to shake like a b*tch. Its because the motor is sitting on 4 wheels (axis). You can balance and blueprint the motor and it still wouldnt take the vibration away. This is why 4-wheeled models have CB's and dirtbikes dont (because they dont need them)