CR500 dragrace quad

[Crash00400ex]

has anyone ever put a cr500 motor in a quad frame for racing i have built the frame its a chromoley 8+ extension frame. just wondering how the motor puls and what i can do for mods.

[LTandRaptorider]

Yes, it has been done. An un-balanced CR500 dirt bike engine puts a lot of stress on a quad frame. But dam, you'd have tons of fun... until things fall apart! :p Don't forget to post pics when you are done, and good luck! :)

[Crash00400ex]

how would i go about balancing out the motor to the frame?

[LTandRaptorider]

Originally posted by Crash00400ex
how would i go about balancing out the motor to the frame?

The CR engine is not counter-balanced, as this is not necessary on a dirt bike. The QuadRacer 500 engine is the only one I know of that is counter-balanced. I believe the 87-88 years of that engine had some probs... 89-90 had some changes.

[wilkin250r]

We all know the CR500 is a powerful motor, but also that the vibration makes it useless for almost anything other than drag racing.

However, if drag- racing is your thing, I still don't see the CR500 matching up to some of 100+ hp banshees.

Now if it wasn't for the vibration issue, the huge torque of the CR500 would make a great all-around quad, duner, TT racer, even a motocross racer. But for drag racing, I just think there are better motors out there.

[Crash00400ex]

i know how im going to build the bike, i am going to mount the motor backwards on the frame, carb toward the front. then eun a snowmobile clutch off it that way its auto and the cled clutch willl help counter balance the engine.

[250xridamatt]

Sounds like a lot of work to me....

[rpyfz450]

Originally posted by Crash00400ex
i am going to mount the motor backwards on the frame, carb toward the front. then eun a snowmobile clutch off it that way its auto and the cled clutch willl help counter balance the engine.

That's just rediculous. You could put a snowmobile engine in the atv a lot easier than cut up a CR500R engine.

You might want to talk to a crankshaft shop about what can be done.

Here's what you should know. Without a counter balance shaft, there's always a significant imbalance on single cylinder engines. You have two choices:
a) The crankshaft can be weighted (more) so the vibrations go in fore and aft directions (X axis).
b) The crankshaft can be weighted (less) so the vibrations go in up and down directions (Y axis).
You need to figure out which of these two choices would be better for your application (ATV chassis).

My guess is you'd prefer option B since you could rubber-mount the front of the engine and allow it to vibrate along the Y axis. Trying to allow it to vibrate along the X axis would probably be more difficult when you consider the rear of the engine is mounted to the swingarm pin. One problem you'll encounter with option B is dealing with the exhaust pipe. I'd guess you'd have to come up with a forgiving way to bolt the pipe up to the cylinder.

One point I've had trouble understanding is why the manufacturers have always used counterbalance shafts in ATVs, but they don't always use them in bikes.

[rpyfz450]

Originally posted by LTandRaptorider
The QuadRacer 500 engine is the only one I know of that is counter-balanced.

Off the top of my head, every liquid-cooled two-stroke four-wheeler has been designed with a balance shaft. The LT250R, LT500R, TRX250R, and Tecate-4 all had balance shafts.

The Yamaha and kawasaki 3-wheelers didn't have balance shafts and neither does the Banshee.

I don't know if the ATC250R, Blaster, or Polaris two-strokes have balance shafts.

[wilkin250r]

Originally posted by rpyfz450
The Yamaha and kawasaki 3-wheelers didn't have balance shafts and neither does the Banshee.


The banshee is a twin, so the two pistons balance each other. Far different from the harmonics found in large-bore single-cylinder engines.

[None2Slow]

I have an 87 lt250r with a cr500r in it and let me tell you, it vibrates horribly, but man does it run. That, plus a twist throttle and your asking for all kinds of bad things.