My 2001 DS650 crankshaft sheared at the flywheel side of the motor, flush with the crankcase. When I took the side cover off, the flywheel fell right out. There are no signs of excessive heat or bluing or grooving at the shaft. There was no detonation. It just broke off. The ATV was a new about 14 months ago, but has only been ridden half this time.

Has anyone ever heard of this happening?

I heard of a guy who had a broken shaft at the clutch on his first ride.

Could this be a defect in the crankshaft? Hardness of the material out of spec?

I noticed the flywheel is very heavy. I am wondering if the inertia was too high. If I replace the crankshaft how do I know this won't happen again? I'm thinking I need to lighten the flywheel.

Should I just order a new crankshaft & rod assembly from the dealer or is there an alternative?

 

RPMs, vibration, and harmonics are usually the culprits behind crankshaft failures. I would highly suggest you have your next one dynamically balanced with the amount of horsepower and rpm you turn. I would be interested to know if anyone makes a better aftermarket crankshaft for the Rotax engine

 

My friend had his Crankshaft seize up on him just a couple of weeks ago and it cost him $1500.00 to have it replaced. $800.00 just for the Crank! As of right now nobody seems to make an aftermarket Crankshaft for the DS yet. Good Luck!

 

time for the big motor scooby, 760 with turbo would be nice.[img]i/expressions/face-icon-small-happy.gif[/img]

 

Given the high HP numbers present on this forum, and all the bikes on NOS and such, I'd call this broken crank a fluke since I haven't heard the like before. I say replace it and ride!

 

I would agree with Rocky's suggestion.

 

Got the motor back in the frame. The counter balancer shaft had negative end play. I installed a thinner washer to set the correct amount of end play.

 

How much did the crankshaft set you back?

 

Seven hundred something with a discount. I had to buy a few other parts as well.

When I tore everything apart, I also noticed that the broken piece of shaft still in the magnetic rotor looked like it was not at a perfect 90 degree angle with the magnetic rotor.

 

Scoobie,

Your signature says it all. 100RWHP!?!? Holy bagezers dude what did you expect?
The tortional loads put on that part of your crank from the (much quicker) rise and drop in RPMs, coupled with the weight of the flywheel will definately have an effect on the crank. This is one of the reasons for lighter flywheels on race engines.

Until someone comes up with a stronger crank, lightening your flywheel is the only way to avoid a re-occurence. Of coarse this will effect your wattage output but that is a small price to pay for a longer lasting engine that puts out more then double the intended RWHP.

PS.
If the rotor was not sraight on the crank, It would have failed sooner and you would have noticed a hell of a vibration. With the taper of the two parts its impossible to put it on crooked unless one was made wrong.