Primary clutch falls off

[rdr99]

900 based bigbore, primary clutch keeps coming off. Tightened the heck out of the clutch bolt, cleaned crank stub. Make it about 3 miles, then it comes loose. Going to check crank run-out tomorrow. If I had the wrong clutch would it still fit on well enough to move the sled? I think it is the 33 mm crank(the clutch has set screw pins).

 

[mtn_extreme]

If your puting it on a 30 mm crank shaft it isn't going to work

 

[1500psi]

wrong taper or wrong harmonics...

 

[rdr99]

The odd thing is, the clutch seems to fit correctly. How can I measure the taper? The 30 or 33mm would be at the base of the clutch or stub...right?

 

[diggerdown]

I think all the set pin clutches were 33mm . I doubt you have the wrong taper. Maybe the clutch is very unbalance or a flat spot on your belt. I just tighten my clutch to 55 lbs. run it and rev it up a few times, then retorque it. Are you sure that your socket is not too big on the outside and you are wedging the socket instead of tightening the bolt.

 

[W.F.O. Boys!]

I do know that an 8 & 900 crank r diff.

 

[spring snow hero]

dykem your crank and see what your contact patern is

 

[SnowXTC]

Here is some more history. Two rides on the sled last year, no problems with the clutch. Three rides this year and no problems with the clutch, just the spacer in the piston. It had some fun in the crank area, made its way up and lodged in the reed. New pistons and cylinders, no real damage to the crank, and the case just has some nicks; not bad though. However the crank was out of the case.

I am thinking the runout is way out and causing the clutch to be out enough that it loosens the bolt after 3 to 8 miles. This theory is furthered by the amount of vibration that the sled has when you are riding it. It has torque stops so the vibration is transferred to the entire chassis. It vibrated before more than what I would like, but it seems worse now. It is in a Polaris Gen2 chassis with an M-10 suspension.

No, it is not my Purple Money Eater.

Any further thoughts would be great.

 

[spring snow hero]

if the runout is so bad it spits the bolt, you better park it. tossing the crank is the next step, when that happens it will cost you a bunch more.....maybe even a leg.

 

[sprockethead]

All fixed pin clutches are not the 33 mm taper. If u had a 30 mm clutch I don't think it would even go on. 800 and 900 twin cranks are the same except the 01 800 which is 30 mm. Like others have said check the run out and make sure ur getting the bolt torqued.

Sprocket

 

[rdr99]

Checked the runout, it is 0.003. Inspected my primary clutch, one of the set screws had loosened off and the weight had moved to the side. Thinking that this was the cause. Is the runout within spec?

 

[longtrack156]

Checked the runout, it is 0.003. Inspected my primary clutch, one of the set screws had loosened off and the weight had moved to the side. Thinking that this was the cause. Is the runout within spec?

My old shop manual, for a different engine, says 0.002 max. I don't think 0.001 would cause your problem though.

 

[Sledjunky]

Runout

The crank runout needs to be checked approx. 1/2" from the end of the crank and should not exceed .002 in. Sounds like you need to pull it and have it trued
and welded.
With the BB done on it I would highly recommend True and Weld anyways. You need to get it done befor you cause any real damage.