I reciently just got my whole motor re-done on my 91' lt250r, The main reason I took the whole thing apart was because I sheered the key on the counterbalancer shaft, plus the crank bearings were getting close to being shot. I was riding today in the trap rock quarry by my house and I am pretty sure I sheered it again, it is doing the same thing as it did before, I wasn't riding hard when it broke either. I have about 6 - 7 hours on my new rebuild, I broke it in pretty good.

What causes the to keep sheering?


thanks alot,

chuck

 

Are you using a torque wrench and high-strength threadlock on the counterbalancer nut? If not, the key will be carring the load which it is not made to do. This is often why flywheel keys break also. A torque wrench and a spec manual are "must haves". Do not attempt any repairs without them.

 

I don't know if the guy that did my motor used thread locker or not when he put it back together but I think he used a torque wrench. I did notice a slight more than normal vibration at very high rpms at high speeds. I will be sure to use a threadlocker and a torque wrench when I fix it this time.

what is all involved in installing a new key, I heared all u need to do is take off the mag. cover, what do u all need to take off to replace it once you get that off?

thanks alot,


chuck

 

my brother had a big problem withthis same thing happening. turned out 2 things were happening-
1- the crankshaft was out of true... we replaced it.
2- the nut would not tighten the gear & weight properly on the counterbalancer shaft. this allowed the weight to shift around even after the nut was tight, which would constantly shear the key and was due to wear & tear of the parts involved on that end of the counterbalancer. the proper fix for this is a new counterbalance shaft assembly. the cheaper fix is a washer that is carefully selected to be only slightly larger than the shaft, but small enough that it allows everthing to clear. properly selected & installed it makes the nut do its job again... of exerting pressure on the balance weight & gear, preventing them from shifting around on the shaft.

as for how to replace it, if you haven't got a manual, get one!!! drain the oil & coolant. you have to remove the clutch cover & the clutch assembly, then you can remove the nut on the CB shaft(which is normal, right hand threads), the gear, CB weight, and woodruff key(or what's left) then follow.

the way to check the crank trueness is by using a dial guage, with the flywheel off, attach the dial guage securely to the motor or frame. place the tip on the cranshaft and rotate it. the needle should not more than 0.002"

 

I put a new crank in mine when I had it rebuilt. I will check to see if the weight still moves after the nut is tight when I put the new key in, I will hopefully do that maybe tonight or tomorrow.

thanks alot,

chuck

 

The vibrations you mention probably signify improper alignment of the crankshaft, crankshaft gear, and counterbalancer gear. I highly suggest that you not do anymore work on that quad (or allow anyone else to) without a manual.