YZ250 stiff transmission and rebuild issues

I bought a 2002 YZ250 with the engine in a box and half the parts on the bike missing. I'm at the point now where I'm putting the cases back together after a flush, new bearings and seals, and crank. This is my first 2 stroke, first time taking a bike motor apart, and thus first rebuild. I'm at a point where I'm kinda stuck so I'm hoping for some assistance!

 

1) I don't know what the transmission was like before the bike blew the previous crank, so I don't know if it was good or not. Before I put the cases together, the transmission sat in the right side case and spun all nice and free. The forks were aligned properly in the drum and on the gears, but I'm not sure if they need replacing because the shift drum would not move the forks by hand. I would try to spin it and it would get locked up at the first "incline" part where the fork lifts up. I thought it would eventually be fine because of the added torque by shifting with your foot. Not sure if you should be able to spin the drum by hand and have it go completely counterclockwise until stopped and back again?

 

2) I put the cases together and the transmission REALLY stiffened up. Like almost impossible to turn by hand. Lots of drag, why is this?

 

3) Crank also has significant drag, even when the case screws are lightly hand tightened with a hex key. Is there something I can do to better align the crank and reduce all drag?

 

Thanks!

Have you used the screws to push the cases together?

Have you used the screws to push the cases together?

I put the crank in the freezer beforehand, got it into the right side case, and was able to push the cases within a few millimeters of each other, then tightened lightly by screws. When the screws are loosened all the way and the cases are split slightly, the drag on both the crank and transmission is almost nonexistent.

I put the crank in the freezer beforehand, got it into the right side case, and was able to push the cases within a few millimeters of each other, then tightened lightly by screws. When the screws are loosened all the way and the cases are split slightly, the drag on both the crank and transmission is almost nonexistent.

Tap the on the cases where the main bearings are to relieve the pressure of pulling the cases together that last couple millimeters w the bolts. You should hear the difference when it bottoms out against the crank. As far as the trans, the shift drum will not work properly till it's together. The drag could come from a thrust washer in the wrong place, missalignment, who knows. I would have to see it. I've split many cases and could help w that if you live close. Those trans are good for breaking 3rd output gear too.

Once I had to repress the crank from the other side to get it moving freely. Do you have equal space between both sides?

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now