Rm 250 Burning oil. Primary drive gear?

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8/15/2018 12:26 PM

Hi, great forums. Been reading for a long time but this is my first post.

My 2002 rm 250 appears to be burning gearbox oil. I rebuilt the engine when I bought the bike. New crank bearings and seals. I recall at the time that the right side bearing taking much less effort to press in than the left.

These bearings and seals have around 8 hours on them. I’ve stripped and split the motor today and the seal looks fine. The right side bearing however came out on the crank and after removing it from the crank realised I could push it back in its hole with very little hand pressure. Could this have caused oil to be sucked through the seal? I plan to use a retaining compound on the bearing.

The other thing I’m curious about is how snug of a fit should the primary gear bush be inside the seal? I mean it takes a little push to get it through the seal and onto the crank splines but I’m second guessing the strength of the seal around it at this point.

Any pointers, advice or pity will be much appreciated.


8/15/2018 12:47 PM

In my experience seals need tapped in with a socket or seal driver. Not many of them effortlessly slip into a hole. And that hole in my opinion is where your oil came from. Your seal between the cases could have been a little lackluster too.

Im not sure what youre referring to on the primary drive.


8/15/2018 1:47 PM
Edited Date/Time: 8/15/2018 1:49 PM

An old trick to help the bearing retain better is you can dimple with a good center punch around the hole the bearing goes into to expand the metal in a few areas... as long as the fits not too loose to start with


8/15/2018 4:49 PM

The rt side crank bearing loose in the case will be an issue, see if you can find a rt side bearing with slightly larger o.d. To tighten up the fit or look for a new case 1/2. I would replace the rt side seal & replace the bushing also. Does the bushing have wear where the seal rides on it? There are a few options when your main bearing pocket is worn, do some research if you cannot find a rt side case 1/2.


8/16/2018 12:40 PM

Thanks guys. Checked over the gear bushing closely today and it does appear worn where it rotates in the seal. I’ve ordered a new one (back order ☹️)

Gonna take the case and bearing to a local machine shop and get that sorted.