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strange gearbox issue, 4th gear (2010 RMZ 250)

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Hey guys,

Backstory:

2010 RMZ 250, bike always ran and shifted great, no false neutrals, everything was fine and good serviced. Did another rebuild recently (3rd one so far). New Rod and athena 290 bigbore kit this time. Gearbox looked fine upon inspection. Bike started, ran and shifted great after rebuild.

So, here's the problem now:

after a few laps, the bike started sputtering and clonking in 4th gear and only in 4th gear. 1st, 2nd, 3rd and 5th had no issues at all. The sputtering felt like a fuel problem, it just won't rev up. When i was trying to figure out what was wrong, the transmission locked up in 4th gear on the bike stand. Sure enough i ripped the whole engine apart again and found a broken shift fork (the one for the 5th gear). Everything else seemed good. So i installed a new shift fork and inspected the other parts. Bike starts, shifts smooth and sounds good. Rolling in all gears is no problem. But again, the 4th gear sputters under load. And that's where i am now. Going to open the engine again. But maybe somebody has an idea what's causing my problem. Seems to make no sense to me.

Mike

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looked good to me, i'm going to take some pictures tomorrow, when it's apart again. it just surprises me, that before the rebuild and the first few laps after the rebuild there were no problems at all.

EDIT:

Quote

How did both fourth gears dogs/holes look?

you were absolutely right. The dogs/holes on 4th gear and on the slider counterpart are pretty much rounded and beaten up. This might cause the gears to engage/disengage under load and putting stress on the shift fork. I'm going to get some new parts now.

Edited by GuyIncognito

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Put a 2013 transmission(everything shifting parts also) in everything fits you also need the 2013 countershaft bearing the inner diameter is bigger sprocket side.

 

 

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i think i found the culprit to my desaster. there was a washer behind the 3rd/4th gear that hammered itself into the gear and shaft. it wasn't flat anymore and so the spaces weren't right, causing the gears to take damage. thanks for your help guys

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