Gears braking - two times in a row

[matt88]

Hi, I have recently bought a gasgas 300 ec 2011, and after 2 hours of riding - third and fourth gears jammed and were trashed. I thought - stuff happens. After rebuilding and riding 2 more hours - same thing happens - the same two gears 3 and 4th jam together and brake. This happened both times when i was downshifting - first time i wasn't using the clutch, the second time - i did pull in the clutch. I had many bikes in past and this has never happened while downshifting in the past. What could be the problem guys? My mechanic is an experienced KTM mechanic, he couldn't find the cause for the gears to jam and brake - doublechecked with another great mechanic - no ideas. I was using BelRay gearsaver 80w one time and another time it was Maxima MTL 80w. Any idea guys what could be causing the problem repeatedly?

 

[GMP]

Shaft look OK? Check OD/bearing fit, etc. Sounds like gear was binding to shaft, too much differential speed when dogs engage. Back in the old days ('00) they had plain bearings on some gears, and occasionally stuff like this would happen when bikes were new, but not common.

 

[twowheels]

Hi, I have recently bought a gasgas 300 ec 2011, and after 2 hours of riding - third and fourth gears jammed and were trashed. I thought - stuff happens. After rebuilding and riding 2 more hours - same thing happens - the same two gears 3 and 4th jam together and brake. This happened both times when i was downshifting - first time i wasn't using the clutch, the second time - i did pull in the clutch. I had many bikes in past and this has never happened while downshifting in the past. What could be the problem guys? My mechanic is an experienced KTM mechanic, he couldn't find the cause for the gears to jam and brake - doublechecked with another great mechanic - no ideas. I was using BelRay gearsaver 80w one time and another time it was Maxima MTL 80w. Any idea guys what could be causing the problem repeatedly?

Did you change the shafts? Internal bearings? End bearings?

 

[matt88]

Shaft and bearings look ok. The spaces between the gears seem to be originaly very tight, and when changing gears they might slide down too far and engage with other gears and then brake. OR the circlip that holds the gears might let down and they slide down too far. The mechanic inspected them and they seem fine, but he replaced them anyway.

 

[adv rider]

gears jamming

Was the engine ever apart before you fixed it the first time? For it to happen twice, it's obviously not being fixed correctly.
Look closely at circlips /washers on the primary/ secondary trans shafts. Also the shift drum,forks. If it was taken apart before you got it, I would try to figure if a incorrect part was installed- shift detent/drum/forks/etc.

I'm sure you already checked, but as you said- it shouldn't have broke in the first place, let alone a second time.