Transmission damage

The small rollers in the first two pictures are from what, the balancer shaft bearing?

No, those are teeth broken off from the gears. Sorry the pics aren't better quality... I need to upgrade my digicam.

What is the diagnosis? Why did this happen?

Sad. :thumbsup:

What is the diagnosis? Why did this happen?

Sad. :thumbsup:

That's what I'm trying to figure out... upon first look, shift forks look ok, but I guess I won't know for sure until I tear it down completely.


what year bike is this?

Is it an '06? Is it a newer bike or a well used one?

What type of oil were you using?

What were the circumstances for the destruction? Missed shift at high revs?


Nice looks at the carnage, pretty bad damage. What were you doing when this happened?

Bike is an '02 426. Oil is Yamalube 4 20W-40.

All I was doing was riding... was out the weekend before this happened with zero indication of any problem. Then, on this trip, we left on our first ride and it just started clunking after only a few minutes (wasn't riding it hard at all)... it got progressively worse as I made my way back to camp.

I have a 98 yz400. It looked the same as yours does. I lost both 3rd gears, no warning just a noisy rattle than my rear end locked up. I also had parts of the gears hit the crank and the bottom of the piston. Before replacing the gears, I magnafluxed the rest of the gears and found three more cracked at the lower part of the teeth, so you might consider getting them looked at before you re-assemble. NOTE: the new third gear I got from Yamaha that replaced the broken one appeared to be shot peened for strength. I think that they have had some problems with that gear in the past.

Look at your rod bearings you can't have any of the metal in there ! clean and clean and clean again before you put it back together :thumbsup:

:thumbsup: that's not good! I feel your pain! :thumbsup:

Ok, I finally got off my lazy arse and finished disassembling this thing... I'm about to order parts but I'm not sure if I need to order a new 2nd gear wheel also... There is a small (but noticable) bit of play when the gear is sitting on the axle. How much (if any) play is normal? The teeth look fine, I just don't know if I should be concerned about the movement.


New gears are cheep compared to losing one later, you already have it apart no time like now to do some preventative maintenance. I would even throw a new rod in her I blew mine in the winter and it's just a boat anchor now (see tic tic snap pics in search in wr forum) it's nasty. I feel your pain, you caught it just in time.

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