I don't know what happened, the bike was pulling hard on 5th speed... suddenly, heard some noise in the engine, it stopped and the rear wheel stoped to. I thought: "that's it, the engine is blown !!" but, I could check that kicking and with the clutch pulled back the piston was working... ... Opened the cranckcase and that it was: one gear was almost completly broken. There was only 2 gears left (on both shafts) in condition. All the other had many theef broken and bent. Can you believe this ? And more: the bits of gear, went into the crankshaft damaging it (fortunally only scratches) and they scratched the down side of the piston and cylinder. I'm very disapointed and I fear the reparation bill... However, I heard some talks that the WR400's gear box would fit in the YZ426F engine and, having all this, I'm considering to purchase the WR400 gear wheels. Have you or some friend of yours ever done this ? Is it possible ? Greetings from Europe.