I recently bought a 1999 WR400 and on the ride home the kickstart ratchet mechanism jammed on. After a little research I discovered this was due to the kickstart stopper [Part No. 5BE 15668-00 which bolts to the r/h crankcase behind the clutch] wearing out - and it seems to have affected a few people on this forum in the past. The stopper is designed to prevent crankcase damage in the event that the kickstarter kicks back. However, and the reason for this post, when I went to replace the stopper, I discovered that not only had the stopper completely worn through, resulting in a large chunk of the crankcase being chewed off, but also the securing bolts had stretched - one so badly that the head was about to shear off - which of course would have caused massive engine damage. A previous post on this forum reported that the bolts had actually torn the threads out of the crankcase. This leads me to believe that in certain circumstances, when the stopper has worn though maybe, that there is very significant perpendicular force on the securing bolts which causes them to either fail or tear out of the crankcase. The bike has covered 10K's and therefore I would strongly advise that when you take the time to undertake a spot of preventative maintenance, and check out this particular component. By the way, all the parts are identical on all WR/YZ 400/426 - so be warned it could happen to you. Also, take care when starting the bike to make sure that that you try to not allow the kickstarter to kick back - I think caused by being a bit eager with the throttle when the engine first fires up. I'm sure that my poor starting technique [2 stroke convert!] finished the stopper off, BUT the wear had definately built up over a long period of time! I have some photos showing the location and damage caused, but being a bit of a luddite, I'm not sure how to post them.