2003 YZ450F - primary drive gear nut backed off - why?

found my metal in oil problem in my 450. The primary drive gear nut backed totally off despite having a lockwasher. the washer was split. also found a a loose circlip. the end of the crank is slightly scored but otherwise the threads are ok. Looking at the manual the crank goes to what looks like a boss that goes to the oil filter cavity. Is there a seal in that boss? My cover is a bit chewed up and I'm not sure if I'm missing something else there. Not sure why this would happen considering a lockwasher. Any thoughts?

The later models went to a heavy spring washer under that nut if you replace the nut and washer with the standard parts put some locktite on the threads for a back up. There is a seal in the clutch cover behind the snap ring you found. If that situation is not obvious then you probably need a new cover. Also look at the clutch basket the gear was probably rubbing like a grinder on the outer rim.

Had to buy a another inner clutch cover. Ground down where crank seal is. If i can get a new nut to thread on the crank end it should be fixable- thanks

Fixed. There wasn't much metal in the oil tank screen and after running it for 5 minutes the oil filter looked pretty good too. Changed the filter and now am ready to go. Thanks for the help TT.

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