2001 KX125 - Loud grinding noise – Likely from transmission

[NorCali@408]

Hi All,
I recently picked up this 2001 KX125 2 stroke to give dirt bike riding a try.  After 3 months of riding (just about every weekend), the motor decided to retire.  Well not exactly; the motor still runs when I kick start it, but now there is a super loud grinding noise.  So here is what happened yesterday.  I was just about to do my last run when all of a sudden, the gears locked and killed the motor.  From that point on, the loud grinding noise started and I'm not sure where to start.  From my research, it looks like I'll need to split the case.

I'm hoping to hear from someone with a similar experience who can offer some helpful advice.  Thanks all.   

[alward25]

would lean toward main bearings

[treedodgingfool]

Most likely not transmission (trans issues not common, but possible) but possibly clutch plate broken, big-end or main bearings.  Do not start it anymore (piston may not be cracked yet, but running it even for a short time on a wasted bottom-end can crack it apart causing catstrophic engine damage)! Being unable to see the bike (long-disance diagnosis), drain the oil (look for metal bits, no metal shavings means the issue is not clutch or trans related), Pop the clutch cover & pull the plates (you'll have to anyway if it's not a broken fiber or trans related). Pop the ignition cover off and see if you can move the end of the crank up & down (shouldn't be any movement).  If the issue isn't clutch or trans, pull the engine because it's time to split cases.