Ok I got a major problem with my dirtbike, it is a 1992 KX250, The other day i was riding on a dirtroad and all of a sudden my motor locked up. Well the back tire was locked up so i grabbed the clutch and it still locked up, so it was not my motor, i put it in netural and had to push it well i thought it was my motor but i tooke off the head and the piston was in Great shape, so i tried to start it up. well it ran but mad a funny noise, then it died, so i put it in netural adn tried to start it and it was like REALLY hard to kick it over, and it dont want to start, well i put it in gear and grapped the clutch and tried to role it and it DID NOT role it was VERY VERY hard to role, but when it is in netural it ROLES fine. but when it is in gear and u grab the clutch it is supposed to role fine but it DONT. What is my PROBLEM. Bottom End? Transmition? Clutch? ROD? Please help me out if u have an ideal of how to check it out please let me know. I dont have much money so i would like to check everythign by my slef. thanks a lot PLEASE RESPOND ASAP

 

Sounds like your 'tranny is toast. Pull it apart and check it out, I'll bet that's your problem.

 

It definitly sounds like tranny or clutches.
Pull the clutches out and spin the inner basket by hand in neutral and then in gear.(just pull the chain off first its easier also pul the plug out so you're not fighting the compresion)That should give you some idea of what you're getting into. You never know you may find that some of the cluthes are stuck together.

 

I had the exact same problem with my Mojave several years back. I was told by the dealer it was due to running too high of octane and I fused the crank to the rod (saw it myself). Had to rebuild it. BTW, tranny was fine on my bike.

Later

 

I will guarantee that it wasn't from running too high of an octane because the higher grade the slower and cooler it burns, thats how it prevents detonation in high compression motors. If the rod fused to the crank I would say you had a junk big end bearing, ran lean or way too high rpms.

 

I didn't say I trusted my dealer....LOL :-)

I knew I should have mentioned that.

I figure it was a lubrication problem, something got in the crankcase somehow, or it was just time for something to go wrong. The bike was 7 years old when it happened. 7 years of extremely hard riding.

Later,

 

Take off your stator side cover and see if the flywheel came loose. That could lock up your motor. Other than that you'll probably have to tear into your motor to locate the problem.

Waymod

 

I would also pay close attention to the connecting rod and the rod bearing. If your bearing started to come apart it would not take much slop to cause the rod to seize up the motor. I once say a 86 YZ 250 that had the same problem as you it was running then suddenly locked up like yours. When the engine was torn apart we found the bent connecting rod.