99 yz 125 seized

Drain the oil and check the spark plug,get a manual and some tools.

Congrats, you've seized your first engine. Get a manual, and prepare for some work. =]

Would the tire spin easily before when it was in gear and the clutch held in?

It is not unusual for there to be a significant amount of clutch drag. I often need to shift to neutral in order to start my bike due to clutch drag. If this hasn't changed then it isn't part of the problem.

Riding along, a sudden loss of power followed by a rear wheel skid to a stop is a very common engine seize sequence. It is very unlikely to be the transmission and even if it is the first steps will be the same: Get the cylinder off and see what you've got. If it isn't a seize you need to tear it even further apart.

Since your piston is still stuck I recommend that you get it unstuck before you remove the cylinder head. Remove the spark plug and then spray in a good amount of WD-40., let it soak for a while. Put the transmission into a high gear (5th/6th) and then rock the bike back and forth and try to get the piston to break loose.

Rod

backwoodsracing said:

well i checked the plug it was good drained the fluid good too pulled the top of the motor where plug is and found some kind of build up so i took it to a mechanic i know across the street and showed him it and asked if this looks like the rings turned out to be plastic sleeve and piston look ok no scratches so i pulled the reeds of to see the crank and saw what looked to be broken metal was wedged in pretty good so i tapped on the piston to free it up pulled out the garbage i thought was metal was really plastic i looked online for somekind of platic bearing of somekind and stumbled upon pictures of a wiesco crank and noticed that there was small plastic peices held in with screws so im guessing these failed ? i did hold the plastic next to a pic of a crank and it looks almost identical to the plastic on a crank problem found ?

Click to expand...

This is ONE sentence! Slow down and we can help you.

The big end of the rod took a crap and over heated the crank halves and melted the filler pieces so you will have to get a complete engine kit from hot rod or wiseco and rebuild the motor good luck and it is hard to type like this without periods and commas