2000 RM125 top end fried. Need Help.

[mkellycole]

My son blew up his motor this weekend. I took off the head and sure enough, the piston was fried and the ring is toasted to it. He took it apart so I didn't see how he did it. The rod and bearing seem fine. My question is. Does the crank have an oil chamber? There is coolant and oil mixed around the crank. I drained the gear oil. It was fine. The bike was low on compression when it stopped running. Should I just tear it down and put a new piston and ring. What should I do about the scars in the nickel cylinder? Is it toast or can it be resleeved?

 

[Chili]

Getting the cylinder replated is a better option than getting it sleeved. You could also use this as an opportunity to go to a big bore setup.

 

[mkellycole]

what about all the fluid in the crank chamber? Do I just empty it and leave it dry or does some fluid go back into it? I thought it was a dry system cooled by the liquid cooling system. Also, to take the motor out, pulling the swingarm bolt, do I need to remove any other suspension items before pulling the main motor mount through the swingarm? Will it cause me problems later?

 

[Chili]

There should have been no coolant around the crank, premix yes but not cooolant. To remove the engine you shouldn't need to remove anything other than the pipe and spark plug wire. Then undo the motor mounts and swingarm bolt and it should come out without issue. *Disclaimer* never worked on a 2000 but that was all that was involved in removing the engine from my son's 03 and 05 RM125's.

 

[NO HAND]

I believe the coolant spill in the crank case is caused by the teardown and not while the bike was running. It happens sometimes when removing the cylinder that some coolant will spill around and drop on the crank. You have to clean the crank case the best you can before reassembling though.