BannedCR500Riders.com

From a Seized piston?

I just did this on a KX60 this week. The bike was given to us after the idiot boy left the bike out in the rain and snow without a spark plug. The piston/rings were rusted tight inside the cylinder and wouldn't budge. I first sprayed the top of the cylinder full of WD40 since the piston was above the ports, and let this set for a couple of days. I applied heat to the cylinder and whacked on top of the piston with a rubber mallet, but still couldn't get it to budge. Next, I submerged the cylinder in a pan of transmission fluid for a couple of days so the oil could run into the ports and between the cylinder and piston skirt. After a couple days of this, the rubber mallet worked and it came out.

Someone else suggested Marvel Mystery oil, and I would have tried that next. I figured out quick that the crankshaft was toast also, so I didn't mind whacking the piston pretty hard. Obviously, the top end has to be replaced/bored/sleeved.

I believe the piston melted to the cylinder walls on this one, Its a YZ250 that was run without any coolant the piston is stuck at the bottom of the bore by the skirt. Im betting on the crank and bearings to be shot to since a bunch of dirt was sucked through the carb

Then pull the cylinder up off the studs and use a cutting torch on the rod. Someone else may have a better solution. Sounds like you're going to need some new parts.

the problem is I cant even get the cylinder to budge off of the cases. Btw this isnt my bike its my friends who really knows nothing about dirtbikes so Im helping him fix it

Sounds like the crank is seized also. I'd try soaking the whole engine in some kind of penetrating oil. Maybe you can get the crank loose so the cylinder will raise up. Good luck!

Chunk of wood on top of the piston, and a hammer. tap, tap, tap

works everytime.

PB Blaster first, use a lot and let it soak, then do it again, and again.
Shoot it in the top, the intake and the exhaust.
Cut the stock from a sledge hammer down to make a bigass hammer.
Cut a piece of the stock down to about 8-12 inches.
Put the stock on top of the piston and hammer that sumbitch with your bigass hammer you just made.
Funny huh?
Truthfully, that's what it takes.

The problem in this case is the piston and crank are already stuck at the bottom. He could beat on the piston until the cows come home and it is not going to move. I assume you have already taken the nuts off holding the cyl. down. Try putting the bike in one of the higher gears and rotate the rear wheel back and forth to pop the cyl. up off the case. Once you get that done you can shim with wood between case and cyl. and have some room for the piston to move. I use a long piece of wood and a big hammer. Good Luck!