Cylinder Removal - Engine seized

Is it possible to remove the cylinder with the piston siezed? It's about 3/4th of the way to the bottom of stroke. I'm reading from the CLYMER manual for my 1991 YZ125, and under Head Removal it says to place the piston in top dead center as the last step for head removal. Then, under Cylinder Removal, it says to follow the head removal directions, then continues with power valve/thrust plate and carburator removal. I want to know if it's gonna be possible to remove the cylinder without damaging it or having to take the engine completely apart.

 

If I have to do a complete tear down, I'm just gonna swap in a new engine.

I think you just get it out however you can. Especially if you plan on getting a new motor, whats the harm? Unbolt it and pull! At least thats what id do. If its toast anyway youll have to resleeve it since its a nikasil cylinder.

Edited by dbart250

If piston won't move. You'll have to take cylinder cover off and drive piston down with a hammer and like a piece of wood to get it out of cylinder sleeve so the head will come off.

Also, if the piston is at TDC it is going to be very difficult to get the cylinder off if the engine is still in the frame. We put the piston at BDC, to give us more space to remove the cylinder.

 

As mentioned above, remove the head, unbolt the cylinder (if there are any extra retaining nuts/bolts) then try to lift the cylinder free of the piston & engine cases. If it will not budge, double check that you have all retaining nuts/bolts removed, then put a piece of wood on the top of the piston and drive the piston down. Then lift the cylinder up, put blocks of wood between the bottom of the cylinder and the cases, and again using a piece of wood drive the piston down in the bore, repeat those steps until the cylinder is free of the piston.

If piston won't move. You'll have to take cylinder cover off and drive piston down with a hammer and like a piece of wood to get it out of cylinder sleeve so the head will come off.

Well, I definitely didn't have to do that. The cylinder came off as normal. Bad news is, it's a shattered piston. Metal bits everywhere.

Not to try to kick someone when they're down but this is why you want to replace the piston on a schedule.

Only had 20 hours on it, maybe 25.

 

The junk leaned out and exploded, man.

Edited by tcan

you leak test the motor after you built it?

I didn't do the last rebuild. I bought it this past spring. But I have no idea what that is. There was plenty of trans fluid in it when I drained it this afternoon, if that's what you're asking after.

Edited by tcan

I didn't do the last rebuild. I bought it this past spring. But I have no idea what that is. There was plenty of trans fluid in it when I drained it this afternoon, if that's what you're asking after.

Leakdown is the test for sealing of the cylinder and crankcase. Basically checking integrity of the cylinder head gasket, base gasket, case halves and crank seals. Any leaks and the engine will suck in dirt or debris and run lean.

Only had 20 hours on it, maybe 25.

 

The junk leaned out and exploded, man.

Usually a plugged carb or blown out gasket gives you plenty of problems running before there is damage. And then you won't get a broken piston but a burned or seized one.

Not trying to beat you up, just want to help you read the signs so it doesn't happen to you again.

If the cylinder is toast, don't re-sleeve it. That's vintage bike technology. Either replate it or replace it.

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