MZ/MuZ Riders

Maybe if you block all the ports with plasticine then fill the cylinder with hydrochloric acid. You would need to keep your skin and eyes safe.

Reading through this topic, it looks like the piston will be shot, so little poiint in trying to salvage it - a new one is only around £30 max and you will most likely need a rebore and new piston anyway.

I would be inclined to get working with a drill and chain drill the piston crown, then join up the chain with a small chisel - aim to leave the centre of the piston intact so that the top of the con rod will not be damaged - aim to be able to pull the outer part of the piston away from the centre, hopefully you get the picture.

This will leave you with part of the piston still seized in the cylinder which you can then put onto your workbench and get to work on with a light chisel / release agents / heat etc, and you wil still have the centre of the piston attatched (snd possibly seized) into the small end.

If you do this I would be inclined to stuff the crankcase with rags to sop the swarf getting into the cases - and support the cylinder during the "operation".

Either way I would think you will need a new piston / rings and rebore.

Good luck.

Puffs, you are absolutley right - why is the piston seized so solidly?

I have had seized pistons in the past and usually the application of diesel or penetrating oil gets things moving.

At then end of the day the piston and rings are probably knackered so I would look at getting the piston apart in some fashion by drilling / chiselling - just try and avoid damaging the cylinder.

In the post mortem examination of my 250 with a similar dissassembly issue, I concluded that the bike experienced a seizure similar to number 1 in Puffs post above , however in over a decade in custody of a luddite previous owner, water was allowed to infiltrate to the crankcase causing the crank and main bearings to rust. So a big part of the difficulty I had getting mine out was that the big end / crank were damaged as well . A frozen crank is not conductive to a freely moving piston. I was amazed by both : how solidly the piston was stuck in the cylinder and when eventually removed; how little damage there was to the bore and piston. Even the rings showed only a section of about 15 mm where they had fused to the piston.
Is it possible that your piston wont move because its got nowhere to go?