Seized piston.

[mazdaman]

I have a badly seized piston on a 62 LI 125 which I have just started to restore. I have no idea when it last run but all my attempts to free it has been in vain. It is badly rusted in. Don't mind damaging cylinder or piston but don't want to dAmage crank or conrod :
Anybody have any ideas? I only have the average garage tools.

Les

[wurzel]

I'll take it you've taken the plug out and sprayed releasing oil down the hole and left it to soak.
If you've done that and still can't get it to move take the head off and turn the flywheel to see
if the cylinder moves away from the block.If it does try wedging some metal or hard timber
between the barrel and block and turn the flywheel to pull the piston down the bore so you're
less likely to twist the rod.Probably worth spraying some releasing oil in behind the piston to lubricate
the bottom of the bore aswell.

[Shineytosser]

Soak it in a bucket od diesel for a good few days.............then gentle tap on the piston with wood / hammer.

[St George]

Try filling the plug hole with oil for a couple of days, remove head and remove head studs with pipe grips if need be( new ones are cheap ) spin the barrels, they will come off. I have done this a few times, be patient. Put a tray under where you are working to catch the oil.

Colin

[ianmac]

I'd endorse all the suggestions so far, plus try freeze spray like plumbers use. In my case nothing worked it was as rusty as a horseshoe. Try wurzel's suggestion of moving the crank because if the big end is also solid you may as well cut through barrel, piston and con rod with a big grinder. I had to do this in the end after weeks of futile graft. If you do this take care using a grinder near the crankcase.

[JETEX]

I had a similar issue. I took the head off and drilled out the piston crown. Then I drilled out the gudgeon pin bosses as much as I could, then put a block of wood on the gudgeon pin / con rod, and hit it with a hammer. Not sure I'd trust the crank and con rod after all that though.

[rossclark]

The likelihood is that if the piston is that badly seized the crank bearings will be in equally bad condition.