What's the best way to un-seize a piston?

[stugordon321]

Hi lads.
I'm trying to un-seize a old villiers 2 stroke engine but not having any luck.
Years ago I used to be into motorcycles & always rebuilding only engines but all I ever did was strip down the engine / remove head & hammer piston down using a hammer & peace of hard wood. This isn't possible with this engine due to the cylinder & cylinder head being one peace so I can't hit the piston crown with any force.
I've left it soaking with WD40, various oils, & diesel etc but still can't move it. I even tryed heating the cast iron cylinder with a gas torch hoping it would expand enough to move the piston but still no luck.
Any ideas how to get it moving??
Thanks Stu

 

[Selectamatic]

I was once told that you should pour Coca Cola down the bore and leave it to soak.

It might be cobblers though.

 

[John 1594]

Find out what thread the spark plug is....make an adapter that will thread into the FULL lenght of the spark plug thread holes

drill right through the center of the adapter and tap the top out to accept a grease nipple, simply pump grease into cylinder to seperate

have used this to get seized pistons out of brake master cylinders more than once

 

[stugordon321]

Thanks Jon.
Only thing is being a two stroke engine I would think all the greese would just get pumped out of the exhaust or inlet ports.
Thinking on similar lines though I might try screwing some threaded bar in the plug hole then gently keep screwing the bar down so it forces the piston down. I know for certain the piston is in the middle of its stroke as the cylinder lifts up a couple inchs.
I think it's so badly seized due to sitting outside with no spark plug. (Why do people do this? Only takes a second to put plug back )

 

[TWi58630]

Firstly clean away all traces of oil by using brake & clutch cleaner, pour vinegar down to spark plug hole and leave it in a warm place. Keep topping up with vinegar, this can take a while but the acid in the vinegar will eventually eat away at the salts that have formed between the cast bore and alloy piston. Just think how long it took to seize up so give it time to free off.

 

[Mursal]

But if the piston isn't at the top (TDC) you can tap it on in to free the rings on the cylinder, or am I missing something?

 

[John 1594]

block exhaust port off with a bit of steel plate and a gasket?

If its mid bore, and you can make something to fit nicely on the crank, how much force would you dare give it to try and get it to move?

 

[gatepost]

Gin, fill it up and yourself then if it doesn't work you won't feel any pain, on the same lines as vinegar but possibly more fun.

 

[Mursal]

Had a think .............
Possibly the cylinder is still on the block and you cant get it off, because of the seizure?
If so you need upward pressure on the cylinder, being ever so careful not to break the lugs off the bottom of the cylinder.
Can you try to rotate the cylinder on the piston (take bottom studs out) to get things moving?.
As john said, you might well be above the transfer port and can pressurize the cylinder to help things along, just be careful

 

[John 1594]

Id be going for the "bolt engine to something solid and get a scaffold pole on the flywheel trick"....it doesnt need to move much, even an eighth of an inch will break the rust seal and allow lubricant to percolate around the piston

 

[renewablejohn]

throw it in a tank of diesel for a month and then see if it moves.

 

[milkloss]

throw it in a tank of diesel for a month and then see if it moves.

Or maybe molasses?

 

[stugordon321]

Thanks all for replying
I've already tryed putting a breaker bar on the nut on end of crank. All it would do is go tighter or end up stripping the threads.
In reply to Mursal I can't just tap piston down as head is part of the cylinder. I can try twisting the cylinder to see if I can get it to move although I don't hold much hope knowing how much pressure I put on the flywheel nut.
I will check how far up piston is to see if I can try putting it under pressure, if no luck try turning nut on flywheel while under pressure. I guess it won't be end of world if I break piston as got another engine I can use to make one good out them both. The crank if f####d otherwise I wouldn't have to worry about this.
Never known a piston to be so stuck.
Thanks Stu

 

[John 1594]

If you have tried turning via the nut on the end of the crank...is there anything you can use on the other side of the crank...tailshaft, keyway etc,

make something to fit on the pulley, cog or whatever there is there, it will allow more leverage than the flywheel nut

 

[stugordon321]

John 1594 that idea of turning both ends of the crank. I've tryed most things I can think of so has to be worth trying.
I'm guessing it spent a good time outside with no plug in the head so guess it's going to take some effort to get it moving. I'm yet to find an old engine like this I can't unsiezed but this could be the one that beats me. I'm hoping not.
Thanks Stu

 

[John 1594]

Have you got a picture of it? both sides of the crank, bore etc?

You will exert a lot more force turning it through the crank direct as opposed to the fine threaded nut holding the flywheel on

get it bolted to something solid so it cant get away from you. Leverage applied to the crank, then tap down on the piston with a rod through the plughole

 

[ladycrofter]

We got some out of an old JCB with plumbers freeze spray. OH made a gizmo to hold tension on it, then sprayed it. Came out with a bang.

 

[Mursal]

I appreciate its a headless cylinder.
Is the cylinder still on the engine, or have you it hanging on the crank?
Have you space between bottom of cylinder and block, when you pull upwards?
If you put a liquid (diesel would be good) in the plug hole will it fill up, or just keep running in?

 

[John 1594]

If barrel will lift, could you not get a couple of those small scissor type car jacks between the cylinder and the crankcase and shove it off that way?

 

[stugordon321]

I've tryed putting a filter strap on the actual flywheel & turning it that way but no joy.
I agree that bolting it to something solid will help although to start with it was in a frame but I still couldn't move it.