IDK, you might break the pistons or rings.

 

I've used 50% ATF, and 50% acetone. Soak for as long as you can stand to wait. Can you get a chain through the holes on the flywheel and use a pipe to put some leverage on it? You could also put it in gear, jack up a rear tire, and try to rock the tire back and fourth. I've also heard stories of people putting a grease fitting in the spark plug hole, and using a grease gun to fill it up. Supposedly, the guns put out more pressure than you'd think.

 

If it is stuck in the block then the piston &/or rings will be throw aways.
What you are trying to save is the bore .
IT would be a great help if we knew what engine and why the pistons are stuck and how many are stuck
My go to is to put some big lumps of metal ( to occupy space ) in the bore , put the head back on then pump the cylinder with grease.
IF it still wont move, apply a lot of heat.
But again i depends a lot on the actual engine

 

Can a mod move this to a jd forum.

 

Done, moved to Big Deeres... is that good? Could also put it in Vintage but that's not brand specific.

 

Thinking on this... do we know why the engine is seized?

 

Rust. It was not super bad. Been setting for 25 years.

 

Rust from sitting is one thing, rust from rain or water in the cylinders can be quite another. Before working on the pistons, be sure there is nothing else jamming the engine like a broken piece of something in the crank case or other moving parts. Your post seems to imply a multi cylinder engine. That will make freeing it up a bit more of a task. The make and model might be helpful to get some good ideas flowing. You never know, someone here may have had the exact same model and experience.

 

A John Deere "A" (that's the model, just "A") will have a two cylinder, liquid cooled, gas (carb) engine. Dad had a '48 model, pretty easy to work on.

Engines were all about the same as far as I know. The cylinders were horizontal and the crankshaft ran across the tractor (left to right) from the flywheel to the belt pulley.

Here it is on TractorData, choose the year range at the top to see differences.

https://www.tractordata.com/farm-tractors/001/0/4/1044-john-deere-a.html

 

The serial number indicates it is a 1952 John Deere A.
AR. 5.3 liter gas.
I towed it home on it's wheels. It had been setting outside with a can over the exhaust pipe. Remove the spark plugs and fill cylinders with coil penetrating oil and let it set for 2 months with a come along to the flywheel with pressure on it. Remove the head and clean Rust from cylinder walls. Rust was not super bad. Now I have a screw Jack with a block of wood against the cylinder with pressure on that. When I drained engine very little water in the oil. Have the plate off of the crank and cannot see any problem in there. No rust to speak of in the cylinder walls the best I can see.
The family tried to free It Up by pulling, but he said not a lot of pulling.