Greetings from across the pond!

[john williams]

I have recently faced the same problem with a seized Mag engine that had been used in a boat. The problem with trying to free the piston with the engine assembled, is you are trying to move all the pistons through the one piston you are thumping. I had to remove the Cylinder Block complete with pistons, to be able to free off each piston in turn.
One of the problems when removing the cylinder block with a seized engine, is accessing the big end nuts to remove the split pins. In my case, the pistons were mid bore so I managed to remove the big ends with a bit of fiddling. If you have a sized piston at the top of the bore, you may have to resort to driving a socket onto the big end nuts, and shearing the split pins.
Once I had the the block off and on the bench, I used spacers on the top of the piston, then fitted the cylinder head and used the cylinder head to force the piston down. The cylinder head was so badly corroded, it split before the piston would move. I then resorted to a 1/2 inch flat bar, drilled to fit across two of the cylinder head studs, and manage to push the pistons out individually. Even this 1/2 inch bar bent before the pistons moved.
The only reason I persevered with this process, was because the crank shaft and big end were in excellent condition, and worth salvaging.

[A Spooky Ghost]

Got # 1 and 2 free. 3 will not budge for anything. I had to remove the rod cap. It has no split pins on any rod nut...

Can the rods, with the bolts be pulled up through the crankcase? Seems like it's just to narrow a fit.

It's not the oil baffles, 3 and 4 were hammered aside many years ago. Yet 1 and 2 are still perfect... The plot thickens.

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Have a look.

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The rings are in multiple chunks, pistons too.

[Duncan Grimmond]

Are you working on the engine with it still mounted in the car? Give your back a break and get it onto a bench lad! You know it makes sense...

[A Spooky Ghost]

Figured it was easier to get it unstuck while in the car. Didn't want it bouncing off a counter top.

[A Spooky Ghost]

Finally got it unstuck. Took a shocking amount of wacking, teasing, and beating to get it to let go.

The pin is seized to the piston.   Now to put the whole block in my ultrasonic cleaner..

[Ivor Hawkins]

Hoorah! Progress at last! I’ll be fascinated to see how the block comes out of the ultrasonic cleaner.