Removing seized piston from a cylinder bore

I am at the moment dismantling a Norman T300, the engine has been stood uncovered and minus it exhaust pipes for an unknown time, I was not able to turn the engine over using the flywheel so did not know the reason for it being seized.
On removing the cyl. heads both pistons are mid stroke in bore and bores have surface rust, all 4 cam followers are seized, and 3 of the valves are stuck open possibly due to water entering due to no exhaust pipes being fitted.
After removing the flywheel I can get the crank to turn using a spanner on the flywheel centre nut so its not a crankshaft seizure but with the cyl. barrel nuts removed turning crank just pushes the barrels from studs so the pistons seized in the bores must be the problem.

So would heat work can get a loan of a calor gas bottle and torch, or is soaking each cyl. the way to go, heads are off, as its a boxer type motor only one cyl. can be done at a time if soaking,  or what idea have you had success with please and what liquid did you find worked best.

T I A

I'd go for the three 'P's - Plusgas, Propane and Patience. It took me nearly a month of daily applications to get a Villiers flywheel off, but got there in the end
If very rusty then maybe citric acid solution first. Good luck.

Definatly time is your winner here, I would look at removing as much rust as possible with coarse emery then flood with plusgas, daily, then after some giving a tap with a hammer lightly (pistons tops protected with something good) until some movement is seen,

Part of the problem here is that if moisture has got onto the bores you many have a reaction between the cast iron cylinder and the aluminium pistons, depends a bit on how bad they got wet.

Don't go smacking the aluminium pistons too hard with the hammer, they only have very thin heads.

Well yesterday had some success, now have one piston moving in cyl. but other one still refuses to move, also have freed the cam followers and now all 4 valves are moving, so its more soaking and as said patience, many thanks for help gents.

One other thing I noticed the pistons are stamped plus 30 so at some time it must of had bother.

Hi I would if possible fill the bore with Coke and leave for a day or two the rock back and fore and repeat in a day or two it dose work most of the time

Thanks Tony RA have tried that in the past, but was a couple of years or so ago with not a lot of success so am just plodding along with as suggested the 3 P`s. only one rally left to go to this year now on coming Sunday the 6th at Water Board pumping station in Darlington so have all winter to sort it.

I put Diesel fuel in a big container and drop the lot in minus any electrical stuff of course and leave it to soak for days if i have other jobs going on, in the end its all down to patience and determination.
Chiefy.