I have recently aquired a 72' Norton Commando. The bike has been outside for12 yrs. YES, it is rusty. Yes, thats rusty too. Anyway, the
aircleaner was missing - resulting in open carbs. Consequently the pistons have welded themselves to the cylinder walls. How can I remove the cylinder with limited distruction? I am willing to replace the pistons and cylinder, I just need to separate them .Please help!
Thank you
Jaye

I'll assume you have removed the head.
If the pistons are all the way up you're in trouble.
If they are 1-1/2" or more down then you can strip everything out of the timing side. Take off the base nuts and lower the cases away from the barrels. You may have to remove the studs also. Then split the cases. Remove the crank from the rods.
You will then have stuck pistons with rods hanging out the bottom of the barrels.
diesel, home heating oil, specialty penetrant for a starter.
I've never tried it, but some claim 400' oil poured in can loosen things up too.

A friend of mine restores antique tractors and he has encountered the same problems, only he needs to salvage the pistons and barrels/block. What he does is get a styrofoam cooler full of dry ice and then puts a jug of gas line de-icer in it to cold soak. Once the de-icer has chilled, he pours it into the bottoms of the pistons (wrist pin side). Within seconds, the pistons (being aluminum alloy) shrink sufficiently that they may be lightly tapped out of the cylinders, relatively unscathed.
HTH,

Derek

If the piston rings are rusted together with the cylinder walls , shrinking the pistons might not be enough . Use a torch . You'll have to rebore anyway .