What is the best way to clean a piston that was stuck? I'll probably have the piston free from my IT400 this weekend and wanted to hear the different methods for cleaning up the piston so I can get the clearance checked.

I think I'd be more worried about the cylinder and if it will need to be bored but I'd use some diesel or denatured alcohol.

My Service Manual states 400 grit sand paper.

400 grit on skirt, broken section of ring for grooves

IF you use emery cloth or sandpaper, I would highly suggest you clean it thoroughly in solvent/etc to get as much of the residual grit off as possible.

If there's no scoring of the cylinder/piston and IF the piston/cylinder wear is within tolerance, then you may get away with what you propose to do. If the piston/cylinder is good, then at the least I would want to install fresh rings while it's apart.

V-man

I would use gray scotch brite with brake cleaner 

The less you do the better. Removal of a thousandth or two in certain spots will have a surprisingly noticeable negative effect.

If the bore is in the condition I would expect it to be it's almost certain to be unsuitable for use with the same piston at this point, even if it was mint before the corrosion occurred.

I'm not so sure about it being unusable.

I got a 1973 Saab 99... (2 liter Swedish engine version, not the Triumph engine...) from a used car dealer for almost nothing back in about 1979. They bought it at auction and then their "yard mechanic" tried to replace the clutch and couldn't figure it out. Finally after bugging him for weeks (every time I delivered parts to them), the owner of the car dealer finally sold it to me for the price of the new clutch parts they bought for it... and were included.

I had heard the engine run weeks before I got it. What I didn't know was engine was now locked up solid. When I jacked up one side of the car after the tow truck dropped it off, water ran out of the sidedraft air intake, Not good. I pulled the head and all 4 cylinders were full of water... and rusty. Not antifreeze, water... like someone stuck a water hose in the carb and filled the engine.

What a mess. The owner of the parts store I worked at said he would buy back the new clutch parts from me so basically I would get most of my money back. The car was SO clean and straight and nice that I decided to take a shot at fixing it.

After drying out the cylinders, every day after school I carefully and tediously removed as much of the rust as I could by sanding and wire brushing... vacuuming as I went.... still stuck solid. So I filled the bores with penetrating oil and let it sit.

In the meantime, I went ahead and installed the new clutch.

I would beat on the pistons with a block of wood and a sledge hammer... no movement at all. Refill with oil.

Finally, me and a couple buddies decided to push the car down the driveway and pop the clutch. Tires just skidded. Then on the third try it broke loose! I carefully cleaned the bores again and got things as clean as I could... there was some pitting in a few spots... but nothing too bad. Did my best "cross hatch" imitation with some fine emery cloth, cleaned again, oiled up the bores, changed the engine oil, and installed the head.

It smoked like hell for about 5 minutes then settled down and ran great. I changed the oil a couple more times in the next couple days and was saving up to either rebuild the engine or get one from a wrecking yard.

I put nearly 60,000 more miles on that old Saab and it barely used any oil between changes. Eventually sold it and it was still running great.

Mark - that's a great example of just how bad things can get and still run if you apply the correct amount of patience and technique.  I had a similar experience with a '69 type 1 that I got for $50 - not water obviously - but rust on an engine that sat for years without plugs that was rusted solid.  It took a few days of cleaning and buffing and then I drove it for 3 years until I sold it on for a $100 profit and  "upgraded" to a 1979 honda CVCC civic I bought for $400 that also comes with a fascinating story I will not bore everyone with.

MarkT that's a great story thanks--& post#9 too.