I was cleaning up an old piston to make into a paperweight or desk art for my neighbor today. I came across a pretty good way of cleaning off the carbon that I thought I'd share.
I chucked a nylon brush cup for a dremel into a drill press, and while keeping the piston head wet with carb cleaner, let the thing wisk away. The nylon did not damage the aluminium, and having it spinning at 3000 rpm or so made much shorter work of the job than if I had done it by hand. It made cleaning the valve recesses particularly easy.
I am a lazy bastard [see a good Australian Thesaurus] and whilst I applaud your work in cleaning the piston you do have the problem of your high speed brush distributing crud that you will eventually have to clean up off other things. It also takes personal effort.
My preferred method for cleaning pistons that are never going to see service again is to pop them in the bead blasting cabinet and spend a few minutes giving them a good going over. The beads leave a very nice "satin" finish. Of course I would never subject a piston I was going to put back into an engine to either bead or sand blasting and any person claiming to be a mechanic who would deserves to be hung inverted over a slow fire.
My second method for cleaning up a piston that I DO intend to reuse (or simply display) is to give it a good soaking in oven cleaner which will remove 99% of all carbon and other deposits. I then do something a bit naughty. My wife and I have a 30l bucket in the laundry which is kept filled with a super-saturated solution of "Sard Wonder Soaker" - we live in the tropics and antiperspirant build up on clothing is a big problem, so to are ink stains, grease/oil stains and in my case, more than the odd red wine stain - we soak clothes in the bucket and renew the "solution" every year or so, or when it shows obvious signs of being at the end of its useful life.
Anyway, without telling "SHE" I slip pistons (and other alloy parts) into the bucket and leave them foe a few days - they come out very clean.
A final method, whilst a highly effective cleaning strategy, unfortunately guaranteed (in my experience) to have an entirely negative effect on domestic relations is to slip assorted engine parts into the dishwasher on a good "pot scrub" setting (don't forget to turn off the "rinse aid" or "glass finish" part of the cycle). A very good way of quickly getting stuff really clean.
As I mentioned, the cause of more than one domestic, particularly when the plastic liner of our old dishwasher got indelibly stained by some oil from a diesel engine.
Still, what she doesn't know won't hurt me and when that dishwasher was replaced I made a point of buying one with stainless steel liner and baskets so no "evidence" is left behind.
