ORIGINAL: downunder

I use acetone to free up engines that have been gummed up with castor from years of sitting around. I did this yesterday with an old Merco 61 that had just arrived in the mail (would you believe a gift from an extremely generous American?). I pour a teaspoon or so of acetone down the carb to get it to the bearings and conrod then slosh it around before putting some pressure on the prop until there's a tiny bit of movement. Once you get that bit of movement it doesn't take long before it's turning free. But on the off chance it had a stuck ring (or rings in this case ) I pour enough acetone into the cylinder, with the engine inverted of course, to get a hydraulic lock then fairly gently force the piston into the lock so the pressure forces acetone into the ring grooves. By rocking the prop so it goes in and out of the hydraulic lock it'll work the acetone through and dissolve the castor.