How about the carbon buildup in the bottom of the piston ring grooves? I've got a couple of dedicated tools for cleaning the grooves out, but a lot of people don't even realize that needs to be done! I've seen pistons get stuck partway down a tapered cylinder when the new rings bottom out on the carbon layer.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!