What's this dimple on the piston?
 

http://i11.tinypic.com/2m61v91.jpg

Next question - Should I remove the carbon from these pistons? What is a good method to keep the scraped off deposits from going places like down the cylinder wall and onto the top piston ring? Thanks....
http://i16.tinypic.com/4ife4gi.jpg

Means that side to the front of the engine. Clean the carbon off with a scraper and hold the hose from a shop vac close as you do. Don't scrape hard enough to mess up the tops of the pistons. If they are smooth they won't develope hot spots.

Coat the cylinder walls with oil, the carbon will stick to the walls and you can wipe them down. I used a bamboo chopstick, chips off the carbon and doesn't scratch the piston.

DOT ALWAYS GOES FORWARD.

I used carb cleaner on mine. Or youcan use a plastic ice scraper.

I used a die grinder with a scotchbrite pad, like you use to remove gaskets, to clean the carbon off. Worked very well.

Gumout carb and intake cleaner works very well. Use a plastic trowel to scrape it all off. I put my piston at TDC when cleaning them and then go to BDC and wipe the cylinder walls down.

I use a steel putty knife and a scotch brite pad.

A scotch brite pad on an air tool will make them look brand new again.

Ben T.

Any type of pad or material that is softer than the aluminum and will not gouge, nick or mark the piston. Scotchbrite seem to work good. I use a similar pad with a dremel tool. Like was mentioned coat the cylinder walls with oil, i've found fogging oil works best as it's a little tackier than regular oil and catches the carbon better. Use a wet/dry vac sucking helps too. Put the piston your cleaning at TDC to clean. I also tape off the other bores and work on one at a time. After your done take the piston to BDC a few times wiping the bore with new oil and clean rags.