If you don't have the groove cleaning tool, use a dull hacksaw or Sawzall blade and scrape the carbon out by hand- - - - -carefully.
Search Ebay for "piston groove cleaner"- - - - - - -there's a bunch of them available, dirt cheap!
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!