Shinny spots on top of pistonscarbon removal

"My 1995 Mariner 225HP with 1,

"My 1995 Mariner 225HP with 1,000 hours started running hot. I change the water pump, poppet valve, thermo's and flush religiously. So I pulled the heads. The water passages were perfect. I noticed four of the six piston heads had dime size shinny spots on the outer edges. The cylinder O ring seals didn't look that bad, however I believe water was bypassing in. I'm replacing all the gaskets and O rings. Would this cause the engine to run hot? Also, what's the best way to remove the carbon film on top of the pistons or should I leave it alone? Thanks..."

"I'd leave the pistons alo

"I'd leave the pistons alone unless there was a large deposit of carbon. If I understand what you are saying the spots on the side of the pistons is where the fuel enters from the ports. If this is the case there is nothing to worry about. If you get a good service manual you can tell a lot about how the engine is running from reading the wash pattern on the tops of the pistons. If you have no deposits on the intake side but the exhaust side has a large build up then the engine could be running to rich. This wash pattern reading takes time to understand but like I said a good manual will show what the wash should look like & what pattern means what.
If you had water entering the cylinders there would be damage on the pistons in the form of pitting etc.
If there is no damage on the piston tops of any type it's best to leave them alone, but a check of the side clearance between the cylinder & side of the piston for ware would be a good idea while the head is off. Inspect the pistons very close at the outside edges for signs of the piston melting from pre-ignition etc. Check the cylinder walls for damage or scoring etc."