85hp force outboard

[thunderbolt500]

ok problem was engine was cutting out when shifted into rev/forw. also backfiring when attempting to start. did a compression check and results are 100,60,100. removed the head piston still intact with no cracks or damages but a hell of a lot of carbon. when removing the head it seems that there had been a head gasket but also a crap load of high temp rtv sealant. also the thermostat doesnt look good.
question is how do i clean the carbon off of the pistons?
and what else should i perform?

thanks guys

 

[Frank Acampora]

Re: 85hp force outboard

At 60 PSI the engine either has a bad head gasket, a broken top ring, or carboned rings stuck in their grooves.

If the head gasket is bad, replace it. In fact, with RTV sealant, somthing was wrong so replace the head gasket anyway.

Next, try running some decarbon through the engine to try and free the rings. If compression comes up---great. If it doesn't, then remove the offending piston and check the rings. If broken replace, if not broken free them by hand and clean the grooves.