1985 Force 85HP #3 cylinder bad?

First time boater. Had the boat on the lake under heavy load (waves). Lost power and heard rattle (almost like metal banging around) in motor. Motor stalled out. Got home and checked compression. 135, 125, 20! Pulled the head to replace gasket and #3 cylinder has a different color, ash color (gray) with corrosion. Replaced gasket, still not enough pressure to start. pulled panel on side of block and the rings look ok. What could cause low pressure like this? I want to replace the piston, do I have to pull apart the block or is there an easy way? Does this even sound like a blown piston? Thanks. Sorry if these are dumb questions, but I am really excited to fix this and I have nothing to loose.

Re: 1985 Force 85HP #3 cylinder bad?

I wish the photo was larger but even so, I can see that the piston is toast. It appears to have damage on the exhaust side and may have broken a ring or suffered detonation damage or both. The color and texture of the piston suggests detonation.

If you pulled a bypass cover, yes, the rings will look OK because the damage is almost always at the exhaust side.

You need to examine the cylinder and check for scoring. If it is heavily scored, the block must be bored oversied. If it is only lightly scored. the block can be honed while on the leg and fully assembled. A new piston can be inserted and the rod reattached through the reed vee block opening. You must remove the carbs and manifold.