I've got a buddy with an older sea ray with chevy sb that he rebuilt last year. He had the cylinders bored and honed, new pistons/rings, head job, pretty much everything. He and his buddies assembled the engine. He ran it a couple of times last year, but said it wasn't running super good, he thought the new carb needed some adjusting.

This year, he took it into the shop, and they put new plugs in, new wires, cap and rotor, and adjusted the timing. When he took it out he said it was doing fine then gradually started slowing down till as fast as he could go was 30mph. He checked the plugs, and found cylinder one plug hand tight, took it out and the electrode was completely cooked, or burned down. When he took it to the shop, the guy checked and found two cylinders with low compression and the other plug was the same.

My buddy pulled the heads now and found both of those pistons were crumbling and coming apart, whatever you wanna call it. Did this happen from a head gashet or intake gasket not installed correctly? Water in the motor, would this do that?

possible intake gasket leak, but more likely carb running way to lean or bad gas left over from last season. The loose plug and meted electrode was cuased by an extremly lean condition.

Detonation, (pinging)it will distroy a motor. Tears up valves, spark plugs, & pistons. What did other spark plugs look like? White in color. If so then motor was too lean. Detonation is caused by too much timming, too hot spark plugs, lean fuel mixture, low octane gas, & engine getting too hot.

I put together a nice small block for a guy, He wanted to go like h77L. and run with the big guns, He brought the boat back after a couple of months. He said it was running like bad. Idid a leak down found two bad cylinders , melted like you are telling. He was running 87 oct and got it hot. fixed motor got him on the right octane and wow It runs great. Cheap beer big head ache, Cheap gas big repair bill.

To little fuel casues detonation and extreme heat. It is engine rebuilding time.

Saw that happen to a friends dad's boat.

During winterization, he pulled all the plugs,
shot oil into the cylinders.......apparently,
he forgot to tighten one....... first time out the following
spring, ran for a while, eventually started losing power,
shortly after that....... hole in a piston.


The loose plugs can't dissapate heat
into the cylinder heads, they get too
hot......preignition......BOOM
holes in pistons and other carnage.

the shop that worked on the boat, did replace the plugs. I don't suppose anything with the motor would cause a plug to loosen up?