Piston Pictures

could have been a big dust storm on the lake or someone munched an impeller and kept on going. not you , but a PO. look for chunks-o-rubber in the heads.

i think you should have chrome upper ring and oil control RING to handle a motor that is run without an air filter. IMHO. are those ductile/moly rings in the photo?

this is an interesting aspect of breakin' one in.moto man

I'l measure the ring gap and post it eventually.

I haven't gotten to the main bearings yet, but the rod bearings looked really good. I don't expect the mains to be much different. The engine has always had good oil pressure.

Last season aside from a tick the engine ran great, good power and didn't use oil. Now that I think about it the boat had a new raw water pump when I bought it. I wonder if the old one went bad and the engine overheated?

Look's like you engine got hot for some period of time, and your oil rings collapsed. Note the varnish above both sets of comprssion rings. The grooves on your pistons and cylinder block are from the piston canting, or tilting sideways in the bore. Usually on a auto motor the rear cylinders will be progressivaly worse, but on a marine motor, when they get hot, they get real hot! Check your main bearings, and your wrist pins, and bushings.