I have a 2004 Mercury Promax 300X outboard.This engine has 59 hours on it. The crank is broken. Looking at the engine (from the front), top left cylinder #2 scored and parts of piston shattered. When removing the head there are pieces of the piston on the front of it. When I took the front half off, in front of the reeds more shavings and pieces of piston. Replaced high pressure fuel pump in vapor separator. Question is why did this happen? I bought a new long block from Mercury. Everything transferred over and ready to mount powerhead. I need help with the cause?? What to look for?? I don't want this to happen with my $7k new long block.
Do these things just happen? All other cylinders seem ok. Is there an oil pump issue (just to that cylinder)??
Engine never overheated and water pressure was always good.
Try this link on scream and fly. It discusses your situation.