TOPIC: burned down 500

a friend of mine scored the lower 2 cyls of his 50 hp, he just had a new water pump installed , the carb rebuilt. has a new belt, and the timing set. new hose, clean tank. all done by a merc mech. he took the boat out and went acouple of miles and said it ran fine and then stoped. would not crank over. he started to paddle back. and tried it and started up, ran ruff. he pulled the wrap and the motor was extemly hot. he checked comp when he got home, and the lower 2 cyls were real low and the top 2 were still ok. now my queston is does this sound like a bad water pump or a lean score? any thoughts. thanks frog

sounds as if the oil mix was wrong

should not that have affected
all 4 cyls?

Maybe the bottom carburator was leaned out?

Sounds like it was overheated. When you pull it down you will know, if it was an overheat the exhaust side of the pistons will be scored, if it was lack of oil the intake side is first to go. An autopsy is needed here.

thanks all. i'll be looking at the pistons this week. greg

Take and post lots of pictures!!

talked to my friend last nite and ask him what side of thepistons were scored and it was the exhaust side. so I told him it might be an over heat problem like gfgarland said, so he pulled the lower unit off and the hub on the impeller was rounded out. so he is going to try to figure that out. frog

I had that happen on my Merc 400 when I started her up dry for about just a minute or 2. Impeller rubber came off the hub. Luckily I had no serious Damage because I noticed it wasn't peeing when I got underway. It still smoked the exhaust side fiberglass.

That is a shame, but hopefully it is rebuild-able. Those engines are tough, but have the bores checked for out of round and scoring. Lucky, there are lots of used parts around.