115 ELPTO head scratcher

[boat86fish]

I recently picked up a 1995 Nitro 170dc in super good condition, the motor had lost compression in the bottom cylinder, 140, 140, 140, 100. I inspected the cyl with a scope and it was scuffed. I'm doing the work myself, having rebuilt plenty of small engines, not outboards though. A light hone remove all the aluminum for the cylinder wall, nice! no boring needed. piston is toasted though. I am trying to figure out what scuffed up that cylinder. Obviously lack of lube. I took apart the bottom carb and didn't see any obvious junk in it. I'm speculating ethanol contamination, but I would have thought the top cylinders would go first. Or maby a loss of fuel pressure, the motor would have bogged down, the person I got from said the motor started making an odd noise so he shut it down. If it was a loss of oil injection, wouldn't that scuff up multiple cylinders, more like the upper ones. I did notice however when I was disassembling it that there was some water droplets in the oil pump housing and at the bottom crank seal, not much though. I am trying to figure this one out so I can fix it, don't want have to rebuild it again. Any thoughts?????

 

[wired247]

Its not really a lack of lube that causes scuffing in cylinders. Lack of oil is more likely to cause wasted bearing journals Scuffing is more a sign of a hot cylinder from lack of water flow overheating or a lean condition.

 

[boat86fish]

I didn't really think about an overheat too much, no alarm sounded. There is no record of the water pump being changed or the thermostat. I will be changing those. Is the poppet valve a part that should be changed as well?

 

[wired247]

The pump on a mercury is only good for 2-3 years at best. Change the impeller. Change the thermostats. Running cold causes damage just as much as running hot so you may not hear an alarm even if damage is being done. Might as well do the poppet too. They are cheap.