complete oil injection system removal

i am in the process of rebuilding an '87 merc 70hp elpto that had a top cylinder connecting rod (crankside) bearing failure.

although the oil tank was full, there seemed to be trapped air in the tubes.

long story short. the oil tank is not going back in, or are any other oil pump parts.

can this be done safely? i am flip floppin on the idea of keeping the oil injection, but cannot risk running too lean on oil.

Re: complete oil injection system removal

I cannot comment on the reliability of Mercury's oil injection system, as I have no experience. I do know that it's common to remove the system on PWC's, as they run into the same problem of oil starvation. I removed the oiler on my jetski.

Bubbles in the line, to me, mean that air entered the system somewhere. Probably in a joint or leaky hose. This assumes that the oiler was correctly primed last time it was apart before being put back into operation.

On a 21 year-old engine, if it were mine, I'd remove it and run premix. If there's an oil level alarm, short (or disconnect) the wires so the alarm stays off. Due to the 50:1 premix ratio, your engine will be getting 2% less gas per intake volume than it use to. You could raise the float level, adjust idle mixture richer, or rejet the carbs to compensate. Or, leave as is, and it'll probably be OK.

Also, maybe test the oil pump by itself to see if it's working correctly. It could be that bad rubber hoses were at fault, and that the pump itself is just fine. Lines have to be purged of all air before a pump can move any liquid. Pump seals could also let in air.

Re: complete oil injection system removal

JT, I had thought Merc oiling systems were self bleeding, due to gravity feed. Also, usually the pistons seize before the bearings, due to lack of lubrication. While it may make sense to remove the Oiling system, you might investigate why the bearing seized. Does it have chatter marks or water marks?

Re: complete oil injection system removal

the bearing's rollers were all squished and layered together entwined with the cage. this caused the connecting rod bolts to chew at the casing, during the engines last 30 revolutions. the casing can be tig welded.

inside the connecting rod, there is a small burr that i will polish out, and the crankshaft does as well. where would i find chatter or water marks?

i dont plan on re-machining the race surfaces, but will do my best clean it up with a fine file and fine wet/dry sandpaper.

i was told it was probable that the oil pump failed, and i saw the 3" air gap in the oil feed tube.

is there a better known reason for failure in this area?