Anyone know what damage might have been done from a 2 stroke mercury 115hp outboard motor overheating?

Question

The water pressure gauge showed good water pressure, but the water intakes were clogged by barnacles etc. The motor was running hard at about 4500 rpm, when it started getting real loud and vibrating terribly. It never stalled & we were able to limp back to the marina at 2500 rpms. Forward & reverse seam to work fine & it will idle. The motor was barely squirting water out when running. After clearing the debris away from the water intakes, the motor is now squirting water out properly when running, but the motor vibrates terribly above an idle, even in neutral. A friend suggested that a cylinder may not be firing, but it doesn't sound like there is a miss, just the heavy vibrations. The motor is a 1987 in-line 6 cylinder which has never given me any problems. Any suggestions?

Answer 1

Sounds like a cylinder isn't firing. Disconnect the spark plugs one at a time to see which one(s) isn't working. Perhaps you threw a connecting rod or fried a piston; if so with its spark plug disconnected, you will see no change in idle speed. You probably have quite an expensive repair on your hands. Time for a new motor?

Answer 2

cracked aliumin some where and also check engine mounts.

Answer 3

Start with a compression test, you should have at least 100 PSI on all cylinders.  My guess is that when you overheated you did some internal damage, pistons, rings or bearings.  Look for debris attached to the spark plug electrode, this will indicate piston damage.  I wouldn't consider rebuilding a motor that old, look for something more current.

Answer 4

Jim S knows his stuff.  I agree that the engine might have major problems, But go through the testing to make sure, then get a couple estimates on "off season" repairs....In other words get the work done this winter.  This season is about over and by the time you got it back it's going to be cold, But some shops will cut their rate for Jan or Feb work.  Good Luck!