Mercury 60 (3 Cyl) problem

60 (3 Cyl)
1984-90
6428681-D000749

I have had this motor for about 5 years and my Dad 10 years, we both have taken very good care of it. Just replaced the water pump and a tune-up, have had it out twice sense the repair. Took it out this past weekend started right up, ran fine until we decided to cross the lake couple miles fully throttle about 1/2 way i notice the engine begin to run slower even thought the throttle was at full. Never staled and would start right backup and idle. I can put the muffs on it in my driveway in gear and it runs at full speed BUT I only do this for a second or two. But i put it in the lake and it won?t run but one speed, slow. Removed the spark plugs and notice some metal flakes on spark plug #1, 2 & 3 were fine. A closer look at the #1 cylinder revealed a divot in the piston. Any insight on this, and how it could have happened, and the repair.

Rob

Re: Mercury 60 (3 Cyl) problem

That is caused by heat, could be pump/thermostat, lean - dirty carb, plugged filter, anti-syphon valve sticking, pre-ignition - to much spark, crappy fuel or all of the above

Re: Mercury 60 (3 Cyl) problem

Welcome to the forum!!
NEVER run your motor more than 1500 rpm's unless you're in the water pushing your boat, not even for a few seconds.

Re: Mercury 60 (3 Cyl) problem

Suppose i'll start with the Gas sense it seems to be the easiest and cheapest (So Far). Thx for the reply Laddies

Had no idea that even running that for a second with muffs could damage the engine, never to old to learn something new.

Have any idea how difficult it would be to replace the #1 piston?

Re: Mercury 60 (3 Cyl) problem

At this point remove the intake port covers and the exhaust water jacket covers so you can look in the cyls. and check for farther damage. Then if you decide it's something you want to try buy a OEM manual. Let us know what you find.

Re: Mercury 60 (3 Cyl) problem

Update to my problem, last weekend i cleaned the spark plugs, and replaced the fuel. Took the boat out yesterday and it ran great for about 2 hours and then the same problem 1/2 speed @ fully throttle. Got it home and removed the plug #1 and sure enough metal on the spark plug. Looked at the piston, and a little more has been eaten away. Looks like i have some work for the off-season.