A mystery to me and the mechanic

[Larry Gregan]

I recently took my Nitro 750 up to the French River in Canada for two weeks of fishing. While I was up there (about a week into the trip) I noticed that the 75 Merc two stroke started to make a strange noise after it had been running for awhile. It sounded like a belt squeeling although I know there are no belts on the motor. It would sound in sequence with the rpm's of the motor. In other words if you rev the motor the sound revs too. Sometimes the sound would disappear altogether only to reappear later. It seemed to happen only when the motor warmed up. It sounded as though it was coming from near the exhaust. After returning home I took my boat to the shop (Marine Max) and described the noise. Of course they ran the boat and it won't happen now. The mechanic has no idea what could be causing it. Does anyone have an idea what it could be or has anyone experienced anything like this. The water pressure is good and doesn't fluctuate and rpm's are also good. Any ideas????

 

[Corey Carrico]

My 115 2 stroke does it on occasion. In my case it is the drive shaft bearing/seal at the bottom of the cowling. Get some silicone lube and lube that bearing and the shaft where it heads out of the cowling and towards the lower unit. I do it once or twice a season and no more annoying squeal.

 

[Larry Gregan]

Corey...Thanks for the response. How involved of a job is it to get to the bearing and lube it???? I am not known for my mechanical skills.

 

[Corey Carrico]

It is really easy...all you need is the Silicone spray, take off the cowling and coat the area where the driveshaft passes through. Do the same on the outside of the cowling where it passes though and for good measure spray the shaft down by the lower unit. Don't be shy with it and DO NOT use WD-40.



There is a fair amount about this problem on the web...do a google search for "squealing outboard" and you can find some pictures highlighting where to spray.

 

[Larry Gregan]

Corey....Thanks again for the help