merc noise

[trautman]

Ok so ive read all the old threads on this high pitch squealing noise with the 75 hp and 90 hp merc from about 1998 to 2002. Seems it was indicated it was some kind of bushing at the drive shaft to engine coupling. Have not found a single thread that verified this or not. SO has it turned into a nonproblem and just ignore it or does it lead to more issues. Could find nothing about a resolution or live with it ending? Mine does the same thing WOT for a period leaves the engine with a litlle slight squeal or chirpping. Shut it down for a few and it goes away. Since I rarely run at WOT it really doesn't bother me often I just would like to know what the heck it is...

 

[trautman]

Re: merc noise

Ttt one time. I know someone else has been here or heard something

 

[eLeShUnut]

Re: merc noise

I have also been watching those threads for a while. I have a 1999 115 that is also a 2+2 setup. I've had the engine for 3 years and it has not changed. I also would say it sounds like a fanbelt...there's just not one there.

IMHO-I think it has something to do with the lower 2 carbs and reeds getting warm during high throttle runs. The noise doesn't appear until the 2 cut out @ 2k rpm and it goes away above that. The butterflies are still partially open so a bit of air will still be drawn in across the reeds. The noise could also be compared to a clarinet I guess...that kind of high frequency reed type of vibration....too much spongebob & squidward.

I'm confident there is not a conspiracy among the Merc gurus...it's probably just one of those engine enigmas specific to the 2+2 configuration. I also take comfort in the fact that none of the experienced contributors seem to be jumping & screaming that they remembered a bunch of 2+2s self destructing after making this sound.

Bevan

 

[trautman]

Re: merc noise

Agreed I decided if it was a fatal issue there would be more to those threads. But being a maintenance guy for 25 years it just drives me nuts not knowing. Mine seems to come from the WOT for a time or hard throttling while pulling a tube of kids for a time. My normal speeds and operation does not produce the sound. Seems like I can find threads that describe the same type of thing but none seem to end in disaster. Guess well see?

Brian

 

[bullet 101]

Re: merc noise

Seems like i read somewhere that this noise is caused by the cowl pan rubbing the front of the engine around the top motor mounts...

 

[trautman]

Re: merc noise

hmmm now that may have some merit Ill check that out. Thanks!

 

[acjc]

Re: merc noise

I'm having the same problem with my 2002, 75 HP, 2 stroke. I first started to have this problem after hard throttling while pulling a tube for the kids. The noise has been re-occurring everytime that the engine gets warmed up (after using it at 4500 - 5000 RPM for 15 - 20 min.) I brought it in to the local Merc repair shop and they haven't found the source of the problem yet - they have never seen this problem in the past. They replaced the exhaust gaskets however this didn't fix the problem. The mechanic is thinking about looking at the reed valves next. This engine is a 3 cylinder so I don't know if this could be the same cause as with a 4 cylinder. My mechanic isn't worried about this noise damaging the engine so I will finish my fishing season (end of Oct.) before taking it back for repairs. I find this noise very annoying so I'm not going to let it rest until I find out what is causing it and fix it
Any other ideas?????

 

[trautman]

Re: merc noise

Well please let me know as I have looked over the cowl and see nothing. My engine is a 98 but the same as yours. Strange how as soon as you shut her down and start it back up it goes away. We have the identical symtoms and causes.

 

[Faztbullet]

Re: merc noise

I have talked to several of the engine refurbishers I know and 2 have had customers complain of this. Investigation of problem(sounds like a high pitch static thru radio speaker or high speed pump running) is its a reed whistle due to harmonic's and temp...when you restart it the cool intake charge makes problem disappear. Solution was to drop 1 pitch when pulling loads..

 

[acjc]

Re: merc noise

My engine has to cool down for quite some time before the noise goes away and it comes back as soon as it warms up again. I'm using the outboard with a 13.25 x 17P prop on a 16.5' aluminium fishing boat - I don't think its a prop issue. The noise is present when the motor is in neutral when warm.
What I find weird about this is that the engine suddenly started making this noise - it was OK before. Would replacing the reed valves fix the issue?

 

[j_martin]

Re: merc noise

My engine has to cool down for quite some time before the noise goes away and it comes back as soon as it warms up again. I'm using the outboard with a 13.25 x 17P prop on a 16.5' aluminium fishing boat - I don't think its a prop issue. The noise is present when the motor is in neutral when warm.
What I find weird about this is that the engine suddenly started making this noise - it was OK before. Would replacing the reed valves fix the issue?

I would check the carb linkage. Maybe one is slightly open when it shouldn't be.

You could position a piece of tubing near the lower carb opening and stick the other end in your ear when the noise occurs to see if that's where it is.

 

[acjc]

Re: merc noise

I took the boat out for a good run today and no more noise I used half of my gas tank and used the engine at 4500 -5000 RPM... go figure why I didn't here the noise this time. The motor hadn't been used for the past 3 weeks and it ran perfectly all day. It was a cool day on the water today - 45 deg and the water temp. was at 55 deg. The noise seemed to occur when the engine would get warm - could the cold temp have prevented it from appearing today????? Still got 3 weekends left before putting her away for the winter..... We'll see what happens next time out (hopefully next weekend if the weather permits).