New Mercury 40 FourStroke Rattling/Screeching

unirocket

Recruit
Joined
Sep 27, 2009
Messages
3
Hello. I just bought a new pontoon with a new Mercury FourStroke 40 motor. When in gear between 1700-2200 RPMs, there is a rattling/screeching sound that noticeably disappears when outside this range. It doesn’t happen in neutral and also doesn’t happen when trimmed up significantly.

Video: https://youtu.be/yEyEFGSXWfo

Doesn’t appear to be the cover or latch since it happens even with the cover off and when ensuring the latch is secure.

I can contact the dealer, but wanted to know if anyone has a
quick fix for this issue. It doesn’t appear to have an impact on performance, but is certainly distracting and annoying. Shouldn’t be happening on a new motor!
 

HotTommy

Lieutenant Junior Grade
Joined
Mar 15, 2013
Messages
1,025
While searching for the source of the sound, keep in mind that it may be coming from something near the engine rather than the engine. Every object has a natural vibration frequency and that vibration will increase when it is being stimulated at that "resonant frequency." It is likely that when your motor in in the 2000 RPM +/- range its vibration is stimulating something in or near the motor.

If you can safely reach back with a boat hook or broom handle to touch areas around the motor while the noise is present, you may find the spot it is coming from.
 

ahicks

Captain
Joined
Sep 16, 2013
Messages
3,957
This is subjective as all get out, but I would never call what I am hearing in that video a rattle or screeching. I would call it harmonics or a resonance. It happens. It's a vibration set up by the motor running in a particular rpm range.

Too, I would not get in too big a hurry to call it a dealer responsibility or defect in the motor. I WOULD ask the dealer to give you a hand - if they are on the water. If it's a "dry" dealer, maybe they could spare a tech long enough for him to go for a ride with you?

Myself, I might be tempted to try a different pitched prop. Maybe one based on prop tuning with a target max rpm of about 5500. There's a chance that the prop itself could be causing the resonance.
 

unirocket

Recruit
Joined
Sep 27, 2009
Messages
3
This is subjective as all get out, but I would never call what I am hearing in that video a rattle or screeching. I would call it harmonics or a resonance. It happens. It's a vibration set up by the motor running in a particular rpm range.

Too, I would not get in too big a hurry to call it a dealer responsibility or defect in the motor. I WOULD ask the dealer to give you a hand - if they are on the water. If it's a "dry" dealer, maybe they could spare a tech long enough for him to go for a ride with you?

Myself, I might be tempted to try a different pitched prop. Maybe one based on prop tuning with a target max rpm of about 5500. There's a chance that the prop itself could be causing the resonance.

Thank you! I’m happy to report that I replaced a 3 blade prop with a 4 blade and slightly different pitch l, and that resolved the issue.
 
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