Mercruiser Alpha One Gen II Strange flapping sound

jfkal

jfkal

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Went for sea trail. All good in the beginning. Then after a while a strange flapping sound started to appear. Got a bit stronger over time. However only appears going forward above 1,400 rpm. Fades away at higher revs ( or might get drowned out by engine noise). Vanishes below 1,400 rpm.
Sound does not vary on turns, nor on different trim or even tilt settings. Does not appear in reverse nor out of gear at any rpm.
Any ideas anyone?
Thanks
Joerg
PS: Got a sound for file but can't upload here.
 
Perhaps check all the rubber belts, assuming that the engine uses some rubber belts. It doesn't necessarily fit all the symptoms but the only time I noticed an intermittent flapping sound on a car engine I decided to ignore it until I had more time. Once the cambelt had completed its disintegration I had plenty of time! :o

Richard

On the other hand .... it could be the primary fuel filter coming loose! ;)
 
Last edited:
RichardS said:
Perhaps check all the rubber belts, assuming that the engine uses some rubber belts. It doesn't necessarily fit all the symptoms but the only time I noticed an intermittent flapping sound on a car engine I decided to ignore it until I had more time. Once the cambelt had completed its disintegration I had plenty of time! :o

Richard

On the other hand .... it could be the primary fuel filter coming loose! ;)
Click to expand...

Oh!!!!! Has that happened to you too???? This happened on a boat I was on and the filter was resting on a drive belt making a noise like a demented waste gate!!
 
Hi.

It is most likely the exhaust flappers. A common issue and easy to replace. Extreme cases and left long enough, they can break up and block the exhaust and cooling flow.
The noise is usually most evident at above tick over to around and up to 1300 rpm. Goes away when running higher rpms because they are forced fully open by the exhaust pressure.
Have a listen to where the exhaust pipe heads down towards the leg. If it's a V6 or V8 have a listen to where the cow horns are each side of the engine at the back.
 
QBhoy said:
Hi.

It is most likely the exhaust flappers. A common issue and easy to replace. Extreme cases and left long enough, they can break up and block the exhaust and cooling flow.
The noise is usually most evident at above tick over to around and up to 1300 rpm. Goes away when running higher rpms because they are forced fully open by the exhaust pressure.
Have a listen to where the exhaust pipe heads down towards the leg. If it's a V6 or V8 have a listen to where the cow horns are each side of the engine at the back.
Click to expand...

Would they not flap in neutral or reverse?

Richard
 
At certain rpms in neutral and perhaps unknown in reverse, because there would likely be a back pressure from the water in reverse.
It's most likely you wouldn't be going hard enough in reverse to hear the sound. If you were, the boat would be trying to sink itself.
 
jfkal said:
Went for sea trail. All good in the beginning. Then after a while a strange flapping sound started to appear. Got a bit stronger over time. However only appears going forward above 1,400 rpm. Fades away at higher revs ( or might get drowned out by engine noise). Vanishes below 1,400 rpm.
Sound does not vary on turns, nor on different trim or even tilt settings. Does not appear in reverse nor out of gear at any rpm.
Any ideas anyone?
Thanks
Joerg
PS: Got a sound for file but can't upload here.
Click to expand...
 
Got a sound file uploaded under https://youtu.be/0tWdM6xwFr8 . Please check it out and let me know whether this sounds familiar.
Relevant clatter sound starts at 4 seconds into the file. I compared this with exhaust flapping noise but it is different :-(((.
Help appreciated.
Joerg
 
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