Help with strange sound

[chartersj]

I have been noticing a different sound coming from my motor. It's not overly loud but It kind of sounds like when you blow across the top of a bottle...like a hollow low pitch whistle... hard to describe. I took the outdrive off and still does it. At an idle it sounds like it's coming from the back of the motor or down low and intermittent with the rotation of the crank. Will pick up with some rpms but not always steady. And cruising on plan it comes and goes when I'm adjusting the trim...any thoughts?

 

[achris]

Exhaust leak? Check for corrosion holes in the exhaust system.

But I do have to ask.... What engine? (you have 2 listed in your signature, but not specified which you are referring to, or maybe a different one all together. :noidea

 

[chartersj]

This is the 496. Doesn't seem like an exhaust leak it has through hull without the y pipe. It's like a harmonic type sound. I checked engine alignment and the tool goes in all the way fairly easy but do have more spline marks on the top then bottom.

 

[Bondo]

At an idle it sounds like it's coming from the back of the motor or down low and intermittent with the rotation of the crank.
It's like a harmonic type sound.

Ayuh,....... My WAGuess is,......

Yer flywheel cover has the tin plate on the bottom forward facin' side, rather than the plastic cover plate,.....
The little bolts have loosened, or fallen out, allowin' the plate to vibrate, makin' the racket,......

 

[achris]

... hard to describe. ...any thoughts?

Hard to diagnose with a video of the sound.. Even harder without...

Chris......

 

[chartersj]

Ayuh,....... My WAGuess is,......

Yer flywheel cover has the tin plate on the bottom forward facin' side, rather than the plastic cover plate,.....
The little bolts have loosened, or fallen out, allowin' the plate to vibrate, makin' the racket,......

I think I might have read something about this before now you mention it. I wonder how I would ever get there to see it that's it. Could crank bearings make that sound?

 

[chartersj]

Hard to diagnose with a video of the sound.. Even harder without...

Chris......

Your very right. I'm not sure you would ever hear it on a video it's not very loud but i will try next time I start it.

 

[Bondo]

Could crank bearings make that sound?

Nope,.....

I wonder how I would ever get there to see it that's it.

Depends on how limber you are, 'n how much "Boat" is in the way,........

 

[chartersj]

Nope,.....



Depends on how limber you are, 'n how much "Boat" is in the way,........

I can get an arm down in there enough to tell that plate your talking about is actually plastic. I can see bolt on either side holding it in there but it is loose enough I can wiggle it. Will hold it next time I start it to see if that's it....the way it seems to go with the rotation of the crank had me fearing the worst...

 

[KJM]

be careful you don't lose that arm

 

[chartersj]

https://youtu.be/r7tGtO_nQi0
This is the sound here. This morning on the hose it wasn't loud enough to hear on the video. So I took it for a good run for an hour and didn't hear it the whole time. Got it home to flush it out and thats when it started to do it... you can faintly hear it at an idle but can hear it good after a quick punch of the throttle when it's reving back down.

 

[chartersj]

The noise isn't coming from the flywheel cover. It almost sounds like it could be coming from the intake manifold but doesn't seem to be louder when I put my ear up to the throttle body filter. But can hear it all around the motor and more toward the transom. Also i replaced the iac and iac muffler and no change.

 

[chartersj]

I found two loose motor mounts today.. opposite corners. I noticed a small gap between the washers on the transom plate and the bell housing. Tried to tighten it but it just kept turning. Nut was stripped. Would it be hard on the coupler? and any chance of that being the source of the sound or something wore because of the loose mounts?

 

[NHGuy]

I think I'd maybe find a way to snug that nut. If the stud isn't stripped maybe you can succeed with a proper nut. Otherwise if only the inner part of the stud is bad you might need to stack some more washers to make the good nut land on functional threads. Or worst case find a way to change the stud.
My engine and drive have a harmonic when the rpms are over 2400 and the drive is all the way down. I just chalk it up to contact between the stops and the rams. Or maybe the drive hits the bell housing when it's down, I haven't looked. But it does annoy me.

 

[achris]

I found two loose motor mounts today.. opposite corners. I noticed a small gap between the washers on the transom plate and the bell housing. Tried to tighten it but it just kept turning. Nut was stripped. Would it be hard on the coupler? and any chance of that being the source of the sound or something wore because of the loose mounts?

Sounds like the engine is 'cocked'. You need to slack off the top nuts on the side mounts, then lift the engine from the hook on the thermostat cover and take the weight. Tighten the rear mount screws to 35 lb-ft, then lower the engine until it's JUST touching one of the side mount bottom nuts. Then spin the other side mount nut up until it also JUST touches the side mount. This is your starting point for the alignment. All adjustments made to raise or lower the engine MUST be done the same on both sides, or you'll end up with a cocked engine again...

See the video in my video links.

Chris.......

 

[chartersj]

Yeah I found a plated nut that I was able to use to tighten the back one up with. The original nut is aluminum I would say. But will order another oem nut. And thanks for that 'achris' that is something i figured i should do and I wasn't sure of the exact method.

 

[achris]

.... The original nut is aluminum I would say. ....

Yep. Not a great fan, but it's done to reduce dis-similar metals corrosion. I replaced mine with stainless steel. I figured if the water was high enough in the boat to get a galvanic cell going between the nuts and the housing, my nuts corroding would be the last thing I would be concerned about!

Chris.......

 

[chartersj]

Was out for a quick run today. It does not do this noise while in the water. Not sure what the difference would be there. also had an extra beep when I turned my key to the on position. Normally I only get one fairly short beep, but this was a longer first beep with an second beep right after. When I got it home to flush it out the double beep was gone, and was only doing the normal single beep. I assume after a couple key cycles the code must have cleared itself. Would that be kept in the history if I plugged it into a computer?

 

[achris]

Depending on the code, yes. Most are stored.

 

[chartersj]

Hooked a scan tool up to it today because the last few times I have use it i had a double beep with the key on but would clear it self after a little run time.
15 - map sensor circuit
40 - manifold / intake
75 - fuel level 1 Ci
77 - camshaft sensor....said 40% power and said it happend at mid 400 rpm. But I don't remember any warning beeps while running or reduction in power since I have had the boat.