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Old 05-10-2008, 17:46   #1
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Possible sources of squealing sound in engine/trannie/shaft

Hi folks,

I have noticed a squealing sound in the engine compartment, that gets loader with higher RPMs. I never paid much attention to it, as I figured it was the belt(s) wearing and with only a couple weeks left in the season, I woudl change them later (have spares of boath belts). I checked theire tensions, and they seems OK.

Anyway, I revved the engine (Yanmar 2GM) up to 3200rpms in neutral today, and noticed there is no squealing, so I assume now, that it can't be belt noise, as I would think they would still squeal in neutral.

The trannie has the proper oil level.
I put new flax in the stuffing box this year, and I could loose it a turn, to see if the noice stops - but it does not run hot all all, and does drip while running.
I did have the engine out in the winter, but the prop shaft seems to line up well, and does not cause any vibration.

Any thoughts on possible sources of this noise?? It is hard to hear where it is coming from, with the engine running, etc!!

I will be hauling the boat in a couple of weeks, but would like to try any in water testing before haulout!!
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Old 05-10-2008, 17:52   #2
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I would not discount the belts.
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Old 05-10-2008, 17:58   #3
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how difficult is it to turn the shaft by hand in neutral
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Old 05-10-2008, 18:07   #4
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Easy to turn shaft by hand! But, then again, It's my 1st boat wit han inboard, so i am no expert in judging!
I have motored for a couple of hours, and checked the stuffing box temp with my hand - not even hot to the touch - barely warm!

If there is anything I can try, to rules things out / find the source, while still in the water, then I can fix it over the winter, if needed.

It seems much louder in forward, than reverse.

It does really sound like a belt squealing, but wouln't a raw water pump, or alt belt still squeal, while revved high in neutral??

I appreciate the input!!
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Old 05-10-2008, 18:14   #5
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put one ear plug in and then listen around for the noise. You can get a better audible picture this way.
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Old 05-10-2008, 18:17   #6
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Lok at the engine box cover and the sidewalls in line with the pulleys and belts. Advanced wear will show the belt "splattering" rubber all over the place. You also may se the belt dust under the engine in line with the belts.

If the belts are due raplacing, change them first and eliminate one cause.

There isn't much else that sounds like belts squeeling.
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Old 05-10-2008, 19:03   #7
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Just as well change the belts now, if it solves the problem fine if not you will have eliminated that possibility. If the belts are "glazed" they could squeal even though the tension seems right
Maybe the bearings on the alternator are going bad?
Good luck, please post the source when you do locate it.
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Old 05-10-2008, 19:29   #8
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Belts or alternator would be my first suspect.

Remember that belts have different "vee" profiles.

If the belt is too deep in the pulley it could be the problem.

I have a feeling tho' you are going to find a bearing problem....this usually occurs when belts are too tight.
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Old 05-10-2008, 19:31   #9
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Does the squealing go away when you have the transmission in neutral? If so, it could be a cutlass bearing.
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Old 05-10-2008, 19:57   #10
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I am a mechanic on diesel engines and am responsible for an F-250, 2 Tractors, A bobcat, An excavator, 2 dumptrucks, 2 Dozers, and any other vehicle that anyone in my immediate or exteneded family aquire. I agree with Cheif and the others that say a belt issue or a bearing I would also have someone check the gears, clutch and shaft bearings if it turns out not to be a belt.
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Old 06-10-2008, 06:56   #11
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To answer a few questions:

- there is no rubber / belt material inside the engine compartment to indicate belt wear.

- as mentioned in the 1st post, the sound does dissappear completely while in neutral!! Yes, I do feel it could be the cutless bearing, stuffing box, or even transmission, but where the cutlass bearing is under water, I am not sure it would produce as loud of a squealing sound as is there!

- Certainly could be a bearing going bad in the alternator, but would that sound (or belts for that ,matter) not still be heard while revved up high in neutral. *** AS MENTIONED, THE SOUND COMPLETELY DISSAPPEARS IN NEUTRAL, AND SEEMS LOUDER IN FORWARD THAN REVERSE***



I mentioned that it "sounded" like a belt noise, as it is a type of squealing noise, but it is no where near as loud or piercing of a squealing noise as you would hear on a car, with a very bad belt!!

the cutlass bearing is only 2 years old, and the engine alignment is good enough to have no vibration. However, it is possible that the shaft could still be missaligned a bit , with the cutlass bearing.
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Old 06-10-2008, 14:54   #12
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It's either the cutlass bearing or the transmision. I would go with the transmision though, because the cutlass is underwater.
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Old 06-10-2008, 16:36   #13
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I would check the connection between the engine and the transmission sometimes there is a dampner plate in there which may be damaged or wearing out.
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Old 06-10-2008, 17:04   #14
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unbolt the shaft from the engine and run the engine in and out of gear. check for noise.

it is possible to have a shaft aligned with the engine and not aligned to the bore of the strut. This will cause advanced wear on 2 points of the bearing. When the bearing rubber goes away, you have metal on metal. Even under water the noise is loud.
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Old 06-10-2008, 17:25   #15
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Some years ago I had the cutlass bearing and shaft replaced and the drive train developed a harmonic vibration in the shaft and prop. The cure was to remove the prop and have the leading edge of the blades knurled. Problem solved.
I would remove the prop and run the engine up to speed and see if the noise goes away.
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