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A very weird shaft noise....

rwthomas1

Sustaining Partner
My E38 is back in the water and its making a very strange noise when in gear. Sounds like a mid-pitch moaning, fairly loud, that occurs between 1200-1600rpm. Above that it seems just audible but I'm not sure I'm actually hearing it and no noise at idle. Only seems to do this in forward. I did notice on the hard that when I rotated the prop by hand I got a similar low moaning noise. Engine is a Universal 5432 with a Hurth trans.

-The transmission has fluid in it of the correct type, at the correct level, it is clean and clear, no debris. It was clean and clear when I changed it last year.

-The cutlass bearing has very minimal play in it, less than 1/32"

-The packing is correctly adjusted, the packing assembly does not heat up at all even after 1/2hr of motoring. 1 drip every 10 seconds when motoring and less at rest.

-Transmission shifts perfectly, is cool to the touch even after 1/2hr motoring.

-Shaft spins easily by hand, smooth.

The only thing I have left to check is that the cables are properly adjusted as they were replaced this winter. IIRC, I did this already but will check again. Is it possible that this is just a "harmonic" noise when everything starts vibrating at the same frequency? With the exception of the noise everything is very smooth, etc.

Any ideas? RT
 

Gary Peterson

Marine Guy
Can you get down in the Stbd lazerette when some one else is driving and closely observe and listen to the drive train when you are having this event?
Could be normal trans thrust bearing sounds, prop tip excitation, or cutless bearing noise.
Just some ideas_____________:confused:
 

rwthomas1

Sustaining Partner
Gary,
Yes, I need to try that. Could this have anything to do with antifouling on the prop/shaft? I know that the cutlass should be getting plenty of water, the strut/shaft opening was clear when launched.... The boat just went back in so its been a bit hectic just dealing with all the issues that come up. Will update when I get a chance. Thanks, RT
 

Steve

Member III
Only worth a cent?

Not recommended but... all my land lover gear-head friends always solve issues with Marvel Mystery Oil .... ???? Not sure if a squirt in the Hurth would do anything or ...ruin anything?
 

Rocinante33

Contributing Partner
I wouldn't mess with mystery marvel oil in the Hurth trans. The fluid seems to be very critical & added viscosity or lubricity may not be good for it. I just replaced mine.....$1K plus and I did the work myself.
 

rwthomas1

Sustaining Partner
Update!

Well I have made certain that the shifter cable is pushing the transmission lever far enough as recommended in my Calder book. I moved the link up one hole on the lever so there is plenty of travel. I re-checked the oil level, its fine. I re-checked the packing adjustment, seems perfect, shaft is loose-spins easily, the drip rate is acceptable, does not heat up. Checked, adjusted alternator belt tension, also correct. So now I'm at a loss. The noise is still present, sometimes loud, sometimes soft. I'm out of ideas. A powerboat mechanic I know said run it till it breaks! Given the situation, I am inclined to agree. RT
 
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