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Old 26-08-2021, 19:40   #1
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Noisy gearbox

I have a Yanmar 2YM15 (350 hours) coupled to a gearbox with 2.62 reduction ratio both purchased new in 2015 which is very noisy when running ahead but does not make any noise when going astern. I have a 2 bladed folding right handed prop and the prop shaft is rotating clockwise in forward gear when viewed from astern as per the Yanmar manual. The noise when in forward gear is a very loud whine that increases with increased revs. This noise does not occur when going astern. I am now advised by the Yanmar agent that I require a new gearbox but I am inclined to think that there may be some other problem or other way to resolve this. The problem has been present since installed new but agent at that time disputed that there was a problem. Is anybody able to throw some light onto why this may be occurring?
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Old 26-08-2021, 19:57   #2
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Re: Noisy gearbox

No gearbox should be noisy when new either in fwd or reverse.
I guess the agent didnt want to step up to the plate & replace under warranty but now you are out of warranty he wont mind throwing your money at it.
At 350 hrs it's definitely a manufacturing fault assuming it had oil in it & installation was correct. I'd have threatened legal action.
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Old 27-08-2021, 00:41   #3
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Re: Noisy gearbox

Echoing Compass790, what oil is in the gearbox and what’s the condition of it? How good is the engine alignment?
I once had a noise in a KM2P so I opened up the coupling to check the rear bearing and noticed that the propeller shaft was hitting the end of the gearbox output shaft. It had a pinch type coupling so I pushed the shaft back 5mm in the coupling and put it all back together and ran it.... the noise was gone and I still can’t understand or explain why the shaft contact would cause a noise when the rigidly connected coupling wouldn’t.
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Old 31-08-2021, 06:50   #4
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Re: Noisy gearbox

The clue is forward versus reverse. When in forward, the prop shaft pushes against the transmission shaft, and that shaft against the next, and somewhere in that sequence something is loose or a bearing is going. In reverse everything tries to pull apart. A reasonable first step would be to tighten up the parts you can reach, as SkipperPete suggests. Homefully, it won't go as far as a tranny rebuild. In any case, do pursue it - having it fail could be embarrassing.
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Old 01-09-2021, 16:29   #5
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Re: Noisy gearbox

Quote:
Originally Posted by Compass790 View Post
No gearbox should be noisy when new either in fwd or reverse.
I guess the agent didnt want to step up to the plate & replace under warranty but now you are out of warranty he wont mind throwing your money at it.
At 350 hrs it's definitely a manufacturing fault assuming it had oil in it & installation was correct. I'd have threatened legal action.
Sorry for the late reply. Oil levels are checked regularly and prop shaft alignment checked and adjusted but still no improvement.
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Old 01-09-2021, 16:32   #6
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Re: Noisy gearbox

Quote:
Originally Posted by skipperpete View Post
Echoing Compass790, what oil is in the gearbox and what’s the condition of it? How good is the engine alignment?
I once had a noise in a KM2P so I opened up the coupling to check the rear bearing and noticed that the propeller shaft was hitting the end of the gearbox output shaft. It had a pinch type coupling so I pushed the shaft back 5mm in the coupling and put it all back together and ran it.... the noise was gone and I still can’t understand or explain why the shaft contact would cause a noise when the rigidly connected coupling wouldn’t.
I originally used same oil as in engine as recommended by servicing agent but now using Yanmar oil as requested by dealer. Engine alignment has been carried out and deemed ok.
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Old 01-09-2021, 16:41   #7
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Re: Noisy gearbox

Quote:
Originally Posted by DonCB View Post
I originally used same oil as in engine as recommended by servicing agent but now using Yanmar oil as requested by dealer. Engine alignment has been carried out and deemed ok.
what make of gearbox? The gearbox of my yanmar uses ATF, not the same oil as engine.

Ignore my question/comment above... just read manual for engine and see it is indeed Yanmar SAE 30....
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Old 01-09-2021, 16:46   #8
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Re: Noisy gearbox

Quote:
Originally Posted by tkeithlu View Post
The clue is forward versus reverse. When in forward, the prop shaft pushes against the transmission shaft, and that shaft against the next, and somewhere in that sequence something is loose or a bearing is going. In reverse everything tries to pull apart. A reasonable first step would be to tighten up the parts you can reach, as SkipperPete suggests. Homefully, it won't go as far as a tranny rebuild. In any case, do pursue it - having it fail could be embarrassing.
Thank you your response is similar to that of skipperpete's. I will take it on board and get it checked out.
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