Yanmar KBW20 transmission whining noice- normal?

[malbert73]

Hi everyone,
I recently upsized in boats to a Tartan 40. The engine is a meticulously maintained Yanmar 4jhe which runs great with hardly any smoking.
Transmission is the KBW20 with an unusual 2.17 gear ratio (as opposed to typical 2.62). Easily cruises at 7 knots 2500 RPM with no vibration or issues.

My question is for anyone with knowledge of these engines and transmissions- is it normal to hear a fairly noticeable high pitched whining noice from the gearbox? engine surveyor blessed engine and gearbox pre-purchase. Transmission fluid was pretty clean (ATF, still pink, not smelling, normal level) and I just changed it to be certain. Definitely the gearbox making the noise as engine by itself in neutral is much quieter. Cutlass bearing is new as is shaft and coupling.

I have put 20 hours of cruising RPMs on engine since I bought boat, with no issues, including 2 good 10 hour days on delivery back to my home slip after purchase.


Thanks!
Mike

[delmarrey]

I believe the trany is supposed to have 30W oil in it. My KB does. There should be a tag on the bell-housing that tells what oil to use. The oil may be too thin or it was changed out so now you can't see the water that was in there, it could be a rusty bearing.

[malbert73]

Originally Posted by delmarrey

I believe the trany is supposed to have 30W oil in it. My KB does. There should be a tag on the bell-housing that tells what oil to use. The oil may be too thin or it was changed out so now you can't see the water that was in there, it could be a rusty bearing.

Thanks- the tag states to use ATF, as does the drain plug.
Could be a bearing I suppose....

[malbert73]

Originally Posted by delmarrey

I believe the trany is supposed to have 30W oil in it. My KB does. There should be a tag on the bell-housing that tells what oil to use. The oil may be too thin or it was changed out so now you can't see the water that was in there, it could be a rusty bearing.

Whoops pressed send too soon. No way there was water as engine and tranny sit pretty high. Entire boat would have to have 1 foot of water in it for tranny to be submerged, and it is not a cooled gearbox.

[Sailmonkey]

Ours has a high pitched whine, it's from the prop singing at lower speeds. Maybe similar?

[a64pilot]

I too have a noise at mid range RPM, I think mine is cutlass bearing?
You might try a mechanics stethoscope (a big screwdriver works pretty good) to try to find source of noise unless of course your sure it's the tranny. If it's the tranny an oil analysis may help determine if there is abnormal wear going on. I'm not a big fan of SOAP, but if you have a bearing going out, your probably making metal.

[delmarrey]

Originally Posted by malbert73

Whoops pressed send too soon. No way there was water as engine and tranny sit pretty high. Entire boat would have to have 1 foot of water in it for tranny to be submerged, and it is not a cooled gearbox.

Condensation is the usual way water gets in the trany. It would have to be sitting a long time in a cold climate, just saying.

[malbert73]

Originally Posted by delmarrey

Condensation is the usual way water gets in the trany. It would have to be sitting a long time in a cold climate, just saying.

Good to know.

I guess I am just wondering also if anyone has any suggestions for what to do. I guess I can just watch and wait since seems to be running fine. Not sure if a whining noise in absence of any other symptoms warrants removal of gearbox and overhaul/exam

[delmarrey]

I'd just keep an ear on it for a couple hundred hours. If it gets louder then you'll know. Also after that you can have the oil analyzed for rust. There's bound to be some metal from the gears and clutch so that wouldn't tell you, unless it's an excessive amount then you may need to have it checked out anyway.

[a64pilot]

Usually gears whine, bearings usually roar.
If your going to fly it and watch it, I'd get a baseline SOAP now once you get say 50 hours on the oil, them another one at oil change and look of course for a large increase in metal.
I wouldn't buy another one based on a whine either, unless I was going way away from help

[malbert73]

Great advice, thanks!

I would say more like a whine. A little like a reverse gear whine in a car.
It sounds like it could be normal, but I wanted to hear validation from others that they too heard this in same gearbox.


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[malbert73]

Also, what does SOAP stand for? I am guessing oil analysis?


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[charliehows]

i think my box is an older kbw (prev. owner ran the damn thing on ATF which killed the clutches, now has its proper 30w oil - acknowledge your box is newer and runs atf)- after new clutches and main seal fitted it still makes a pretty loud high pitched whine - but have you seen the size of the teeth on the gear sprockets? - they're bloody huge so in my case i'm pretty sure the noise is from that rather than any problem. Might be noisy but its pretty well indestructible...

[malbert73]

Now that is what the optimist in me wants to hear. Don't mind the noise if it's normal....
Sounds like a gear noise to me but my prior boat's 3YM30 never had same sound, but different, likely more lightweight, tranny


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[Jim Cate]

I don't know if this is relevant, but our ZF10 tranny whines when motor-sailing if the boat accelerates due to a wind increase... ie when the load comes off a bit. Has done since new, don't think it is a problem. Is your whine constant or is it load related?

Jim