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Old 19-04-2021, 02:00   #1
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Grumbling prop/saildrive

When under sail we can hear one of the props grumbling/humming. When I put it in gear (reverse) the noise stops dead.

Aside from a bad bearing in the Saildrive, what are the possible causes.

I recently has the Saildrive (Yanmar SD31) apart and the bearing looked solid. Changed the oil seals and oring on drain plug. The seals had been bent damaged and they unit was full of creamy gunk too thick for the drain hole.

Added fresh oil, but now level is down 20-40ml, and when I stir the pot there's cloudy oil. (Could be residual cream that I didn't flush properly)

Don't think SD31s can be drained from the top.

Also there's an oil leak of about that scale which manifests from the lower starter motor bolt (flywheel seal on engine or gearbox side?) Hard to know if it's engine or gearbox oil. Could it be leaking from the top?

Is the gearbox lubricated from the SD or is there a sealed unit that might be dry? (Yanmar 3JH3E)
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Old 19-04-2021, 02:44   #2
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Re: Grumbling prop/saildrive

Any salt water in the leg even mixed with lube oil will soon destroy the case hardening on the gears and bearings ,maybe rebuild time re the oil leak ,engine oil will be black g/box oil should be realitvely clean .⛵️⚓️
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Old 19-04-2021, 10:57   #3
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Re: Grumbling prop/saildrive

"seals had been bent damaged"

Not condradicting Searles in any way, but is it possible you've got a bent shaft that is leaking oil by a seal and doing unspeakable things to your bearings?
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Old 19-04-2021, 13:38   #4
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Re: Grumbling prop/saildrive

It is probably is a bad bearing race. In reverse the thrust would be transferred to the opposite bearing. If you were leaking oil from the top of the saildrive, it could possibly end up on the lower starter bolt. You can dive it (holding breath with mask) and turning the prop by hand evaluate for roughness, tightness, or slop. Do not overfill with oil or it will suck water in on cool down. If you have two, compare it with the good side. Cavitation is another possible source for a strange (but harmless) noise. You would notice the cavitation sound at highrevs with low boat speed.
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Old 19-04-2021, 14:00   #5
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Re: Grumbling prop/saildrive

Well, anytime you let it spin it will grumble some even with a shaft drive.
But maybe you have an issue.
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