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Old 23-07-2018, 04:46   #1
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Location: Manly, Qld, Aust
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Yanmar SD20 Prop Shaft Seals

I have replace the seals each slipping for the past 3 times as the oil was milky. This time the oil was good so I thought if its not broke...... However you guessed it 2 mths after slipping the stbd leg is contaminated. I have read extensively in these forums on the solutions and have installed a header tank as an interim measure to manage the problem and this appears to work well.

However thinking about the issue I'd like to float some ideas past the brains trust and really would like to hear from anyone who may have experimented along these lines.

Mod #1: Shift one of the spacers between the seals to the outer most position behind the outer seal so the seal runs on a fresh surface.

I can see no real reason for these spacers to be there and doubt the spacing between these seals is critical. I have noticed the problem seal seems to be the outer seal that wears a groove in the shaft possibly due to calcium or other particle buildup where the seawater interfaces with the seal.

Mod#2: Reverse the inner seal so that the seal is more effective at preventing water ingress rather than the oil egress.

This could allow some oil to leach from the drive, fill the annular space and lubricate the outer seal thus minimising the scouring of the shaft from the outer seal. Would a lot of oil leach from the drive if this were done.

Scrubby
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Old 23-07-2018, 16:53   #2
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Re: Yanmar SD20 Prop Shaft Seals

I installed my header tanks close to 15 years ago, and haven't looked back.
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Old 23-07-2018, 18:54   #3
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Re: Yanmar SD20 Prop Shaft Seals

We've resealed ours 3 times, never had moisture issue, have repositioned seals but wouldn't change the recommended direction the seals face. We did smooth the shaft a tiny bit with emery cloth and have done the header tank conversion. Drives are 1995 sd20s.
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