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Old 14-06-2019, 14:57   #1
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Join Date: Jun 2019
Location: New Zealand
Boat: Beneteau First 45
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Yanmar SD50/Flexifold random slipping and not engaging

Hi all, first time poster long time reader.

We have just bought a new boat (for us) with a Yanmar 4jh4ae and SD50 saildrive with a flexifold 3 blade 18inch propeller. The combo has 550 hours on it. The last week it intermittently has not been engaging in forward drive. Sometimes it engages in both forward and reverse, other times only reverse, and forward only engages at high revs (with a clunk), or only partially engages, and other times it doesn't engage at all no matter what. I've dived on it several times, and on those occasions (n=2), when in forward with the prop spinning at idle, and revs are increased, the prop starts to increase speed but then slows down again almost immediately, despite the increased engine revs. However, on occasion it will still provide full power and drive the boat forward at >6 knots as expected.

The Morse, linkages and cables all appear to function well, and a mechanic has just adjusted them thinking this could be the problem, however the fault is still there. The engine, gear box and clutch makes no unusual noises. The prop seems to be properly fitted, not loose, and folding and functioning correctly.

I understand the cone clutches on these need regular re-lapping, but imagine if the clutch was degraded this should result in almost complete loss of drive - which is not what we experience some times. I'm bamboozled!

I'm hoping to hear from the community whether these symptoms sound like the cone clutch, or possibly something else (the prop slipping on the shaft?)? All thoughts greatly appreciated, as we are currently cruising through the Med on our way back to New Zealand so don't have our usual service people to call on, and budget constraints require as much self-resolution as possible!

Cheers Tim
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Old 05-08-2019, 22:52   #2
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Location: Australian Itinerant
Boat: Lagoon 420
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Re: Yanmar SD50/Flexifold random slipping and not engaging

Hi Tim,
Sounds like cone clutch symptoms to me. The lapping procedure not difficult and you should know how to do it if you are going to own them, especially if venturing into remote parts. Can be done in the water. Get a pro to do it and ask to watch. Mechanic did mine in about an hour each, so should not be expensive. Get both done if a pair, its a known maintenance item. Avoid official dealers as they will try to sell you all new parts as the fix, very expensive! Some online descriptions are quite informative, see attached.
Good Luck with it. Pete.
Attached Files
File Type: pdf Yanmar_SD50_Clutch_Repair_v03.pdf (571.5 KB, 29 views)
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Old 06-08-2019, 04:25   #3
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Location: Esperance, Western Australia
Boat: Expedition 36 Aluminium
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Re: Yanmar SD50/Flexifold random slipping and not engaging

Agree with pirate Pete, I followed the directions on the PDF attachment about 6 months ago. It was easy to do and had the yacht operational the following day. Just take your time and better to do it now as it wonít get any better.. The symptoms you describe are identical to what I was experiencing.
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Old 14-08-2019, 00:25   #4
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Re: Yanmar SD50/Flexifold random slipping and not engaging

Thanks PiratePete and Diamondlife, much appreciated for you comments - right you both were - I lapped the cones and have a fully functioning sail drive again - much appreciated!
To anyone considering this procedure, with the right tools (and access to a vice mounted solidly somewhere) it's easy, so give it a try!
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