Yanmar SD20 prop shaft stub fracture

[Somadoc]

Doing some research on the internet it looks like the problem I have with my SD20 sail drive prop shaft is not unheard of! Putting the boat gently into reverse after a 4 hour motor (no wind) last week, the propeller came off and has gone forever!
As if this wasn't bad enough having hauled the boat onto a cradle it shows that about half of the externally and internally threaded stub has sheared off where a pre-drilled cross hole is. I understand Yanmar did away with the hole drilling on replacement shafts.
Has anyone succeeded in getting any compensation/ replacement from Yanmar as it seems to be a production failure as obviously weak and vulnerable to shearing.
May I ask one more thing? Has anyone repaired a shaft like this instead of replacing it? In the UK they cost well over $1000 and she`s an old boat but with a replacement Yanmar engine and sail drive 9 years ago , one that`s done very ]few hours since.
Thanks for your thoughts, Robin.
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[Somadoc]

Having thought about the risk associated with repair I have `bit the bullet` and bought a new prop shaft ..................

Do you think there`s the slimmest chance Yanmar might feel vaguely responsible?

[fstbttms]

Replace a nine year old part for free? That doesn't seem likely or even reasonable to expect, frankly.

[colemj]

Originally Posted by Somadoc

Do you think there`s the slimmest chance Yanmar might feel vaguely responsible?

Look at your receipt again and think about that question

Mark

[DotDun]

Originally Posted by Somadoc

Doing some research on the internet it looks like the problem I have with my SD20 sail drive prop shaft is not unheard of! Putting the boat gently into reverse after a 4 hour motor (no wind) last week, the propeller came off and has gone forever!
As if this wasn't bad enough having hauled the boat onto a cradle it shows that about half of the externally and internally threaded stub has sheared off where a pre-drilled cross hole is. I understand Yanmar did away with the hole drilling on replacement shafts.
Has anyone succeeded in getting any compensation/ replacement from Yanmar as it seems to be a production failure as obviously weak and vulnerable to shearing.
May I ask one more thing? Has anyone repaired a shaft like this instead of replacing it? In the UK they cost well over $1000 and she`s an old boat but with a replacement Yanmar engine and sail drive 9 years ago , one that`s done very ]few hours since.
Thanks for your thoughts, Robin.
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My sail drives are 11+ years old with no hole. I'm guessing that drive is at least 15 or more years old.

FWIW, the prop shaft in the US is ~$550.

[Cotemar]

Originally Posted by Somadoc

Having thought about the risk associated with repair I have `bit the bullet` and bought a new prop shaft ..................

Do you think there`s the slimmest chance Yanmar might feel vaguely responsible?

Just be glad that you do not have the defective Yanmar SD40 and SD50 sail drives. Some cruisers are spending thousands per engine and still have a piece O sheet sail drive.

[colemj]

Our 1998 Volvo saildrive shafts have that hole also. I don't know about newer models. I have not heard of this problem on Volvos before (or Yanmar, for that matter - although you said it was an issue with them).

Make sure you buy the shim set because those shafts have to be shimmed exactly so that the helical gears mesh with the correct lash. There is a stamped number on the shaft and a calculation you do with it after taking a careful measurement. The answer tells you which shims you need to install.

Mark

[Rapanui]

Its no help to you now, but it would seem to me that the cause of the failure was that the nut had been torqued up too high at some point in its history and that led to a fatigue failure. Its human nature to feel that torquing it up will make it more seure but the spline takes the prop torque and the nut only takes thrust in reverse. The split pin stops the nut coming off, not the nut torque. Saildrives are precision engineering and need a torque wrench otherwise you will get stripped threads etc

[worms1970]

H
Did you manage to get a new shaft? I am based in Ireland and just had the same thing happen, but I cannot find a new shaft to buy. Can you tell me where you got yours?
Thanks

[squaw999]

Same happened to me. I think, reason is very bad condition of washer?

[ggray]

Mine have the holes in them.

Not much to do about it, but I replaced the bolts with some I cut to the maximum length that would fit in the (axial) hole.

Figured that would help distribute the load over more of the end of the shaft.

[squaw999]

Maybe you have photo of that “action”? 🙂

[ggray]

No, I don't.

This is a preventative measure. If yours is broken, it's too late.

There is nothing magic... just a longer bolt so that the load from the bolt (which I assume is what breaks the end of the shaft at the point weakened by the unnecessary hole) is spread over a longer distance.

Just measure the depth of hole plus washer and make the bolt nearly that long.