Yanmar SD40/50 cone clutch problem solved

[Panache5000]

We had a problem with our SD50 saildrive cone clutch, where if we selected forward, it would not always engage, however if we bliped the throttle it would then engage. Once engaged there was no slippage and it performed well. The Yanmar agent told us that we should replace the whole cone clutch assembly which is very expensive. So with a bit of dexterity and a lot of thought we have solved the problem.

If this non/partial engagement of the cone clutch is allowed to persist for a period, it will lead to damage of the cone and seat assembly, which in turn will lead to slippage of the cone clutch.

I suspect that a lot of the failures /slipping of the cone clutches originate from partial engagement, and with not enough attention paid, rapidly leads to cone failure.
Once the cone and seat have made contact under load, and stay under load, slippage can not occur, due to the friction between the two conical faces.

[DeepFrz]

Would you tell us how you solved the problem? Some pictures would be nice.

[Cotemar]

Maybe this will help you see the cone clutch problem.

J/30 Rhapsody #348: Transmission Disassembly & Clutch Resurface

[DeepFrz]

Thanks for the link Cotemar. Not quite the same as the SD50 I imagine but it gives me a better idea of the Yanmar clutches.

[Cotemar]

This info on the Yanmar SD40/50 cone clutch may be better.

See attached Yanmar SD40/50 cone clutch.pdf

[Cotemar]

Yanmar SD40/50 cone clutch repair steps 1 through 12

[DeepFrz]

Thanks for the info Cotemar. That's great to have on file for others that need it.

[Panache5000]

Thanks for the interest, the proceedure outlined by Cotemar is the standard Yanmar cone clutch service / lapping procedure, however, lapping the cone clutches on its own will not ensure long term trouble free operation, the problems will re-occur for the same reason that they occured in the first place.
The standard Yanmar cone clutch assembly is equipped with brass/bronze thrust washers in increasing thickness of 0,5mm only. These thrust washers are prone to wear and do not allow accurate assembly tolerances.
Our revised installation consists of thrust needle roller bearing assemblies and revised lower collar and top nut assembly resulting in minimal wear and increased tolerance accuracy (this is how the Volvo drives were made for years!)

[Frix]

Hi everyone,
I tried to repair my SD 50 Cone-Clutch with both the Yanmar Service Manual and the great manual posted prior.

Unfortunately, there are some minor errors in that manual. I corrected these and posted them on our blog. Please feel free to download.
Fixing the Yanmar SD-50 Cone Clutch. In Galapagos. | Alytes – Drei segeln um die Welt

By the way: Yanmar US Service was extremly helpful in solving the issue. Tip to the hat to them!

Big thanks again to the skippers of S/V Leucat and S/V Isabella, as they are the actual authors of the original document.

All the best,
Fritze (S.Y. Alytes, Alytes – Drei segeln um die Welt | Auf einer Lagoon 400 in einem zweijährigen Sabbatical um die Welt)