Slipping Yanmar SD50 Cone Clutch

[matauri500]

We have again (second time in one month) experienced a slipping cone clutch in the stb transmission on our Lagoon 500. It is a SD50 transmission. Last month we pulled the cone clutch assembly and resurfaced (lapped-in) it and reinstalled. It was a very straight forward project and it worked great for a few weeks. After puting about 30 hours on the newly resurfaced clutch going from Nassau to the Abacos and around the clutch slips in forward. Now ther is no drive at all. I noted in a post on Oct 10 2013 by Panache5000 that he had to add shims to reduce the verticle play on the center shaft. Does any one know what the Yanmar part numbers are for the required shims as I want to purchase them and have them ready for the upcoming service on the slipping clutch.
Also if there are any other suggestions related to this problem please let me know. Thanks,
Doug

[Southern Star]

Matauri, I can't help you with respect to shims but I do know that this is recurrent problem with the SD50; indeed, I believe that Yanmar are now recommending replacement/resurfacing as necessary every 500 hours! I know of some owners who are replacing them and keeping the old ones as emergency spares.

Why Yanmar went to cones from the dog clutches on the SD20 is beyond my understanding. The latter are virtually bulletproof - the SD20's on my Yanmar SD20's have needed nothing more than fluid/anode replacement and one seal replacement in 20 years and over 3000 hours.

Good luck and keep us posted as to whether you are able to make a somewhat more permanent repair with shims.

Brad


PS I just saw that this is your first post. Welcome to CF! Hopefully someone else will have some more specific information on the shims.

[colemj]

At some point, dog clutches cannot handle torque. That is why the largest engine the SD20 is mounted to is 30hp. Larger engines need cone or disc clutches.

Cone clutches by themselves are not a problem. Hence, you almost never hear of Volvo clutch problems - Volvo does not use dog clutches, although their most recent drives use disc clutches instead of cone.

Yanmar, on the other hand, has always had an engineering and quality problem with their cone clutches. They have never been rugged or reliable throughout their history and different models.

I have never understood why they could never get on top of that problem.

Mark

[Hud3]

There are a number of earlier threads on the subject of Yanmar Saildrives. You can find them with the Google custom search in the "Search" menu. I think you'll find a lot of useful info in them.

[DotDun]

Originally Posted by colemj

I have never understood why they could never get on top of that problem.

They have, SD60 is a plate clutch.

[DotDun]

Originally Posted by colemj

At some point, dog clutches cannot handle torque. That is why the largest engine the SD20 is mounted to is 30hp. Larger engines need cone or disc clutches.

My Yamaha 115hp four-stroke has a dog clutch. (I know, you qualified with high torque! :^)

[Captain Bill]

Originally Posted by colemj

At some point, dog clutches cannot handle torque. That is why the largest engine the SD20 is mounted to is 30hp. Larger engines need cone or disc clutches.

Cone clutches by themselves are not a problem. Hence, you almost never hear of Volvo clutch problems - Volvo does not use dog clutches, although their most recent drives use disc clutches instead of cone.

Yanmar, on the other hand, has always had an engineering and quality problem with their cone clutches. They have never been rugged or reliable throughout their history and different models.

I have never understood why they could never get on top of that problem.

Mark

Dog clutches are used on outboards up to 150 hp and more. Dog clutches are not as good at swinging large slow turning props which require lots of torque, but I don't see that any saildrive I've ever seen has been paired with a big enough engine and prop that this should be a problem. Dog clutches on the other hand do not require close tolerances and are cheap and easy to replace should that be needed. The SD50 is limited to an 18" prop so the torque requirements should certainly be within the range of a dog clutch. It's not like one is trying to turn a 30" wheel. I'm not sure I understand why they have gone to a multidisk clutch on the new saildrives rather than just a more robust dog clutch to handle the torque.


There are two different shim sets associated with the cone clutch area of the SD50 Two are the same part number and go below the lower bearing and above the upper bearing. These are part number 196322-02320. The third set which goes between the sleeve bearing and the upper gear is part number 196320-02230.

[Panache5000]

Hi. Solving the cone clutch issue is a little more complex than just shimming thd vertical shaft free play. It involves accurate adjustment of the gear selector as well as ensuring the correct vertical free play with the top nut torqued to spec.
The thrust washer supplied by Yanmar come with 0.5mm thickness increments. This is either too little or too much. The correct free play for a used assembly should be less than this. Refer to my original discussion in this regard.
PANACHE

Sent from my GT-I9082L using Cruisers Sailing Forum mobile app

[matauri500]

Thanks to everyone for the suggestions. Panache5000 in his earlier post on Octover 2013 suggests a 2mm free play in the shaft. Am I reading this correctly? As Yanmar makes the shims only in 5mm thickness I believe he is saying that you get to the correct 2mm freeplay by a combination of using the right shims and adjusting the gear selector arm so that the system engages correctly and fully releses the Center Shaft so that the clutch fully engages. Am I getting this right???
Thanks, Doug

[Panache5000]

The shim dimensions are 0.5mm increments (1/2mm). NOT 5MM. The free play should be 0.2mm NOT 2MM make sure about this!
PANACHE

Sent from my GT-I9082L using Cruisers Sailing Forum mobile app

[colemj]

Originally Posted by Captain Bill

Dog clutches are used on outboards up to 150 hp and more. Dog clutches are not as good at swinging large slow turning props which require lots of torque, but I don't see that any saildrive I've ever seen has been paired with a big enough engine and prop that this should be a problem. Dog clutches on the other hand do not require close tolerances and are cheap and easy to replace should that be needed. The SD50 is limited to an 18" prop so the torque requirements should certainly be within the range of a dog clutch. It's not like one is trying to turn a 30" wheel. I'm not sure I understand why they have gone to a multidisk clutch on the new saildrives rather than just a more robust dog clutch to handle the torque.

OK. Then why has Yanmar always limited their saildrive model with a dog clutch to 30hp and less, and have always used a cone clutch model of saildrive for larger engine sizes? If they had a dog clutch model, and it isn't limited in any way, why make a completely different type of drive for larger engines?

I'm not saying you are incorrect - just that the reasoning doesn't make sense to me. I was under the impression that the dog clutches could not handle the torque, but don't have any specific facts supporting that.

Mark

[Captain Bill]

Originally Posted by colemj

OK. Then why has Yanmar always limited their saildrive model with a dog clutch to 30hp and less, and have always used a cone clutch model of saildrive for larger engine sizes? If they had a dog clutch model, and it isn't limited in any way, why make a completely different type of drive for larger engines?

I'm not saying you are incorrect - just that the reasoning doesn't make sense to me. I was under the impression that the dog clutches could not handle the torque, but don't have any specific facts supporting that.

Mark

I have no idea why they chose to go to the cone clutch. Knowing a few engineers, I suspect that the engineers they put in charge of the project decided that they weren't really earning their pay unless they came up with something new and wonderful and much more complicated than the old design. That is just a supposition of course. Even high HP stern drives use dog clutches. I just found exploded views of 250-300HP outboards and they are using dog clutches. They swing good sized props and have lots of torque. I can't imagine that a 40-75 horse diesel has more torque than a 300 HP outboard. The only difference I see in the clutches as the HP increases is the diameter and the size and number of dogs.

I did finally figure out why I was getting so much more life from my cone clutches than everybody else. For reason unknown to me whoever originally set up my boat set the props up for CCW rotation. This means that the upper gear is my forward gear rather than the lower gear. If you understand Panache5000's explanation of the problem the lower gear has a spring between it and the cone. My guess is so that it disengages properly against gravity. If there's too much play in the mechanism the spring slightly lifts the cone causing it to slip. I'm now starting to have a problem in reverse in my port engine and in my case reverse is the lower gear. My experience now makes sense. I have about 2500 hours on my SD40 sail drives and this is the first cone clutch problem I've had.

[matauri500]

Thaks again to everyone for the good information. I am anticipating the replacement of the cone clutch as one of the alternatives to solving this problem along with making the necessary adjustments. The work will be done by myself and a mechanic down in Georgetown, Exumas. As parts are not readily available there can anyone tell me exactly which parts I will need to bring with me to Georgetown to make the change over of the cone clutch so I can get this sucker back sailing safely. I have the full parts list for the SD 50, the exploded view drawings and all the part numbers but I have not been able to figure out just what I should anticipate needs replacement when doing a change over. The sail drive has about 600 hours on it at this time. Thanks,
Doug

[wcrosby]

I've just experienced the wonders and the joy of the Cone clutch problem on my Jeanneau 409 (2013). I had just over 500 hours on it, and it failed. My Yanmar tech was supposed to be out yesterday to fix it, but has begged off as too busy -- this is after they told my charter manager to haul the boat so they could properly fix it. Needless to say, I am not happy.

[matauri500]

It is not normally necessary to haul the boat to resurface or replace the cone clutch. That work can easily be done from inside the engine compartment if there is room enough around the transmission.
I had both of mine done by Multi-Ted Marine in Ft Lauderdale. The boat was out of the water for a bottom job but the work was done from the inside.
I carry a spare cone clutch and polishing compound now in case I have to do it again which is inevitable. If so it will be done from inside the engine room.
Doug