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Old 30-05-2015, 21:35   #16
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Re: Slipping Yanmar SD50 Cone Clutch

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After puting about 30 hours on the newly resurfaced clutch ...
I am pretty sure it was not done correctly, or cone is worn (which should have been checked during lapping procedure). How many times has this cone been lapped? Did you measure how much life (thickness) cone has? You need to know this value exactly in order to shim correctly. Also, I came across one installation where shifting lever did not move all the way when engaged. Check that too.
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Old 30-05-2015, 23:18   #17
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Re: Slipping Yanmar SD50 Cone Clutch

Look down at the bottom of this page and you will find more threads on this topic. One of the threads contains detailed information on shimming the clutches.
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Old 03-06-2015, 08:40   #18
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Re: Slipping Yanmar SD50 Cone Clutch

Well, the Yanmar tech came and ripped apart my engine and transmission, even though I told them it was unnecessary. Removed the saildrive, the bell housing, the SD50, and yanked it all out of the boat -- this is after they hauled it when I told them it was unnecessary. We didn't take the core out with the cones, but you could see they were glazed.

So these yahoos are running up the bill on me -- when they know what it is already. He wouldn't admit that he had seen it before, but he was able to tell me how they would bead blast the unit to get it back into shape.

I had to have them do the work this time, because there is a prayer that it will be covered under warranty. But I've already decided that if they don't cover it, I'm suing.

I've told them if they replace the cones, I want the originals, so that I can at least have a set of spares.

At this point, they haven't even given me an ETA when the pieces will come back together.

This whole thing stinks to high heaven. What a disaster.
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Old 03-06-2015, 15:56   #19
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Re: Slipping Yanmar SD50 Cone Clutch

i have 2 sd 50 and work fine with throttle increase blip inserted between gear shifts.

My theory, if it does not slip, does not get glazed, thickness levels remain the same -> no issues.

Noticed that fully engaged clutch starts slipping when RPM go below around 1300. So, there must be force that undoes the link. Gravity is one. Cable probably another and lesser force due to leess rpm third.

What is wrong with adjusting cable so that push force remains even at 1300 rpm ? This will lessen chance of unintended slipping and deterioration of surfaces therefore increase time between service. It will however disadvantage reverse engagement. As reverse is used rarely in closed quarters, with full engagement, that shouldnt be an issue.

Comments ?

to me clutch makes sense as protects the whole system against shock loads.
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Old 04-06-2015, 06:25   #20
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Re: Slipping Yanmar SD50 Cone Clutch

I don't have experience with the Yanmar drive specifically, but on our Volvo drives, the shift cable/lever simply moves the cone into place. After sufficient travel, there is no further force available - the cable doesn't hold the cone or provide any force that can be increased with adjustment.

I don't think bead blasting is a good idea - actually, I think it is a very bad idea. The cone needs to be lapped in with its mating receptacles so that they fit perfectly.

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Old 04-06-2015, 08:58   #21
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Re: Slipping Yanmar SD50 Cone Clutch

I agree that bead blasting may not be as good as lapping. However, this is Yanmar's reps tech -- and they are going to do what they think should be done. We'll see how that turns out.
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Old 15-06-2015, 13:00   #22
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Re: Slipping Yanmar SD50 Cone Clutch

We also had one our SD 50's start slipping in the Bahamas (Lagoon 450 with about 850 hours on the engines). It was a very straightforward job to pull them out myself but I let a machine shop in Grand Bahama take them apart and do the lapping. It took about 20 min each side to remove/re-iinstall and the machine shop charged $360 to do both units. So not a huge deal but slightly annoying, finding the right gear oil can be a challenge in the islands.
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Old 15-06-2015, 13:31   #23
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Re: Slipping Yanmar SD50 Cone Clutch

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We also had one our SD 50's start slipping in the Bahamas (Lagoon 450 with about 850 hours on the engines). It was a very straightforward job to pull them out myself but I let a machine shop in Grand Bahama take them apart and do the lapping. It took about 20 min each side to remove/re-iinstall and the machine shop charged $360 to do both units. So not a huge deal but slightly annoying, finding the right gear oil can be a challenge in the islands.
that seem like excellent approach. Once I get this issue, will follow what you have done.
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Old 28-06-2015, 08:02   #24
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Re: Slipping Yanmar SD50 Cone Clutch

I also have been through this process - once on each motor with ending hours at the time 400 and 500 respectively .
Recently when we went to replace the gearbox oil we found data that suggested the Mercruiser oil Yanmar recommend is " too slippery" and exacerbates the problem - after presenting our mechanic with the data he agreed and said it made sense and w eased a different oil - the details of which I don't have at the tip of my tongue.
I am away ( not on boat) but could look into it again and pull up the data if it is of help ..
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Old 28-06-2015, 08:26   #25
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Re: Slipping Yanmar SD50 Cone Clutch

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I am away ( not on boat) but could look into it again and pull up the data if it is of help ..
Yes please post it here. Thanks.
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Old 28-06-2015, 15:38   #26
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Re: Slipping Yanmar SD50 Cone Clutch

what i found out that change new oil improves clutch performance - mercruiser.

Also, I discovered that after clutch engaged sucessfully, lowering RPM below 1500, even for a moment, disengages clutch. If one is not careful and increases rpm with disengaged clutch that is when bad stuff happens. Correct action in my case is to disengage completely, quick reverse, and re-engage.

So, I will look at clutch cable next, see if I can lower 'disengage' RPM. Yanmar manual mentions low RPM issue as well.

One has to rely on engage/disengage in close quarters, which I found not too annoying. Also need to get a feel when to disengage when approaching fuel station, mooring, etc.

Although initially I was alarmed by it, now just become another boat "stress point" to worry about.
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Old 29-06-2015, 07:06   #27
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Re: Slipping Yanmar SD50 Cone Clutch

You should be alarmed by it. There should be no valid reason for an engaged clutch to disengage at any rpm. Disengagement should only happen when the shifter physically pulls the clutch cone out - when the shifter is in neutral.

If Yanmar is saying your clutch behavior is normal, they are wrong.

Assuming the shift cable and shifter mechanism are adjusted and working correctly, your clutch is not disengaging - it is slipping. This can be because of glazed cone or incorrect fluid. It should be corrected.

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Old 29-06-2015, 15:48   #28
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Re: Slipping Yanmar SD50 Cone Clutch

Hi Andy.
Hope you had them measure and adjust the free play on the Thrust Washers correctly. As well as adjusting the selector correctly. If not done correctly you will experience the same clutch failure again in a while.
We have identified, and solved the slipping clutch problem. It is more than just lapping the cones. Lapping the cones is part of the procedure. Refer to my earlier posts on what has to be done.

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Old 31-08-2015, 03:45   #29
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Re: Slipping Yanmar SD50 Cone Clutch

Hi all.
We have managed to source the parts for the rework/upgrade of the SD50 clutch assembly at long last.
The replacement of the Yanmar thrust washers with Thust Bearings allowing a closer tolerance upon assembly. The rework consist of the replacement of the original Yanmar parts with the following new items which completely replaces the original Yanmar items; Top Nut, Nut spacer, 2x Thrust Bearings, Needle cage Spacer and Collar Assembly.
The rework also includes the lapping of the Cones, as well as adjusting (not shimming) the Selector.
Hopes this all makes sense!!

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Old 01-09-2015, 03:06   #30
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Re: Slipping Yanmar SD50 Cone Clutch

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Hi all.
We have managed to source the parts for the rework/upgrade of the SD50 clutch assembly at long last.
The replacement of the Yanmar thrust washers with Thust Bearings allowing a closer tolerance upon assembly. The rework consist of the replacement of the original Yanmar parts with the following new items which completely replaces the original Yanmar items; Top Nut, Nut spacer, 2x Thrust Bearings, Needle cage Spacer and Collar Assembly.
The rework also includes the lapping of the Cones, as well as adjusting (not shimming) the Selector.
Hopes this all makes sense!!

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I thought you already resolved that issue based on earlier emails. Trying to improve ?

I actually like cone clutch concept. Clutch (also) starts slipping when needed - like rope or similar.

I see not much issue relapping/changing even every 100 hrs, assuming one takes out and in cone assembly by himself and let expert do cone assembly service.
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