Yanmar SD20 Fails To Shift Into Reverse - SailNet Community
 
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post #1 of 8 Old 06-16-2016 Thread Starter
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Yanmar SD20 Fails To Shift Into Reverse

Well, sometimes it does, sometimes it doesn't. Which makes docking interesting. I've experienced no reverse, and then trying moments later, reverse would engage

I wondered if this might happen more when the engine (transmission, really) is hot, so on our last return to the dock (and I have a particularly difficult-to-access berth) I made sure to not run this port engine (on a cat) until I arrived. Shifted fine, but who knows next time.

I had checked to make sure that the shift linkage was working properly externally, and everything looked fine, while I was watching anyway. So it seems the problem is inside the transmission. SD20 has dog clutches rather than the cone clutches of other models, which I understand have more problems.

Has anyone else had a problem of this nature? If so, what was the solution?
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post #2 of 8 Old 06-20-2016
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Re: Yanmar SD20 Fails To Shift Into Reverse

Have you checked/changed the fluid?
Dis you remove the cable to see how far the lever travels without it attached?

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Re: Yanmar SD20 Fails To Shift Into Reverse

Most of the time it is the shifter or cable that is the problem. lube the cable? What year? How many hours? the early ones before 1986 had a shifter arm that could come apart during operation. either the shifter lever is not moving the dog enough to engage the gear or the dog is very worn and not engaging. make sure the shift lever clamp that holds the lever on the shaft is not slipping on the shifter shaft. not likely, but there is a taper pin that holds the internal shifter arm in the shaft and they can get loose.

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Re: Yanmar SD20 Fails To Shift Into Reverse

Thanks; I'll look at those items, just to be sure. As I said, it seemed to be making a full throw of the bell crank when I watch, but since the problem is intermittent, that wouldn't be definitive. Hmmm, maybe mount a GoPro so I could watch each shift....
And oil has just ebbs changed, and is full. I do have a header tank (probably since 2003, so nothing new) so eventually gets completely full, I suppose.

Overboard, 1999 or 2000 SD20 with about 2000 hours. If this taper pin is loose, can it fall out? I need to check this out.
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Re: Yanmar SD20 Fails To Shift Into Reverse

pin could fall out but not likely. there are only a few parts in this system the lever makes the dog slider move up and down for forward and reverse if it travels all the way then the dog is engaged if the dog is ok then the gear drives the dog and the shaft. very simple system external lever is clamped to the shaft and the dog lever is held on the other end of the shaft with the pin. if pin is out you most likely have no For. or Rev.
https://j109.org/docs/yanmar-sd20-sa...ts-catalog.pdf Fig. 7 is the shifter assembly
https://j109.org/docs/yanmar_sd20_sa...operations.pdf Pg. 12

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Last edited by overbored; 06-21-2016 at 03:11 AM.
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Re: Yanmar SD20 Fails To Shift Into Reverse

Did you remove the shift cable and attempt to shift the gear by hand? Only way I would know whether the cable was properly deflecting the lever. Also, just because you see the shaft move at the dock, doesn't always mean it's properly in gear and will turn against pressure. Does the shaft spin with equal force in forward and reverse (shifted manually, without the cable attached)


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post #7 of 8 Old 06-21-2016 Thread Starter
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Re: Yanmar SD20 Fails To Shift Into Reverse

Overbored (sorry about spellcheck last message), thanks for the parts diagram. That really helps make sense of this and what you are suggesting. I'm hoping to find that the pinch bolt needs to be tightened. This makes me wonder if shifting to reverse requires lifting the dog, as opposed to gravity helping engagement, but next trip to the boat will answer that as well.

Minnewaska, I've done nothing manual yet, but may be able to next time.

Thank you both for the help!
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Re: Yanmar SD20 Fails To Shift Into Reverse

I believe the problem has been corrected, at least it hasn't happened since I adjusted the cable a bit. I also replaced the cable end as the old one had gotten quite rusted and perhaps worn.

Thanks for the ideas and drawings that have been forwarded!
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