Yanmar SD31 saildrive: No drive

[Jon Hacking]

We recently had an argument with a coral head (don't do this - the coral heads ALWAYS win). One result is that the engine is no longer turning the propeller on that side. I removed the shift mechanism & checked the dog-clutch, & it seems OK. The 2 crown-gears that engage the input shaft gear are both solid, which shows that the connection from there to the engine seems OK. I can turn the dog-clutch (which turns the upper vertical driveshaft) with my fingers very easily (too easily?), but the prop doesn't turn, which tells me that the problem is downstream of the dog-clutch. There's no grating or catching when turning either the dog-clutch or the prop - both spin pretty freely.

I'm suspecting that I've shattered the small joiner-sleeve between the upper & lower driveshafts. But we're in the Solomon Islands, so I need to order the *correct* parts in before we slip, & I'm trying to make sure.

Has anyone had a similar problem?
Is that joiner-sleeve the weak link in the drive system?
TIA

[Privilege]

Most props designed for sail drives (certainly all the fixed-blade props) have a rubber bushing which holds the spline that slides over the shaft. It is designed so that if you hit one of those steel-back turtles, rather than damaging your drive, it strips the bushing. The result is that if you turn the drive slowly, the prop will turn with it, but as soon as you put any load on the prop it will just stay in place while the drive shaft spins inside.

Of course, this is a boat and the easiest to fix, cheapest solution is rarely the one that is required. Good luck.

[Jon Hacking]

Thanks, Privilege. I don't think I've blown the rubber prop bushing. The prop turns too easily, & even turning the dog-clutch by hand, with no load on the prop at all, doesn't turn the prop.

Replacing the prop would be the easiest, but probably not the cheapest. That joiner-sleeve is only $30 (but replacing it *does* require a haulout)

[DougR]

I have zero experience with the SD31, but plenty of experience with Volvo saildrives and sterndrives, and I agree that all symptoms point to the coupler sleeve having fractured. It's a bit strange that you feel no catch or hang up when turning, but it could have sheared cleanly.

One other possibility.....on some of the older Volvo sterndrives the lower vertical shaft had a necked down section which would shear if there was a high speed impact, or even a high speed shift from forward to reverse with a heavy stainless steel prop. If this happened the surface of the shear was so smooth you would think it was machined. I don't know if this is a possibility in the SD31, but it might be worth considering.

In any event I would find it interesting that you could damage the shaft or coupler without some pretty good impact damage to the propeller......unless, as mentioned, a high speed shift into reverse caused the shear.

DougR

[Moontide]

Sounds like you are turning the prop with the gear in nuetral. Try putting the engine in gear and see if you can turn the prop both directions. Might be hard one direction but if it spins both ways then the hub is shot. If it is firm in forward try the same thing in reverse. If it turns the engine over while doing this then prop is probably OK.


Can also try switching props between the engines and see if the problem moves with the prop.


Bill



Have heard of people using epoxy as a temporary fix for this problem. Can't run at high rpm, but enough for manuevering.

[Jon Hacking]

Hi Bill - I'm pretty sure it's not the prop. Yes, it felt like I was turning the prop in neutral, but it was, in fact, in gear. Either fwd or reverse, it made no difference - the prop turned very smoothly.

[ckeijser]

Hi Jon,
On the Sd20 and I think also on the SD31 the shift lever has tapered breakpin. If that is broken it will move very lightly but not shift gears. Easy fix without having to haul out if it is that. Remove shifting gear to check. Partnumber for Sd20 is 22301-040250.
Best of luck!

[Jon Hacking]

Originally Posted by ckeijser

Hi Jon, On the Sd20 and I think also on the SD31 the shift lever has tapered breakpin. If that is broken it will move very lightly but not shift gears. Easy fix without having to haul out if it is that. Remove shifting gear to check. Partnumber for Sd20 is 22301-040250. Best of luck!

Thanks for this. I didn't know that pin was supposed to break.

I removed the shift mechanism & it seems OK. The break seems to be between my dog-clutch (what that shifter moves) and the prop.

[DougR]

So Jon, what did you find?

DougR

[Jon Hacking]

Hi Doug - Yeah, good question.

I removed the foot & out fell ... a perfectly intact coupler ... with the splines from the sheared-off upper driveshaft still stuck in it. And we're up on an expensive slipway in the Solomon Islands...

Luckily, Solomons respects "In Transit for Foreign Yacht" so we didn't have to pay duty, & the DHL woman in Honiara is wonderful & forwarded the parts to us. Got the shaft & 6 related bearings from CLLS in Singapore in just a few days (& for cheaper than I was expecting).

Taking the top off the SD31 & the upper (reverse) gear comes off with it, & the vertical driveshaft just lifts out! Replaced all the bearings, dropped in the new shaft, put it all back together, & voila! I also replaced the shifter, as it's bronze & the other side had worn badly (causing reverse to slip sometimes).

A side note, that probably works on your Volvo drives as well. In taking the foot off, I found 3(!) plastic bags in the cavity at the joint. They'd been sucked up from the bottom of the foot & gotten stuck. On port side I found 2 more bags, extracted with one of those grabbers used to retrieve lost bolts from under engines. So I drilled 4 small holes around the water inlet at the bottom of the foot & threaded some seizing-wire through them. This should keep out any more bags when motoring in badly polluted waters (parts of Indo can be terrible). I'll be putting this idea on our Sail-Drives page to go with our other recommended sail-drive modifications.