Yanmar SD20 - play in prop movement and no power

[toolbar]

Hi,

for the last three weeks I haven't had full power in forward or reverse.

If I go beyond 1400rpm on the engine it feels like the prop is ventilating or slipping. Going higher doesn't feel good. This way I can only reach 3 knots in flat water, less if going against any kind of wind.

When I put the engine in gear and turn the prop underwater, there seems to be some play: I can turn the prop for something between 90 and 120 degrees without any resistance. Only after that free movement there is sudden resistance on both sides (as I push against the engine).

The SD20 has a dog clutch and not a cone clutch like the bigger saildrives.

Has anyone experiences something like that? And maybe even found a solution?

Paul

[tkeithlu]

I'm suspicious regarding the prop. That's not to eliminate clutch problems, but your description sounds like either a spun hub (if the prop is rubber hubbed) or a broken pin. For some reason, it all slips when you apply power, and is loose to turn by hand. Given that props are more likely to be damaged than components farther up the drive train, and that a repair at the prop is a bunch cheaper than digging into the transmission, I'd eliminate a failure at the prop before proceeding.

First, does the prop move relative to the shaft?

[toolbar]

Originally Posted by tkeithlu

First, does the prop move relative to the shaft?

Yes, it would be great if it was "just" the prop. Unfortunately I can't do too much while still in the water. I tried taking apart the Flexofold on the other side, but without proper scuba gear that prop is too complicated for me to remove (let alone reassemble it).

Without taking the prop of the saildrive I can't see if the prop shaft turns while I move the prop. I can say that the pinion shaft on the other side of the saildrive inside the boat does not move during the 90 degrees that I can move the prop without resistance. After the 90 degrees it's like something is hit/something engages and there is suddenly strong resistance. Then the pinion shaft moves (so strongly, that my wife can't hold it with pliers when I turn the prop).

If it is the rubber hub, I can't see how there can be some free movement and then suddenly a full stop.

Paul

[GordMay]

The Older ‘SD-20' used a “dog clutch”, not a cone*.
Props designed to fit this drive are supposed to have a rubber bushing in the hub [page 16 of Operation Manual], that acts as a shock absorber, since, unlike the outboard the SD-20 resembles, there's no shear pin to save the drive, if you hit something big or binding. The bushing is not meant to slip and re-engage, like a clutch, it's more like a failsafe device to save the drive.

* With later saildrives, Yanmar went to cone clutches, which apparently have a tendency to slip if not adjusted exactly right. The linked Operator’s Manual indicates “Cone Clutch”.

[1] Yanmar Saildrive Service Manual ➥ https://j109.org/docs/yanmar_sd20_sa...al_epb5547.pdf

[2] Operation Manual ➥ https://www.yanmar.com/media/global/...OM_27MAR09.pdf

See also ➥ https://www.kiwiprops.co.nz/cms/inde...al/yanmar-sd20

And ➥ https://www.cruisersforum.com/forums...hes-22570.html

NOTICE: When sailing, set the remote
control lever in neutral. Not doing so WILL
introduce slippage and void your warranty.
NOTICE: Running for long periods at low
rpm with the Sail-Drive engaged can cause
slipping and premature wear of the cone

[tkeithlu]

QUOTE: "sounds like either a spun hub (if the prop is rubber hubbed) or a broken pin."

This is what Gord is describing. If it may be the case, then remove the prop and look at the rubber hubbing, which is visible from the back side. If it is torn, then that's the problem. Send the prop to a propeller shop to be re-hubbed.

Very modern propellers have field replaceable hubs. The hub is a separate rubber layer between the prop itselfand the core that bolts to the shaft. It grips the prop and the core with a wavy shape. If you have that,you just buy a new hub and reassemble. Here's a Youtube on the topic:

https://www.youtube.com/watch?v=iA__CVRHcFc