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Old 21-09-2015, 14:43   #1
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What Is Crankshaft V-pulley Clamp Nut Yanmar SD50 Saildrive?

After losing power on our starboard fixed propellar we replaced the cone in the cone clutch since we'd had a similar issue previously on the port side. Unfortunately did not resolve the issue this time. Talked to our local Yanmar mechanic and he explained how to check that the shifter and cone clutch are engaged by simply removing the cap of the cone clutch, detaching the shifter cable, holding the nut on top of the cone clutch with a wrench while manually putting the shifter in gear and making sure the nut locks in one direction. It did so at least we know that is not the issue. Then checked the propellar to see if it locked in one direction when the gear was engaged (once in forward and once in reverse) and found it turned in both directions, although with slight friction on one direction. All this while the boat is still in the water. Before going the expensive haulout route I'd like to remove the propellar to see if the bushings on the hub are worn and possibly causing the slippage. Problem is with the boat in the water and the inability to lock the prop by putting it in gear we can't figure out how to take it off. The manual mentions "holding a crankshaft V-pulley clamp nut with a wrench to stop the propeller rotating", but there is no schematic showing what that is?? Couldn't even find help on Google. Would like to at least eliminate one more possible (less costly) cause before the expense of a haulout. Any help much appreciated.

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Old 21-09-2015, 14:52   #2
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Re: What Is Crankshaft V-pulley Clamp Nut Yanmar SD50 Saildrive?

Take a look at the lower belt pulley on the engine. It's on the end of the crankshaft.

Should be a fairly large bolt or nut there in the center of the pulley. Holding it with a wrench securely will prevent engine rotation.

Transmission should be in gear of course to prevent prop rotation during removal.
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Old 21-09-2015, 15:10   #3
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Re: What Is Crankshaft V-pulley Clamp Nut Yanmar SD50 Saildrive?

Okay. Thanks. Will give that a try first thing tomorrow and let you know if that works.

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Old 21-09-2015, 15:21   #4
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Re: What Is Crankshaft V-pulley Clamp Nut Yanmar SD50 Saildrive?

But check this thread again before you take action.

I'm sure someone will come along and tell you what I posted is incorrect.

Or maybe offer more detailed advice, such as whether it should be shifted to forward or reverse. I don't know which is best for your setup.
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Old 21-09-2015, 16:09   #5
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Re: What Is Crankshaft V-pulley Clamp Nut Yanmar SD50 Saildrive?

Just reread your suggestion. Sorry if I wasn't clear. Already checked putting transmission in gear to prevent prop rotation, but prop still moves in both directions. This was why I checked cone clutch and shifter to see if gear was in fact engaging and it appears it is. Yanmar suggested this indicates issue is lower in the saildrive, either in the shaft itself (requiring haulout) or in the propellar hub itself. That's why I want to check the propeller before going through the expense of a haulout.

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Old 21-09-2015, 17:52   #6
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Re: What Is Crankshaft V-pulley Clamp Nut Yanmar SD50 Saildrive?

Copy that, understood.

I was just thinking you may be turning the engine over as well. The mechanical advantage of the gear ratios would make it easy to do I think.

And the manual suggestion to hold the pulley nut suggests this can happen while trying to remove the prop nut as well.

In fact if you wrench on the prop nut while in gear and the engine doesn't turn, then something is definitely slipping or amiss in some way.
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Old 22-09-2015, 06:18   #7
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Re: What Is Crankshaft V-pulley Clamp Nut Yanmar SD50 Saildrive?

Put a block of wood between the hull and one of the prop blades to hold the prop from turning.

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Old 22-09-2015, 07:56   #8
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Re: What Is Crankshaft V-pulley Clamp Nut Yanmar SD50 Saildrive?

Thanks DougR. I think that is what we'll try. I appreciate Four Winds suggestions, however we already know the cone clutch and shifter are engaging , which is downstream from the crankshaft, so have to conclude the issue is further downstream under the hull in the arm of the saildrive or hopefully the simpler and more economical fix in the prop hub bushings. Will let you know how it goes.
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Old 22-09-2015, 08:08   #9
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Re: What Is Crankshaft V-pulley Clamp Nut Yanmar SD50 Saildrive?

DougR presents the better/simpler suggestion that I knew would be forthcoming. I just didn't know what it would be.
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Old 22-09-2015, 11:30   #10
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Re: What Is Crankshaft V-pulley Clamp Nut Yanmar SD50 Saildrive?

I've found that, after flattening the locking tab washer, a sharp tap with a large hammer on the T-bar of a socket on the prop nut does the trick, without the need to put it in gear. The 'tap' turning the socket in an anticlockwise direction, of course.
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Old 22-09-2015, 13:39   #11
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Re: What Is Crankshaft V-pulley Clamp Nut Yanmar SD50 Saildrive?

Success! I put the control lever in gear which locked the prop shaft. Prop still spun in both directions as expected. However the diver was able to hold a prop blade with one hand and the locked shaft allowed him to unscrew the nut in the counterclockwise direction with the other hand and remove the prop. Sure enough the prop hub bushings were worn.

Thanks for the quick response and suggestions. Issue resolved.
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Old 23-09-2015, 18:51   #12
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Re: What Is Crankshaft V-pulley Clamp Nut Yanmar SD50 Saildrive?

Quote:
Originally Posted by trosenthal20 View Post
After losing power on our starboard fixed propellar we replaced the cone in the cone clutch since we'd had a similar issue previously on the port side. Unfortunately did not resolve the issue this time. Talked to our local Yanmar mechanic and he explained how to check that the shifter and cone clutch are engaged by simply removing the cap of the cone clutch, detaching the shifter cable, holding the nut on top of the cone clutch with a wrench while manually putting the shifter in gear and making sure the nut locks in one direction. It did so at least we know that is not the issue. Then checked the propellar to see if it locked in one direction when the gear was engaged (once in forward and once in reverse) and found it turned in both directions, although with slight friction on one direction. All this while the boat is still in the water. Before going the expensive haulout route I'd like to remove the propellar to see if the bushings on the hub are worn and possibly causing the slippage. Problem is with the boat in the water and the inability to lock the prop by putting it in gear we can't figure out how to take it off. The manual mentions "holding a crankshaft V-pulley clamp nut with a wrench to stop the propeller rotating", but there is no schematic showing what that is?? Couldn't even find help on Google. Would like to at least eliminate one more possible (less costly) cause before the expense of a haulout. Any help much appreciated.

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I use a 1/2" drive socket wrench on a long breaker bar. Put the socket on the crankshaft nut and brace the breaker bar on the cabin floor. It has to be on the correct side to hold the crankshaft against the prop nut being undone. Someone could hold it by the engine so it doesn't drop off but against the floor will stop it turning. I usually do that on my own and tie the bar in place to keep it there.
The nut on my smaller Yanmar is around 1". No doubt your 50 will be larger.
When you replace the prop do the same the opposite way around. Then your prop won't fall off later.
Hauled out of course you use the same procedure.


I once had an outboard prop start slipping because the "rubber" bush inside the prop became unstuck and showed similar symptoms to yours. I pulled the bush off the prop and glued it back in with epoxy glue. I then placed the prop across the sides of a frypan over a gas stove on low heat so it would harden fairly quickly and with some heat more strongly. I'm sure it was as strong or stronger than originally and never gave a problem again.
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