Possible Transmission Coupling Failure?

[TopherTopher]

I just bought a 1987 C&C 27.
It's my first inboard engine (Yanmar 1GM 10) and my first folding prop.

I had been having a tough time getting the prop to fold out, and was experiencing intermittent heavy vibration when, I assume, it wasn't folding out properly. I spend the last week or so, shifting back and forth from forward - to reverse, trying to get the thing to spin right.

Then the other day, I was out for a sail, and fired up the engine, and motored for about 20 minutes before I started seeing my knot meter fall to zero.

The engine ceased to provide thrust in forward or reverse.
I could see via the cockpit locker access that the prop shaft is turning a little.
So after sailing back to my mooring, I grabbed a GoPro and made this video:

https://www.youtube.com/watch?v=Pxl4-ZhUdvc

I had the Yanmar running around 1200 RPM.
I shifted the engine from neutral into forward, then reverse, then forward again.
The prop shaft doesn't seem to be spinning consistently or much at all.

Then engine runs well, and the transmission is shifting, but something seems to be broken somewhere between the stuffing box and propshaft.

Thank you for your kind consideration - any advice would be greatly appreciated.

[Hudson Force]

It's a very interesting first post that uses the underwater camera to view the behavior of the prop. I like the opportunity to view the activity. There's no question that the propeller is not rotating at the speed that is expected in forward or reverse and at the speed that would be required to deploy the blades of the folding propeller. This would cause us to investigate if the shaft is spinning appropriately with the geears from the engine. There is the possibility that the transmiission is working correctly and the prop is not secured well to the shaft with a slot key in place. Then, the other alternative is that the transmission is not properly engagesd and we would see this by looking at the rotation of the shaft. Good luck! It seems like you have an easy opportunity to find out where the problem is. I hope you have an easy fix!

[Cheechako]

"...The prop shaft doesn't seem to be spinning consistently or much at all..."
Would indicate to me you have a transmission issue. It is not spinning inside the boat right? can you see it? Have you checked the transmission oil level? (dipstick under the nut on the top of the transmission)
If the prop shaft was broken inside the stuffing box it would probably fall out of the boat.
I don't know for sure, but suspect if the key inside the prop was mangled the prop would still turn more than that.
Neither a broken shaft or mangled key is very likely at all. Never seen either.

[westwinds]

I agree that it is the transmission. A coupling or shaft is very simple, so either it transmits power, or nothing at all. If nothing at all, then you see the various parts separated lying there.

So, what make and model of transmission? There should be an identification plate on the transmission; otherwise, although not as accurate because who knows what engine swaps or options happened, you have stated the engine, make and model of boat and so it is probable the transmission can be determined from that.

[bornyesterday]

Could be the gearbox of course but I'm finding it hard to imagine anyone not spotting that the shaft coupling flange wasn't rotating.
If the prop shaft flange is a taper fit on the prop shaft the nut might have come loose - so the flange rotates but not the shaft. Might be possible for that to go unnoticed. And for the shaft to fall out and sink the boat...
Either that or the prop itself could be slipping/spinning on the shaft taper. Less likely, obviously.

[TopherTopher]

Update:
I just discovered a terrifying pile of freshly shredded metal beneath the stuffing box nut and collar.
See photo.

[bornyesterday]

If it's been lifted out recently a lifting strop may have bent the shaft - reviewing your video it does seem unwilling to turn the full 360.

The flange on the prop shaft in your photo appears to have something on the side - as if bolts had been inserted from the side - maybe to replace a key? Yes this is a wild-ass guess but need to see close-ups.

[sailr69]

I am pretty sure the damper plate is the issue, that is the coupling that connects the engine to the trans. looks like a clutch plate without the clutch lining. it is always connected to the trans. there are small springs just like a clutch plate to absorb the shock load. these do break at times.
s

[bornyesterday]

Found this on wiki - the two locking screws secured by wire are what I thought I could see in your photo. If they're loose the flange will rotate with the gearbox but the prop shaft won't move - especially if the shaft is bent. Easy to miss.

File:Small boat stuffing box.jpg - Wikipedia, the free encyclopedia

[westwinds]

Originally Posted by bornyesterday

Found this on wiki - the two locking screws secured by wire are what I thought I could see in your photo. If they're loose the flange will rotate with the gearbox but the prop shaft won't move - especially if the shaft is bent. Easy to miss.

File:Small boat stuffing box.jpg - Wikipedia, the free encyclopedia

Looks like I am wrong about the transmission. The obvious thing to do is clip the safety wire and see if the two set screws can be tightened. These should be secure, tight, but if you can screw them in, then the screws have been working on the propeller shaft. If the screws are loose, get the boat out of the water, loosen the packing gland nuts, put the transmission in gear to prevent the flange from moving, take hold of the propeller and see if you can work the propeller shaft to the rear, if so then pull the propeller from the propeller shaft and slide the propeller shaft out. If you cannot work the propeller shaft aft, then use a slide hammer on the propeller to hammer the propeller shaft out, then use a propeller puller to get the propeller off the propeller shaft.

[Cheechako]

Originally Posted by bornyesterday

If it's been lifted out recently a lifting strop may have bent the shaft - reviewing your video it does seem unwilling to turn the full 360.

The flange on the prop shaft in your photo appears to have something on the side - as if bolts had been inserted from the side - maybe to replace a key? Yes this is a wild-ass guess but need to see close-ups.

The set screws with the wire retainer are common. It is very unlikely that they have somehow loosened up. even if they did loosen a little I doubt the shaft wouldn't turn 360 when in gear..

Most I have seen also have a key way. here's a pic:

I guess I don't get it. Can you see the shaft turn inside the boat when in gear or not? My guess is not turning. Start at the engine with it in gear and determine where the3 rotation stops. this is simple.

[Terra Nova]

Perhaps the shaft key has fallen out. Disassemble the coupling to check.

[Cheechako]

Originally Posted by Terra Nova

Perhaps the shaft key has fallen out. Disassemble the coupling to check.

Where would it go? Cant go toward the engine far enough and cant go aft. What are the odds with a key and two wired set screws?

"Update:
I just discovered a terrifying pile of freshly shredded metal beneath the stuffing box nut and collar."
Not sure what you are seeing from the photo... if it's just that grey stripe on the white gel coat that is pretty common from a stuffing box but not metal chips. Are you actually seeing/feeling chips? If so, it may be from the collar (is that a zinc?) someone put between the stuffing box and the engine coupling. It looks rather tight in there. This is often done on boats that have more space to keep the shaft from walking back if it becomes uncoupled etc. But not necessary in your application. Take it off.

[bornyesterday]

Originally Posted by Cheechako

The set screws with the wire retainer are common. It is very unlikely that they have somehow loosened up. even if they did loosen a little I doubt the shaft wouldn't turn 360 when in gear..

Most I have seen also have a key way

I guess I don't get it. Can you see the shaft turn inside the boat when in gear or not? My guess is not turning. Start at the engine with it in gear and determine where the3 rotation stops. this is simple.

Yes, I was clutching at straws a bit wasn't I? Realised too late to edit that a missing key was a baseless assumption

I'd also assumed that the flange must be turning or it would have been noticed - another mistake.

What took you so long?

[NahanniV]

Not a great pic., but looks like you have a zinc on the shaft between stuffing box and shaft coupling. Some people put these on the shaft as a safety measure in case the coupling lets go; It's not functioning as an anode here.

It looks like the zinc may be too long. Perhaps it is binding on the stuffing box. Needs to have some clearance as the engine (and shaft) will move slightly backwards when in reverse.

Or possibly your shaft is spinning inside the coupling on the back of the transmission; In which case the zinc may be doing it's job and keeping the shaft from falling out of the boat.

Can you turn the shaft easily by hand (from inside the boat) ?

If the shaft turns, is it turning the coupling too ? Try to hold the coupling and turn the shaft, should be no movement between them. Try moving the shaft forward, see if it moves into the coupling, it should not.

Cheers,
JM.