Solace prop shaft fore/aft movement

[Tmacmi]

I am working my way through the list of items that must be done while the boat is on the hard. Next item. Propeller shaft and stuffing box.

When I first got it, there was a "singing" sound coming up the shaft at a specific band width of RPM. It was like the resonance you get when running a wet finger around the rim of a glass. Ultimately it disappeared, except under heavy load of people stern wave.

There was also a good bit of water coming out of the stuffing box under power. It was just about one large drop coming out per second. Its dry at standstill.

When I hauled it I found the wear mark shown in the photo below. The shaft moves back and forth into the boat by the distance of that wear mark. There is no side to side play in the cutlass bearing.

https://imgur.com/oJrDPaD

When I went inside I found this condition. I'm not sure you can see it clearly, but the red line is pointing to where a wire has broken. I am not entirely certain what the wire is there for, but it appears that the back and forth motion of the shaft sheared it.

https://imgur.com/pCj7KgP

I don't know if the cause might be a propeller change. The PO told me he changed the propeller from a 2 blade, with details shown below to a three blade (I couldn't get details of the 3 blade because its mounted.) The motor is a Yanmar 2qm15. It has a Kanzaki transmission showing a 2.14 gear ratio. I know the gear ration has some interplay with propellers but I don't know details. Up to this point I thought I had to simply restuff the stuffing box. But I'm guessing I have something more than that.

https://imgur.com/zHL9PLe

Thoughts?

[billknny]

Its hard to tell just from those pictures but I'll give it a go...

First, every prop shaft moves fore and aft when under load, at least a little. All the force of pushing the boat is transmitted along that shaft. When under load the engine mounts and other parts move, and the shaft moves with them, but that is under heavy load. If yours is moving fore and aft a half inch by hand, that indicates a problem.

The wire you pointed to is used to prevent that bolt in the side of the prop shaft flange from unscrewing. That bolt is used to secure the flange to the shaft. If that bolt is loose or broken and the flange is moving on the shaft, that is a REALLY BIG DEAL. It doesn't look like that bolt has turned, but it's out of focus and I can't quiet wrap my head around what I see... But the short answer is that ANY movement of the shaft relative to that flange is 100% unacceptable.

On a "proper" installation all the nuts securing the two flanges together would also be wired, but nylock nuts are a reasonably acceptable substitute, neither of which are being used for your installation.

The danger here is that you put the engine in reverse and the shaft pulls backward and disconnects from the engine. In the best case leaving you suddenly adrift without power, in the worst case it falls out of the hull leaving you with a 1 1/4 inch hole in your hull, likely sinking you very quickly.

If you were in the water I would consider a loose prop shaft to be an emergency repair to be done before moving the boat

There is a lot to know about this system. If you don't know what to do get a professional mechanic to help. If that flange is loose, after it is secured the engine should have it's alignment checked.

[jkishel]

The solid coupler has one or two set screws that engage with dimples (or sometimes flats) in the shaft to prevent the shaft from moving aft and eventually coming out of the coupler. The set screws are wired to prevent them from backing out of the coupler. The photos indicate that the shaft has moved aft out of the coupler (lots of key showing - the wire may have caught on the key somehow and broke as the key moved aft) and the original post implies that the shaft can be moved fore and aft by hand. If so, the coupler is worn and must be replaced. The set screws vibrated loose due to excessive vibration in the drive train. The root cause of the vibration should be identified and corrected; worn engine mounts, cutless bearing, engine misalignment, prop imbalance, bent shaft, bent strut or just the worn coupler. Optimally; remove the coupler, pull the prop and shaft, balance the prop (confirm that the prop is a proper fit for the engine), check and straighten the shaft, fit and face a new coupler, reinstall and align the engine.
The stuffing box has nothing to do with this.

[Tmacmi]

Does this photo help with the diagnosis at all? I realize I have to get to the boat and visually see where the shaft is moving from the inside.

Yes to an earlier comment, I am getting that much fore/aft play by hand.

The set screw that appears to jamb into the shaft in the fitting doesn't appear to have loosened. Interestingly the stainless wire that goes through the nut also appears to go through the shaft key.

https://imgur.com/c99DMXH

[jkishel]

Originally Posted by Tmacmi

Does this photo help with the diagnosis at all? I realize I have to get to the boat and visually see where the shaft is moving from the inside.

Yes to an earlier comment, I am getting that much fore/aft play by hand.

The set screw that appears to jamb into the shaft in the fitting doesn't appear to have loosened. Interestingly the stainless wire that goes through the nut also appears to go through the shaft key.

https://imgur.com/c99DMXH

That much fore/aft movement by hand suggests that either the shaft is moving in and out of the coupler or that the transmission output flange is moving on the transmission shaft (locknut has come loose). This should be apparent to someone watching the shaft/coupler/flange while someone else moves the shaft fore and aft at the prop. In either case this was likely caused by excessive vibration in the system; bent or unbalanced prop. bent shaft, worn coupler, engine out of alignment, etc.