Prop Shaft Appears Disconnected

[SeaplaneDriver]

Hi Everyone,

This is what’s going on with the Universal 25 on my O’Day. It appears to me that the prop shaft has come disconnected from the transmission.

This is my first mechanical issue I’ve really had to deal with. I’d appreciate whatever diagnostics or advice you all could help me with. Thanks!

[two-rocks]

There should be two set screws on the white coupling - secured with ss or monel safety wire.

If not, get a new coupling.

Looks like a new transmission.

[Hudson Force]

My guess is that your last powered maneuver was in reverse. I had an event about fifty years ago when I was backing to set my anchor and my entire shaft pulled out. I had to quickly break off the end of a broom handle to plug the hole. I suspect that when you rotate the collar that accepts the shaft (white in the photo) you will locate a threaded hole that accepts a set screw to secure the shaft. Sometimes the separation of the shaft can result from increased vibration due to improper alignment or loose motor mounts. You well likely be able to resolve this with little effort or expense.

[a64pilot]

Originally Posted by two-rocks

Looks like a new transmission.

Yep, and whoever installed it, forgot to tighten those set screws.
Assuming they tighten onto the prop shaft, I’d “spot” the shaft, that is drill a divot for the set screws to tighten into, without a divot and just tightened onto the smooth shaft, they can easily lose their grip.

Most likely those divots already exist, look for them and ensure you line them up through the hole in the coupling so that they screws tighten into the divot.

[SeaplaneDriver]

That doesn't sound like nearly as bad a fix as I was anticipating but it makes sense! I'll take a look when I get back tonight and keep y'all updated. Thanks for the quick replies!

And yes, last maneuver was in reverse holding for a bridge opening with a current and got no forward/reverse thrust when I tried to motor through. Unbelievably lucky she just happened to drift through the middle, didn't get into the rocks, didn't lose the prop shaft, and that my coworker just happened by chance to be there in his boat to give us a tow!

[Cheechako]

Yep, check your set screws and have some monel or ss wire to affix them.

[jkishel]

Looks like the set screws backed out of the coupler and the shaft pulled aft in reverse. Excessive vibration may have caused the set screws to back out. Possible causes include worn engine mounts, vibrating engine, misaligned engine, worn coupler, bent shaft, worn cutlass bearing, loose strut and/or prop imbalance. All these should really be checked. Getting the shaft back into a one piece coupler like this can be a challenge with the boat in the water. If it goes in part way, it may be possible to drive it home by running the engine in forward while tied to a dock. If the shaft slides in too easily it is probably worn beyond reuse. Replacement with a split coupler is often only way to do this without pulling the engine.

[Davidhoy]

Originally Posted by SeaplaneDriver

And yes, last maneuver was in reverse holding for a bridge opening with a current and got no forward/reverse thrust when I tried to motor through. Unbelievably lucky she just happened to drift through the middle, didn't get into the rocks, didn't lose the prop shaft, and that my coworker just happened by chance to be there in his boat to give us a tow!

Ah yes, you must have been on the New River ;-). So many bridges to wait for. You got very lucky, both with the current, and with your friend being there to give you a tow. And that your shaft did not pull all the way out of the boat.

Regards,
David

[a64pilot]

It should be a real easy fix, start by removing the coupling from the transmission, and reinstalling it on the prop shaft.
Then read up on checking alignment, your there, best to check it now, then hook it up.
Should be as easy as changing a flat tire.

[Bill Seal]

Look closely at the pics, IT HAS A KEYWAY. Might be a bit of a struggle getting the shaft back into the coupler, might even have to remove the flex coupler or have a diver pound it back in from the prop end. Have fun.

[mcgann454]

I had the same thing happen several years ago. The P.O. did not tighten the set screws. I took the coupling apart after marking where they were in relation to each other and reset it on the shaft. The key stock will align that. I then bought long bolts and used them in the couplings to draw the shaft back to the transmission. Use progressively shorter bolts and tighten around all four bolts as you go to keep even pressure. be careful that the bolts do not warp the coupling. You need to check the alignment when you get the couplings back together.

[Squanderbucks]

All the things said above are correct except no one mentioned that you need to look for the WHY.

I could be just improper tightening of the set screws but could be other stuff such as excess vibration Causing the loosening. Anything from bent prop, bent shaft, barnacles on either as well.

As long as you have things apart now is a good time to check shaft/transmission alignment before tightening back up.

Depending on how tight your coupler is - putting it fully back into place can be a problem. Usually assisted by tapping or pushing on the prop end of the shaft.

Be sure to check the shaft key for being bent or rounded over.

This coming out on it's own should be considered the "canary in the mine shaft".

[kenbo]

It's hard to tell definitively from the photos but the key looks to be too long or the key is the correct length and the shaft cracked and the forward end is still in the coupler.

If that is a new gearbox and the shaft was removed from the half coupling I bet the shaft wasn't removed from the boat and fit and faced to the coupling. Without that step, it's a roll of the dice of ever getting the alignment correct in all three axes.

[kenbo]

Looking at the pics again it doesn't appear that the key is too long but a can see a bad fit between the shaft and coupler by the different shadings and coloration on the shaft.

[Sailing August]

Yes. It looks like the shaft has slipped out of the coupling and the propeller shaft has slid aft. The coupling would usually have set screws and possibly a key way.
Pull out the coupling. See if the shaft slipped out and why.
If it just slipped out; drill and tap new set screw holes or drill out and tap the existing set screw holes for larger set screws. install new 316L set screws and use locktite blue. Don't use the red.

Good luck
Sailing August