Prop Shaft coupler loose at transmission

[Eddieclemons]

In my quest to find my missing rpms, I have run my boat a lot the last few weeks. From time to time, I will wrench my shafts around to see how they feel. Well, I discovered that on my starboard drive line I have some movement between the transmission coupler and the prop shaft. Further inspection revealed a rock in the key when turning the shaft back and forth. I have run several WOT tests the last couple of weeks. If the coupler is that loose, how did it not shear the key right off?

I have tightened the nuts on small inboard couplers but never anything close to 2.5" shafts. If I was able to separate the couplers and get the shaft to slide back, couldn't I just tighten the nut? Is there a cotter key?

What is the recommended path forward to repair?

I have a trip planned the end of the month; these old boats will definitely test your commitment.

 

[bigbill]

some use cotter pins, some dont. i would not run her any more until that is inspected and torqued to spec

 

[Captain Ralph]

In your pictures, Looks like the shaft is also traveling for/aft in the coupling also.
Inside the coupling is a big nut like a prop nut holding all together.

A pull bar is not going to tighten that nut down well. Big impact air gun will.
Security nut, lock-tite, cotter-pin and blood,, what ever it tales to lock a fresh nut in place.
You will not know if a cotter pin is usable till you get in there.

bigbill is correct, don't run her any more till fixed.
I am glad you found this before your deployment.

 

[Cricket]

Eddie, been thinking about your issue since I read it last night. Could there be something going on that's hidden under the coupler that's out of sight? Really feel like this should be an out of the water repair, is it far to get a haul out?

 

[Captain Ralph]

If you have room to slide the shaft back 9-11 inches, can be serviced in the water.
Pending the length of the air impact gun.

Before you slide the shaft back;
If you use gland packing, loosen it a good bit.
PSS or lip seal, make sure the shaft is real clean before you slide the shaft back.
Smear the shaft with liquid soap.
More or less what you would do if on the hill without removing the prop.

 

[Captain Ralph]

Could there be something going on that's hidden under the coupler that's out of sight?

The coupler's tapered shaft nut is out of site.
Hence why the coupler has to come off of the clutch flange and slide back.
Think of a prop nut inside the coupler.

 

[Eddieclemons]

Thanks for all the comments, getting it to the yard is the preferable solution for further inspection. It's about 55 miles down river with two locks enroute. They currently do not have power on their docks due to a large Stationary power support barge sinking in the harbor, but the yard does have power.
With all this in mind I just really would like to slide it back and look in there before I take off down river and see maybe what's going in there.
I feel like I could pull the shaft back up on the coupler but not sure exactly how I would push it back to take a peek unless I can get out Club diver on board if needed.
I plan to talk to all the players involved tomorrow and make a decision.

 

[jmooney]

I had my shafts out a couple of years ago. When tightening the shaft nuts, it can be hard to line up the cotter pin holes . The yard owner told me about using what he called an aircraft nut , available from McMaster Carr , these are self locking, one time use nuts . I didn’t try this , but it might be a good idea to be able to get the proper torque.

 

[Eddieclemons]

The current plan is for the yard to come to the boat and slide the shaft back with the assistance of our Club diver. Does anyone know of a source for stainless keys? Yard believes that is a stainless key in the picture. I will attempt to have multiple keys available if needed.

 

[Boatsb]

Don't use dish soap on the tides seals. They are not resistant to the surfactant in the soap and can be damaged.

 

[Captain Ralph]

Don't use dish soap on the tides seals. They are not resistant to the surfactant in the soap and can be damaged.

Oh, I did not know that. Thx.☺
In a case like here, sliding an ole shaft down/up (if a seal), Is there a recommended lube?

 

[SKYCHENEY]

Vaseline seems like the least likely thing to cause any issue.

 

[Sadey]

Astroglide is not a petroleum product so that might be a less toxic lubricant to use.

 

[ageless]

Oh, I did not know that. Thx.☺
In a case like here, sliding an ole shaft down/up (if a seal), Is there a recommended lube?

I use spray butter when doing impellers, might fit your need here, as well.

 

[rsmith]

If it’s rocking back and forth on the key the key way or the key is worn. Kind of néed pictures of the coupling to tell what type it is. Most Hatts had a straight shaft with a split coupling and a dowel pin. That would have been the setup for the Allison MH trans but since you have the 3406 engines and different trans I’d suspect it’s a taper fit shaft and coupling. If the key or key way are worn just tightening the nut won’t solve the problem. The main worry is stress cracks may have occurred in the key way which is machined into the shaft and a weak point. I’d be real gentle about shifting from forward to reverse and let the shaft spool down in neutral before shifting until you figure it out.

 

[Eddieclemons]

Well.....I got into the coupler today. I took the bolts out, cleaned the shaft, and backed off the packing gland nuts. Diver jumped into the water and pulled the shaft back to allow room to work. Tapered shaft as expected with only a nylon lock nut (unexpected) that was loose. Removed nut and coupling came off by hand. Cleaned everything up. Brass key was damaged by the rocking of the uncoupled coupler. I had 316 and Brass keystock ready for replacement. Brass I could work with onsite, The 316 would have needed to probably go offsite.
This was the Divers last dive for the season (amazing guy) and it would not go over well at my Club if I brought someone else in to finish the job in the coming weeks. New key fit wonderful after cutting and shaping. Tightened the old nut up until I snapped a 1/2" Snap-on breaker bar. There was not enough room for my impact gun set up on the 2 3-4" socket. Everything looks and feels great, but boat has not been run yet.

I feel pretty good about it, but I will be finding a new nylon nut for a replacement soon. It just seems that I need something more than a nylon locking nut??

 

[whoover]

I would have thought there would be a castle nut with cotter pin in there.

Walt Hoover

 

[madhatter1]

Mine has the single use nylon nuts. They work if only used once as designed.

 

[Captain Ralph]

Like the propeller on the shafts other end; The tapered coupling works the same way on the clutch end.
Once set and locked on, effort is required to get it apart.
Castle nuts, ny-loc nuts, cotter pins and shaft keys are assembly and safety tools to the tapered coupling. When correctly assembled, they are just rotating mass.
I hope alignment was spot checked during re-assembly.

Now, one less thing to worry about during your big trip.

 

[Eddieclemons]

Alignment was .004 or a tight .005 or less before rebolting. Factor in painted surfaces on the flange edges that I couldn't completely remove I didn't dare attempt to improve that yesterday.