Shaft Separation from Paragon Coupler

[RMK818]

Looking for a little help here:
While backing out of my slip and taking my 1979 42 LRC (Perkins T6.354) out for an engine run, I heard and felt a clunk (thought I hit a submerged log). I noticed my port RPM engine was at 2500 rpm yet my stbd engine was at 1700 RPM. both engine throttles were matched. After some quick trouble shooting, I learned my port propulsion was not working even though the port engine was running. After limping back to the slip on one motor, and inspecting the port engine, I noticed my port prop shaft had decoupled from the Paragon transmission. The square block key was sitting inside the engine pan. My questions are: how could this happen? What type of shaft couplers are used on this vessel (Solid, Reverse Tapered, or Tapered)? Do I have to remove the old Coupler to reinstall it on the shaft and then slide the entire assembly back up to the transmission (would require new alignment)? Any other comments are deeply appreciated. The shaft is about a foot set back (picture below)

 

[tiltrider1]

I can’t tell a lot from the picture but I am guessing that you have lost a set screw that held the coupler in place on the shaft. Great time to upgrade to modern couplers that use compression to hold the shaft in place.

You can probably reach in grab the shaft and pull it back into place.

 

[Comodave]

If you replace the coupler the I would do the engine alignment. In fact it might not be a bad idea to do one anyway. It is pretty easy to do but do it in the water after a couple of days after launch.

 

[jgwinks]

There should be one or two set screws in the coupler and/or a pin driven all the way through the coupler and shaft. There should be dimples drilled into the shaft under the screws to make it more secure but these are often not present. The pin can sheer or the screws may fall out. Normally pulling a shaft out of it's coupler is very difficult and if it goes back in easily both the shaft and coupler may be worn out and need replacement. I'd replace the square key regardless because if it has any play at all it will allow movement that wears out the coupler and shaft, sheers the pin or screws, etc.

 

[RMK818]

There should be one or two set screws in the coupler and/or a pin driven all the way through the coupler and shaft. There should be dimples drilled into the shaft under the screws to make it more secure but these are often not present. The pin can sheer or the screws may fall out. Normally pulling a shaft out of it's coupler is very difficult and if it goes back in easily both the shaft and coupler may be worn out and need replacement. I'd replace the square key regardless because if it has any play at all it will allow movement that wears out the coupler and shaft, sheers the pin or screws, etc.

Thank you for the great information, any idea where I can get a new square key?

 

[Delta Riverat]

Any hardware store should have key stock on hand usually in 1 foot lengths, cut it yourself to fit.

 

[Comodave]

Or a machine shop.

 

[CPD]

Suffered the same fate in summer 2023. The Coupler set screws wore away (there was dry black set-screw dust below the coupler), and the shaft came out when reversing from the dock. The keyway in the prop-shaft had enlarged so that the original key was no longer a secure fit. Had to have the boat hauled out to shove the prop shaft back in with a larger (temporary) replacement key. Too much force and precision required to shove the shaft back in from in the water. Over the winter had both Couplers replaced with Split-Couplers which moreso use compression force over set screws to secure the shafts (and unfortuneately new shafts also due to the longterm damage sustained from the old set-screw couplers).

 

[Don Armstrong]

Looking for a little help here:
While backing out of my slip and taking my 1979 42 LRC (Perkins T6.354) out for an engine run, I heard and felt a clunk (thought I hit a submerged log). I noticed my port RPM engine was at 2500 rpm yet my stbd engine was at 1700 RPM. both engine throttles were matched. After some quick trouble shooting, I learned my port propulsion was not working even though the port engine was running. After limping back to the slip on one motor, and inspecting the port engine, I noticed my port prop shaft had decoupled from the Paragon transmission. The square block key was sitting inside the engine pan. My questions are: how could this happen? What type of shaft couplers are used on this vessel (Solid, Reverse Tapered, or Tapered)? Do I have to remove the old Coupler to reinstall it on the shaft and then slide the entire assembly back up to the transmission (would require new alignment)? Any other comments are deeply appreciated. The shaft is about a foot set back (picture below)
View attachment 161607

As others have mentioned, each shaft coupling must have a locking set screw that goes in to a dimple in the shaft that should be at least 3/16" deep. But if the coupling is a little loose, as yours must be, all is not lost. Remove the coupling and drill and tap two rows of holes for about 3/8" screws and insert Grade 8 locking set screws (see photo). Tighten as much as possible against the shaft, and check them for tightness now and then. I did this 5 years ago and none have loosened yet and the coupling is solid. Note that the coupling face may no longer be quite square with the shaft centerline so don't use the coupling face for aligning the shaft.

 

[luna]

As others have mentioned, each shaft coupling must have a locking set screw that goes in to a dimple in the shaft that should be at least 3/16" deep. But if the coupling is a little loose, as yours must be, all is not lost. Remove the coupling and drill and tap two rows of holes for about 3/8" screws and insert Grade 8 locking set screws (see photo). Tighten as much as possible against the shaft, and check them for tightness now and then. I did this 5 years ago and none have loosened yet and the coupling is solid. Note that the coupling face may no longer be quite square with the shaft centerline so don't use the coupling face for aligning the shaft.

I would think that having a coupler's face that is not square to the shaft would be a problem.

If you can't use the shaft mounted coupler's face as a reference point to use when moving the engine/gear assembly's output flange into alignment, what reference point do you use?

 

[Don Armstrong]

I would think that having a coupler's face that is not square to the shaft would be a problem.

If you can't use the shaft mounted coupler's face as a reference point to use when moving the engine/gear assembly's output flange into alignment, what reference point do you use?

 

[Don Armstrong]

Your welcome! Turn both shafts together with a feeler gauge between the same points on both coupling halves to check the alignment. And, better still, when the alignment is spot on, or within .002", install a flexible coupling as per the earlier photo. The coupling shown is an R&D 910-009, but check with R&D for the correct sizing for your setup.

 

[luna]

Ok, I don’t think that works for me.
I think I will just stick to having the coupler faced, once it is firmly wedged on the taper of a newly trued shaft. That way I know it is square to the world.

Provided that your isolators are not shot, once you move the engine/gear assembly into alignment with the shaft coupler there is no need for some kind of flexible coupler in the drive line.