How do you install a prop shaft coupling with only 2" to spare?!

[Project_Mayhem]

I had a new prop shaft and coupling machined. It's a very tight fit and there's only two inches between the transmission's output flange and the coupling. Here are my ideas so far:

• Bolted a piece of plywood to the coupling to protect it, used a ratchet strap attached to the strut to keep the shaft from moving, used a slide hammer to try to install the coupling. I was able to make a little bit of progress but I'm still not sure if it will work
• I've read that you cant push the coupling up against the transmission's output coupling and tap from the inside as damage could occur. There are some unused bolt holes in the transmission housing. I was thinking about bolting a piece of wood and then the coupling would have something to push up against while it's being tapped from the outside
• Heat. I was going to try baking the coupling for at least an hour but unfortunately I couldn't get the stove to light. I can pickup a toaster oven
• Move or remove trans/engine is another option. I'm thinking it'd be easier to slide the engine back than to remove the transmission

This coupling is a really tight fit on the shaft. Feedback on proposed strategies or suggestions would be much appreciated. How did you get yours installed?

 

[dlochner]

This is why split couplings were invented. Replace the coupling with a split coupling is the easiest solution.

 

[Tally Ho]

Do you have a photo?

When I replaced mine, the shaft/coupling interface was tight, especially with the key in place, but not so tight that I needed to hammer it on. A tap or 2 maybe, but nothing dramatic.

What did you decide to use for a shaft seal?

Greg

 

[Hayden Watson]

Split coupling helps and a Sigma coupling makes it dead easy. Heat is your best friend.

 

[jssailem]

My boat was out of the water. I assumed the original engine/transmission shaft setup was proper. I tried to replicate the new shaft and coupling to match the ones I had removed.

The shaft length was determined based on the original one, making the new shaft the proper length for the engine in its original location. With the engine and transmission installed on the mountings, I slipped the shaft forward from outside the boat as the mechanic guided the shaft coupling to the transmission. This allowed me to ensure that the prop and shaft were in the same position under the hull as measured in the original setup.

There was no hammer or heat treatment necessary. The shaft was slipped through the cutlass bearing, shaft log, and new PSS shaft seal. The coupling was attached. The engine and transmission were installed. The shaft and coupling were married to the transmission. I then installed the prop and annodes on the shaft. The initial alignment was set, and the PSS was compressed to allow the boat to be splashed. Once the boat was back in the slip, we again checked that the rotation of the shaft in the PSS and Shaft log was smooth and could be done manually. The final alignment was made, and we got the expected clearances between the transmission and coupler, indicating proper alignment.

Happy Days. I thought I was running in the right direction. There appeared to be a light at the end of the tunnel.

In my case, we then tried to address the water pump issue that appeared when moving the boat back to the slip.
That was the start of the next nightmare.

 

[Ralph Johnstone]

Heat is your best friend.

Cooling is also a good friend ......................... on the prop shaft at the SAME TIME as you're heating the coupling. Use dry ice (CO2).

 

[BigEasy]

I had a new prop shaft and coupling machined. It's a very tight fit and there's only two inches between the transmission's output flange and the coupling. Here are my ideas so far:

Sounds like you had the shaft & coupling machined locally. Return it to them, explaining your situation. They should be able to obtain a more passive fit and possibly shorten the shaft if specs permit. I am also concerned that once the coupling is installed, it will be impossible to remove it without destroying it because you’re not going to have sufficient space to use a puller. A split coupling as recommended by others, may be your better option.

 

[Hayden Watson]

Cooling is also a good friend ......................... on the prop shaft at the SAME TIME as you're heating the coupling. Use dry ice (CO2).

You are correct. If you do not want to deal with dry ice, you can get similar results with CRC Freeze-off. It is designed to literally freeze your nuts off. Just make sure that you put the sensors for a propane sniffer in a sealed baggy before using it.

 

[Project_Mayhem]

Getting the old one off was actually pretty easy thanks to the custom tool that @Tally Ho let me borrow (Thanks Greg!).

According to multiple sources a light interference is best practice and that usually requires a light tapping of a hammer to install on the shaft (Fitting & Facing A Marine Shaft Coupling)

Unfortunately, the prop shop didn't really explain split shafts properly and steered me towards a solid coupling. Shame on me for not doing my own homework.

Is there a potential for metal fractures by putting a 450F coupling on a -100F shaft?

Debating between hot/cold vs having the shop take off some more metal

 

[dlochner]

Debating between hot/cold vs having the shop take off some more metal

A new split coupling will probably cost about the same as having the machine shop remove a little more metal.

 

[Tally Ho]

If it were me, I would first determine how much “tapping” is required to get the shaft into the coupling (on mine, the orientation of the key made a difference). If not too much pressure is required, but tight enough to need some tapping… I would put a board between the coupling and the transmission output flange, and have someone hold it as tight as they can while I tapped it from the prop end…maybe with a rubber mallet, dead blow hammer or the like.

You might get creative and put some legs on the board that can rest against the engine mounts, engine cradle or any hard points to keep the board from hitting the transmission.

Who made the shaft? Crowleys?

Greg

 

[Project_Mayhem]

A new split coupling will probably cost about the same as having the machine shop remove a little more metal.

They just machined this shaft and coupler for me. I'd expect them to take a bit more metal off free of charge so I have something usable

If it were me, I would first determine how much “tapping” is required to get the shaft into the coupling (on mine, the orientation of the key made a difference). If not too much pressure is required, but tight enough to need some tapping… I would put a board between the coupling and the transmission output flange, and have someone hold it as tight as they can while I tapped it from the prop end…maybe with a rubber mallet, dead blow hammer or the like.

You might get creative and put some legs on the board that can rest against the engine mounts, engine cradle or any hard points to keep the board from hitting the transmission.

Who made the shaft? Crowleys?

Greg

I'll refrain from releasing their name for now as I haven't reached out to them.

There's some unused bolt holes in the trans case. I was looking at putting some bolts in there to hold a piece of wood. This would give the coupler something to rest up against while it was tapped from the prop end. I also took a look at using a piece of wood across the engine mounts. Next time I'm there, I'm going to pull the shaft and see how hard it is to tap it on without space restrictions

 

[jssailem]

Is it possible that the weight of the shaft is binding against the cutlass bearing and the shaft log, causing resistance to your moving the shaft? If the shaft is supported and centered in the shaft log, you should be able to (without pounding) slide the shaft in or outwards. On my boat, I can manually rotate the shaft when it is centered in the shaft log.

 

[Tally Ho]

I'll refrain from releasing their name for now as I haven't reached out to them.

No worries…and a good thing to follow up with them first.
Crowleys did mine and I was very satisfied with It. A light press fit, that I could tap slightly to get the shaft into the coupling…as long as I had the key in the one particular way.

I like the idea of some sort of standoffs, so the board doesn’t hit the output flange of the transmission.

But if you really have to pound the shaft to get it in the coupling, I would get it looked at by the shop. Have you engaged them before putting the shaft in the boat?

Greg

 

[Project_Mayhem]

Is it possible that the weight of the shaft is binding against the cutlass bearing and the shaft log, causing resistance to your moving the shaft? If the shaft is supported and centered in the shaft log, you should be able to (without pounding) slide the shaft in or outwards. On my boat, I can manually rotate the shaft when it is centered in the shaft log.

I have not tried to tap from the prop end of the shaft. It's a new cutlass. It's difficult to rotate or move the shaft due to the new bearing

No worries…and a good thing to follow up with them first.
Crowleys did mine and I was very satisfied with It. A light press fit, that I could tap slightly to get the shaft into the coupling…as long as I had the key in the one particular way.

I like the idea of some sort of standoffs, so the board doesn’t hit the output flange of the transmission.

But if you really have to pound the shaft to get it in the coupling, I would get it looked at by the shop. Have you engaged them before putting the shaft in the boat?

Greg

Removing the shaft and putting the cutlass on outside the boat is my next step. Another advantage of the standoff idea is that the angle of the board will be about the same angle as the output shaft. Other ideas suffer from an incorrect angle so their success is limited

 

[dlochner]

I have not tried to tap from the prop end of the shaft. It's a new cutlass. It's difficult to rotate or move the shaft due to the new bearing

The cutlass is water lubricated. Spray some water in there or some water soluble lubricant like K-Y Jelly. Don't use a petroleum lubricant.

 

[sesmith]

I'm assuming you're working on a boat with a pss seal? If so, I had a really tight fit on one of my previous boats, like you have here. I used the old pss collar and screws to temporarily compress the pss enough to get the coupling on. Then I parked my truck behind the boat and put a ratchet strap between the prop and my truck hitch. Tightened the ratchet strap to compress the pss seal and it gave me plenty of room to tap the coupling into place. Warming it up will also help.