Propshaft alignment with split hub - visible movement

[svsonora]

I'm using a
1. new shaft
2. new split coupler
3. new shaft bearing

The shaft is 20 inches long, going into a direct drive transmission. Vessel is a Bristol 30 with a hard-mount (e.g. shim aligned).

The old prop shaft and coupler exhibited no vibration or other problems, despite a worn out shaft (cutlass) bearing.

Things I did that might have been out of the ordinary - I loosely bolted on the coupler, with a few threads of play. I aligned the key, hub and shaft and lightly tapped the shaft into the coupler from the outside with a rubber mallet. Then I tightened the hex bolts and set screws, then tightened the hub onto the output coupler. I did not reface the coupler - I imagine that was done before I ever got the coupler.

There is visible movement of the shaft - the stuffing box moves a bit when I crank on the engine. Its enough to be visible on a cell phone camera (and more visible in person).

I'm trying to avoid having to realign the engine.
What can I try? I already tried loosening up the stuffing box and the hose clamps and re-bolting the coupler. I don't think its prudent to install a flex coupler in between. I could try removing the shaft, then bolting down the coupler firmly onto the output coupler and then re-installing the shaft. Or perhaps I should try reusing the old coupler? Boat is on the hard.

thanks in advance. (I'm so happy Moyer Marine exists so I can keep my old engine running!)

[romantic comedy]

In my experience the cutlass bearing is hard mounted to the hull so the shaft must pass thru in only one position. The shaft is supported by the engine and the cutlass only. The cutlass cant move to position the shaft so the engine must be moved. I see no other way.

Many times the cutlass bearing is worn because the shaft was not aligned- engine was not aligned. Sometimes you can see the cutlass worn on one side from misalignment.

[svsonora]

Thanks. Any chance that my coupler was misaligned to the shaft when I tapped it in?

[Ando]

Thanks. Any chance that my coupler was misaligned to the shaft when I tapped it in?

Did you use a feeler gauge?

[svsonora]

No. I'm going to try it next time I'm at the boat.

I wonder if I ruined the output coupling when I was trying to pop off the old shaft from the old coupler. I'd give the bolts about a turn, rotate, turn, rotate..

[ndutton]

How the shaft rotation appeared previously with a worn strut bearing doesn't mean the alignment was correct. What matters is that it is correct now. You can't draw conclusions on what might be off unless you carefully align it yourself.

To that end my suggestion is to remove the stuffing box and its connecting hose. With the new shaft in place in the new strut bearing, center it with small wedges in the inboard end of the shaft log and align the engine using a feeler gauge as suggested by others. Only then can you perform a meaningful test. Once every thing is resolved the stuffing box is reinstalled.

[svsonora]

Okay. so big DUH moment. After 5 days of wrestling with this...

I went in with feeler gauges, working my way down from 0.003" to 0.0015" Slowly tightened the sections where there was a gap until I could not find a spot where I could fit either of the gauges. When I got there, my coupler would bind up again. What the heck?

So I started getting the longer bolts in with a spacer on hte shaft to remove the new shaft. As I tightened down, the same thing happened - it would bind up after going in a bit.

I caught a glimpse of something shiny in the output coupler. I took a flashlight and looked at it, and realized the bolts were coming out the other end and hitting the transmission. DOH!!!

I thought about it and realized the flange on the split hub is a bit thinner than the flange on my old coupling. Even with the OEM length bolts, it was touching the transmission when it was fully tightened down.

I took a trip to the hardware store to get some stainless steel bolts that were slightly shorter than the OEM bolts.

The coupling turns fine now, with 0 visible wobble. So many questions answered. I could not get my head wrapped around the fact that my new shaft and coupler would not align when the old one did just fine.

This incident had the worst complexity/grief ratio, and I had so many before! Thanks for the help. Regardless, I learned a lot.

[sastanley]

svsonora...Now, that I recognize the similarities, I have been replying to your thread over on the FB too. Everything I share on FB in the Atomic4 group, I have learned here! You are generally in good hands at either, but I've been hanging out on this forum since 2008 when I got my A4 powered boat and was totally clueless.
Neil Dutton was the one that said to me, 'the tail wags the dog' and made the light bulb turn on with regards to alignment...he and lots of others have been at this longer than me..this is a really great group here.

[svsonora]

svsonora...I have been replying to your thread over on the FB too. Everything I share on FB in the Atomic4 group, I have learned here! You are generally in good hands at either, but I've been hanging out on this forum since 2008 when I got my A4 powered boat and was totally clueless.
Neil Dutton was the one that said to me, 'the tail wags the dog' and made the light bulb turn on with regards to alignment...he and lots of others have been at this longer than me..this is a really great group here.

Thanks. I've been wanting to join much sooner, but I think my application for membership got overlooked. I used a different email or something. But I did read through a lot of the posts here.

Hopefully this thread is here for anyone who needs a slap on the backside of the head to check for obvious things. Key words for search: coupling, coupler, alignment, binding, bolt, too long, hub, shaft

[sastanley]

All good..I have my alignment saga chronicled here too. It is not always obvious. The community always helps us see the things we can't see.

[tenders]

Shaft alignment and coupling issues are a huge source of frustration for me too. I'm limping through this season with misalignment and spattery shaft rotation following a late-spring last-minute need to replace the shaft and stuffing box, but will need to properly realign the engine after haulout.