Split shaft coupling question

Comodave · May 26, 2021

Again, make sure that you have enough shaft to pull it forward. You don’t want the prop pulled against the back of the strut and be rubbing on the strut. You need some shaft sticking out behind the strut so cooling water can exit the cutlass bearing.

sbman · May 26, 2021

socalrider said:
Plan:
1. Head dunk to check for shaft clearance from prop to strut
2. Remove a single coupling pinch bolt to check for dimple.
3. If sufficient clearance and no dimple, remove PSS set screws & ensure I can move the ring on the prop shaft
5. Remove second pinch bolt and unbolt coupling from transmission. Push the shaft aft a few inches carefully w/ pry bar if necessary (minding the PSS coupling & not marring the mating surfaces). Remove coupling from shaft, clean & light oil on everything, re-assemble. The coupling *should* slide right on and bottom out if everything's clean and de-burred.
6. Carefully torque (new, grade 8) pinch bolts, alternating.
7. Draw the coupling flange to the transmission flange with oversize bolts and/or pry bars operating on the back face of the shaft coupling.

I did many of these steps when replacing the drivesaver (at anchor off Catalina) last year by myself with minimal tools so I'm pretty confident I can move the shaft fore and aft. I'm more worried about the coupling being seized to the shaft - there's some rust visible in the keyway in the photo.

Sounds like a good plan. I've spent far too many hours struggling with shafts, couplers and stuffing boxes to envy any of that work. I'm afraid I've got a bit more to go prior to launch as well. If the coupling doesn't slide right on in step 5, I've got a shaft collar in 1 3/4" that can be used to help draw it into the coupler with some all-thread, nuts, washers and various other bits, depending on your space constraints. If you have a different size shaft, the collars are easily available on McMaster's web site.

I'm going to take a guess and assume there was a reason someone got lazy and didn't assemble it correctly and you'll find the reason somewhere along the way in this job.

sbman · May 26, 2021

Here is a picture of the shaft collar in action. I was trying to remove a stuffing box that was extremely stuck. I used the shaft collar as a hardpoint to pull from, it clamps on the shaft and does not mar it. It could be used to pull on the drive coupler to pull it onto the shaft with appropriate hardware employed.

I made these horseshoe shaped pieces out of mild steel to straddle the shaft, butt up against the collar and provide places to use bolts/threaded rod to pull with.

I also have these commercially produced horseshoes that could be used for the same thing but have a larger overall size which might be more appropriate for pulling with in your case. These are part of my StrutPro kit which I bought to change cutlass bearings.

socalrider · May 26, 2021

Comodave said:
Again, make sure that you have enough shaft to pull it forward. You don’t want the prop pulled against the back of the strut and be rubbing on the strut. You need some shaft sticking out behind the strut so cooling water can exit the cutlass bearing.

Thanks

sbman said:
I'm going to take a guess and assume there was a reason someone got lazy and didn't assemble it correctly and you'll find the reason somewhere along the way in this job.

Yeah, that's probably right unfortunately. If the shaft's just too short I can get a spacer made up.

Comodave · May 26, 2021

Yeah, that's probably right unfortunately. If the shaft's just too short I can get a spacer made up.[/QUOTE]

I got mine at Spurs. They did great work but not cheap. No affiliation. Sounds like you are going swimming...

C lectric · May 28, 2021

Some wee wedges made from ground screwdriver bits can be used, CAREFULLY, to open the splits in the coupling just enough to slide the coupling onto the shaft.

If the dimples in the shaft sides are in the wrong place the shaft may have to be pulled to correct it. Maybe the shaft is to short and they did not consider a machined spacer. The shaft end should be at the end of the bore hole in the coupling or close.

As the shaft end enters the solid part of the coupling is where you may need some pulling or pushing ability using a split collar , or two, and threaded rod.

I just went through this a month ago. My shaft needed straightening a bit and I ended up with a new coupling faced to the shaft and a new cutless bearing.

My boat was out of the water for this work. Made things much easier although still a lot of work.

I've mentioned this before but even with a dripless shaft seal water in the form of a VERY fine spray will enter the E.R. It is fine enough to travel causing rusting of nearby components.
I don't have a dripless so I cover my stuffing box with an old fender hacked into a cover which catches the mist so it drops into the bilge.

But I have seen the results of that mist at work even though the seals used were the same general type as the so called dripless. Consider a hacked fender cover and maybe stop/reduce the rusting of parts like the coupling.

socalrider · May 28, 2021

Update:

Back on the boat today; I went ahead and pulled a pinch bolt and indeed the shaft is dimpled. I took a closer look at the gap identified in the split with a bright light and feeler gage & found that it's not actually a gap - there's a ~1/4" deep hole drilled in the shaft right under the split, making it look like the shaft isn't fully engaged! So I'm not sure why that hole is there but it does look like the shaft's in its correct place.

I'm going to replace the pinch bolts on both couplings with fresh Zn-Al coated 7/16" grade 8 bolts, nuts & split washers & torque to proper spec, but otherwise I'm gonna leave this one alone. Sorry for the false alarm!

HypnoBob · May 31, 2021

Looking closely, I can see the line on the shaft where it was previously secured so it does look like it just slipped back.

I would follow your own thoughts on fixing it. Loosen, pull till it bottoms out, take a look at the space between the prop and the bearing - should match the other prop. Tighten to torque specs.

You might need to devise some way to get a little leverage to pull it through the bearing (loosen packing for example).

We had shaft savers on our DeFever 49 CPMY. They saved us more than a few times around the loop. We started from Houston and on our way, we wrapped a 2 inch hauser around the prop in Louisiana. Our Prop-Protector line cutters took a while of reverse and forward shifting before it cut the line.

Tiffany · May 31, 2021

Better option than Drivesavers?

Comodave said:
Our boat had Drivesavers on it. Too much vibration since we couldn’t do a proper alignment. Replaced the Drivesavers with spacers from Spurs, no more vibration.

I installed a Drivesaver on my boat after seeing how a pair of transmissions can be blown apart by not having a break-apart joint between shafts and the power. $60,000 worth of replacement and parts throughout the engine room. If there is a better option than "nothing" I'm interested to hear more.

SteveK · May 31, 2021

HypnoBob said:
Looking closely, I can see the line on the shaft where it was previously secured so it does look like it just slipped back.

............................

I saw that too and thought it was pulled forward after a drivesaver was removed but since no mention of one on other shaft dismissed the thought.

Alisske · May 31, 2021

sbman said:
Here is a picture of the shaft collar in action. I was trying to remove a stuffing box that was extremely stuck. I used the shaft collar as a hardpoint to pull from, it clamps on the shaft and does not mar it. It could be used to pull on the drive coupler to pull it onto the shaft with appropriate hardware employed.

That is a super slick set up and great idea. Thanks for posting. Will put it in the “Get’er done” rolodex.

Leatherneck · May 31, 2021

My starboard driveshaft slid completely out of the coup0ler and luckily the rudder stopped it from going to the bottom. Found a couple of sheared bolts lying in the bilge. It appeared that several bolts loosened and then the remaining bolts sheared. a local marine mechanic was able to pull the drive shaft back in using a chain come-along and then a pipe wrench to orient the driveshaft. Quick trip to hardware store for six new number 8 bolts and back in service in 3 hours. Checked port side and found loose bolts there. Bolt check is now on my annual checklist.

Nautica · Jun 1, 2021

Even if it is slid right home, it's still only the split part that does the clamping and carries the drive. Not sure why you think it's going to suffer cracking if shaft is straight & in line. If it's not, there is stress anyway, fully home or not.

Comodave · Jun 1, 2021

My split couplers have the shaft slid almost all the way onto the coupler. The couplers are short about 1/4” from being all the way onto the shafts. It is a little tough in the photo to see but the shaft is almost all the way into the coupler, not just the split part in the rear.

Tiffany · Jun 1, 2021

Nautica said:
Even if it is slid right home, it's still only the split part that does the clamping and carries the drive. Not sure why you think it's going to suffer cracking if shaft is straight & in line. If it's not, there is stress anyway, fully home or not.

Nautica, There is always a degree of vibration on the shaft, but what is important is that the end point of the vibration not be before or at a 'stress riser' point, such as the end of the split of the coupling. That would magnify the vibrational stress to the corners of the split, where the vibration has to change direction at the inside corners.

Getting the shaft tail end to bed after the split moves the stress riser point up into the solid part of the coupling, where it dissipates further.
More information: https://www.sciencedirect.com/topics/engineering/stress-raiser

sbman · Jun 1, 2021

Comodave said:
My split couplers have the shaft slid almost all the way onto the coupler. The couplers are short about 1/4” from being all the way onto the shafts. It is a little tough in the photo to see but the shaft is almost all the way into the coupler, not just the split part in the rear.

Tiffany said:
Nautica, There is always a degree of vibration on the shaft, but what is important is that the end point of the vibration not be before or at a 'stress riser' point, such as the end of the split of the coupling. That would magnify the vibrational stress to the corners of the split, where the vibration has to change direction at the inside corners.

Getting the shaft tail end to bed after the split moves the stress riser point up into the solid part of the coupling, where it dissipates further.
More information: https://www.sciencedirect.com/topics/engineering/stress-raiser

Exactly, stress points at cuts, dings, scratches, etc... all the same reasons you smooth out a scratch on any piece of metal subject to high stress, a scratch or sharp edge can be the location where a crack begins to form. Machined components will have all of their edges deburred and smoothed to remove stress risers. There are a lot of forces involved and the shaft coupling suffers through them all, all sorts of vibrations, twisting forces which vary a lot each rotation of the engine. It's certainly not guaranteed to form a crack, but installed incorrectly there is a greater risk of that type of failure.

Now that the OP has discovered that the shaft is actually inserted fully, and has dimples to prevent the shaft from sliding in/out of the coupler, there's not much to be concerned about.

HypnoBob · Jun 1, 2021

There should be a couple inches between the Cutless Bearing and the prop to allow water to flow freely through the bearing as that is what keeps it lubricated.

Comodave · Jun 1, 2021

HypnoBob said:
There should be a couple inches between the Cutless Bearing and the prop to allow water to flow freely through the bearing as that is what keeps it lubricated.

Absolutely. That is why he needs to see if there is enough shaft to pull forward and engage the coupler fully. If not then time to have a spacer made.

socalrider · Jun 1, 2021

sbman said:
Now that the OP has discovered that the shaft is actually inserted fully, and has dimples to prevent the shaft from sliding in/out of the coupler, there's not much to be concerned about.

Yup. Thanks again everyone - even though the problem turned out to be a false alarm I have learned a ton from this thread. Pinch bolts came in from McMaster-Carr today so I'll put 'em in shortly and re-torque every faster on the prop shafts.

Split shaft coupling question

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