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Should I unfasten PSS collar and redo the alignment?

  • yes, redo right away.

    Votes: 3 100.0%
  • get the engine running again and revisit after a few short cruises

    Votes: 0 0.0%
  • seems like the alignment is fine, congratulations

    Votes: 0 0.0%
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Discussion Starter · #1 · (Edited)
Update: I loosened the PSS and redid alignment and now it's much better.

I edited the post for readability. Here is the sequence of events that took place:
  • I took my inboard engine out onto the cabin sole and replaced the little gearbox that connects it to the prop shaft.
  • The gearbox has a 3.5mm greater drop (vertical distance between input and output shaft axes) than the old one, so I adjusted the four engine mounts by an estimated 3.5mm. Engine sits about 3.5mm higher now to compensate for that greater drop.
  • I placed the engine back into the engine compartment.
  • I brought the shaft coupler and the gearbox output shaft together by hand, noting that to the naked eye they seemed to line up pretty well.
  • I compressed the PSS shaft bellows and put in the set screws. This took quite a bit of force, at least 50lbs. That means it's now pushing the shaft coupler forward with 50lbs
  • I observed, with a feeler gauge, that the shaft coupler was totally flush with gearbox output shaft. This surprised me because I thought I would have to do alignment.
Questions:

I wonder whether the forward pressure from the PSS bellows is causing the shaft to bend slightly, which makes the couplers appear to be aligned.

I wonder if I need to unfasten the steel collar the holds back the PSS bellows, and then do shaft alignment before compressing the bellows and fastening the collar again.

But then again, I wonder whether 50lbs or so pressure on the couplers really has any power to bend the prop shaft like that.

Your thoughts and advice are appreaciated!

A few pictures:

An older picture from the outside, when my boat was out of the water. Standard stuff here...
Propeller Propeller Automotive exhaust Aviation Aircraft engine


My new gearbox where it meets the shaft coupler
Automotive tire Motor vehicle Hood Steering part Bumper


The PSS shaft seal and prop shaft
Creative arts Pattern Rope Art Wool

Edit: I clarified my original message, which can be found below.

I recently replaced my gearbox with the engine on the cabin sole, with the boat in the water. The gearbox has a 3.5mm greater drop than the old one, so I adjusted the four engine mounts by 3.5mm, and then plopped my engine back down into place. The shaft coupler seemed to line up, to the naked eye, so I went ahead and compressed the old PSS dripless shaft seal bellows and secured that to the shaft with new set-screws. I found the bellows took a lot of force to compress the requisite 20mm (for my 7/8" prop shaft), so much that I had to pull the collar and bellows back with a strap, using some leverage to tighten it. This probably doesn't occur as much with a new bellows. Finally, I went around the coupler with a 0.004" feeler gauge and found that it was perfectly flush all the way around. Furthermore, although I can turn the shaft by hand, it seems like it resists more than I expected, given what I remember of turning the gearbox in neutral, and turning the prop shaft on its own.

I wonder whether the forward pressure from the PSS bellows is causing the shaft to bend slightly, which makes the couplers appear to be aligned.

I wonder if I need to unfasten the steel collar the holds back the PSS bellows, and then do shaft alignment before compressing the bellows and fastening the collar again.

But then again, I wonder whether 50lbs or so pressure on the couplers really has any power to bend the prop shaft like that.

Your thoughts and advice are appreaciated!
 

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I went around the coupler with a 0.004" feeler gauge
I may not be following your procedure. That's the generally allowable difference permitted between two opposing positions on the shaft, after you've hand tightened the coupler against a larger feeler, but not necessarily the gap itself.

To answer your question, I doubt the PSS tension is bending the shaft, but that's not to say your shaft isn't bent. I had a prop guy tell me once that he's never removed an old shaft, under 2" in diameter, that wasn't slightly bent.

Did you put new cutlass bearings in? They might bind more than you remember, especially if the shaft is out of plumb.
 

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One of None
Hunter 34
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This is hard to understand but reads like your shaft is not moving back or it could hitting the rudder. Without pictures who knows.

If you have all this apart you should at least replace the bellows on the PSS. And the PSS pressure against the its mating surface is usually only enough to hold them together that you could easily pull apart with your fingers.
Best guess you need to do some more aligning maybe even move the engine forward a little bit but, you certainly want to be sure the propeller is not going to chop up your rudder.
 
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I'm trying to picture this. 3.5 mm is not that big of a drop, but I wonder if it was enough to sufficiently change the
angle through the shaft log, and apply unequal pressure through to the cutlass bearing? Sounds like you should try aligning the shaft.
 

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OK, I only know a little about alignment, so hoping you get smarter advice. I would check my alignment with the bellows loose. That way if it's impacting the alignment, you'll know. But this is a guess, not based on anything I've done.

But here's something I do know. Those grub screws on the donut are one time use. If you loosen to move the donut, get new ones. I had a donut come loose underway and turn my engine room into a rotary salt water sprinkler system. Luckily I had a bilge alarm, so it didn't go on for long. Also, on same topic of grub screws, I think the system assumes a clean shaft, then the grub screws sort of dimple it or they deform a bit or both. I'm worried about the scoring on the shaft making the donut attachment questionable.

Since the incident, we've put a collar against the engine side of the donut. I believe we got this from the manufacturer, but I've seen others use a zinc as belt and suspenders against this failure mode.

Good luck, and don't trust my advice on alignment, but the grub screw thing did happen to me, wasn't a particularly good day :).
 

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I wonder if I need to unfasten the steel collar the holds back the PSS bellows, and then do shaft alignment before compressing the bellows and fastening the collar again.
Yes, I think you do. You also need to loosen the coupling to the transmission. You said it looked visually aligned, but the tolerance is usually 4 thousandths and you can't see that. The bolts or studs should smoothly slide in the coupling, or the gross height alignment is off. Without any pressure from the PSS bellow, you put a larger feeler gauge between the coupling halves, say something around 0.02. Once lined up, you just finger tighten all the nuts and bolts around the coupling, just until they meet. No torque whatsoever. Now pull out your feeler gauge and test the other four quadrants. None should be more than 0.004 diff from the original spot.

Once you tightened down the bolts, could have easily put some stress into the alignment. It seems nearly impossible to think that all four motor mount adjustments were perfectly reestablished for the new transmission offset, prior to dropping the engine back in.

Good luck with the alignment procedure. I think you have an easy fix here.
 

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It doesn't look like the grooves would have been from a loose PSS, or it would have been leaking everywhere. I'm guessing it's from whatever was installed prior.

Nevertheless, PSS sells a split safety ring that you can install behind the compression ring. I wouldn't go without.

p.s. you should not need to do anything more than twist the compression ring and work the bellows into compression. Something is also wrong there. You can't use grease, but I do think there is a hack with dish soap.
 

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I've only done engine alignments only about 4 times (all on a new pss seal), but here's my 2 cents.

I've never been able to compress a pss to specs with only using my hands. I always have had to use a couple of prybars placed on either side. It never seemed to take any 50 lbs of force, though. That said, the way you did it with a strap would have side loaded it and made it more difficult to compress and may have seated it a little crooked, as well.

I usually do a quick check before I compress the bellows to get things in the ballpark. You need to start with the shaft centered in the log or you can end up going down a rabbit hole by chasing it way out of position side to side. I do the final alignment with the bellows compressed as it holds the coupling tight but does not effect whether it is aligned or not. Then use feeler gauges to determine the gap. Not just the .004" one. Find out what fits and determine it's within the required tolerance (likely .004") side to side. Rotate the shaft and shake the engine between adjustments. Once it's aligned, then tighten the coupling bolts and recheck it once the boat has been in the water a couple of weeks.
 

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I did all 4 engine mounts and had to re align the shaft/coupling. The geometry did not change. I changed one mount at a time and there was hardly any adjustment for alignment. No vibration or leaks. PSS was unaffected. looks like this:

Bicycle Tire Wheel Crankset Bicycle frame
 

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Emmalina
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Looks hellishly over compressed to me I have fitted a few PSS and always compress to spec with one hand ! Generally check the alignment with the old packing in place then if its all good fit the PSS, Last one was an 1-3/4" shaft and compression was 1 inch ! And I might ad the "donut" or "collar" are actually the SS Rotor.
 

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Discussion Starter · #14 ·
I redid the alignment last night, thanks to some prompting and encouragement here. What I had done was DEFINITELY bunk! my engine was still too low and the shaft was not going straight through the cutlass bearing, so it had a lot of resistance when turning. After loosening the PSS collar and bellows I could pull the shaft back a bit and easily tell what what was going on.

Spent 5 hours doing alignment under a tarp in the pouring rain and now it's perfect. Thanks!
 

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Discussion Starter · #15 ·
Looks hellishly over compressed to me I have fitted a few PSS and always compress to spec with one hand ! Generally check the alignment with the old packing in place then if its all good fit the PSS, Last one was an 1-3/4" shaft and compression was 1 inch ! And I might ad the "donut" or "collar" are actually the SS Rotor.
The problem is that my bellows are quite old (10y+) and have lost their ability to come back to full length. So when I added 20mm of compression, they became very compressed. Going forward I think I will do less than 20mm, but the jury's still out.
 

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The problem is that my bellows are quite old (10y+)
PSS says to replace the bellows (and other wear items) every 5 or 6 years, I believe. This is not a part you want to split, while in the water, and it sure sounds like yours could be old and getting brittle. The irregular surface could make it impossible to temporarily repair underway. It's a potential sink the boat failure, if it happens while you're not aboard.

By the way, the service kit is a big percent of the cost of a new unit, because most parts are tossed. Replacing everything with new is often the answer.
 

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One of None
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It's been said once I'll say it again replace the bellows! 🔨🔨🔨😵
 
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