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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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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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