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Old 12-05-2006, 16:23   #1
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Help! Prop shaft woes

I could use some real-time help. I've just installed a new transmission and, after six hours, progress has stalled. The transmission went in OK (well, after about three hours) and it appears the dimensions are indeed the same as the old one. Now the rub.

To get the old one out, I had to push the prop shaft out about three inches using a long wrench to gently nudge it. Now it is time to pull the shaft back in, and after three MORE hours I am stumped. I've loosened the stuffing box and the shaft rotates with some effort, i.e. I can rotate it by hand with some effort. The shaft is about six feet long.

First thing tomorrow I'll don SCUBA gear and see if I can push it in from below the water. Should this be easier than I'm finding? Are there any tricks? I'm so close, yet so far, and have run out of energy so have taken a happy hour break.

Dave
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Old 12-05-2006, 17:46   #2
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Some points to consider...

You may care to consider first did the installation cause the problem or was it there to start with.
Then think about what might make a prop shaft hard to move.
Possible pre-existing conditions (other forum members could add more):-
Shaft bent
Shaft corroded
Shaft worn
Rope or similar wound round shaft
Incorrect size shaft for bearings or vice versa
Marine growth
Boat bent
Possible conditions caused by the installation
Any/all of the above made worse by moving the shaft.
First check as far as you can that the shaft is straight
I would try rotating the shaft while pulling it towards the engine. Be careful that you dont jam jour hand/fingers or skin your knuckles.
Depending on the cost of removing the boat from the water this is certainly a job that would go better with the boat out of the water.
My guess would be that the installation was originally done and/or modified with the boat out of the water and that the boat has distorted slightly when put in the water so that the shaft is binding.
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Old 12-05-2006, 18:56   #3
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Haul Out! There are a number of things that can cause the shaft to bind, from packing jamming into the shaft log when you pushed the shaft out, to a damaged shaft tube, to a bad cutlass bearing. Bottom line is, you need to solve this before you start the engine. If the shaft is binding, you will destroy your new transmission, and possibly more. The cutlass bearing is unlikely to be the culprit, but would be visible when you dive on it. a bent shaft would have caused vibration and could have caused the old trans to fail. a failed shaft tube could have jamed material between the shaft and the hull. if it is the simplest possibility, a piece of the packing jamming between the shaft and the tube, you might get away without hauling out, but it is rarely that simple. Any other repair will be more trouble than it is worth. If you do not need to haul for any other reason, you might check if your yard will hold the boat in the slings for a few hours while you do the repair. This could save you some money.
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Old 12-05-2006, 21:46   #4
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Are you sure it only backed up 3 inches could it be touching the rudder
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Old 12-05-2006, 22:29   #5
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It's those simple solutions that are always the best. Computer won't work. Is it plugged in Now why didn't I think of that?
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Old 13-05-2006, 04:46   #6
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Dave:

Before you go to the expense of hauling (or the delay, given where you are...) you might first get the shaft back in an inch or two and see if the shaft is still so hard to turn. With the cutlass bearing loosened up, you should not be finding the shaft too hard to turn.

Given the small tidal range there, can you put her in a spot where perhaps she can lean just a bit on a piling with the keel on sand for the last part of the tidal cycle? That will allow you plant your feet and work the shaft from the outside, and perhaps also give you more of a 'feel' (physically) for how the shaft turns as you bring it forward.

If you have a lot of friction and resistance to turning even after the shaft is brought forward to mate with the xmission coupling, then I'd be concerned and would probably pull the shaft...as something is obviously not right. Please tell us - what led to the xmission failure, do you think?

Jack
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Old 13-05-2006, 05:55   #7
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Transmission failure

Jack, the transmission was 22 years old and I think just gave up the ghost. It had probably never been serviced or adjusted. I don't think there was an issue with a misaligned shaft or bent shaft. The first thing I'll try is to remove all the packing material and see if that loosens things up. If that doesn't get it, the next step is to push from underwater.

soulsearcher, There are several feet before it would hit the rudder, so that isn't the issue. It would be an issue for some full keel boats, though.

Kai Nui, thanks for the list of possible issues. I have hope that removal of the packing material will make it more freely rotate. Of course, as my son says, 'hope means nothing in the boating world.' Hauling the boat will be my last resort if I can't fix this by Monday. Moving the boat over to the yard without an engine is my biggest issue. Getting help from a small powerboat puts me in the hands of someone whose experience I don't trust.

Dave
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Old 13-05-2006, 09:12   #8
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All done. Backing off the stuffing box nut completely and using a Spanish windlass (i.e. twisted rope) made the shaft relatively easy to move forward to mate with the transmission.

Dave
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Old 13-05-2006, 09:37   #9
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So the sky wasn't falling, after all…
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Old 13-05-2006, 13:25   #10
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Oh, the sky is falling all right...
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Old 13-05-2006, 16:54   #11
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Dave-
Two thoughts. If you are going to beat on the prop shaft from the outside, use a "dead hammer" aka "shot hammer". It is much easier to deliver impact with this in the water. The typical one you find in larger hardware stores looks almost like a plastic toy, there is about a pound of lead shot in the big plastic head so that when you smack something, the hammer does not bounce back--the impact is all delivered and passed on. Masons, metal workers and auto body shops also use them.

The second trick isn't going to be as effective with the boat being in the water...but you can try packing the shaft & shaft log (inside the boat) with a slurry of dry ice and alcohol. Let it cold soak, this expands the ring of the shaft log and contracts the shaft, so you may get a little more clearance. And with any luck, if there's any icing it won't make the shaft stick once you give it that first whack.<G>
It could just be that the rougher parts of the shaft are now in the shaft log and the cutless bearing, so there's more friction making them bind.
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Old 13-05-2006, 21:43   #12
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Cantilevered force

This problem is common with sailboats that have only the cutlass bearing mounted in the hull with no external strut (I'm not implying that this is necessarily bad, just normal). With a little marine growth the weight of the prop and shaft without the transmission coupling to act as an alignment force against the cutlass bearing fulcrum the friction is very high.

When the transmission coupling is properly aligned (assuming that the engine is also properly aligned) there is actually a force downward on the shaft in side the boat counterbalancing the weight of the shaft and prop extending outward from the cutlass bearing fulcrum outside the boat so that the shaft is exactly in line with the bearing.
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Old 14-05-2006, 03:42   #13
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Propeller Overhang:
Rick’s “Cantilevered force“ is why ABYC Standard "P-6.5.5.4" specifies that:
”...The distance between the foreward end of the propeller hub and the aft end of the last strut bearing shall be limited to one shaft diameter ...”

Section P-6 , “Propeller Shafting Systems” contains a wealth of pertinent information on shafting, struts, bearings, seals, couplings et al.
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Old 04-06-2006, 07:00   #14
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When you backed off the packing gland nut I hope you removed all the old packing and replaced it with new?
Just wondering.
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Old 17-11-2006, 16:12   #15
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Thanks Gord May,

I'm reinstalling prop shaft and engine and that is very helpful.

Kind Regards,

JohnL

Propeller Overhang:
Rick’s “Cantilevered force“ is why ABYC Standard "P-6.5.5.4" specifies that:
”...The distance between the foreward end of the propeller hub and the aft end of the last strut bearing shall be limited to one shaft diameter ...”

Section P-6 , “Propeller Shafting Systems” contains a wealth of pertinent information on shafting, struts, bearings, seals, couplings et al.
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