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Old 05-13-2014, 08:49 AM   #1
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Stuffing box "wobbles"

Yep, like the title implies I have a problem!

So I launched after being on the hard last weekend and doing some repairs.
1. Removed and replaced propeller.
2. Removed and cleaned, then replaced prop shaft.
3. Removed, cleaned, installed new stuffing box hose, installed new PTFE packing, and reinstalled stuffing box assembly.
4. Aligned prop shaft.

When driving back at 1000RPMS I noticed the stuffing box was moving. It did not do this before. There was also the expected and associated vibration.

When I put it in neutral but still had way on I looked and the shaft was spinning but there was NO movement in the stuffing box.

My thoughts:
I screwed up the alignment to the motor.

The prop is too big and causing the shaft to wobble.


It was difficult to figure out how to align everything. I read several posts and spoke with friends that have done this before. The problem was is the shaft is about 15' or longer.

With it installed through the cutlass bearing and then into the coupler that was seated on the tail shaft the "droop" was such that it was laying in the bottom of the stern tube where it entered the hull. Note that I had the stuffing box pulled forward at that time so it was not helping support the shaft.

I had read that the stuffing box does help support the shaft so I installed the stuffing box but still had enough droop (the shaft goes another 7' to the coupler) that the shaft was 1.5" ?? down from the tail shaft of the tranny.

I put the coupler "ring" ( the piece you can slide into the tail shaft to hold it while putting in bolts, etc.) and lightly snugged down the bolts. I was able to align the shaft to within .003 and thought that would be fine. Apparently NOT fine.

I may have to hire this in and watch how this is done. I am going to run this by everyone this morning as I am going through Bob Smiths class here at Trawlerfest. I really appreciate any constructive ideas. I have already beat myself up and said what an idiot I am so I am good on that front!

As a side not, I just motored at about 800RPMS keeping the wobble to a very minimum and made sure plenty of "drips" we're coming out so I didn't seize the stuffing box. It was a beautiful day and enjoyable drive to the slip other than that. The wife did a great job on the bottom paint! At least one of us is competent....

Jeff
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Old 05-13-2014, 09:09 AM   #2
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I am far from an expert, but since I am considering doing similar work, I have been speaking to a few good marine mechanics about it.

A couple points I have learned:

On a long shaft there is a huge amount of sag. The shaft must be fully supported to align, as the shaft straighten only when it is spinning.

Many boats cannot be accurately aligned on the hard, as the hull shape changes a surprising amount when out of the water. They alignment must be rechecked when back in the water.
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Old 05-13-2014, 09:49 AM   #3
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Quote:
Originally Posted by AusCan View Post
I am far from an expert, but since I am considering doing similar work, I have been speaking to a few good marine mechanics about it.


Many boats cannot be accurately aligned on the hard, as the hull shape changes a surprising amount when out of the water. The alignment must be rechecked when in the water.
bingo.

HOLLYWOOD
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Old 05-13-2014, 10:09 AM   #4
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Interesting Jeff. We went thru maybe something similar this weekend with my friends. GB. He had new cutlass bearings installed and new PSS dripless seals. We were in Garrison Bay and started on our way back and the starboard engine made loud noises and vibrations. We put it in neutral and the vibration stopped. Finally narrowed it down to the cutlass bearing as the vibration source or possible the connection to the transmission. It was difficult to do at the time. We went to Roche Harbor and proceeded to lock the shaft with a pipe wrench and vice grips so we could use the port engine to make it home till he could get it checked out this week. Still do not know the problem yet, he is getting it checked out as I write this.

I'll talk with you at the class this morning.

Keith
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Old 05-13-2014, 12:13 PM   #5
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If I read the OP correctly, 7' of unsupported shaft seems excessive with 1/1/2" diameter.
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Old 05-13-2014, 12:18 PM   #6
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Attachment didn't go with previous post. Sorry still can't get attachment to load
I was trying to attach ABYC specs for shaft support.
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Old 05-13-2014, 12:52 PM   #7
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It didn't vibrate before the work so it was obviously something that was done, but with that length of unsupported shaft, a small mis-alignment would really produce a wobble.

With little stubby shaft like mine you can get away with much more.
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Old 05-13-2014, 01:57 PM   #8
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I always mark the couplings so they all clock the same way after reassembly.

The thing that bothers me here is that at 1000rpm it vibrates and while turning w a bit of way it dosn't. It should wobble while turning slow .. I would think.

boatpoker if all is aligned and true I would think 7' w 1 1/2" dia shaft should be fine. I had 6' w 1" shaft on a small Albin but it was never w/o some wobble.

Jeff let me get this straight. You had the stuffing box fwd (out of the picture) and the shaft attached to the transmission output flange so the shaft was unsupported between the stern bearing and the transmission flange. That was on the hard and the shaft rested on the stern tube at the stuffing box location.

I would have stopped right there and raised the engine. That length of shaft droops droops x amount (1/4") or so. If you support the shaft w the stuffing box the coupling and transmission flange will be out of ..... I'm running out of time but if you aligned the shaft on the hard w the shaft resting on the bottom of the stern tube you won't be even close to being aligned.


If you have X amount of shaft between the stuffing box and the transmission attach a spring scale to the fwd end of the shaft showing 1/2 the weight of the shaft plus the weight of the coupling. Then you can align the engine to the shaft. This is assuming the shaft has been aligned. And of course it will need to be realigned when in the water.
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Old 05-13-2014, 05:17 PM   #9
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Time for DIY and TF advice to take a break unless eyes on and experienced. If it were me I'd have North Harbor Diesel do an in-the-water alignment and if that doesn't work haul it out and look for the gremlins. While you're at it have them re-torque all the coupling bolts and do the "anti backoff" wire ties properly.
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Old 05-13-2014, 07:27 PM   #10
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And please be very careful locking a shaft with a pipe wrench. A marked shaft is a damaged shaft and any marks you put in it will have to be polished out one day.
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Old 05-13-2014, 07:59 PM   #11
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Recheck your alignment now that you are back in the water.
Normally a 15' shaft should have a center bearing. It depends on the diameter & material which I dont think you mentioned. How much shaft "showing between cutlass and prop hub. No other bearing between the cutlass and the transmission? Shaft diameter? Stainless?
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Old 05-13-2014, 08:44 PM   #12
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I know that it is too late now but with the work you had completed I do not see any reason to mess with the alignment. Boat "shape" or movement of the engine is the only thing that should screw up the alignment. The replaced cutlass should be in the same plane as it was previously and the same with the stuffing box. If you made any marks and can get the engine back to where it was originally you would probably have at least a rough alignment. I replaced both my shafts last year with new shafts, replaced the cutlass bearings, re-packed the stuffing boxes and new couplers. I did not touch the alignment as none of this work should call for it. I have 1 3/8 shafts and they are about 12 feet long and they ran smooth both before and after the work.
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Old 05-13-2014, 10:49 PM   #13
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I was hopping to get some opinions on this method of alignment.

"If you have X amount of shaft between the stuffing box and the transmission attach a spring scale to the fwd end of the shaft showing 1/2 the weight of the shaft plus the weight of the coupling. Then you can align the engine to the shaft. This is assuming the shaft has been aligned. And of course it will need to be realigned when in the water."

The idea is to get the shaft in the position it would be in when the boat is running and the shaft is aligned to the stern bearing and the end of the stuffing box. Since the stuffing box and the stern bearing actually determine exactly where the shaft should be one just needs to put the engine exactly where it should be ...... As determined by the prop shaft.

Tell me what you think of my idea good or bad and I'll promise not to get sensitive about what you say .. about my procedure.
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Old 05-13-2014, 11:05 PM   #14
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Greetings,
Mr. M. Why 1/2 the weight of the shaft? The location of the fulcrum (cutlass bearing) will determine what percentage of the shaft should be weighed.
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Old 05-13-2014, 11:47 PM   #15
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This won't help if the shaft is really misaligned but how did you treat the coupling faces. They must be flat and clean, both the gear side and the shaft side. Any dirt, scratches, rust, can force the coupling out of alignement.
I clean mine with a flat stone. Not trying to remove metal but take off any dings or dirt.
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Old 05-14-2014, 07:35 AM   #16
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If your engine is bearing down unevenly on its mounts it could cause it to wobble. Picture the engine hard against a front outboard corner and aft inboard corner mounts and soft against the other two or even one mount not jacked up tightly. It will allow the engine to seesaw.

I recently surveyed a Carver 455 MY with diesels that had a wobble on the port side during the trial run. Later in the day as I was working through the boat I was checking behind a panel in the aft stateroom to look in the engine room. Found the bottom adjusting nut on the aft outboard engine mount had worked down about a 1/2" below the transmission mounting flange. Yard realigned the engine and cured problem. You could experience the same thing without the mounting nuts actually being loose. Uneven weight on the rubber mounts could allow enough play to cause the same thing.
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Old 05-14-2014, 07:53 AM   #17
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There are split bearings made to be installed with OUT removing the shaft.

Installing an intermediate bearing would be a help.
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Old 05-14-2014, 08:15 AM   #18
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Does it have a drive-saver? Ours slipped when we were on the hard last time.

Other reading you might want to try:

A New Prop Shaft Photo Gallery by Compass Marine How To at pbase.com

Replacing A Cutlass Bearing (Sleeve Bearing) Photo Gallery by Compass Marine How To at pbase.com

Replacing Motor Mounts & The Obstacles Photo Gallery by Compass Marine How To at pbase.com
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Old 05-14-2014, 08:43 AM   #19
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Thanks for all of the replies. I was going to try and answer many specifically but I'm on my ipad on my boat and can't go and look at the entire thread.

The shaft was working perfectly fine and I shot temp readings on stuffing box prior to doing any work. Absolutely no movement.

I cleaned the mating surfaces of the coupler very well. I didn't even look at the tail shaft mating surface. I was told to make sure there was no dirt and I forgot. I will pull it apart and look at it.

Though the shaft is long it was working fine before and has for the last 37 years so I will go with it is not a design issue.

Yep, I should have not touched anything and only made adjustments in the water if needed.

A few people have mentioned the spring scale thing. I guess my problem is that I don't have the setup, have no idea how much the shaft weighs, and even though I usually can read something and then do it, would need to be shown how to do this. I would assume it would only be the weight of the shaft where it exits the stuffing box to the tail shaft... Last supported pieces type of thing.

Yep, if I can't figure it out it will be North Harbor time. I do not mind doing that. Just like to do and learn things myself. In many cases you can learn what you need to do as there may not be a huge amount of "skill" needed. LET ME EXPLAIN that statement. Bolting a motor together is mechanical, you twist bolts, use a torque wrench, etc. no real skill per say. If you are sewing canvas, well, that really requires some skill that you would learn over several years. Putting a feeler gauge in and checking alignment doesn't require much skill, sure that would help how long it takes but usually not the final result if you do it right. Knowing HOW to get everything setup to do that apparently requires skill! Ha ha. I may have to hire that in! In no way am I taking away from the trades that work on anything, I perform a trade and after 20+ years am pretty good at it. I also know someone can drag the same cable as me and hook a phone to it and it will work just fine with little or no skill.

Yep on the motor bearing down unevenly!!! Possibly Bingo. Everyone will now see I have no pride! Whomever posted that along with the "alignment in the water" made me think about what I had done. I knew the alignment had to be checked in the water SO I left the flipping top lock nuts loose on the rear motor mounts! Idiot! I had so many things going I completely forgot.

I don't know for sure if that is the problem. I will check it tonight. I do know it was spinning fine in neutral with no load but was wobbling with it engaged. Makes pretty darn good sense.

I will check alignment again, tighten bolts, and let everyone know. Again, thanks for all of the great input as I really appreciate it.

Jeff
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Old 05-14-2014, 10:08 AM   #20
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RTF, Jeff and others,
1/2 the weight of the shaft because 1/2 the weight of the shaft is resting on the stuffing box and when installed 1/2 the weight of the shaft is resting on the transmission output flange. And of course there's the weight of the coulping.

Shaft weight per foot is easy to look up and spring scales are cheap and also easy to find. So if there's 4' between the stuffing box and the TX flange you use the weight of 2' of shaft plus the coupling. Hang the spring scale above the coupling showing the weight of 2' of shaft + the weight of the coupling and you've located the shaft as it would be installed in the boat resting on the transmission output flange, the stuffing box and the stern bearing. Of course there are other forces involved like the droop of the shaft between the stuffing box and the TX but somewhere one needs to draw the line and say all else is fly stuff.

Anyway I thought it was/is a good and easy way to align the shaft and engine very very close to perfect.

One could hang the shaft end (w the coupling) from the scale and block up the coupling underneath it or measure and otherwise fix the shaft end w the coupling on it. Positioning the engine then would be more or less easy to do. All the up and down adjustments are much easier than the sideways adjustments but it's then a straight fwd operation. It can take some time though and require some extra words of encouragement.
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