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Prop Shaft replacement


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Hello all.

I fear the boat needs a new prop shaft and stern gland.

 

We have nearly always had a leaky stern gland. We have repacked it on occasions, but recently, as we were having other work done, decided to get a professional to repack it. Since, every time we move the boat (turn the prop) I have to retighten the flange nuts. Over the past three weeks or so this has happened every time. At times it doesn’t drip, it runs. But to tighten maybe three flats of the nuts stops water ingress. If we remained moored the ingress does not start again. Until we move. Then same again.

 

I realise the packing needs to settle in place, is it normal to take this long? Should I go for broke and tighten the flange more than I think or is that pointless?

 

Now the question. Well possible the last one. What does the panel think. A new shaft and gland? More packing?

What’s the cost of a job like this be done? I know it’s an out of water jobby. How long is a piece of string I guess?

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If the alignment is correct and the shaft is not scored where the gland packing runs all it needs is repacking properly. All the old stuff out and 3 rings of the right size packing carefully fitted, by someone who knows how to do it.

Sounds like you had a poor installer last time.

  • Happy 1
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Before deciding on a new set of stern gear you need to find out if the existing is worn.  The best way is out of the water, but  you can do ità in the water if you have a weed hatch. 

Detach the shaft from the gearbox.  Loosen the stuffing box.   Using a suitable bar down the weed hatch lever the shaft firmly left to right and up and own.  Repeat on the inside.  You should not be able to feel any movement where the shaft enters the stern tube, either inside or out.  If there is no movement then the bearing is OK , and the shaft in the bearing is OK,  but there may still be wear where the packing runs on the shaft.   You can sometimes overcome this by fitting a spacer between gearbox and shaft, if there is room for the prop to go back.  The  packing then runs on a new bit of shaft.  The overhang between stern post and the front of the prop boss should not be more than 2 shaft diameters though.

 

Refit shaft to gearbox and repack and re-tighten the stuffing box.  Nip it up a bit at a time, evenly on both nuts, until it is  just tight enough to notice when you  try turn the shaft by hand.  Check engine alignment.

 

N

 

  • Greenie 2
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24 minutes ago, Tracy D'arth said:

If the alignment is correct and the shaft is not scored where the gland packing runs all it needs is repacking properly. All the old stuff out and 3 rings of the right size packing carefully fitted, by someone who knows how to do it.

Sounds like you had a poor installer last time.

The chap who repacked the gland knew what he was doing. He removed all the old stuff and repacked with three ‘rings’.

 

Theres no play in the shaft fore and aft.

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Bengo is correct. The shaft on our boat is one that was removed as scrap from another boat, the worn part is now somewhere deep in the stern tube. My guess is that the problem is caused by misalignment. This can be tricky. Ideally there should be a plummer block - a bearing fixed a short distance in front of the stuffing box / gland. This ensures that the shaft always runs in the same concentricity (not sure if that's a real word) and doesn't run in ever changing ovals or tries to wear one side of the gland. That packing cannot accomodate more than the slightest side to side or up and down movement, If you tighten it down too much it will wear a groove in the shaft. If the engine is mounted on flexi mounts it will move around a bit so there must also be some sort of flexi coupling between the plummer block and the gearbox, there are many types but Aquadrive or Python are possibly the best (but expensive) and make alignment much easier. There are others but something must absorb the engine movement. Engine alignment is a black art. Long chapters have been written on engine installation and alignment and I have spent ages trying to get it right on various engines and more than once I have made it worse than it was before before I started.  

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9 minutes ago, ditchcrawler said:

Here is a photo of a worn prop shaft

 image.png.205d61d8c46fa1f96b969a46cd42d166.png

Is it ok to remove a worn shaft and simply reinsert the other way around so the groove is elsewhere?

 

 

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You need to consider the prop taper. On the hire fleet I insisted on a taper coupling that was the same as the prop taper so easy to reverse. Nowadays, the parallel clamp on couplings seem to have done away with that.

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4 hours ago, Nightwatch said:

The chap who repacked the gland knew what he was doing. He removed all the old stuff and repacked with three ‘rings’.

 

Theres no play in the shaft fore and aft.

Fore and aft play does not matter to the stern gear.   My prop shaft goes backwards and forwards in normal operation and the stuffing does not leak.    Is there up/down and/or port/starboard play?  

 

B

  • Greenie 1
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Nightwatch, A carbon copy of my experience two years ago. I replaced the shaft, tube and gland in a day (diy) on a slip. I was lent a gismo to unscrew the tube. As I recall the shaft  tube and gland cost around £200. Cause was a broken engine mounting bracket. The 1.5" shaft was down to under 1.25" Somewhere on here I posted a photo. 

  • Greenie 1
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We just got a whole new tube shaft and coupling on Mintball as the previous one had worn out  - it had lasted about 30 years.

 

  • Stern Tube Boss 1 1/2" £19.99
  • Centre Tube 1.5 Long £134.50
  • Stern Stuffing Box 11/2" £208.99
  • Prop shaft £185.00
  • Split coupling £104.99
Plus dry docking and labour.
  • Greenie 1
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2 minutes ago, StephenA said:

We just got a whole new tube shaft and coupling on Mintball as the previous one had worn out  - it had lasted about 30 years.

 

  • Stern Tube Boss 1 1/2" £19.99
  • Centre Tube 1.5 Long £134.50
  • Stern Stuffing Box 11/2" £208.99
  • Prop shaft £185.00
  • Split coupling £104.99
Plus dry docking and labour.

Thank you. I have just checked the gland. Slight drip. A quarter turn on each nut stopped it. We haven’t moved today though. I’m hopeful that the last move for a while in the morning will see if I’ve wound in the nuts enough. We go into a dreaded marina tomorrow. Recent security issues has persuaded us to seek refuge. 

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I have to say poor engine alignment seems probable, exacerbated by the missing pillow block bearing to hold the shaft straight on many clone craft nowadays.

 

 Fix the engine alignment (probably a knackered or busted engine mount) then see if you can move the prop shaft in or out a bit to line up an un-worn section with the gland, and Bob's your brother's father, or something like that..... :D

 

 

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12 hours ago, Slim said:

Nightwatch, A carbon copy of my experience two years ago. I replaced the shaft, tube and gland in a day (diy) on a slip. I was lent a gismo to unscrew the tube. As I recall the shaft  tube and gland cost around £200. Cause was a broken engine mounting bracket. The 1.5" shaft was down to under 1.25" Somewhere on here I posted a photo. 

Correction. Initially I bought a new gland but when I stripped everything down the gland was unworn. From memory the shaft was just under £100, the tube £70 ish. packing £10 ish . Receipts are on the boat so can't check. 

  • Greenie 1
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This is the exact problem we're having, and already resigned myself to an expensive additional cost at next blacking. Ours will stop leaking with use of greaser, but will always leak after running, regardless of stern gland adjustment. 

 

Haven't got round to examining ours yet so studying replies carefully. What I can say is ours has definitely been repacked correctly as done it myself. Engine alignment should be fine as well as it uses aqua drive, but there is some slight side to side play at the prop end, so suspect the whole lot will need replacement😥

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My stern gland too leaked a bit more than normal last summer. I checked engine alignment with feeler gauges and had to pack one front  foot 4mm. This seemed to fix it though it has started to leak again when running. I am going to check the engine mounts as the one front foot is 10mm higher than the other 3 which seems a bit odd though this could be caused by the beds not being parallel.

IMG_3509.JPG.7cca6436c49c7ffe67591f0a96c33839.JPG 

When I bought the boat 5 years ago I replaced the shaft as the old one was badly worn as above. I repacked the stuffing box on the water and am pretty sure I did it correctly.

IMG_8512.JPG.97d0a44ddd93844a2ee60141041379e0.JPG

When I disconnect the coupling I would like to disconnect take the pusher (it is the type with two studs and nuts) off the stuffing box, remove the packing and then inspect the new shaft to see if it is at all worn to rule that out.  This will mean somehow inspecting the shaft while it is inside the stuffing box as I can only slide the shaft forward approx 20mm. Does anyone know of a clever way of doing this? the gap between the shaft and stuffing box is obviously the thickness of the packing.

Correction I replaced the packing not the stuffing box on the water!

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Having posted I may have come up with an idea. If I drop a dial indicator in the grease nipple hole and move the shaft in and out and around will that give me an indication of how worn the shaft is or is that a totally daft idea?

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5 hours ago, Peugeot 106 said:

Having posted I may have come up with an idea. If I drop a dial indicator in the grease nipple hole and move the shaft in and out and around will that give me an indication of how worn the shaft is or is that a totally daft idea?

Why worry? If its in line, well packed and doesn't leak, accept it is fine and enjoy boating instead. It takes years to get wear to that level on a shaft in normal use.

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11 hours ago, Peugeot 106 said:

Having posted I may have come up with an idea. If I drop a dial indicator in the grease nipple hole and move the shaft in and out and around will that give me an indication of how worn the shaft is or is that a totally daft idea?

I think it will work, but only if the grease hole is at right angles to the shaft.  Many are not.  You will want to protect the DI plunger by withdrawing it before moving the shaft.

 

I wish you luck in getting the grease out of the hole so the plunger will go in and be free moving.

 

N

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Just an example and I am not an expert but Bee has a conventional stuffing box / stern gland with a grease nipple on it. It gets a stroke or two from a grease gun daily when we move so it probably gets a bit more than with the screw down type of greaser. I only have to just nip the nuts up at the end of every 'season' and then next spring I slacken them off a bit, apart from that they are never touched and the boat has done many, many miles. I am convinced that the reason for this is because of the pillow block that supports the shaft just in front of the gland, the shaft can only go backwards and forwards very slightly if it has to and cannot go sideways or up and down at all. Ever. Therefore the wear on the packing or even the metal bearing is non existent. I have never repacked it either. Its all about that pillow block that was only a few quid on E Bay and a bit of angle iron that it sits on. 

  • Happy 1
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12 hours ago, Peugeot 106 said:

Having posted I may have come up with an idea. If I drop a dial indicator in the grease nipple hole and move the shaft in and out and around will that give me an indication of how worn the shaft is or is that a totally daft idea?

I once tried that . I couldn't get meaningful readings. Tried removing the pusher and looking with an endoscope, again nothing. Over a couple of years people pushed, pulled and wiggled all the components and all said "no significant wear". In the end I decided to pull the shaft and inspect it. It was well worn. Even at that stage the broken mounting bracket was not evident. That only surfaced when I was re-aligning the engine.

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44 minutes ago, Slim said:

I once tried that . I couldn't get meaningful readings. Tried removing the pusher and looking with an endoscope, again nothing. Over a couple of years people pushed, pulled and wiggled all the components and all said "no significant wear". In the end I decided to pull the shaft and inspect it. It was well worn. Even at that stage the broken mounting bracket was not evident. That only surfaced when I was re-aligning the engine.

Thanks for that. I just thought there may be a quick easy way to check it while I had the engine coupling undone to check alignment. It sounds like the only realistic way is to remove the shaft so I'm not going there for the moment.

 

I measured the distance from the bottom of the engine brackets to the engine beds and the gaps were

Front Left 50.2

Front Right 61.8

Rear Left 51.6

Rear Right 50.5

This is after I shimmed up the Front Right 4mm to realign the engine when on holiday. 

The engine sits on top of the mounts - there is no room for the bottom adjusting nuts and the mounts are shimmed between the mount and bed. It does seem odd that the one mount is 10mm different. Maybe this is usual I don't know?  I can't check the bed flatness without removing the engine.

So my plan is to take the weight of the engine using an air wedge and then unbolt the engine support brackets and engine mounts for inspection making sure they are not damaged. They are fabricated from 12mm thick steel bar so I may get them altered so that I can fit the bottom adjusting nuts which could make life easier.

Due to the tight configuration of my engine bay its a bit of a performance undoing everything and the engine is pretty tight against the front bulkhead though I wish I had fitted it 10mm further forward!

8 hours ago, Tracy D'arth said:

Why worry? If its in line, well packed and doesn't leak, accept it is fine and enjoy boating instead. It takes years to get wear to that level on a shaft in normal use.

Hi Tracy. Why Worry? an interesting question indeed. I've seen boaters with the engine firing on half its cylinders belching smoke and the engine hole half full of water, diesel. engine oil and grease and the odd dead cat not giving a toss. Others worried that a teaspoonful of water in there is a portend of imminent doom and disaster. I like to think I'm Mr Average but I'm sure I'm not!  Your advice is often useful and I think I need to bottom the engine alignment and mounting first as you originally advised when the gland first started leaking more than usual during the summer. 

As usual a little knowledge in my case can be dangerous and I do like to fiddle.............

Thank you as ever

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