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Prop Shaft replacement


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8 minutes ago, Peugeot 106 said:

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!

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

I would not waste time measuring the engine beds for level, it matters not a jot, its the alignment of the gearbox output coupling with the stern bearing that matters, both radially and axially.

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1 hour ago, Tracy D'arth said:

I would not waste time measuring the engine beds for level, it matters not a jot, its the alignment of the gearbox output coupling with the stern bearing that matters, both radially and axially.

Thanks Tracy I realise that but the footprint of the mounts is around 700 long x 400 wide so the 10mm difference in height seems a lot for such a small distance apart and is leading me to believe that the mounting brackets, and mounts could do with checking. I realise that the beds and thus the baseplate as the rsj beds are welded to it could all be wildly out as could the propellor tube.

if i was clever i'm sure i could work out using maths  if all the 4 distances are in the same plane. Of course the odd mount out is in the most inaccessible corner.

Is it usual to find one corner 10mm higher than all the rest?

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It would be unusual, but not impossible It depends who built it.  Engine beds are heavy stuff, and take a bit of welding, which invites distortion.

 

You can do a quick alignment check with a set or ideally two sets of feeler gauges.  Remove  the flange bolts. Slide the coupling apart.   Bring it together again.  The register in one half should slide easily into the other.  If it does not try and spot where it catches.  Usually the engine has dropped because the mounts have gone soggy.  Adjust the engine mounts and/or the engine position to get a nice sliding fit.

 

 Refig the flange bolts.  ÀSeparate the flanges a bit, about enough to get a 15 thou  feeler gauge in at 2 o'clock.  Nip the flange bolts up just  tight enough to hold the feeler in place. If you only have one set of feelers use a bit of sardine or similar tin lid.

With feelers, measure the clearances between the two halves of the flange at top, bottom, left and right. They should be the same, give or take a thou.  Rotate the shaft 90 degrees and repeat.  Slack the flange bolts.   

 Adjust the engine mounts to correct any errors.  Do left right first as you only need the mounts to slide sideways for that.  A scissor jack is handy for a controlled push.

  Think very carefully what you are doing, with vertical alignment  or you can end up  in a reet mess.  It is a lot easier if you can use the bottom nuts on the mounts.  Shimming up for alignment can difficult.  Again a scissor jack under the gearbox can be helpful.

 

In your case I would want to investigate the engine mounts.  I think the one that is 10 mm different may well be either knackered, or not the same as the rest.

 

N

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4 hours ago, BEngo said:

It would be unusual, but not impossible It depends who built it.  Engine beds are heavy stuff, and take a bit of welding, which invites distortion.

 

You can do a quick alignment check with a set or ideally two sets of feeler gauges.  Remove  the flange bolts. Slide the coupling apart.   Bring it together again.  The register in one half should slide easily into the other.  If it does not try and spot where it catches.  Usually the engine has dropped because the mounts have gone soggy.  Adjust the engine mounts and/or the engine position to get a nice sliding fit.

 

 Refig the flange bolts.  ÀSeparate the flanges a bit, about enough to get a 15 thou  feeler gauge in at 2 o'clock.  Nip the flange bolts up just  tight enough to hold the feeler in place. If you only have one set of feelers use a bit of sardine or similar tin lid.

With feelers, measure the clearances between the two halves of the flange at top, bottom, left and right. They should be the same, give or take a thou.  Rotate the shaft 90 degrees and repeat.  Slack the flange bolts.   

 Adjust the engine mounts to correct any errors.  Do left right first as you only need the mounts to slide sideways for that.  A scissor jack is handy for a controlled push.

  Think very carefully what you are doing, with vertical alignment  or you can end up  in a reet mess.  It is a lot easier if you can use the bottom nuts on the mounts.  Shimming up for alignment can difficult.  Again a scissor jack under the gearbox can be helpful.

 

In your case I would want to investigate the engine mounts.  I think the one that is 10 mm different may well be either knackered, or not the same as the rest.

 

N

Thanks for that it sounds like I am correct in thinking I need to look at the mounts. When I have aligned the engine I have never bolted the flanges together I just pushed the flanges to meet and put feelers in. Why do you bolt them?

I haven't really room for a scissor jack though I have used Spanish windlass and thought I would try an air wedge as my small bottle jack won't work om its side. 

I may well get the engine brackets altered (i have measured up) so that I can use mount nuts top and bottom. I used a mooring pin to lever the engine sideways and up and down when on holiday which was not very straightforward!

 

I'm actually wondering now (I'm not down on the boat) if the front left mount hasn't dropped and I have put it into temporary alignment by raising the front right. If i raised front left 4mm and dropped front right by 4mm where it was before I shimmed it during my holiday they would be a lot closer to being the same height.

Thank you for your interest

 

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On 21/11/2022 at 15:05, Nightwatch said:

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

 

On 21/11/2022 at 21:37, Nightwatch said:

Thank you. I have just checked the gland. Slight drip. A quarter turn on each nut stopped it.

 

This is a fundamental mistake, but understandable.

 

It is desirable, and indeed, essential for the gland to drip water.  (Based on years of repacking uncountable numbers of pumps and valves for a living)

If the gland is tightened to the point where water (or grease) cannot penetrate through the interface between shaft & packing then cooling and lubrication of the gland/seal is being prevented. The result will be uncontrolled friction, the heat from which will burn the packing and induce a hard glaze to the material that cannot be recovered. The elasticity of the packing, where it matters most, is lost, and eventually excessive water will leak through the gland which will then encourage the operator / boat owner to tighten the gland even more. This will lead to more friction between the shaft and packing to the point where both components wear excessively with catastrophic consequences.  When the packing goes hard it will then become an abrasive and wear away metal from the shaft, the steel particles will lodge in the packing (that is now becoming an ever increasingly abrasive material) escalating damage to the shaft.  Pictures from other contributor's to this thread illustrate what can happen. 

Water resistant grease is the lubricant to use and the drips of water, if allowed to pass through the gland, will both cool the gland and carry away any generated heat.

 

The amount of water that drips when under way – or rate of drip – should be approx. one or two drips per minute or thereabouts depending on the condition of the components. If the stuffing box gets hot increase the drip rate.

If the components are in good condition then the rate of drip can be controlled with judicial adjustment of the gland follower nuts. Light tightening of the gland nuts is the key word so that you don’t overtighten the packing and the use of lock nuts to prevent backing off due to vibration is recommended.

 

Management of the leakage is what is required.  Place a suitable container underneath the stuffing box gland to catch the drips and install an automatic bilge pump into that container to discharge the collected water overboard. 

If you do not wish the gland to drip water overnight or whenever the boat is stationary for long periods then pump some water resistant grease (such as Ramanol White Lithium Grease - other brands are available :)) into the gland/bearing with a grease gun which will displace the water and effect a seal in the voids.

 

If, as the OP states, water is pouring out, then a new shaft may be the only remedy together with a new approach to gland maintenance.

It is unlikely that the stuffing box will need to be replaced, it does not come into contact with any moving parts.

 

Just before lockdown I used the dry-dock at Ellesmere to black the bottom of my boat and took the opportunity to remove the prop shaft for inspection.  It showed no sign of wear and was as good as the day I installed it more than twenty years ago. I repacked the gland with new packing as a matter of course even though the old packing was still supple.  The moral here is get it right and you will have no problems in the future.

 

On 21/11/2022 at 15:56, Nightwatch said:

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

But have they been fitted correctly?  If three turns of packing are used these should be inserted with the ends of each turn 120˚ apart with the final turn having the ends at the 6 o’clock position.  e.g. 10 o'clock, 2 o'clock & 6 o'clock.  If the turns of packing are not cut to the correct length (i.e. short at one end!) and the ends are all in line then……!!!

21 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 agree with BEngo but if the hole is not perpendicular you could use a Telescopic bore gauge tool such as these for hard to get to small internal measurements. https://measuringtoolscentre.com/product/telescopic-gauge/ 

Several measurements between the Stuffing box wall and the shaft at different depths should give you an indication of wear.

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Interesting idea to use a telescopic gauge if I could get my hands on one. My hole isn't perpendicular but is there any reason why it won't work on a slant? I can do simple trig?

 

Re the drips. About 1/2 cup in 5 hours for 2 drips per minute if this is to be believed!

 
water.usgs.gov
 

There is no scientific definition of the volume of a faucet drip, but after measuring a number of kitchen and bathroom sink faucets, for our calculations below (numbers are rounded), we are going to use 1/4 milliliter (ml) as the volume of a faucet drip. By these drip estimates: One gallon = 15,140 drips. One liter = 4,000 drips.

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3 minutes ago, Peugeot 106 said:

Interesting idea to use a telescopic gauge if I could get my hands on one. My hole isn't perpendicular but is there any reason why it won't work on a slant? I can do simple trig?

 

Re the drips. About 1/2 cup in 5 hours for 2 drips per minute if this is to be believed!

No reason at all and no need for trig. If you see any movement of the readout you have wear. Question is will the DTI plunger reach the shaft? you could use an extension I suppose if you have one. 

 

Never worked out the capacity of the accumulated drips! - I will take your word for it!   My bilge pump discharges it!

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21 minutes ago, Rincewind said:

No reason at all and no need for trig. If you see any movement of the readout you have wear. Question is will the DTI plunger reach the shaft? you could use an extension I suppose if you have one. 

 

Never worked out the capacity of the accumulated drips! - I will take your word for it!   My bilge pump discharges it!

Thanks Rincewind I'm thinking about using a digital tyre tread gauge . max depth 25mm. stated accuracy 0.01mm £6 amazon. you can push the needle down from the top of the gauge so should cut through the grease. Propose to just use it axially ie push shaft in and out and not rotate to avoid more errors. 

could rig it through 1/8" bsp plug with hole drilled in as reference point.

I should have thought all this through when I blacked it a month ago!

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When the yard changed Katy Ĺouise engine mounts, they supported the engine with a strap from a 4x2 over the hatch opening and changed the mounts one at a time.  You might be able to use a similar arrangement to remove yours for inspection.

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Thank you. My engine is underneath the deck so that the only part accessible to a lift from above is the gearbox which is where I use a Spanish windlass on a timber across the hatch mounting for the rear. Its only 2 cylinder and weighs around 100Kg so air wedges should lift it at the front. If I take it out, I slide the engine backwards underneath the hatch opening and use a front loader off a tractor.

Thank you for your comments 

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