Excessive Engine Vibration at Idle Causing Stuffing Box Leak

[Railbob]

I have An MD 2020 D fitted in my boat. I just changed the seal on the water pump and managed to stop that leak but I still continued to have water ingress, I traced it back to the stuffing box but it was dry. I then started the engine up an lo and behold a leak at the stuffing box as the engine was vibrating, on speeding up the engine the vibration ceased and the stuffing box stopped leaking. Any ideas in how to solve this very annoying problem?

Railbob

 

[vyv_cox]

First question - are you certain it's the packing that is leaking, not the hose to the stuffing box? Assuming it is, you can gradually tighten the packing adjustment bolts until the leak stops but check that the box is not getting too warm. If this is not effective you might need to repack it.

 

[Railbob]

First question - are you certain it's the packing that is leaking, not the hose to the stuffing box? Assuming it is, you can gradually tighten the packing adjustment bolts until the leak stops but check that the box is not getting too warm. If this is not effective you might need to repack it.

Thanks vyv_cox, yes it's definitely the stuffing box, I should have said first that it's a Volvo seal/box.

 

[Tranona]

Thanks vyv_cox, yes it's definitely the stuffing box, I should have said first that it's a Volvo seal/box.

Does this happen with the gear in neutral, or only when under load? If the former it could either be the lip seals worn, or failing engine mounts causing excessive movement at tickover. If the latter could still be seals worn, but could also be the shaft out of alignment.

 

[Railbob]

Does this happen with the gear in neutral, or only when under load? If the former it could either be the lip seals worn, or failing engine mounts causing excessive movement at tickover. If the latter could still be seals worn, but could also be the shaft out of alignment.

Tranona, it only happens in neutral, once engaged and rotating the drip disappears, the engine is 13 years old and I don't know when the mountings were checked/replaced.

 

[pcatterall]

Tranona, it only happens in neutral, once engaged and rotating the drip disappears, the engine is 13 years old and I don't know when the mountings were checked/replaced.

My own experience was similar. I had a lip seal; we had crevice corrosion at the lip which resulted in a 'worn' ring under the seal which dripped. I either gear the prop moved in front or behind the worn ring and there was no drip. Rather than crevice corrosion you may just have a worn patch under the lip. Can you push back the seal to see/feel if this is the case?
I was able to slightly shorten the bellows on my Tides marine seal which put the lip on an unworn part of the shaft.

 

[Spyro]

Is the idle speed too low causing excess vibration. You could turn it up a bit. Otherwise it's a new seal as there is nothing serviceable in a volvo seal other than burping or greasing.

 

[Tranona]

Tranona, it only happens in neutral, once engaged and rotating the drip disappears, the engine is 13 years old and I don't know when the mountings were checked/replaced.

That sounds like the lip seals have worn a groove in the shaft as pcatterall suggests. When you go into gear the engine moves either backwards or forwards 3-4mm, enough for the seals to run on clear shaft. it sounds counterintuitive that the hard metal wears rather than the rubber, but it does happen.

The only way to find out is to pull the seal forward if you have room. If the seal is original it is well past its recommended life, although many do last much longer.

 

[GrahamM376]

Could well be the engine mounts have gone soft, we had similar problems with a club launch which was cured with harder mounts.

 

[Railbob]

Thanks everyone , I'll try the following to see if a groove has been worn into the shaft, I'll put her into neutral and then throttle up, if the drip disappears as the vibration dampens down the that should mean no groove and I'll set the idle speed a bit higher to stop vibration. If that doesn't work then it looks like it's a new seal and or mounts.

 

[Norman_E]

That sounds like the lip seals have worn a groove in the shaft as pcatterall suggests. When you go into gear the engine moves either backwards or forwards 3-4mm, enough for the seals to run on clear shaft. it sounds counterintuitive that the hard metal wears rather than the rubber, but it does happen.

The only way to find out is to pull the seal forward if you have room. If the seal is original it is well past its recommended life, although many do last much longer.

What actually happens is that the soft seals pick up grit, and the abrasive grit wears the shaft. If you move the shaft to get an unworn bit against the seal, the grit will just start the process again, so the real cure is move the shaft and replace the seal.
The other issue is the vibration at idle, if a slight increase in idle speed does not stop it then replacing the engine mounts is the most certain cure. If they are old they have most likely softened.

 

[slipknot]

My Volvo seal leaked at the start of this season, particularly at idle as that noisy old Volvo bounced around at tickover. I started to check engine allignment, shaft allignment, raising tickover, engine mounts worn out, perhaps injectors need a service. But I realised that I probably hadn't been greasing the inner & outer seals quite as well as I should have been so I popped down to MacDonalds and grabbed a straw and did a proper job if greasing the inner & outer lip seals. Sorted. No drips.

 

[CAPTAIN FANTASTIC]

Could be one of the mounts that has gone.

 

[Railbob]

Thanks to everyone so far, you've all given me good advice in where to look for problems, I'm back up the boat next Sunday and I'll go through everything suggested.

 

[fisherman]

Having had engines that bounce around, what does the panel think about a transverse stabiliser bar or two on top somewhere, like the old Mini? My original thought would have been to put the engine on a raft and have six mounts, and/or extend the mount positions further fore and aft.

 

[Railbob]

Hi Folks,
Well problem solved, the idle speed was about 150 rpm below standard so increased the idle to correct speed and that took care of the vibration, I still had a bit of water coming through but nowhere near what was originally leaking so really greased the stuffing box and took care get under the second lip. Success ��Beaune Dry!!!

 

[vyv_cox]

A volvo seal is not a stuffing box, which was the cause of confusion when you started the thread. Lots of info about stern glands on my website.

 

[Birdseye]

What actually happens is that the soft seals pick up grit, and the abrasive grit wears the shaft. If you move the shaft to get an unworn bit against the seal, the grit will just start the process again, so the real cure is move the shaft and replace the seal.
The other issue is the vibration at idle, if a slight increase in idle speed does not stop it then replacing the engine mounts is the most certain cure. If they are old they have most likely softened.

Not necessarily Norman. Its a fact of engineering life that the soft usually wears the hard so all lip seals, and that what the Volvo is, wear the shafts they run on. For example, on the crankshaft of your car where there is no grit.

Railbob - I see you have altered the revs and filled the seal with grease. If I remember rightly the instructions on the Volvo seal warn against packing with lot of grease as it will quickly make the leak worse by stopping the lips on the lip seal from moving properly. Been in your situation, tried what you have done and not really solved the problem. As you havent because there should be no water leak at all from the seal.

Anyway, having laboriously typed out all the rest of this post, I'm not going to bin it now. Likely you will have to re-visit the issue later this season.

Likely there is a groove worn in your shaft but it that was the problem then the leak would occurr when the engine is running and the shaft rotating more than when it wasnt.. So:

1/ is your engine idling too slow and therefore shaking at idle?
2/ if not, have the engine mounts failed or gone soft. On a previous Volvo I had a similar problem to yours and even our local engine expert couldnt find it. I succeeded when I put a crowbar under the engine, heaved it up and discovered that the threaded part of the mount had sheered. On a previous Yanmar, the issue was the rubber had de laminated from the steel of the mount. So arm yourself with spanner, a bar and a block of wood and go out and check your mounts. Its commonsense so you dont need a mechanic.
3/ if the mounts are OK then the next check is the alignment. When at rest is the shaft in the centre of the stern tube and is the volvo seal centered on the shaft.
4/ It cant not help to change the volvo seal and to have it in a slightly different location, or better still try the similar seal from Silette ( Eliche Radice seal) which will locate the rubbing surfaces differently. Cant help but notice your original comment about the seal being dry - it should never be dry. You are burping it to let air out arent you?

 

[Railbob]

Not necessarily Norman. Its a fact of engineering life that the soft usually wears the hard so all lip seals, and that what the Volvo is, wear the shafts they run on. For example, on the crankshaft of your car where there is no grit.

Railbob - I see you have altered the revs and filled the seal with grease. If I remember rightly the instructions on the Volvo seal warn against packing with lot of grease as it will quickly make the leak worse by stopping the lips on the lip seal from moving properly. Been in your situation, tried what you have done and not really solved the problem. As you havent because there should be no water leak at all from the seal.

Anyway, having laboriously typed out all the rest of this post, I'm not going to bin it now. Likely you will have to re-visit the issue later this season.

Likely there is a groove worn in your shaft but it that was the problem then the leak would occurr when the engine is running and the shaft rotating more than when it wasnt.. So:

1/ is your engine idling too slow and therefore shaking at idle?
2/ if not, have the engine mounts failed or gone soft. On a previous Volvo I had a similar problem to yours and even our local engine expert couldnt find it. I succeeded when I put a crowbar under the engine, heaved it up and discovered that the threaded part of the mount had sheered. On a previous Yanmar, the issue was the rubber had de laminated from the steel of the mount. So arm yourself with spanner, a bar and a block of wood and go out and check your mounts. Its commonsense so you dont need a mechanic.
3/ if the mounts are OK then the next check is the alignment. When at rest is the shaft in the centre of the stern tube and is the volvo seal centered on the shaft.
4/ It cant not help to change the volvo seal and to have it in a slightly different location, or better still try the similar seal from Silette ( Eliche Radice seal) which will locate the rubbing surfaces differently. Cant help but notice your original comment about the seal being dry - it should never be dry. You are burping it to let air out arent you?

Thanks Birdseye,
I think I should clarify a few things, firstly when I said I really greased the seal I meant about 7ml out of a 25ml tube that came with the seal. As for burping the seal yes done on launching every time. I think it's been a combination of insufficient revs and grease which has caused the leak. Before I tried the remedy I ran the engine in neutral without adjusting the idle speed,the engine was vibrating quite a bit and water was dripping in from the seal, I then with the gearbox in neutral, so no rpm to the shaft, applied some throttle , the vibration decreased significantly and the seal dried.quite a bit with just a very very small drip. I then set the idle speed to the correct speed and put in about 7ml of grease into the seal ensuring I put it right into the second lip.
I then ran through every combination of neutral low revs, high revs and in gear forward and reverse to check for leaks , thankfully everything was dry. I'd say it's been a combination of low rpm and insufficient greasing of the seal, I probably didn't put enough in and in the right places.

 

[macd]

Glad it seems to be sorted, Railbob. If and when the seal needs replacing, suggest you consider the Radice equivalent mentioned above. It has a dedicated greasing point (no need for straws), and is self-burping. Also cheaper, despite evidently being made by the same bods who make the Volvo seal.