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SD20 Yanmar propeller shaft issue

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sgrhma2 View Drop Down
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Joined: 20 November 2021
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Post Options Post Options   Thanks (0) Thanks(0)   Quote sgrhma2 Quote  Post ReplyReply Direct Link To This Post Posted: 19 December 2022 at 01:05
I’ve just noticed this post and recognise the seal / shaft ware problems. As a hobby I restore to full working condition old outboards and the gearbox on some of them display similar and worse ware. There are a number of solutions that I have found that worked. These are;
1. In cases where the shaft isn’t too badly worn just fit new seals. If single lip originally move to double lip ones. It is important to ensure that the seals being fitted have a stainless lip control spring. These seals are easily sourced on line.
2. If the grooves are deep (your fingernail catches in them is an easy test for deep) or pitted in anyway use a speedi seal. When doing so make sure you use a good liquid tread lock on the shaft when fitting the sleeve as this prevents capillary action under the sleeve (extremely rare but I have experienced). This will give you a good water / oil tight solution but there are things that you need to be aware of. i) the shaft is now over size and as such there is additional lip pressure on the seals that tends to make them ware out sooner. ii) if there is a retained bearing on the shaft it’s removal involves removal of the sleeve. iii) removal of the sleeve at a future date needs to be done with care to avoid further potential damage to the shaft.

The last two options are ones you take if you want to do an as new or better repair and or intend to own the boat for a long time

3. Have the shaft ground and hard chromed. This retains the dimensional properties of the original OEM shaft but provides a significantly harder and longer lasting surface for seals to run on and is extremely corrosion resistant. The best place to get this done is by an engineering firm that re-chromes motorcycle front forks. This is my preferred solution that I have done several times and has proven to be highly successful. Not cheap but generally works out between a 1/3 and 1/2 the price of a new shaft.
4. If available, buy anew shaft from the manufacturer. Provides as new sealing surfaces, but every time I’ve looked at it there’s always been an eye watering price attached.

My preferred options are 1 and 3. I regard option 2 as a get you in the water quick if time is an issue with option 3. But in all cases, ensure you use double lip seals and lube between the lips and the shaft with grease when assembling.

Hope this is useful 
Simon 
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sgrhma2 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote sgrhma2 Quote  Post ReplyReply Direct Link To This Post Posted: 19 December 2022 at 01:11
I also meant to add that based on the photos above, I feel that option 1 would definitely do the job. 

You have to remember, it’s not just the shaft that has worn, the seal has too ( and generally significantly more than the shaft)

Simon 
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perry View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote perry Quote  Post ReplyReply Direct Link To This Post Posted: 19 December 2022 at 09:12
Thanks very much for your post, I bought a Speedi sleeve when I had shaft wear problems, but could find no evidence of other users and no supprt from SKF. So opted to just move the new seals along shaft.  I've have done  engineering design on North sea pipeline/pumps and valves; my wife is a materials Scientist, so I'm very aware of sea water corrosion and materials choices.
I realised the potential for crevice corrosion between seal and shaft, and intended to try a Loctite solution. Your post gives me confidence. Always nice to know your not the first.
I'm just refurbishing a Johnson Seawater pump, only a very small wear ring on shaft which polished out, but as you say the seal itself was worn approx .6mm on 12mm dia.
In past I have bought Viton seals foroutboards [they usually have Stainless garter spings] and I have used both Nitrile and Viton seals with equal success. I fact I bought Nitrile and Viton then swapped springs, to use the Nitrile.  On this pump I intent to run with the Viton as I doubt that Nitrile is any better. And I dont see this pump as such a critical application as Sail Drive.
The Nitrile seals I have seen fail has often been because the fitter put the steel garter spring on the sea water side? mostly outboards.

My question is have you any experience on the different performance of Nitrile or Viton seals.
Happy Christmas to you,
Perry
East Cowes
Isle of Wight

Current Yacht Hanse 315 2007
Last Yacht Hanse 301 Round GB in 2017
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sgrhma2 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote sgrhma2 Quote  Post ReplyReply Direct Link To This Post Posted: 19 December 2022 at 10:49
From a sealing performance my understanding is that there is little difference in them. The properties of the seal itself are related to the hardness of the polymer used, the shaft material it’s running on, the fluid pressures you’re trying to seal and desired life expectancies. All a very specialised area of knowledge. For our purposes the environment that the sail drive operates in requires no more than readily available seals.
The main reason for using Vito over nitrile is for chemical resistance (viton o rings are used for high oxygen gas mixes in tech diving due to the risk of nitrile ones failing in this environment). There are a number of fuels, lubricants and chemicals that significantly reduce the life of nitrile and if used for a seal if fails. As you pointed out, the majority of Viton seals have stainless lip springs, so there use is often an easy way to ensure having a stainless lip spring and a fully polymer enclosed seal body. All good for corrosion resistance. The single biggest step is the move from single to double lip seals. You will gain more from this than moving from nitrile to viton (assuming that a suitable corrosion resistant lip seal is on both). The second lip is a second seal, not as good as the main seal but it still adds to the overall sealing integrity, especially in circumstances involving contaminants.

Simon 
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Jojo View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jojo Quote  Post ReplyReply Direct Link To This Post Posted: 19 December 2022 at 13:21
Hallo 
This was my axel after a light sanding engine time 1874h 
I say no need to address that as a problem 
I moved the new seals about 2mm so the lip had a fresh part to rest on
As previously said a seal with stainless spring made of viton and fomblin grease would work for at least another 1800h 
Guess then I do not have to worry about changing that once more 


3 Cabin, Hanse 342, Tiller version.
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