Silicon or rubber Shaft seals?

[Caer Urfa]

I have to replace the existing 'rubber' stern tube shaft seal (the one nearest aft before the stuffing box with jubilee clips either end), it is about about 2" dia x 3" long (not got it off yet).
I am told that a new (blue) 'Silicon' seal will be better and last longer, anyone had experiance of Silicon seals bearing in mind it will be eventualy full of grease around the shaft.

 

[boatmike]

I should not use Silicon if I were you as that's rock. Silicone rubber however is simply a variety of rubber with self lubricating properties and therefore preferable to nitrile rubber for shaft seals.

 

[Tranona]

Don't think that is a seal. The seal is the stuffing box. The rubber hose just mounts the stuffing box to the stern tube and allows movement. They differ depending on the make so best to try and get the replacement for the original from a stern gear supplier like T Norris, Sillette or Lake Engineering.

 

[TigaWave]

Are you sure it should be full of grease?
The reason I say that if you have a bearing aft of the seal that is fed by water the grease can block up the water channels in the bearing and cause it to fail or wear rapidly.

Grease is a poor conductor of heat and not as good at lubricating a bearing as water.

 

[boatmike]

Reading your post again I think Tranona is correct. That is just a connector pipe to allow movement. If it is a grease filled stuffing box it is important to use a grade of rubber that is grease resistant and has some reinforcement to stop it "ballooning" out when you pump in the grease. Most will be but certain types of grease and/or oil will degrade certain types of rubber. Nitrile rubber is usually OK but I would follow the makers recommendations. I think Silicone tube is possibly better as you have been advised but to answer the question properly you need a chemist not an engineer. I am also not sure if it should be full of grease either. most grease filled stuffing boxes are self contained and have a seal either end, but without seeing it we can't see what type it is. Suggest you look for a makers name and see if they have a website.

 

[Tranona]

Yes, missed the "full of grease" bit. No, don't think there should be grease there. The grease should be in the stuffing box helping the packing make the radial seal. There should be just water in the hose. if it is full of grease it suggests the packing needs replacing or the shaft is worn and you are getting leakage past the packing. Easy to check both, but if you need to replace the stuffing box consider a different style such as the Volvo seal. Not compulsory, but IMHO a much better solution. But if it is just packing and hose needed, do that.

 

[MoodySabre]

Presumably you are talking about the hose that joins the stern tube to the packing gland - the bit on the left of this pic

It's made of grease resistant rubber as stated above. That's what you want.

 

[Caer Urfa]

Hello Roger Moodysabre
Yes that looks like the rubber seal and I assumed as I have not taken it off yet it was also filled with grease!
I have found what 'boatmike's post discribes as a small balloon on one side (like a small blister) so I am taking no chances and replacing it.
Silicone rubber hose is what I have been recommended to fit by our local RNLI boatcheck guy but I was looking for others experiances hence this post, as said without taking it off it looks to be about 2" dia x 3" long similar to your picture amd I can get it from ASAP but only in 1m lengths!
Thanks everyone for your comments
Regards
Mike

 

[Skyva_2]

You do need special rubber, last time I paid about £12 for a 7 inch length, and that was 8 years ago. It resists fuel, grease, etc. Exhaust hose will not do. I have not heard of silicon rubber for this purpose.

It should be replaced every 5 years or so, and certainly if it goes soft and 'balloons'. Any engine agent should be able to supply it cut to length. Or try Sillette Sonic.