Re: SM Prop Shaft Seal direction and Bushing

Craig Briggs

OK, Jose, we've got a date for two years from now (or 400 hours, or milky oil; whichever comes first!).

My reading of the SKF engineer's recommendation was that the inner seal would face the oil and the outer two would face the water, but on re-reading it he really wasn't explicit on that, possibly assuming a conventional oil-facing orientation.

Not that I'm "buying it" yet, but I do follow your logic of putting the inner seal in "backwards", ie. facing out to allow oil to seep out and lubricate the other seals (and water to seep in through the outer seal and also provide lubrication). I say "backwards" as compared with a conventional lip seal application, say your engine's main crank shaft where the seals face the oil and get no lubrication (other than microscopic oil seepage, perhaps, or, of course, if it's the rear seal of a Perkins 4-108 that always leaks profusely!). 

Moreover, in "normal" applications the lips are rubbing against a very hard shaft, which I really think is the crux of the problem, ie., our bearing is too soft, rather than the orientation of the seals. 

To be continued...
Cheers, Craig SN68 Sangaris

---In amelyachtowners@..., <jvenegas@...> wrote :

Thank you Craig, A truly interesting post.

I was interested to see that in your post about the SKF expert he/she states 
 "Finally, I would arrange the seals with 2 facing the water and one facing the oil as long as there is no pressure difference."
THIS IS EXACTLY WHAT I DID IN MY EXPERIMENT! Plus I would add that the 2 seals facing the water should be the central and inner seals to make sure they get lubricated when the grease wears out AND THE OUTER SEAL deteriorates.

PS;  Since you used the AMEL seal configuration and the standard bronze bushing, and I did it at the same time but with the two seals facing the water, in two years we should compare results.

Fair winds


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