lip seal on propeller shaft

I have a 2000 390 Mainship. I am replacing the rubber lip seal on the propeller shaft. How does the propeller shaft disconnect from the transmission. Do you have to undo several bolts and nuts or can you just undo the 2 set screws.

where shaft goes into flange is there a key way or is it splined

Greetings,
Mr. jc. Welcome aboard. You may get lucky and be able to simply undo the 2 set screws and slide the prop shaft back for clearance but the more likely scenario is you will have to undo the several nuts and bolts that connect the prop flange to the transmission flange and then remove the prop flange. There was a recent thread on how to remove the potentially stubborn prop flange-shaft connection.

thanks i am new to this and not sure if i am posting properly

This job is not an easy one for the average boat owner, and is best done with the boat hauled. The shaft will need to come out of the coupler and that tends to require a tool such as a shaft puller that are more typically owned by a yard. The one I use most often looks like an extra large slide hammer and screws onto the end of the shaft, so the prop has to be pulled first. That's the easy way.

The hard way, which can be done in the water requires you to unbolt the coupling, release the set screws and then insert a short piece of metal between the coupling faces and bolt them back together as its own puller. You will need to have some longer bolts on hand. While a socket can be used in a pinch, some short pieces of shaft, slightly turned down work best. You will need to repeat a few times with longer inserts as you go. As I said, this is actually the hard way. Hauling the boat, popping the prop off and using the slide hammer is the quick method.

Be sure to protect the seal as you slide it down the shaft any burrs might damage the lip. I have Tides Seals unit they supply a plastic split "top hat" which slips under the seal lip and protects it, I guess a piece of thin plastic sheet would do as well

390 mainship prop shaft nut

i am trying to remove my shaft so i can install a new seal,i have the flange unbolted from the transmission but there is a castle nut holding the shaft to the shaft flange.its such a tight fit i cant measure to see what size socket i need to remove the nut,it looks like maybe 1.5 inch or so but im not sure because i got to grind a socket to fit would anyone know the exact size thank you very much

Size varies from mfr to mfr. Get a pair of calipers and measure across flats. Hardware stores should have cheap calipers. Measure the inside dia of coupling so you know how fat a socket will fit. Also, some truck shops have thin wall sockets.

Fortunately, this means you have a tapered coupling which is a good type.

Jacobs, Have you been able to remove the coupling yet? If not this might help. I have a 2004 Mainship Pilothouse and I just did this. It sounds a little silly but it worked perfectly. Get some play-doh (I did not tell my granddaughter I was liberating some of hers) and push it into the coupling and then slowly pull it out. You should be able to measure the impression in the play-doh to determine the size socket you need. I used a 1" 1/2 socket I got from Auto Zone. I thought that I needed to have a socket ground down myself because I could not get what seemed to be the correct size socket on the nut, What I overlooked was backing the set screws out of the path of the socket. Once the set screws were out of the way the socket without it being ground down slid right in. There are several ways to proceed from here. I placed a smaller socket into the coupler and used the coupler bolts to press the socket in and push the shaft out. It only took a few easy turns on the bolts and the coupler popped right off. The process took about 20 minutes to remove the coupling and slide a new seal on. The ideal situation would be to have the boat out of the water but it can be done in the water. Just have everything ready before you start and if possible have a helper as well. I had to change out a leaking seal with the spare on my trip from Fla to NY. I would suggest to sliding 2 seals on once you remove the coupler then bolt it all back together. Place the plastic shield on the second one you put on then cut out the damaged seal and slide the new one up, slip it in and reattach the cover with the screws.
This article was very helpful and a good read before I tried it. PSS Shaft Seal Installation Photo Gallery by Compass Marine How To at pbase.com
Hope all goes or went well.