115 hp 1978/79 inline 6 lower unit seals

[OKTwainer]

I have a Mercury 115 hp inline 6 that according to the registration is a 79, but serial number is 5056101 which I think is a 78. I know I have a lower unit seal problem (I can see the lower unit oil leaking out when I remove the prop and thrust hub, or if that is not enough I can drain water and oil when removing the fill plug and vent screw). The closest boat shop would be 2 hours away, so I bought the 2 seals for around the propeller shaft with the hopes of doing it myself (also included was about a 3" O ring). I have a few questions, though that I wanted clarification on before I start the project. The place I got the seals from said I would need to remove the bearing carrier in order to replace the seals. Numerous posts on this website mentioned it also. I have a Seloc manual, and based on the diagram I saw you would only need to remove the bearing carrier in order to replace the O ring, as the seals were shown next to each other in front of the bearing carrier. Is this correct? The diagrams also show the seals with a mention of which way the lip goes. What is the "lip"? When my propeller is removed I can see the inside of the seal that has the spring around it. Is this one the correct outermost seal towards the prop or have I already lost one? Are the seals installed right next to each other? And if so, are they installed with the solid edges back to back, or the spring sides back to back? If I need to remove the bearing carrier can I use a normal bearing remover a shop would have around this area (or O'Reilly's)? For a 30 year old motor it still runs good, (probably due to the new electrical harness I installed last year) but it won't be getting wet again until I can get the seals done. Any advice would be appreciated.

 

[Chris1956]

Re: 115 hp 1978/79 inline 6 lower unit seals

The Bearing carrier may be removed with a puller or slide hammer. In the older motors they get quite stuck. You need a special spanner to remove the retainer (donut shaped thing).

I have heard the rumor that you may replace the seals w/o pulling the bearing carrier, however, I have never tried it. BTW the o ring is the seal for the bearing carrier.

You might get a OEM Service manual. What you are doing is one of the more complex repairs.

 

[OKTwainer]

Re: 115 hp 1978/79 inline 6 lower unit seals

Thanks for the reply. Sounded good until your last sentence. Just spoke with a friend today that used to have an older mercury also and he didn't remove the bearing carrier either, (which means he did not replace the O ring) and used a screw to remove his seals then just installed the new ones. He couldn't remember if the seals were installed smooth side to smooth side or open side to open side. I will find out when I pull out the one I can see when I remove the prop and thrust washer.

 

[AMD Rules]

Re: 115 hp 1978/79 inline 6 lower unit seals

I have one in pieces right now. Let me know if there is anything specific you need to see, and I'll be happy to take a pic.

 

[OKTwainer]

Re: 115 hp 1978/79 inline 6 lower unit seals

It will be next week before I can dig into it. If you have one in pieces, the main questions are: Do you need to remove the bearing carrier to do anything with the prop seals? Or do you just need to remove the carrier to replace the O ring? Are the seals installed smooth side to smooth side or open side with spring back to back. I can see the open side with the spring when I remove the prop, but that doesn't tell me anything, because it could be that I have both seals, or lost the outside one and won't know until I can start dismantling things. The boat may get used 3-8 times a year (closest lake is 80 miles and closest boat shop is 2 hours) so that is why I am trying to do it myself. Replaced the electrical harness in the motor last year and now it runs great - just need to take care of the lower unit leak.

 

[Chris1956]

Re: 115 hp 1978/79 inline 6 lower unit seals

I would not think the oring replacement is important. If you can replace the seals w/o removing the bearing carrier, I think that is the way to go. I also thing the seals should both be installed spring side in.

 

[daveswaves]

Re: 115 hp 1978/79 inline 6 lower unit seals

I would not think the oring replacement is important. If you can replace the seals w/o removing the bearing carrier, I think that is the way to go. I also thing the seals should both be installed spring side in.

The spring side always faces the fluid you do not want to move across the barrier, so one faces in to the oil, and the other faces out to the water and n'er the twain shall meet. Thats why he can see the spring when he takes the prop and thrust washer off.

 

[OKTwainer]

Re: 115 hp 1978/79 inline 6 lower unit seals

Thanks - that cleared it up - now I know I haven't lost one of the seals, it just leaks. I know I could have figured it out when I actually dig into it, but I prefer to have prior knowledge before I start tearing things apart, because typically it will be around 2 hours before I want to hook it to the hitch and take it to the lake. What do you know about the O ring bearing carrier seal? Need to replace?