Mercury 40HP lower main seal?

[Mudshack]

Hi guys. First time post here.

We have a 1980's Mercury 40HP motor that has a leaking lower main seal. I fix my own cars but have never attempted to even take the cowl off of an outboard. The local shop wants something like $600 to make the repair, and I just figured I would do some research before turning it over to them. Not to mention finding the cash is tough right now.

What is all involved? Does anyone have a factory service manual for this seal replacement? Should I replace the water pump while I am in there?

 

[Ron Allison]

Re: Mercury 40HP lower main seal?

Mudshack:
I read your question and hesitated to send you this message because it doesn't make me sound very bright ---but --- it might help you.
I have a 40 HP Mercury which approx. 3 years ago showed water in the bottom end - I was to say the least, a bit upset. I decided to change the seals in the bottom end -- never having done it before I charged at the task --- after making a tool to remove a specialized nut that hold the whole thing together I was successful in changing the seals . At the end of the year --- guess what --- I still had water in the bottom end oil --- it was in the fall and I wanted to winterize the motor so I proceeded to drain the bottom end completely and added fresh oil. when I was finished adding the oil -- I proceeded to put in the top drain plug and then noticed that the "o" ring was missing --- I replaced --- and guess what - I haven't had a drop of water in the bottom since ---- it was just a simple 'O" ring on the oil plug.
Give it a check before you tear the bottom end out --- might just be that simple..
good luck!

 

[Mudshack]

Re: Mercury 40HP lower main seal?

Ron, thanks for the reply. It is responses like yours that make these forums worth more than any service manual. That is how we all learn. And we learn from the actions of others. I passed this information on to my buddy who has the boat and he is going to check. We already bought the Lower Unit Seals kit, but sure would be nice if it was just a fill plug o-ring issue. Thank you very much for your reply.

 

[Mudshack]

Re: Mercury 40HP lower main seal?

BTW - do you have any pictures of that special tool you created? Any hints on what to do to get around that specialized nut?

 

[Maxz695]

Re: Mercury 40HP lower main seal?

If the impeller hasn,t been done in quite some time replace it while your there also if you want to buy the full waterpump kit including the base it would be a good idea. Tha lower base of the waterpump goes down into the lower unit which has an oring that can be the cause of water getting into the gear case. Also it,s good to know your waterpump won,t need further serviceg for 2 more years, and even then just an impeller should be needed. Some bases come up fairly easy after removing the upper housing. I had to remove the stainless pins and drive 3 inch screws into the base being very careful not to go to deep and score the casing after the 2 screws where somewhat into the nylon base I took a prybar and used the top of the LU bolt for leverage and it came up nicely. I then put it all back together and I,m happy it,s done Hope this helped. I really also hope you can stop the leak with the simple fix.

 

[Mudshack]

Re: Mercury 40HP lower main seal?

Well, we ordered a new water pump at the same time as the lower unit seal kit. We pick them up tonight/tomorrow morning, and dig into everything tomorrow. My biggest concern is that we don't have the bearing puller. You know...the think that has the little outward hooks at the end that you then pull/beat with a hammer. Trying to find something at O'reilly's or NAPA that is similar for pulling the bearing out down on the propeller shaft area.

I am going into this completely blind....but with the knowledge that I have taken apart a lot of my trucks and put them back together. My buddy needs to save the cash, and it is his motor....needless to say, he is nervous.