Help! How to get into a merc lower unit?

J

jwilkey84

Chief Petty Officer
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Jun 26, 2005
Messages
524
I have been working on a merc 1958 58a (45 hp) and the lower unit is leaking. I have had it off many times messing with the impellor and such, but I think I want to replace all of the lower unit seals. The problem is I have the prop off and big screw looking thing that is behind the prop, but how do I get further. I still have the shaft for the prop sticking out but I cannot seem to get past the big 3-4" wide screw/plate thing that I took off with my spanner wrench.
 
J

jwilkey84

Chief Petty Officer
Joined
Jun 26, 2005
Messages
524
Re: Help! How to get into a merc lower unit?

Please help, anyone! I hate to be rude, but I really want to get into that lower unit to check out the seals. Thanks
 
diaric

diaric

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Jul 8, 2006
Messages
532
Re: Help! How to get into a merc lower unit?

before you rip it apart. pressure test it to see where its leaking. they leak most commonly at the filler vent seals, then the water pump base seals and lastly the prop seals. prop seals are pretty tough. take a blow gun and put the rubber end in the filler hole and give no more than 5 psi, you'll find your leak pretty quick. the driveshafts usually corode and the seals under the pump don't hold anymore.
 
J

jwilkey84

Chief Petty Officer
Joined
Jun 26, 2005
Messages
524
Re: Help! How to get into a merc lower unit?

blowgun? And what is this waterpump base seal? Is that the rubber piece above the screw-on cap above the impellor that slides up and down the drive shaft. What is below the impellor? Is there any need to go below the impellor?
 
diaric

diaric

Chief Petty Officer
Joined
Jul 8, 2006
Messages
532
Re: Help! How to get into a merc lower unit?

ok, you got a good classic motor, getting a manual will help a lot. where the impeller goes in, its the bottom base to the water pump. under this are the seals for the gear lube. they seal oil in and water out. it has to be taken off carefully as some arn't available anymore. easy way to pressure test, is hook up your gear lube pump and give it a couple gentle pumps with the vent still in. lube will push out your leak. a leak under the water pump comes up into the water and drips out the prop exhaust, looking like a prop leak
http://www.oldmercs.com/mark58a.html
 
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