1972 mercury 500 lower unit leak

archiezift

Cadet
Joined
Oct 4, 2008
Messages
7
My 1972 mercury 500 (50HP) normally develops a milkyness to the oil every second year or so and i get it fixed at the shop, now I have all the tools and ability to take the leg off and do the work, does anybody know which seal normally leaks first, or is it a case of replacing them all?
 

1960 Starflite

Petty Officer 1st Class
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Jun 23, 2011
Messages
351
Re: 1972 mercury 500 lower unit leak

My 1972 mercury 500 (50HP) normally develops a milkyness to the oil every second year or so and i get it fixed at the shop, now I have all the tools and ability to take the leg off and do the work, does anybody know which seal normally leaks first, or is it a case of replacing them all?

Two seals, one in the bottom of the water pump (replace impeller while in there) and prop shaft seal. Could also be shift shaft seal. There is a drain hole visible on the outside of the lower unit for the shift shaft cavity, make sure it is open.
 

Moody Blue

Captain
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May 24, 2004
Messages
3,136
Re: 1972 mercury 500 lower unit leak

The simplest and cheapest to repair are the sealing washers under the vent and drain plugs. It is recommended that they be changed and not reused once the plugs are removed.

I would start simple and go from there. What has the shop done in the past?
 

bgc

Ensign
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Jul 13, 2011
Messages
980
Re: 1972 mercury 500 lower unit leak

We use this connected to a hose attached to the metal fill adapter to Pressure/Vacuum check lowers. Pressurize the lower and submerge in water to verify what seal is leaking. Several of my old Mercs leaked from corrosion on the drive shaft at the seal.

pump_zps77881dc1.jpg


pumpadapter_zps32048ba6.jpg
 

Faztbullet

Supreme Mariner
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Mar 2, 2008
Messages
15,589
Re: 1972 mercury 500 lower unit leak

As posted, its most likely the driveshaft is corroded/pitted at water pump seal area as these where mild carbon steel. These can be repaired with a speedi sleeve
 
Joined
Oct 27, 2013
Messages
18
Re: 1972 mercury 500 lower unit leak

If you have a 0.75" driveshaft (where the waterpump seals run) then the SKF Speedi Sleeve P/N is CR 99076, you will need 2 of them, as they are only 0.300" long. I used a bit of Mastinox under the sleeve to try and stop the corrosion.
 

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archiezift

Cadet
Joined
Oct 4, 2008
Messages
7
Re: 1972 mercury 500 lower unit leak

Thanks for everys help, bought a pressure test kit, made special tools, oil was milky when I drained it, replaced the propshaft seal & new oil, gave it a run and hey presto, no water in the oil
 

bgc

Ensign
Joined
Jul 13, 2011
Messages
980
Re: 1972 mercury 500 lower unit leak

Good news!, Hope it works out!
 
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