Older Mercury 75HP General Questions

Struwing1

Recruit
Joined
Jul 13, 2008
Messages
3
Hi I am new here and have been using an older Merc 75Hp 4 cyl with serial A707205 for the last few years with little to no issues. It has always been a very strong runner! Some idle issues but never a major issue over the years.

I now have the lower end oil getting milked up in a few min of operation. So I am here looking for help. I am good at auto repairs and industrial mechanical repairs so I do not think I will be too challenged!

First what is my motors year of build?

What is the best/most comprehensive manual to use for repair?

What brand of parts should I buy and from where as I am in Ontario Canada?

What am I looking at for the milked oil repair!

Time is of major concern right now with the kids and work, any idea time wise?

Thanks Eh! :D
 

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TriadSteeler

Petty Officer 1st Class
Joined
Oct 26, 2006
Messages
237
Re: Older Mercury 75HP General Questions

It seems that you have a bad seal and your coolant water is seeping into the lower unit.

I am going to assume that you have already changed out the lower unit lube and the fresh lube is milking up.

You can test this by doing a vacuum/pressure test on the lower unit. Search vacuum test on this forum. There is a complete set of instructions on how to do it. That will tell you if there is a seal that is leaking. The vacuum test will be the telltale for coolant water intrusion into the lower unit and the pressure test will be the telltale for lower unit lube leaking into the exhaust. A failure of either test will confirm bad seals.

If it does turn out that you need to replace the lower unit seals, then order the factory manual for your motor. I would stay away from the clymer/seloc manuals as they are often vague and incomplete as each manual covers a wide array of years/models in one manual. You may also need to order some special tools as some of the lower unit parts require them for disassembly.
 

Struwing1

Recruit
Joined
Jul 13, 2008
Messages
3
Re: Older Mercury 75HP General Questions

Yes I have changed the lower lube twice now and run it for a few min and it milks up!

Thanks for your input!
 

Struwing1

Recruit
Joined
Jul 13, 2008
Messages
3
Re: Older Mercury 75HP General Questions

I have no idea what year this motor is to order the manual, can someone help!
 

Yepblaze

Lieutenant Commander
Joined
Jun 1, 2001
Messages
1,686
Re: Older Mercury 75HP General Questions

It appears to be a 1975 Canadian Model
http://www.maxrules.com/Merc_model_files/60-100.html

That being said, I have found that after draining the oil,

and removing the lower unit,

I can use a tire inner tube valve stem torn (or cut) out of a bicycle tube then ground down to a blunt rubber point,

I am able to screw that into the drain hole and apply a bicycle pump or so of air into the unit to pressure test it.

Drop it in a big barrel of water or spray iy down with real soapy water and look for bubbles.

Do not let the shift shaft come out of unit as it is only held in by gravity.
 
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