1974 Mercury 500 Lower Unit Seal Kit

[kbradley1983]

Boat: 1982 Lowe Bass Catcher pro
Motor: 1974 Mercury 500 2 stroke 4 Cylinder
SN: 4075319

This is my first post so please excuse any errors in etiquette.

I've recently purchased the boat above. There was water draining from the lower unit when I replaced the gear lube. In addition, after replacing the lube I've noticed gear lube leaking from the lower unit. I suspect I need to replace the seals in the lower unit, but I'm having trouble locating the seal kit for the serial number. Every kit I find says for SN 4357640 & up. I'm beginning to the kit is discontinued. It is possible to buy a kit or will I have to try and source each part individually? Thanks in advance.

KB

 

[carholme]

Re: 1974 Mercury 500 Lower Unit Seal Kit

It is a 1974:

50 1974 M 3816308 - 4140999

From here:

MERCURY OUTBOARD MODEL YEAR GUIDE 40 HP (4-CYL) - 50 HP -- Mastertech Marine

Parts list:

MERC 500 - Mercury, Mercruiser, Force, etc. Parts Lookup

You will have to purchase the parts individually I think. Where is the oil leaking from?

The service manual you will require is P/N: 90-68647

Mercury Outboards Service Manual C 90 68647 | eBay

Excellent price if you are interested.

In the interim, here is a link to the condensed version of the Clymer manual. Download it soonest to your computer as the link is short lived.

MERCURY - MERCURY FOUR-CYLINDER MODELS (1969-1989).: Small Engine Repair Reference Center Home

Gerry

 

[kbradley1983]

Re: 1974 Mercury 500 Lower Unit Seal Kit

Thanks for the prompt reply and for the condensed link. This is all great information. I figured I was going to have to purchase the parts individually, but I wanted to verify before I spent the time identifying the necessary parts.

Will the service manual help to identify the wear parts? I've been putting off purchasing one because I have read/heard nothing but horror stories about Seloc manuals. This one is superior to the Seloc manual correct?

The gear lube is leaking down the skeg plate and appears to be coming from the gear housing. Do you recommend replacing all the wear parts while I have the lower unit off, including the impeller and all its seals?

 

[carholme]

Re: 1974 Mercury 500 Lower Unit Seal Kit

The manual on ebay is the Mercury manual, definitely not Seloc. It is the best you can get for the age.

I understand the oil leak is from the LU but from where? Is it leaking out the prop area or the small approx. 1/8" drain holes just underneath the cavitation plate towards the front, or the Fill/Drain screws?

Gerry

 

[kbradley1983]

Re: 1974 Mercury 500 Lower Unit Seal Kit

It is coming out of the prop area and not the fill/drain screws.
KB

 

[carholme]

Re: 1974 Mercury 500 Lower Unit Seal Kit

You can do a quick check of the leaking oil to see if there is a slight fuel smell to it indicating that it is out of the exhaust and if so. this wouldn't be coming from the LU. If you are sure it is LU oil, it may be time to drop the LU and see if you have any oil on top of the LU, either from a leaking shift shaft or water pump seal. Barring all that, you could just pressure test the LU and see if and where the leak is.
Have you noticed or did you measure the oil in the LU to see if that is decreasing? And just how much oil has leaked?

Gerry

 

[kbradley1983]

Re: 1974 Mercury 500 Lower Unit Seal Kit

It doesn't smell like fuel at all. I'm pretty sure it is from the lower unit. I'll try to drop the lower unit this weekend to see if it is the water pump seal. I'm not sure how much but it's at least a half cup or so far in about a month. How would I go about pressure testing the lower unit, does it require and special tools?

 

[carholme]

Re: 1974 Mercury 500 Lower Unit Seal Kit

You can make your own pressure tester and it doesn't have to be complicated. If you have a small compressor with a good regulator on it, you can set it to about 8psi and it will suffuce.

Here is a link with some pictures.

http://forums.iboats.com/johnson-evinrude-outboards/diy-lu-pressure-tester-627658.html

Let us know what you find on the weekend.


Gerry

 

[Roadblock]

Re: 1974 Mercury 500 Lower Unit Seal Kit

Question, is this basically the same motor as the Merc Thunderbolt 500?

I just bought a boat with a Merc Thunderbolt 500 and the oil was milky so I drained it and let it drip for a day then filled it up and took it out today for about 4 hours. Drained it when I got home and it was milky again.

It's currently dripping right now. Going to go fill it back up here before I go to sleep so no rust can form. I saw no indication of trust in fluid that was in it when I bought it or mine today so that is good!

I will have to follow your thread and see what you come up with either way.

 

[Powerwind78]

Question in the vicinity. I have leak that appeared last week when I brought the bout home out of storage put new gear lube in on Friday to play on Saturday and it all leaked out at the prop down the scag, I pulled the bearing carrier but the bearings did not come out with the carrier. Do I need to get a new set or is that the degeneration of the seals?