1978 Mercury 50-HP Oil Leaks from Gear Case

Repair or modification of Boston Whaler boats, their engines, trailers, and gear
cleep1700
Posts: 20
Joined: Fri Oct 30, 2015 11:48 pm

1978 Mercury 50-HP Oil Leaks from Gear Case

Postby cleep1700 » Thu Jun 07, 2018 1:24 pm

The bottom of the skeg on my 1978 50 HP Mercury is leaking oil. Upon close examination, it looks as if the previous owner had repaired the bottom with a Bondo-like substance. What are my options?

Craig, who loves his 15 but the engine not so much

jimh
Posts: 4919
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

Re: 1978 Mercury 50-HP Oil Leaks from Gear Case

Postby jimh » Thu Jun 07, 2018 2:30 pm

If there is a crack or fracture in the housing of the gear case, repair options might be:

--try to repair the crack with epoxy adhesive

--try to repair the crack with some sort of weldment of the gear case material

--buy a new gear case housing (only the housing no internal parts); disassemble the existing gear case; reassemble all the components of your existing gear case into the new housing

--buy a used gear case from an identical engine whose power head has failed but whose gear case is good

cleep1700
Posts: 20
Joined: Fri Oct 30, 2015 11:48 pm

Re: 1978 Mercury 50-HP Oil Leaks from Gear Case

Postby cleep1700 » Thu Jun 07, 2018 3:10 pm

Thank you, Jim.

Craig feeling hopeful this is a speedbump

jimh
Posts: 4919
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

Re: 1978 Mercury 50-HP Oil Leaks from Gear Case

Postby jimh » Thu Jun 07, 2018 10:25 pm

Also, on the option to buy new housing and reassemble all the original components from the cracked housing into the new one: you have to know what you are doing because often there are clearances that have to be shimmed to the proper tolerance. The housings are castings and probably are not precision machined to perfect tolerances. If you do get a new housing, get professional help in installing the old gears, shafts, and bearings into it.

Epoxy with the right fillers can do marvelous work. I'd give that a try first.

Yellowjacket
Posts: 13
Joined: Mon Jul 31, 2017 9:33 am

Re: 1978 Mercury 50-HP Oil Leaks from Gear Case

Postby Yellowjacket » Fri Aug 10, 2018 10:44 pm

Best thing to do is to clean the paint and bondo off and see what the problem really is. Seals generally leak and that's the usual reason for leakage. Just because someone used bondo on the lower skeg area doesn't mean the case was cracked. You've got to really hit something hard to crack a case.

First pull the prop and look for evidence of seal leakage, if it is dry and no sign of oil, make sure the fill screw isn't leaking, and then if there's still oil, figure out if it has a crack.

If it's leaking from a crack, you'll need to clean all the paint off the affected area and then drain the oil and clean the crack with Brakeclean, first from the inside flushing the oil out and then using a good bit of cleaner flushed thru the crack. After that it can be welded, but that is really a crap shoot.

If you have a long shaft engine, lower units for these engines are generally available for around $200 on ebay or on craigslist. Swapping the lower unit is a 20 minute job, so the reality is it is likel less expensive to get another lower unit and be done with it. The Merc 500 is a classic and taken care of will serve you well for a long time. They're ligher and smoother than anything else you can buy today in the 50 hp class... Modern 50's are heavy and vibrate because they're mostly 2 cylinder motors. The late 70's 500's have modern ignition systems and are pretty much bulletproof... Feed it non-ethanol gas and good oil and it'll run forever so long as you change the waterpump impeller every few years.