1977 Mercury 500 Thunderbolt rebuild

ONeils

Recruit
Joined
Feb 23, 2020
Messages
3
Hi,
Last Christmas we took our boat out and on the way home the engine suddenly died on us. Long story short one of the cylinders got so far corroded that it got a hole and water got into it. Because we didn't have money for another outboard I decided to try and breathe new life into the old Merc. I got the power head welded up which surprisingly went really well! The mechanic also sold me a 1972 Merc 500 which has some parts missing. This is a fresh water engine though so it is in a good condition. There are however quite a few different parts between the 72 and 77.

The power head is all back together and now I'm looking at what other parts need to be replaced and or fixed. The pin locking the engine in the up position and the pin locking it in reverse were really corroded so they got a good clean and a coat of paint. (What a pain to remove them!) Right now I'm working on the manual tilt / lift rams. These aren't working on either engine so I've taken them apart and I'll try and get some new seals for these. What I'm curious about though is does anyone know what kind of fluid they take and how much should they be filled up? I've heard power steering fluid or ATF would be fine but I'm not sure about this. I couldn't really identify the fluid that came out as it was just black or there was no fluid to start with. Would anyone be able to help with this? Thanks!
 

merc850

Commander
Joined
Jul 7, 2010
Messages
2,055
"Manual tilt / lift rams" have the fluid in them like the shocks on your car do, they're meant to stop the motor from flying out of the water if you hit an object with enough force. There's also a mercury switch that shorts out the ignition while the motor is up then restarts again when the motor enters the water; this happens very quickly at 25+ mph.
If you can remember how much fluid came out then replace it with some of a similar viscosity.
You can leave them off, or go to a dealer and find another set.
 

ONeils

Recruit
Joined
Feb 23, 2020
Messages
3
Ok. So these seals don't seem to exist :( There is no mention of them anywhere. I'm a bit stuck on that to do now. I've considered a power trim unit but from what I've seen online so far these are really expensive. As Merc850 said I could leave them off but i don't really like that idea. I'm based in New Zealand too and parts here are just super difficult to come by.
 

jimmbo

Supreme Mariner
Joined
May 24, 2004
Messages
14,113
In the 80s the 50hp didn't have the Shock Absorbers, they were removed to reduce costs. They weren't considered rebuild-able, just as complete replaceable units. I know they offered Resistance to the motor tilting up, but almost none in the downward direction
 

ONeils

Recruit
Joined
Feb 23, 2020
Messages
3
Hi guys! Sorry it took me so long to get back. I have been successful though! The hydraulic rams are working again. I found some seals at a local engineering company. I went there for new crank bearings and seals and showed them the seals from the rams. 2 minutes later they came back for their warehouse and had some seals that did the job perfectly! Sounds like they're not that special. I can share the specs of the seals if anyone wants them :) Thanks for all your replies.
 
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