1979 Mercury 70hp 3 Cyl

Hi all,

Last night I bout a 70's Monark 15' Monark Fiberglass tri hull boat, with a partially diasassembled 1979 Mercury 70hp 3 cyl motor. I plan on building a stand maybe this week of next weekend to mount it on that way I can get a better look at everything rather than it laying on the deck. The big thing that has me worried is there have been no spark plugs in it for who knows how long. I sprayed deep creep in the cylinders earlier today to let that soak in for a little while and the motors does not seem to be locked up I barely spun the crank (maybe an 1/8 of a rotation) and it rotates the prop but i wont know for sure until i get it up off the deck. Does anyone have any experience with these motors, I feel like a 70 is a pretty stout motor to put on the back of this boat.

Thanks,
Drew

Might need new rings, and the bearings might be shot as well. Not good leaving them laying about like that.

Jeff

That a crank rated 70hp and is equal to a 55-60hp at prop, will work fine on that lil boat.

http://www.maxrules.com/oldmercs/Wiring/1966ona/54.jpg
This should be your motor what kind of controls does it have for the motor? It looks like the orange wire is for the kill circuit never apply battery pos to that wire. You should get a good manual with the proper wiring diagram for the ignition switch.

fastjef said:

Might need new rings, and the bearings might be shot as well. Not good leaving them laying about like that.

Jeff

Click to expand...

I agree, I'll know more once I get the motor upright.

http://www.boats.net/parts/search/Merc/Mercury/1979/parts.html


I took yesterday off, and built a stand for it in the morning, got it mounted later in the afternoon. Thankfully the engine is not seized up, and has decent compression, with just a drill on the crank shaft I was getting 70-72 psi in all cylinders. Im going to atleast get the starter set up to where I can get power to it and check actually pressure. Does anyone know what the specs on that should be?

Im looking for parts on boats.net, and at the bottom of their mercury page theres a chart that references serial numbers, and tells me that this motor is a 1979 year but then it lists 40 or so models (I've linked the website above) how do I find out which motor this is?

The serial number is 5128949



-Drew

I see 140 psi regularly on mine. Above 120 should be fine.

Jeff