Mercury 4.5 Been sitting for 25+ years

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Run

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Jun 7, 2015
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Alright BITOG crew, I have one heck of a project on my hands with this little engine. This has been sitting longer than I have been alive. I dare not try to turn it over until I consult with some mechanically inclined minds. How should I approach this beast? What can I use to free it up if the piston is seized? The first problem is old fuel and rotten fuel hose. That should be the easiest fix. I also have a Honda generator that has been sitting for 15 years. I will make a thread on that another day.
 
Take out the spark plug squirt some oil in the hole to lube the piston rings and see if the engine turns over. Report back. Do the same with the Honda.
 
This is where I actually trust MMO and have had good luck. starting ancient 2 strokes

Pull the plugs and squirt some in and turn the engine over by hand (at the prop nut) Let sit and do it again

The water pump is shot (pretty sure its a rubber impeller) so don't even fire attempt firing it till you replace that.

aside from sth rotten stuff you mention - do the impeller buy some fresh plugs and clean the carb(s) and it'll probably fire right up.

Looks like a nice specimen- these thing can last forever.

UD
 
ditto with oil or mmo in the cylinders. also disassemble the carb and clean it well. I agree that the water pump impeller should be checked. probably stuck and or rotted.
 
Make sure you look over the wiring harness throughly. I recently brought back to life an early 70's Mercury 500 outboard (50hp). The insulation on some the wiring was completely rotted away and this motor was in dry storage for 25 years also.
 
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How cool!!

If it was kept in clean dry storage all those years, I would not be surprised if it fired right up. I doubt it will pump water though. The water pump impeller will probably fall apart immediately.

We had a similar experience years ago when we bought a late 1950s model Evinrude 9.9 Sport-twin from it's original owner, on it's original Evinrude stand, with owner's manual, etc. It had only been used twice and looked it.

Water pump impeller needed to be changed, as did the ignition coils soon after.

The old pressurized fuel tank was the worst part and why we don't use the old girl anymore. I don't think Mercs of that vintage need a pressurized fuel tank thankfully.
 
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Don't let its clean appearance fool you. This was stored in a shed that wasn't climate controlled. It has seen hot summers and bitter cold winters.
 
Originally Posted By: Run
Don't let its clean appearance fool you. This was stored in a shed that wasn't climate controlled. It has seen hot summers and bitter cold winters.
Potential rodent damage? plugs are probably fine but the wires'insulation is shot. Carb and points condenser maybe. Nest inside housing?
grin2.gif
 
I didn't get a chance to dig into it. I suspect dry rotted gaskets.
 
Most of the gaskets will be OK. As mentioned, the impeller will be toast, replace before firing.

1.) MMO in the plug holes.

2.) Leave plugs out, lay on it's back with cover off and carb facing up. 1/2 cup MMO down the carb and pull the rope to suck it into the crankcase.

3.) Pull rope until you get oil splattering out the plug holes onto the ground/cardboard under the motor. Now you know there is enough oil in the motor to stand a fire-up.

You also know how it felt when you pulled it over. If it freed up and felt smooth'ish - you are on right path. If it felt gritty, you got issues ...

4.) Lower leg comes apart to change water pump impeller. Get book, or look at exploded diagrams on the web until you see exactly how to do this.

5.) Use Vaseline on all rubber mating surfaces when you re-install the water tube and any rubber bushings. Use it on the shaft splines going into the bottom of the crankshaft.

6.) Get a "nub" greaser. It's a small grease gun that does not really lock onto a zerk. It's a press fit onto grease nubs and it will feed a zerk unless it's frozen. Lube all points that have nubs or zerks.

Carb will prolly be OK, but needle and seat will be dry and powdery. Drop float bowl and clean them gently with nylon scouring pad until the needle is shiny. Make sure the float will move easily and will close off the fuel inlet.

Did you get a tank too? Fuel hose?

That's a nice motor - One of Mercs better ones
smile.gif
 
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