Please Note: This technique works for the style used on Kiekhaefer models of Sea King, Wizard and Mercury up thru KE3. Later models are not same.The example used is the following pictures are from a Model K2.

1) Take it apart down to individual parts

2) Clean and degrease

3) Prime and paint

Then comes the put it back together part.

Really grungy...on the other hand someone was kind enough to do the hard work of taking it apart...this proved to be a restoration with several difficult
to resolve problems which required services of a welder,machinist and a tank and radiator shop to resolve. A nice first year Mercury single worth 
the effort to restore. It really took some doing though. Louis
Moral of the story is beware of motors that have been taken apart and left that way...unless of course the price is right.

Not yet completed. It has been a long learning experience.
I am awaiting warmer weather to smooth tank surface and apply decals
Tank & Radiator shop repair left a rough surface which has required a
lot of sand and fill while being careful not to go to deep.

I acquired Parts in a Bin because it looked like a project with my name
on it. It came to my notice at the end of a large well attended meet. If any
one had given it a glance they passed it by. There was room on my bench for a
new project and this looked like fun. It proved to be all the fun I could
handle but in the end it all worked out.
The dark motor is a 1940 Kiekhaefer single that someone had modernized
with a coat of green paint. Obviously not factory. I could have saved
myself a lot of trouble by making use of this parts motor...that did not come
to mind until Parts in a Bin was as you see it.