Johnson Md-39 Cooling System

[willyboy]

In my budding addiction for this old outboard hobby I recently picked up a 1939 Johnson md39 1.1hp to add to my small but growing collection. Surprisingly after a quick spark plug clean and quick test I had spark.I added some fuel to the tank and dropped it on my test rack in the water barrel and it started after 6 or 7 pulls. It runs strong and idles down to low speed no problem,i’m assuming either I got really lucky with this old timer or someone before me has had it apart and gone thru it at one time and that’s why it seems to run good. My question is does this motor have to be in motion to cool itself or should it be ok running in the barrel? I only ran it for a minute or so in the barrel and when I shut it down it smelled a little hot and the bottom of the cylinder was quite warm.I haven’t taken anything apart as of yet and figured i’d ask before going exploring.Hopefully I can come with a parts manual or diagram of her on ebay to see where everything is.

[david-bartlett]

Willy,

If I am not mistaken, your motor has a piston pump for cooling. I have no experience with one, so I will leave it to others to elaborate, but if it seems hot, I would look into it before I ran it much more.

[willyboy]

Thank you,yes,it does have a piston pump cooling system. I’m not familiar with how they operate having only dealt with the rubber impellar type cooling systems. I know the inlet nut and screen are missing,maybe a passage way is blocked perhaps or there are other pieces missing.

[marvk]

I have a similar setup on a 1940 Johnson HA-15. Yes, it is a piston style pump. If you are missing the inlet nut and screen, you are also missing on of the 2 check balls for the pump to work properly. Mine was missing also. The first one sits on top of the inlet nut/screen, and the other sits above that incased in an outlet assembly.

[willyboy]

Thank you MarvK,can I ask where you got another check ball and inlet nut/screen? I’ve been surfin the net all morning just trying to find a parts diagram with no luck. Perhaps Doug Penn may have parts?

[marvk]

Yes, that’s where I got mine from. Can’t get them new anymore. I needed to find a donor motor. You can also try Dan Gano. He may have NOS parts for that motor.

http://www.ganotech.com

[willyboy]

Thank you,very much appreciated!

[willyboy]

Just a quick update on my little md-39 project,acquired the part from Doug Penn for the piston pump cooling system and it now cools without a problem. After seeing how that system works with the check balls,spring and ram riding on lobe on the prop shaft I cant believe someone thought that up as a cooling system and it worked that well lol. Unfortunately a little carb work is needed as now it only seems to run for a short time off the bowl gas and then stalls out. I can watch the float pin as the engine runs and when it bottoms out she stalls until more fuel runs into the bowl and raises the float.

[Doug Wilson]

might check the filter in the tank could be blocked with crud keeping the fuel from getting to the carb.

Doug

how is it motors multiply when the garage lights get
turned off?

[willyboy]

I haven’t checked the tank as of yet but I did take the carb off the engine and disassemble it for a mineral spirit bath to degrease it.The packing washer on the rich/lean needle was pretty much disintegrated and in need of replacement. The float actually looked great-no flaking. What type of gasket material would be suitable for reassembly of the carb plate to the water jacket on the side of the engine? The original was destroyed when I took the carb off and looked like it needed replacing anyway.

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