Home › Forum › Ask A Member › New Motor Questions, 1950 Johnson SD-20 › Re: New Motor Questions, 1950 Johnson SD-20
New to the forums but have been involved with the AOMCI off and on since 1985.
I have two SD20’s that I purchased around 1973-75. One was a runner and still is and the other was somewhat cobbled but not butchered, so it provides me an excellent spares engine. I was working as a Johnson/Evinrude mechanic at the time (still am) and purchased these immediately. Never saw any others come through the dealer which had been in biz since the 40’s. I was also able to buy the few NOS parts that we had on hand.
This week I pulled the SD out for recommissioning after nearly 40 yrs of not being on a boat. It had been run in a test tank maybe 15 yrs ago. At that time it was run, fogged, the fuel system drained, and put away.
The sea trial was on a 14′ Sea Nymph and it ran great. I brought along an infrared temp reader to monitor the cooling system performance which I had no real experience with. As a matter of fact it had never been run on a boat at planning speeds while in my possession. Strong runner and the separate mag and carb controls allows one to really dial it in.
From what I could decipher the front intake only feeds the exhaust cavity coming up from the bottom and then out the discharge hole.
The intake at the exhaust snout eventually ending at the aft side lower gear housing assisted by the prop cools the powerhead. Powerhead temps ran in the 120’s to 140’s with the "dimple" (lower bump of exhaust manifold0 hit 200-220.
Steve