Marine Engine Collection of Mystic Seaport


Johnson Motor Co. SR-50


Engine Builder:
Model: SR-50
Make: Johnson Motor Co.
Inboard/Outboard: Outboard
Engine Type: Gasoline
Production Date: 1931
Engine Design: Two-Stroke
Overall Condition: Good
Rebuilt/Restored:
Horsepower: 16
Cylinders: 2
Bore:
Stoke:
Coolant:
Accession:1996.28

Remarks: Originally used for racing, where it was fueled by alcohol mixed with caster oil for lubrication. Engine has no exhaust manifold and also no water pump, since the SR-50 relied on boat speed to force water through the engine. Spark plugs are Champion K-60R. They are special racing plugs with fully shielded electrodes and an adjustable ground pin.The bronze plates on the cylinders are called "cylinder catchers". They were required by the racing committee. If the boat flipped over, water would enter the cylinder. The catchers prevented them from blowing off and causing injury. The SR-50 had a geared rotor valve which forced the fuel/air mixture into the crankcase. The faster the engine turned, the more fuel was forced in.


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1996.28-a.JPG
1996.28-b.JPG
1996.28-c.JPG
1996.28-d.JPG