Letters: More on the Junkers Opposed Piston Diesel Engine

The Junkers opposed-piston diesel engine, explained by C.H. Wendel.


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In reference to August 2008's "The Man Behind the Books": I am confused on the line, "a single-cylinder opposed-piston engine diesel." Opposed to what? Another piston? No, "single piston." I hope you can explain more on the Junkers diesel. How about construction plans? Sounds like a good project to build. 

Bob Comer

Regarding the Junkers opposed-piston diesel engine design: It was proposed by Hugo Junkers, of Germany, prior to 1911. The Fairbanks-Morse OP engine was introduced in 1933. Some engineers claimed Fairbanks pirated the Junkers design.

The schematic above shows the basic design, two pistons coming together, with ignition between the piston heads. The top piston was connected through rods to the crank, the latter having three throws.

Junkers was the first to apply a modified opposed-piston engine to aircraft, building some diesel-powered aircraft during World War I. The partial cross-section photo shows a Junkers aircraft diesel of World War II. The Ju205 was a formidable heavy bomber.

During World War II, the Junkers factory at Dessau was completely destroyed.

The single-cylinder Junkers engine in my collection was shown at the Brussels Fair of 1933. Mr. Hobart of Hobart Welding Machine Co. bought it, with plans to use this 12-1/2 hp engine to drive his welding machines. Instead, it sat in a warehouse for many years, and I eventually ended up with it. In many travels, I have discovered a few Junkers engines, but mine is the only one I know of that is running.

It is a remarkable engine: It requires only one quick snap over center, and it is running. That is because of its many features far ahead of the time, including an injection pressure of 3,000 psi. On one of my trips to Germany, I found an instruction manual for it. Fortunately, I can read German!

C.H. Wendel
Amana, Iowa