Letters and Miscellanies

KC Lightning

| February 2005

The Lightning engine described in the November issue of GEM was most interesting. It would be very interesting to know more of the details of how the valves and fuel induction worked on the Lightning.

The design approach of two opposed pistons in one cylinder was used in a number of engines in later years. Some of these were large industrial engines, usually diesels. However, the push-pull connecting rod system was new to me. Other two piston engines I have heard of used two crankshafts.

Probably the largest number of this style engine built was the Junkers Jumo 207, a 1,525-cubic-inch turbocharged diesel of 1,000 HP. It was an inline six-cylinder, two-stroke, liquid-cooled engine and probably ran around 2,000 rpm. It was used in a number of German military planes in WWII.

In the Jumo, one crank was at the bottom and the other at the top, making a narrow, streamlined, low-drag installation. The two cranks added weight, but required much shorter crank throws to reach the needed compression ratios. Fuel economy was very good.

Another thought that comes to mind is that the prices of old machines usually quoted are of the period and seem very low by current thinking. If adjusted to current values, they give a far different picture. The price of $900 quoted in the article on the Lightning engine was mentioned as being quite high for its time and limiting sales. A rough estimate would indicate the price for that engine today would be about $18,000. However, you can buy a modern engine of about 6 HP for under $400. Not everything has gone up in price.

Another thing I wonder about is the engine speed listed for many old engines. In the 1940s, my construction business owned an old Jaeger concrete mixer with a Hercules hit-and-miss engine of about 6 HP. The manual listed the maximum rpm at 250, but a check of the speed indicated it ran at about 125 or 150. Anything over that caused the whole mixer to jump around. Was that normal? Although it still worked, it was too hard to move, and ready-mix was available, so it was scrapped for junk.


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