Letters and Miscellanies

By Staff

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.

Stuart Faber
5512 Evergreen Ridge Dr.
Cincinnati, OH 45215
stuartlfaber@msn.com

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