Probably the most-recalled name would be John Deere, a/k/a Johnny
Popper, so named for its "make and break" or "hit and miss ignition."
That was a type of ignition used in the early days of gasoline engine
development, primarily for engines that needed to run at more-or-less
constant speed, as tractors do, and pumps, churns, generators, prime
movers, etc.
Advertisement--- the CT Antique Machinery Show, in which dozens of
owners (myself included) of these old rigs show off their operating
antiques, is this coming Sat & Sun in Kent, CT. Lots of early engines,
tractors, Stirling-cycle (hot air) engines, and steam engines both
stationary and portable are running, and a small steam locomotive, steam
road graders, tractors and more are always there. It's a fascinating
look at machinery of the 1880s - 1930s. On Rte 7, just outside Kent,
it's shares grounds with the Stanley-Eric Sloane Museum.
Using the Briggs & Stratton as an example of a current engine, for
comparison, the operating cycle of these M&Bs is similar, yet different.
While using the 4-stroke cycle of intake, compression, expansion and
exhaust, there is an interesting variation. Intake is similar except
that the intake valve is opened not by the cam, but by the suction of the
descending piston pulling the valve open against a light spring.
Compression stroke is the same. Ignition is similar, though the spark is
usually provided by a "buzz" coil. On these low rpm engines (250-650 rpm)
the points close, closing a circuit and the vibrating "buzz" coil
produces a spark at the plug as long as the points are closed. THis can
be over several degrees of crankshaft rotation, so the mix will always
burn. Piston pushes down, crank turns, etc.
Now, where the "hit and miss" comes in begins. Since you wanted the
engine to run at, say, 400 rpm, and the piston comes down with great
acceleration, the rpm rate exceeds 400. The flywheel weights move out and
push against a latch. Latch moves and pushes up the exhaust valve,
holding it open. At the same time, it may also hold the points so that
they won't close. The engine coasts until it drops to 400 rpm. During
this time you hear the characteristic wheeze as the piston moves up and
down while the exhaust valve is open. It's coasting--no compression, just
friction and inertia resistance. When the rpm drops below the set point,
the latch releases. Next intake stroke, since the exhaust valve is now
closed, the descending piston sucks in a charge through the carburettor
and, rising, compresses it. Near TDC the sparks begin and it fires, thus
bringing the engine's rpm rate over 400, and the coasting begins again.
Depending on the load on the engine, of course, it may not coast much,
or at all. It can fire on a regular 4-stroke pattern, but it doesn't have
to. So, if you heard the ol' John Deere heading from the barn to the
field you might hear the Pop, wheeze, wheeze, wheeze, Pop, wheeze etc,
then when the plough bit into the earth the sound would change to POP POP
POP POP.
These things are really neat. It's so interesting to imagine the
thought process of the engineers (probably self taught in 50% of the
examples) who worked out these rigs in order to lighten the incredible
daily labor of the majority of the population who lived on farms.
Perhaps an apocryphal story, but it's said that a group of women was
asked "What is the most useful kitchen appliance you have?" Some said
dishwasher, some said microwave, some said fridge. One older woman said
"running water."
Water weighs eight pounds per gallon. A cow will usually drink upwards
of 40 gallons per day. How many gallons per flush--if you had a flush
head? Running water.....
Bob
On Sun, 21 Sep 97 10:00:56 -0400 Larry Macy
<macy@bblmail.psycha.upenn.edu> writes:
>Hello??? Larry Dickstein
>
>>I could remember the tractor engine name that hit occasionally on one
>>cylinder and had a multi ton flywheel.
>
>Gravely?
>
|