Hit - n - Miss Engine Governor
I have often been asked why Antique Hit - n - miss engines fire
the way they do. Many have noted that when a hit - n -miss engine
is runnning at idle speed, it will coast for several revolutions
and then fire. While not all Antique Engines fire this way (Volume or
throttle governed engine do not), most of the earlier ones do.
The answer as to why some engines run this way is actually quite simple
and is due the way the engine is governed (how the speed is maintained).
To get a visual idea of what I'm referring to, see the sketch below:
As one can see from the sketch, there is a small pair of weights that are
hinged near the hub of the flywheel (locations and configurations may vary).
As the engine spins, the weights in the flywheel begin to fly out due to
centrifugal force. When the weights fly out, they cause a guide that is free
move back and forth on the crankshaft to be pulled inward. Also located in the
guide on the crank of the engine is a small catch lever. The catch lever sits parallel
to the pushrod of the engine and is able to pivot like a seesaw. It's fulcrum is a stationary point
sticking out of the base of the engine. When the guide on the crankshaft of the engine is
pulled inward, it in turn, pulls in one end of the catch lever. The catch lever then pivots about
it's fulcrum and the opposite end of it move in toward the pushrod of the engine.
The catch lever then latches the pushrod of the engine and holds it in a forward
position via a small "catch block" that is fastened to the pushrod. Since the pushrod
of the engine is stuck in a forward position it causes the exhaust valve on the
end of the head to remain open. As a result, the all compression is vented out of the
exhaust port and the engine beings to slow down.
As the engine decelerates, the reverse of the process occurs and the engine
will unlatch the pushrod and allow the engine to fire again. If the engine were
put under a load, it would cause the flywheels to spin slowly and make the
engine fire more often.
This type of system is not by any means the exact system used on all makes and
models of hit - n - miss engines. It is however, probably one of the most common
setups you'll see (if you see) on an antique stationary engine.
Click here to email me
Return to the main page