Hit Miss Gas & Double-Acting Steam Engines
A scale Economy
Hit
Miss, rough cast gas engine kit that my brother & I machined.
This old engine
design did not have a carburetor with a throttle.
A series of combustion cycles occur (hit) until it reaches the set speed.
When the brass centripetal governor weights move outward due to the increasing
speed,
linkage is engaged that holds the exhaust valve open (miss). The motor then
coasts,
with the cylinder open to the atmosphere, using the momentum of the two heavy
flywheels.
As the motor speed free wheels down, the two governor weights move inward
unlocking
the pushrod linkage, closing the exhaust valve, and allowing combustion cycles, again.
There is no pushrod for the gas-intake valve. It is held closed by a spring & sucked open
by the vacuum that is created in the cylinder when the exhaust valve is closed.
This cycle pulls the gas/air mixture into the cylinder for the next
combustion cycle.
This engine will run at its lowest
speed for 1 hr 10 min on 1 oz of gas.
[click on photos for movies]
Making this
engine involved many different machining setups & procedures: broach cutting,
deep hole
drilling/boring,
precision reaming, angles requiring a sine vise, rotary table, turning on
centers.
Irregularly-shaped cast parts are a challenge to orient & hold requiring
many standard & custom
fixtures.
Note brass governor weight on a pivot.
Using a 20° angle setup on
a sine vise, first spot drilled with an end mill followed by
drilling & 8-32 tapping for a cast
iron, fly wheel hub set screw. The flywheels have
broach-cut keyways.
Note the rough-cast crankshaft has three centers to
lathe the shaft, throws, & connecting rod journal, separately.
A
counter-weight was added to the faceplate for better balance.
All parts were machined from either
rough castings (iron or aluminum) or raw materials, following dimensioned
engineering drawings.
Drilling 1" hole in cast iron
before precision boring the cylinder to size.
Cutting the piston off.
The small, bull-nose live center helps to eliminate most chatter.
This particular center has seven interchangeable tips.
[click on photo for movie;
engine running on compressed air]
A double-acting steam engine from a castings kit.
