How Does an Engine Work?
An antique engine works on a 4 stroke principle
much the same as a car does. A process similiar to
the 4 stroke principle is loading and firing a cannon.
While many people can't relate to this, I'm sure they've
seen a cannon operate in the movies.
In order to fire a cannon, the
operator must first pack the cannon with gun powder and
wadding material. After these materials are in place,
the cannon ball is dropped into the end of cannon. Once
the cannon is ready, the operator will use a flame to ignite
the gun powder and eject the cannon ball. After the cannon
has been fired, the cannon is cleaned so that it will fire
properly the next time.
This same process provides a good analogy as to how a
4 stroke engine works. Most 4 cycle antique engines operate
by these methods:
First, the piston is drawn backward in the cylinder
by the crankshaft. As the piston moves backward, the
volume of the cylinder increases, which results
in a drop in pressure within the cylinder (A vacuum
is generated). The pressure soon reaches a critical
point, and causes the intake valve to be "sucked" open.
Fuel is then "sucked" from the gas tank into the
carburetor. Once the fuel reaches the carburetor,
it passes into the cylinder along with air. As soon
as the crankshaft starts to revolve the piston forward
in the cylinder, the volume of the cylinder decreases
and the intake valve is forced closed. This is known as
the intake stroke, or in my cannon analogy, the
step where gun powder and wadding are added.
Second, the piston continues to move forward and
compress the air and fuel that is trapped inside of the
cylinder. The piston will then keep moving forward until
the crankshaft just about starts to pull back on the
piston (for technical types - Top Dead Center, or the top
of the stroke). At this point, the fuel and air in
the cylinder becomes highly compressed. This is the
compression stroke or in the case of the cannon, the
"packing in" step.)
Now that the piston has compressed the air and fuel,
a battery or some other power source will cause a single
spark to jump the gap of the spark plug. Since the spark
plug is screwed directly into the cylinder of the engine
and in direct contact with the air and fuel, it will cause
the air and fuel to explode and throw the piston backward.
This stroke is known as the ignition or power stroke. In
the case of the cannon analogy, this is the time when the
fuse would be lit.
Finally, the crankshaft will spin 180o and
cause the piston to move forward again. The push
rod and rocker arm will then open the exhaust valve
so that the remaining fumes can be forced out by the
piston (In your cars case, the valve may be opened
by a cam instead). This is known as the exhaust
stroke or "swabbing" in the cannon's case
This entire process is the same process which most people
are (unknowingly) familiar with because they own automobiles.
While cars today have many added things such as fuel injection,
cams, and a zillion added electronics, this same process is the
base for how the engine functions. A car simply completes this
process by using 4, 6, 8 or more cylinders
Now that you (might) understand the 4 cycle process, why
not see what makes a hit-n-miss engine a hit-n-miss engine?
Click here to see an explanation of an antique engine governor.