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:
  • 1. 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.
  • 2. 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.)
  • 3. 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.
  • 4. 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.