Gasoline Engine basics

The majority of the passenger vehicles sold through out the world are powered by a gasoline internal combustion engine. This time Lord Funkatron will walk you through the workings and parts of a four stroke gas engine. So hit the bump and read on about the powerplant in your ride.

The four stroke gas engine. The motivating force inside you car. It’s theory is simple. It can be broken down to four simple steps. Suck, bang, squeeze, blow. I’m going to cut away all the rest of the engine and just focus on one cylinder for right now. We start by hitting the starter and getting the internals moving. The piston is at its highest point, top dead center or TDC. As it is moving down the cylinder, the intake valve has opened up. Air and fuel mixed together is being sucked into the cylinder by the downward movement of the piston. (Suck) Once the piston hits its lowest point, the intake valve closes and the piston is now moving up the cylinder compressing the air and fuel mix. (Squeeze) Now that the piston has reached back to the TDC position again the compressed mix is ignited by the spark plug. The resulting burn is rapidly expanding and pushing the piston back down the cylinder. (Bang) The piston finds itself back at the bottom and now starts moving back up, at the same time the exhaust valve opens up and its pushing the spent gases out of the cylinder. (Blow) This happens over and over again until you get to where your going and turn the engine off by killing the power to the ignition. This is its basic operation in a nutshell. You add back the other cylinders timed out to push when other pistons aren’t firing and it keeps the works moving along in a nice, smooth fashion.

four stroke cycle

With basic operation explained I’ll move on to the identifying the parts by following the path of the air into and out of the engine. I’m going to use a older carbureted, overhead valve design for simplicity. The function of a later fuel injection system works the same except the addition of the fuel is mixed at a later time. The air’s path starts by passing through the air filter and moving through a carburetor. The carburetor has a multifunction job. Its throttle opening allows more or less air to move through it. Allowing for more or less power. It also is also where the air is metered and mixed with the now incoming fuel. Now mixed, the air/fuel mixture moves into the intake manifold and waits for an intake valve to open up.

Carburetor and intake

The camshaft lobes push up a lifter, that moves the pushrod, that in turn pushes on a rocker arm and opens the intake valve situated in the cylinder head.

valvetrain cutaway

Once that happens, the mixture flows through the head and into the cylinder and the four stroke cycle as explained earlier happens is runs into the piston and its rings that stop the majority of the burn from blowing by. This is all happening within the engine block. As the burn pushes down the piston, the power is transmitted to the crank where the up and down force is turned into a rotational force.

engine cutaway

The air moves out of the cylinder and past the exhaust valve, thanks again to the cam and its followers, and is moved out the exhaust manifold and back out into the atmosphere.

The ignition spark that lights the fire gets stored in an electric coil. That at the right time gets sent to the distributor. That sends the spark to the individual cylinder’s spark plug through a spark plug wire.

ignition diagram

Now the distributor gets its motion and timing by being connected to the camshaft, usually by a gear. The cam gets its motion and timing from a chain connected to the crank, which got its power from the piston, that got its….. . Also connected to the distributor through a shaft is the oil pump, which keeps the whole works nice and slippery.

Keeping the whole package nice and cool is the water pump connected to the crank usually by a belt on the front of the engine. Also on this belt or other belts powered by the crank is the alternator, that produces the electric charge.

As you can see its all connected and if one thing breaks down, the whole engine becomes a useless lump. Keeping the oil changed and filters clean, as well as normal replacement of other wear items like the spark plugs and wires will keep your engine humming for a long time. I hope this clears up any questions you might have about the function of a four stroke gas engine. The performance increasing aspects will be outlined in articles on each individual part or segment of the engine.

As always, any questions, comments, requests, leave them in the comments. We’ll get to them eventually.