• How Small Engine Operate

How Small Engine Operate

How Small Engine Operate

All gas-powered brush cutter, mower, blowers and chainsaws use a piston engine that is similar in significant respects to those used on automobiles. There are differences, however, most notably in the use of two-cycle engines in chain saws and grass trimmer.

Now Let’s begin at the beginning and see how the two-cycle and more common four-cycle engines work. This will greatly help you understand what’s happening when an engine doesn’t run.

The engine develops power by burning a mixture of gasoline and air in a small enclosure called a combustion chamber, showing in the picture. As the mix fuel burning, it becomes very hot and expands, just as mercury in a thermometer expands and pushes its way up the tube when its temperature rises.”

The combustion chamber is sealed on three sides, so the expanding gas mixture can push its way in only one direction, downward on a plug called a piston-which has a close-sliding fit in a cylinder. The downward push on the piston is mechanical energy. When we have circular energy, we can turn a brush cutter blade, a chain saw, a snow blower auger, or the wheels of a car.

In the conversion, the piston is attached to a crankshaft, which is in turn attached to a crankshaft with offset sections. A crankshaft functions much like the pedals and main sprocket on a bicycle.


When you pedal bike, the downward pressure of your foot on the pedal is converted into circular movement by the pedal shaft. Your foot pressure is similar to the energy created by the burning fuel mixture. The pedal performs the function of the piston and connecting rod, and the pedal shaft is the equivalent of the crankshaft. The metal part in which the cylinder is bored is called the engine block, and the lower section in which the crankshaft is mounted is called the crankcase. The combustion chamber above the cylinder is formed in a metal cover for the cylinder, called a cylinder head.

As the piston connecting rod is forced down, and it pushes on the crankshaft, it must pivot back and forth. To permit this movement, the rod is mounted in bearings, one in the piston, the other at its connection point to the crankshaft. There are many types of bearings, but in all cases their function is to support any type of moving part that is under load. In the case of a connecting rod, the load is from the downward moving piston. A bearing is round and super-smooth, and the part that bears against it also must be smooth. The combination of smooth surfaces is not enough to eliminate friction, so oil must be able to get between the bearing and the part it supports to reduce friction. The most common type of bearing is the plain design, a smooth ring or perhaps two half-shells that form a complete ring, as in l-l.

Although parts that bolt together are machined carefully for a tight fit, machining alone is not enough. A seal must often be placed between them to prevent leakage of air, fuel or oil. When the seal is a flat piece of material, it is called a gasket. Common gasket materials include synthetic rubber, cork, fiber, asbestos, soft metal and combinations of these. A gasket, for example, is used between the cylinder head and engine block. Appropriately, it’s called the cylinder head gasket.

Now let’s take a closer look at the gasoline engine’s actual operation, which may be either of two types: the two-stroke cycle or the four-stroke.

Post time: Jan-11-2023