Forklifts are classified as vehicles with small engines, the same category in which lawnmowers are classed. Forklift engines all follow the principles of internal combustion. Various lift truck models and brand names will have varying engine design and layout. Forklifts are designed more toward producing high torque than for speed. They normally are geared to low speeds. The engine runs the forklift's drive wheels. The engine is also required to lift and lower the forks via a series of chain pulleys. Most modern lift truck engines are fueled by propane as they would be used for indoor applications, where gasoline and diesel engines will be inappropriate due to the exhaust they produce.
Usually, the lift truck is a four-cylinder engine-block. Forklift engines are similar to car engines because they hold pistons connecting to a camshaft. Every cylinder head consists of an exhaust hatch, a spark plug and an exhaust hatch, each of them one-way and spring-loaded.
When the driver starts up the engine of the forklift, propane passes through the opened throttle-plate in a fine spray and mixes with air which comes from the mass air intake prior to moving into the head intake hatches of the cylinder. Each and every one of the four pistons is staggered to rise in an exact sequence, compressing the propane and air mixture as each piston rises to the top of the head. With very precise timing, the alternator and battery of the engine create an electrical current that passes through the spark plug. The fuel ignites resulting in an explosion that drives the piston back down to the bottom of the cylinder, causing a continuous turning of the camshaft. An air pressure imbalance in the cylinder causes the the exhaust hatch to draw out exhaust when more fuel passes into the cylinder. Propane burns a lot cleaner than gasoline and diesel and the exhaust is not as harmful.