A motorcycle engine is responsible for enabling your motorcycle to move, and it is one of the most complex motorcycle components. They are mostly four-stroke or two-stroke engines with internal combustion, but you can find electric-type engines or Wankel as well. Engines are interesting motorcycle parts, and we will show you their working principle.
So how does a motorcycle engine work? The pistons move up and down, and their movement happens because of explosions of the fuel-air mixture that gets ignited by a spark. Valves open and close so the fuel-air mixture can get in the combustion chamber. The pistons turn crankshaft, which transmits the force to the rear wheel.
Since the motorcycle engine has many components, we will explain how they impact the engine’s working principle further in this article.
Table of Contents
How Does a Motorcycle Engine Work?
The motorcycle engine working principle includes gasoline that increases pressure once it gets heated. Hotter gas makes its molecules move very fast, and they collide with each other inside the engine walls. The release pressure is used to run the gasoline engine’s piston. Mixing fuel into the air is an easy way to heat the air. This mixture is then used to create power that allows the motor to rotate your bike rear wheel, making your bike move.
The top of a piston is the floor of the combustion chamber, and it slides down inside of the cylinder walls. A spark plug is placed in the combustion chamber roof, which starts combustion by igniting the fuel-air mixture. This fuel-air igniting is called ignition and is responsible for starting your engine.
The piston is attached to a rod known as a connecting rod, which is linked to a crank. The crank turns as the combustion pushes the connecting rod and the piston down. Momentum in the crank swings the piston and connects the rod again in the cylinder. This momentum is helpful because it makes the burnt, exhausted gas leave the cylinder of small valves that open and then to the exhaust system through which it leaves the motorcycle system.
A chain that runs from the crank to a camshaft or a spindle above the valves controls opening and closing valves timing. A piston is at the stroke’s top, and the crank is turning because of the momentum it has developed. The crank pulls the piston down the cylinder and allows the descending pistons low pressure to get another amount of fuel-air mixture to the cylinder.
Here is a great article about How to Remove a Motorcycle Engine, so click on this link if you want to learn more.
One more time, the piston gets to the bottom of the stroke while the cylinder is filled with a fuel-air mixture. Once the piston reaches the top, the fuel-air mixture ignites by the spark plug, and the piston is pushed down the cylinder again. The piston is still affected by crank momentum, and it rises again for the second time, and this time it compresses the fuel-air mixture.
This was an entire internal combustion engines cycle. In this cycle, the piston made two upstrokes and two downstrokes, indicating that this is a four-stroke engine. Like we said earlier in this article, there are many other engine types besides four-stroke, and two-stroke engines are another most widespread engine type.
What Makes the Motorcycle Move Forward?
The four-stroke cycle is a process that happens extremely fast. When your bike idles and is in a neutral position, the crank spins pretty fast at around 1400 revolutions per minute. 1400 revolutions per minute mean 700 squeezes, 700 sucks, 700 blows, and 700 bangs every single minute at each cylinder.
Note: 700 (not 1400) because every one is half a crank revolution.
So we established that the crank spins at high speed, but this doesn’t mean that if we connect it to the back wheel with a chain, our motorcycle will go fast; as a matter of fact, it would be quite the opposite, the bike would be pretty slow since it would have enough power just to drive your motorcycle slow enough, so it doesn’t stop.
It would be like you trying to race downhill with your mountain bike in the first gear while pedaling as hard as you can. It wouldn’t have much effect since you need to place your mountain bike in a higher gear to transmit your pedaling power to the rear wheel.
The same goes with motorcycles, and that is where the gearbox comes into play. The gears system allows us to lower the rate at which the crank spins, and this increases the force strength (torque) because of mechanical advantage to the point where the engine works at optimal revs, and it makes a motorcycle move forward at an optimal rate.
Note: What we want to achieve during a ride is change low torque and high crank speed and get high torque and low crank speed.
The crank has a gear that rotates other gears that we can select with a gear lever mechanism. We have described a one-piston operating process, and your motorcycle can have from one up to six cylinders.
There are a couple of ways that these cylinders can be positioned and installed on your bike, but most often, they can be found:
- Straight engine: inline fours, sixes, parallel twins
- V type cylinders: V-twin or V-four
- Flat engines: flat-six, flat-four, or flat twin
Many factors are impacted by the number of cylinders and how they are positioned on your bike. It impacts how your engine vibrates and how the power is delivered when a rider opens the throttle. Another thing that it affects is the way you handle your bike and your bike size.
Each cylinder configuration has its specifications that benefit different motorcycle types, and we will give you some examples.
- Single cylinders: Dirt bikes have the best performance abilities with single cylinders integrated with them, while single cylinders are not performing well on touring motorcycles.
- V-four cylinders: They are extremely good on sportbikes, and they make the best out of their engines, while they are very low performing on off-road engines.
These are some basic outlining of the engine’s working principle, and every engine has its strengths and weaknesses.
Two Stroke Engine
A power cycle is completed in a single crankshaft revolution. A two-stroke internal combustion chamber completes the two-stroke power cycle of the piston in a single power cycle. The combustion stroke end and the compression stroke beginning occur at the same time in a two-stroke engine, and the scavenging (or exhaust) and the intake happen simultaneously. One characteristic of two-stroke engines is that they have fewer moving parts than four-stroke engines.
Four Stroke Engine
A stroke means the complete piston moves through the cylinder in both directions. A four-stroke internal combustion engine completes four strokes while it turns the crankshaft. These four strokes are called:
- Intake: Intake is also called suction or induction, and it begins at the dead center top and finishes at the dead center bottom. The intake valves need to be opened during this stroke so that the piston can pull a fuel-air combination in the cylinder.
- Compression: In this stroke, the fuel-air mixture is compressed by the pistons; it is prepared for the ignition in the power stroke. The exhaust and intake valves are both closed in this phase.
- Combustion: Combustion is also called ignition or power, and this indicates the second revolution in the four-stroke cycle. The crankshaft made a 360-degree revolution in this stroke.
- Exhaust: Exhaust is sometimes referred to as outlet, and in this stroke, the piston gets from bottom dead center to top dead center, and the exhaust valve is opened.
Note: You can remember these four strokes by the following calls, and they are ” suck, squeeze, bang, blow”.
Here is a nice video you can watch that explains How a Motorcycle Engine Works:
Final Thoughts
This article has explained how a motorcycle engine works and the differences between four-stroke and two-stroke engines since they are mostly integrated into motorcycles. Make sure that you are familiar with your bike and its engine since it is a complex part that needs proper care.