Pistons are common in many mechanical systems. To help you get the drift of the piston meaning, I will start with its definition. After that, I will delve into the working of engine pistons, which is the subject of this guide. That will include its design, function, and operation. Discover also, the piston price further down the chapter, especially if planning to buy one for your car engine.
The piston definition first; A piston is defined as the plunger-like cylinder or disk that moves inside a pressure-tight chamber. In some applications, the movement helps pressurize a fluid. In others, fluid pressure causes the movement to happen.
Piston uses are many and varied.
- In automotive systems such as IC engines and brakes
- Industrial equipment like the piston water pump and piston air compressor
- Automated manufacturing systems such as valves
- In robot development to produce motion
- In medical equipment such as the piston syringe
The piston mechanism can be simple or complicated. A good example of simple piston is the medical syringe. On the other hand, one of the most complex and robust pistons you will ever come across is the piston of an engine.
Talking about the automotive piston, your car has this part in the brakes. Here, pistons are used to pressurize hydraulic fluid through the braking system. They are also used to push brake pads or shoes toward the rotor and brake drum.
The most important use of pistons on a vehicle is inside the engine. More about the engine piston and its working below.
Engine Piston: What is Piston in a car Engine?
The car engine piston is the moving component inside the cylinder bore. Engines that use pistons are commonly called piston engines. The part helps convert combustion pressures into motion. This motion is then transmitted to the wheels via several parts and systems. In other words, the piston movement makes your car to move.
The piston assembly consists of an upper cylindrical section called the head and skirt. This part connects metal sleeve called connecting rod, which then links to the crankshaft. Engine pistons form part of the crankshaft drive mechanism. They also seal the combustion chamber from below.
The number of pistons in an engine varies by application and ranges from 1 to as many as 8 or more. The 4 piston engine is the most popular, while the 1-piston engine is common in smaller machines such as lawn mowers.
It’s good to note that the number of pistons matches the number of cylinders in an engine. The number is also used to identify engines. A V6 engine, for example, means a 6-piston engine, a V8 8-piston engine. These large engines are normally found on large trucks and SUVs.
Away from the piston-cylinder relation, let’s see how this important car part works as well as its purpose.
The piston movement is key to the working of your car engine. As the part moves up and down the cylinder, it helps convert the force of expanding gases into motion. That in turn, means your car moving. Before delving into its working, let’s discuss the functions of a piston as listed below.
This is the main piston function. After igniting, the fuel in the combustion chamber burns explosively. The resulting force acts against the piston, pushing it down the cylinder. The piston then moves the crankshaft as the process repeats itself.
Seal the Combustion Chamber
The combustion chamber must remain pressure tight. This helps to build up pressures that cause motion. The piston facilitates that by sealing the chambers using one or several rings and a steady supply of lubricating oil.
Facilitate Intake and Exhaust
Another major function of pistons is to pull intake gases in and force exhaust gases out. The downward piston movement creates a partial vacuum that draws in air. The upward movement has the opposite action, pushing the products of combustion out of the cylinder through the exhaust valve.
Guide the Connecting Rod
The rod is held to the piston by means of a wrist pin. That way, the piston directs the movement of the rod so that motion transfers to the crankshaft smoothly. The method to connect the piston and connecting rod varies across pistons, with some fitting specific engine applications.
A piston is made up of metal parts. Usually, the material used offers a high thermal conductivity. That helps to conduct heat away through the cylinder walls, preventing damage to the piston assembly parts and other components.
The piston upper surface, known as the piston head or crown, is designed to regulate the combustion process. Some pistons have the crown in a profile that enhances compression, others a design to reduces it. That way, the amount of power that the piston movement generates is controlled to suit engine application.
Piston Operation: How does a piston work?
The piston operation helps with converting the energy of combustion into motion. It then transmits the motion to the crankshaft. From there, various parts of the transmission help to transfer the motion to the wheels and move your car. The operation is usually described in 4 steps called piston strokes.
- Intake stroke
- Compression stroke
- Combustion/power stroke
- Exhaust stroke
Intake Stroke– during the intake stroke, the piston is in the upper part of the cylinder moving downward. This movement is usually initiated by the starter motor. The downward motion leaves the space above a partial vacuum, thereby pulling air into the cylinder or combustion chamber.
Compression Stroke– the piston now begins moving upward, compressing the air fuel mixture in the process and helping prepare the mixture for combustion and intense pressure. This is the compression piston stroke.
Combustion Stroke- with the piston position still in the upper part of the cylinder, the fuel ignites. In a gasoline engine, the spark plugs provide the spark to ignite air fuel mixture. In a diesel engine, the force of compression heats up the mixture to ignition. The burning fuel releases energy and pushes the piston downward with tremendous force.
Exhaust stroke- this stroke has the piston moving up again under the action of the crankshaft. The piston movement sends the products of combustion, known as exhaust gases, through the exhaust valve. This piston stroke completes the cycle and the process repeats itself.
During these movements, the piston has to bear the pressure produced by the expanding gases, which are usually very high. Here, we are talking about up to 160 bar for diesel engines and up to 100 bar for a gasoline engine.
The piston operation described above also happens repeatedly when your car is in motion. During the process, the intake and exhaust valve must open and close at the right times, based on the piston position. This is automatically enabled by the engine timing system.
The timing system primarily consists of the crankshaft, camshafts, and timing belt or chain, among other parts. Auto manufacturers usually place these parts to operate the valve-opening sequence in a way that matches the engine configuration.
Piston Material: What are Pistons Made of?
Piston material is an important consideration among engine manufacturers and car owners. The engine cylinders where pistons are located are fiery chambers that experience extreme temperatures. High pressures, too, from the energy generated by the combustion process, among other harsh conditions such as physical impacts. The piston must weather all these. In general, the piston material must possess these properties.
- Rigidity to stand up to combustion pressures
- High melting point to withstand the big temperatures in the cylinder
- Excellent thermal conductivity to dissipate heat quickly
- Low thermal expansion to prevent what’s called piston seize
- Lightweight to allow a high enough engine rpm and efficiency
Piston manufacturers mostly use aluminum or cast iron to make the product. Aluminum alloy is the most common today, owing to its lightweight nature, good thermal conductivity, and the ability to offer better finish than many other materials. The material wears faster than iron, though, and does not produce durable pistons.
Cast iron is a hard wearing piston material and is still preferred in some applications. It also offers impressive rigidity and has a low rate of expansion. However, cast iron pistons are heavier than aluminum and not suitable for higher RPM applications.
When rebuilding an engine, pistons are among parts that need replacing. As such, you may want to be conversant with their prices. And if doing a piston upgrade, the price of the desired type of the part.
Most aftermarket pistons go for $200 to as high as $1000. This can be confusing, especially when planning to replace the part. So why the wide range for the cost? There are several factors that cause that.
Car engine pistons come in different types and designs. Some are made from higher quality materials than others, while others use a more complex and costly manufacturing process. There are also heavy duty pistons that cost more, or piston manufactures who sell their products at higher prices.
The piston to rebuild an engine usually comes as a kit. A piston kit contains parts that you need to install it, such as rings, pin, and circlips. Some vehicle owners choose to only replace the rings. If you do, you may be interested in their price.
Piston ring price ranges from $30 to about $100 for most pistons. The best piston rings will often cost a higher amount- and last longer. Other piston parts that are sold separately include bearings, connecting rods, and connecting rod bolts. Theses normally cost between $30 and $50 at most auto part stores.
Pistons find use in almost every industry. Automotive pistons are among the most common, the engine piston in particular. We have already discussed the appearance and working of this type of engine part. In the next chapter, I will explain the components that make a piston. You will also be learning about the process that manufacturers use to make this vital engine part.