Piston And How It Works
What Is A Piston?
A piston is a mechanical device that moves upward to compress gas and downward due to an explosion in a cylinder to transform heat energy into mechanical work. A piston follows a cyclical process for the continuation of the heat-converting process. The process is achieved in three ways:
1. Providing heat to the gas inside the cylinder for useful work
2. Removing heat from the cylinder to decrease the pressure so that the gas can easily be compressed
3. Applying work to the piston when it’s in its initial state, ready to perform the cycle again.
Functions Of A Piston In Internal Combustion Engines
Pistons play a vital role in an automobile engine including the spark ignition gasoline engine and compression ignition diesel engine. These two internal combustion engine process is different but they utilize piston for their processes. Below are the functions of the piston on an automobile engine:
1. The major function of a piston is to transfer the force output of a small gas explosion in the cylinder to a crankshaft. This provides rotational momentum to a flywheel.
2. It moves forward so that gases can be compressed and an explosion can occur for the backward movement.
3. The piston contains a pin called a piston pin, which allows the gas in the chamber to escape.
4. A connecting rod attached to the piston’s bottom allows the mechanical work to be transferred.
5. Pistons help to carry the air-fuel mixture within the period of the combustion cycle.
6. Pistons aid the control of oil flow in the cylinder walls using the oil control ring.
How Does A Piston Work?
Asking how a piston works, you will be exposed to the entire working principle of the internal combustion engine. This is because the piston does the major work during the four-stroke cycle.
Just as earlier mentioned, an internal combustion engine is of two types and they work in two different manners. One of them works with a spark plug, hence it’s named a “spark ignition engine” and the other a “compression ignition engine”. Their work is quite different. Well, the working of this engine has been covered in another article.
Major Parts Of Pistons And Their Functions
Below are the major parts of the piston:
1. Piston skirt: A piston skirt is a cylindrical material attached to the round portion of a piston. It is usually made from cast iron in order to resist wear and its self-lubricating properties. There are grooves on the skirt that allow the piston rings to perfectly sit. The function of the piston skirt is to travel up and down the cylinder.
2. Piston rings: Piston rings are the pieces of split rings that are mounted on a recess area of the piston. There are usually three piston rings in an engine. Sometimes the ring can be one, depending on the engine type.
3. Piston bearings: The bearings are great piston parts that aid the effectiveness of the movement. It’s located at the points where the pivotal rotation occurs. These bearings are usually semicircular metal pieces that fit in the bores of these points.
4. Piston pin: The piston pin is a piston part that is also known as a wrist pin or gudgeon pin. This pin is the hollow or solid shaft in the skirt section. There is a piston rod pivoted on this pin, held in the piston ring bushing. The function of the piston pin is to offer bearing support so the piston can function properly.
5. Piston head: This part of a piston is also known as a crown or dome, which is the top surface. It’s the part that contacts the combustion gases, making it experience an extremely high temperature. The function of the piston is to receive pressures, temperatures, and other stresses of the expanding gas.
6. Connecting rod bolt: Another piston part that cannot be left behind is the conrod bolt. It is used to mount the rod to the crankshaft. There is a rod caps and bearings at the bottom end of the rod bolts. A nut is then used to lock the components down together with the bolt.
7. Connecting rod: A connecting rod is one of the major parts of the piston most time shortened as a conrod or rod. It connects the piston to the engine’s crankshaft and allows the piston’s movement in the chamber. The component is designed to bear mechanical strain which is why it’s sturdy enough. The piston parts are made from forging and sometimes casting process.
Types Of Pistons
Below are the three types of pistons:
1. Dish pistons: a dish piston is shaped like a plate with slightly curling up outer edges. It is easy and simple as well as giving fewer issues to engineers. It’s often used in boosted applications that do not require a high-lift camshaft or high compression rate.
2. Flat-top pistons: the flat-top type of piston has a flat top. It has the smallest amount of surface space, giving the chance of creating the most force. It’s perfect for creating efficient combustion. The flat-top pistons create a high explosion in the chamber, but compression might be too much for smaller combustion chambers.
3. Dome pistons: the concept of dish pistons is quite opposite to the dish type. The middle bubble in order to increase the surface area left on the top of the piston. Well, more surface area means less compression, while more compression indicates more force created. The combustion chamber has an upper limit it can handle, so reducing the compression rate is the best option for preventing the engine from breaking down.
Common Piston Problem
Although your engine’s pistons are durable and do not require a lot of routine maintenance, problems can occur that can affect your overall engine performance, especially in older engines. Below are the most common problems that can occur with your engine’s pistons.
1. Piston slap: The “piston slap” is the name given to the noise that the pistons create when they get worn out. As your pistons wear, the gap between the piston and the cylinder it is encased in increases. When this gap gets too large, the extra space will cause the piston to get noisy, creating the piston slap sound. This is a sign to get your engine’s pistons replaced.
2. Worn piston rings: Piston rings are wrapped around the outside of the piston and are essential in removing heat off from the piston and dissipating it alongside the cooler cylinder wall. They also create an airtight seal that ensures that engine oil does not flow past the piston and into the firing chamber of the engine. Piston rings will wear over time and you can usually notice that the seal is broken through when you notice a drop in engine oil level or white smoke coming out of the exhaust tailpipe.
3. Burnt piston: When errors are made in the setup of your car and engine components, the tops of your pistons can get torched as a result. In severe cases, holes can be created in your pistons as well. This is usually due to a dirty fuel injector or the wrong type of spark plug being installed in your car. Burnt pistons will greatly reduce your engine’s output.
4. Cracked piston: Consistent use of poor-quality gasoline will lead to your pistons becoming cracked, which may impact your car’s ability to run at all. Cracked pistons can also be a symptom of larger vehicle problems, such as a failure in the exhaust gas recirculation (EGR) system.
Piston Maintenance And Repair
Piston repair is labor-intensive and expensive since it requires the engine to be taken apart and reassembled with the repair or replacement is complete. The best way to avoid problems with your piston is through preventative maintenance with the rest of your vehicle, particularly the engine.
Piston Repair Options
As we have seen, you can only repair an engine piston by changing bad rings, worn bearings, and damaged piston bolts. These parts are also sold in the auto parts market, either as separate parts or in a kit. Below is a description of what it entails to fix engine pistons.
Piston Repair by Replacing Rings
Piston rings usually wear down over time, or they can deform under the harsh conditions inside the cylinder bore. In order to replace them, the piston must come out of the engine. Different types of piston rings also go into different grooves.
Damaged rings cause blow-by, overconsumption of oil, and other symptoms of bad pistons such as piston slap. Before changing them, it’s crucial to perform tests such as compression and leak-down tests. A physical examination is also required.
Installing piston rings requires one to follow the replacement instructions. That’s because incorrect installation can result in engine problems, even piston damage. You also need various tools, such as the piston ring expander.
Most of the time, the cylinder bore requires machining to accommodate the new rings. This is usually better done at a repair shop or by an engine rebuilder.
Piston Repair by Replacing Rod
The connecting rod joints the piston assembly to the crankshaft. It rarely gets damaged unless an incorrect piston is used in an engine. The rod may also break if the timing goes wrong and the piston hits the valves, or if the bearing is starved of oil and seizes.
In order to replace piston rods, the piston assembly itself must be removed. Rod installation is a labor-intensive job that many people might not want to undertake. Selecting the correct rod for your engine might also be cumbersome, given the many different materials used to make them.
Piston Repair by Replacing Bearings
Piston rod bearings are positioned at the big end and small end of the connecting rod. The piston needs these crucial parts to operate smoothly. To replace them, you only need a few tools and materials.
Piston bearings get damaged in many ways, such as through oil starvation, which causes excessive friction and wear. Particles in the oil or from other sources can also cause abrasion and wear down the bearings.
You can easily replace the bearing without removing the engine or pistons. However, you would need to raise the car and access them from underneath. There are also the undercarriage parts and the oil pan to remove.
Piston Repair by Replacing Bolts
These are also known as the connecting rod bolts and are located at the point where the piston and crankshaft meet. The process of replacing bolts requires regular tools such as a torque wrench, ratchet, socket set, and some lubricating oil. You also need the manual with you.
Conrod bolts can get damaged in many ways. Most of the time, it’s the violent piston movement that takes a toll on them. Corrosion also causes damage or wear that happens over time and loosens the bolts.
The bolts are made from a wide range of materials, such as steel, aluminum, and nickel alloys. They also come in different designs. It’s crucial to match the bolt specifications with those installed on your engine. Most importantly, ensure the correct torque during their installation.
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