The following are the key takeaways from this article:
- The piston is a cylindrical component responsible for compression and sealing the combustion chamber.
- The major piston parts include piston heads, bores, pins, skirts, and rings.
- Due to different issues, the pistons can face snapped timing belts, damaged rings, piston slaps, and burned piston heads.
- Common symptoms of this problem are excess white/grey smoke out of the exhaust, excessive engine oil consumption, and overall loss of engine power.
- The typical cost to resolve piston issues can range between $100 to $4000 (from single piston ring replacement to entire piston replacement).
An engine transforms the chemical energy of fuel into mechanical energy driving the vehicle. The main component responsible for this conversion is a piston.
When ECU guides the fuel injectors, the inlet valve opens, and a fuel stream is injected within the combustion chamber. The ECU then guides the piston upwards in the chamber, compressing the air-fuel mixture into a smaller space (1). The sparkplug then plays a role by igniting the compressed air-fuel mixture resulting in the combustion process. This resulting explosion pushes the piston downwards, completing the engine stroke. This article will particularly analyze the history of pistons, their major parts, their role in engines, issues, and the impact of these issues on engine performance.
Early History of Piston
The engine piston was first designed in 1866 by Nicholaus August Otto when he first designed the engine system. The piston in the old times was much different compared to the modern era. The design and manufacturing of pistons are evolving with time. Still, the function of the piston has remained the same. The piston is the lower half of the combustion chamber, and the purpose is to transfer the force to the engine’s crankshaft via connecting rods. The piston rings were usually round and made of metal (1). This round shape metal ring moves over the cylinder in an up-down direction. It helps in limiting oil usage and combustion blowby (4).
Major Evolvements in Piston
The piston’s most important area is the ring-shaped area. This area helps in limiting emissions. Thus the area is balanced so that the movement of the rings helps reduce emissions. The distance between the ring and the piston in 1990 was set between 7.5 to 8.0 mm. Modern designs reduce the distance to 3.5 mm (2). The design of the pistons has become compact. There is a small neck-shaped metal part above the piston, and it is the part where the combustion heat did not impact this area.
Major Parts of Piston
Following are a few major parts of the piston:
The piston head desires these characteristics to perform its operation effectively (2). Furthermore, aluminum alloys are machineable (casting/forging), making it easier for auto-makers to manufacture piston heads.
Piston Bore and Piston Pin
Two other components of the piston are the piston bore and piston pin. A piston bore is a simple small hole grooved at the side of the piston. This helps the manufacturers to keep the piston pin perpendicular to the piston. It is important because the piston pin is a small yet important component keeping the connecting rod at the right position of the piston (1).
Another important component within the piston is a piston skirt. The skirt portion keeps the piston closed to the crankshaft. This is helpful to align the piston at the right position when it moves in the cylinder bore during the combustion process. Some automakers also make profile cuts into the pistons to reduce the piston mass (2). This also provides clearance for the shaft and the counterweights playing their role within the engine.
Piston rings are retained within a groove located around the piston’s perimeter. There are different types of piston rings, but their main function is to provide sealing between the piston and the cylinder wall. The size of these piston rings can vary depending on the engine design and cylinder size. In smaller engines, the piston rings include a wiper ring, an oil ring, and a compression ring (1). The compression ring seals the combustion chamber from leaking during the combustion process.
The wiper rings also function to seal the combustion chamber and prevent any leakage. These wiper rings also perform a cleansing function, cleaning off the oil from the cylinder walls. While the oil rings, clean the excess oil from the cylinder wall and return it to the oil reservoir (1). That is why oil rings are missing in the pistons of the two-stroke engine, where the excess oil is required for ignition during combustion.
Common Problems in Piston
Following are a few common problems of the piston:
Snapped Timing Belt
But, if the timing belt is damaged, the movement of the piston is uncontrolled. Due to this constant movement, the piston will collide with the engine’s cylinders and ultimately create holes in the engine block (2). Thus, the engine block will break into pieces due to the piston’s hard collisions, and the engine can get damaged. Also, due to the snapped time belt, a harsh sound is observed from the engine, and there are chances that misfires can occur in the engine’s cylinders.
Damaged Piston Rings
Thus, it prevents the engine from getting overheated. However, the piston rings can get damaged due to errors in the combustion process. Due to faulty combustion, the fuel accumulates in the cylinder walls, and the friction increases, damaging the piston rings (3). Also, the pressure of the oil is disturbed due to the damaged pistons. Thus, due to the damaged piston rings, the engine’s efficiency is affected, and greyish-white smoke is released from the vehicle’s exhaust system. In addition, the engine oil is dropped below the level, and the required amount of power is not generated, which results in the poor acceleration of the vehicle.
Due to the piston slap, the engine becomes weak and is unable to perform well. The harsh noise is created in the engine (3). When the temperature in the engine is high, the piston in the engine becomes damaged. Also, because the piston slap distance becomes large between the piston and the cylinder wall, it makes harsh noises. As a result, the engine efficiency is reduced, making it difficult for the vehicle to travel long distances.
Due to the high temperature, the piston body will melt, or there are chances that a hole will be created in the upper part of the piston. As a result, the required amount of pressure in the engine will not be generated (1). This will result in the engine’s poor performance, and grey-colored smoke will be released from the engine system, indicating the issue with the performance of the piston. Besides, the engine will consume a large amount of fuel, and less power will be generated in the engine.
Common Symptoms of the Piston Problems
Following are a few common symptoms of bad pistons within the vehicle:
Excess White or Grey Smoke
One common symptom of bad pistons is excess grey or white smoke from the exhaust pipe. Excess grey/white smoke indicates that the engine is facing a leakage issue and the engine oil is burnt. This can indicate that either one or more pistons are malfunctioning and might need replacement (3). The leakage issue can be due to leaked piston rings, worn-out cylinder walls, and damaged valve seals.
Excessive Oil Consumption
Engine oil needs to be refilled after a particular time in the four-stroke engines, which helps in the lubrication of different engine components. After the combustion process, the oil piston rings clean the oil from the cylinder walls and send it to the oil reservoir (4). But in case of faulty rings or burnt pistons, the engine might burn more oil, and the driver might face excessive oil consumption.
Overall Loss of Power and Poor Engine Performance
As discussed above, the pistons play an important role in compressing the air-fuel mixture. But a burnt or deformed piston will be unable to seal the combustion chamber resulting in the release of pressure maintained within the chamber. Further, the burnt piston will not compress the air-fuel mixture in the same way as desired by the engine for optimum performance (5). This will eventually result in the loss of power and poor engine performance. So, suppose you are experiencing low RPM when even accelerating the engine. In that case, there is a chance that the piston/piston rings have gone bad and need replacement to avoid any further damage.