The piston, heart of the engine: what is it, function, parts, characteristics, price

Pistons attached to connecting rods and crankshaft

The engine of our car has a lot of moving parts, but without a doubt, the piston It is one of the most important pieces. There is one per cylinder (except on opposed piston engines) and they are located inside the cylinder. engine block. They are in charge of compress the air-fuel mixture and receive combustion which moves it down.

What is a piston and how does it work?

When the mixture explodes, the piston receives a strong impulse that pushes it to the bottom dead center (BDC). Subsequently, this impulse is transmitted to the crankshaft through the connecting rod. to convert that vertical motion to rotary. The piston must be very resistant, since it supports high pressures and very high temperatures.

Today, most pistons in modern cars are built with a aluminum alloy with other material, such as magnesium or silicon. Thanks to this, the piston can reach a higher speed, increasing the rpm reached by the engine. Even so, there are also pistons made of nickel and iron alloy, cast iron and common iron.

Pistons of a four cylinder engine

Piston Features

Some basic characteristics that a piston must have are the following:

  • very robust structure in the areas that suffer greater stress (head and housing of the bolt or bolt).
  • must be light and all the pistons must have the same weight, thus avoiding possible imbalances in the cylinders.
  • The material with which it is made must have good thermal conductivity, being high temperature resistant.
  • must have great resistance to wear and corrosion.
Lambda
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The piston inside the cylinder of an engine

parts of a piston

  • piston head: It is the upper part of the piston where the mixture of fuel and air is compressed. Therefore it is also where the piston receives the enormous pressure and temperature that is produced when igniting said mixture.
  • moorland area: it is the vertical part of the piston where the compression grooves are carved
  • compression slots: there are usually two and it is where the segments are inserted to maintain compression in the combustion chamber.
  • oil control groove: normally it is one and it is where the segment or oil scraper ring is inserted. It is usually differentiated from the compression ones because they have vertical slots or holes for the control of expansion and draining of the oil.

piston rings

  • piston rings: are the rings that are coupled to the grooves of the piston. There are two types depending on the slot they are in and therefore on the function they perform:
    • The compression rings ensure that the combustion chamber is tight enough not to lose pressure, but not too tight so that the oil can lubricate the passage of the piston inside the cylinder. Normally there are two and the one on the front line against combustion is also often called the ring of fire.
    • The oil scraper ring is the one that allows part of the lubricating oil to pass towards the upper part of the cylinder to lubricate its movement, but at the same time eliminates the excess by sweeping. In this way, oil does not accumulate in the combustion chamber, which would mean excessive oil consumption, worse combustion and emission problems. The typical bluish smoke It is the one produced by burning too much oil.

grooves of a piston

  • Basin: it is the hole that goes through the body of the piston to house the pin, which is the one that fixes the piston and connecting rod assembly. It is called that because the tool with which it is made is an auger. That is, a steel instrument with a spiral thread for drilling.
  • inbar plate: is a cylinder mounted inside the piston around the bore. It is anti-dilating to prevent the parts from deforming with the heat and ending up wearing out the axis formed by the piston, the pin and the connecting rod.
  • Skirt: it is the lower part of the piston that safeguards the pin and the foot of the connecting rod
Segments of an engine piston
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Piston rings, rings or segments: types, functions and placement

piston types

Pistons with connecting rods inserted

We can find different types of piston according to its upper part or head. In most cases, the piston surface is flat, or slightly curved. However, in some models we can find specific shapes that facilitate the mix flow of air and fuel.

We can also meet small notches whose mission is to prevent the tripping Válvulas during its opening. This is because some engines can hold the valves open when the piston is still at or near Top Dead Center (TDC). If they weren't these notches the engine would suffer serious damage and expensive to repair. If the piston hits a valve, it is commonly called a "valvulazo".

inside of an engine
Related article:
Self-ignition, detonation and connecting rod knock

piston price

The price of a piston is very variable

Buy pistons for an engine not very common in cars, because internal repairs are usually very expensive. This is primarily due to the large number of hours of professional labor required to complete the job, rather than the cost of the parts themselves. A new piston can come at a price between 50 and 200 euros depending on the make and model. However, the labor can be thousands of euros.

In other types of vehicles, such as motorcycles, the change of pistons is more common. It tends to require less labor and parts are usually cheaper. It is easy to find pistons with a price between 10 and 100 euros depending on the brand and the displacement of the motorcycle.

Images 3, 4, 5 and 6 – Nick Ares, Craig Howell, Tony Harrison, Andrew Napier


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