Major parts of pistons and their functions

Piston parts work together for the transformation of heat energy into mechanical work and vice versa. It moves upward and downward inside the cylinder in order to expand and contracts air-fuel mixture. For this reason, a piston is inevitable in an internal combustion engine.

complete parts of piston

Read Everything you need to know about automobile piston

Today we’ll be going deep into the major components of pistons and their functions.


Major parts of pistons and their functions

Below are the explanations of major components of a piston:

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.

The primary function of a piston ring is to seal off the combustion chamber and control lubricating oil usage. The rings also help to convey heat away to the cylinder bore.

The first ring nearest to the combustion chamber is known as compression ring. It is also called a gas or pressure ring. It prevents combustion gases from leaking and transfer heat from the piston to the cylinder walls.

Scraper or wiper ring is the ring located at the middle of compression and oil rings. It’s designed with a tapered surface and serves the function of the first and last rings. Its purpose includes sealing the combustion chamber and wiping off oil in the piston’s cylinder walls.

Finally, the oil control ring is the lower ring on the piston. It consists of two thin surfaces carrying holes around them. Its function is to allow the backflow of oil back into the sump and to remove excess oil from the cylinder walls.

piston rings

Read: Components of an automobile engine

Piston skirt:

A piston skirt is a cylindrical material attached on the round portion of a piston. It is usually made from cast iron in order to resist wears and its self-lubricating properties. There are grooves on the skirt that allows piston rings to perfectly sit.

The function of the piston skirt is to travels up and down the cylinder. It’s designed to withstand the side forces developed while changing the angle of the connecting rod. There two main types of piston skirts namely; full skirt and slipper skirt.

The full piston skirt is also known as a solid skirt. It’s designed in a tubular shape, commonly on used in large automobile engines. While the slipper piston skirt is commonly found on motorcycles and few cars. There is some part in the skirt that’s cutaway leaving only the surfaces on the back and front of the cylinder wall. This reduces the weight and minimizes the contact area between the cylinder and piston wall.

If the skirt is worn, it will be difficult to obtain a proper seal for efficient combustion. The piston will also rob the cylinder in an uncontrolled manner which will cause piston slap. With this, piston slap noise will occur, especially during cold starts. The noise will suddenly disappear as soon as the engine gets warmed. This is because the resulting expansion closes the gap between the piston and cylinder.

In situations where the noise does not stop, the cylinder may need to be tightened and probably some other measure. If not, the issue could cause more damage to the engine.

skirt of piston

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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.

Piston pins are created from alloy steel in order to offer a good tensile strength. it’s then machined to fit the piston bearings. Oil is delivered to this pin through holes in the connecting rod, helping to reduce friction.

The function of the piston pin is to offer bearing support so the piston can function properly. This is because the piston pins form a connection or pivotal point of the pistons and connecting rod. This is to say the pin assist the back and forth movement of the piston. There are three types of piston pin out there.

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The stationary or fixed pin is one of the three types. It’s attached to the bosses of the piston through a screw which allows the piston rod to be positioned into it.

A semi-floating is another type of pin which is attached to the connecting rod at the middle. It’s designed to freely move the piston bearing and at the bosses. Finally,

The full floating pin is a type that is not attached to the piston connecting rod. However, it’s securely plugged, clip or snap ring mounted to the piston bosses. This design then allows the pin to oscillate at the bosses and the rod.

piston pin

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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 to experience an extremely high temperature.

Well, the piston is made with special alloys such as steel alloy that can withstand the temperature and prevent it from melting.

The function of the piston is to receive pressures, temperatures, and other stresses of the expanding gas.

Piston head also serves other purposes such as creating swirl to make combustion uniform and knocking regulation. Pistons head acts as a heat barrier between the combustion chamber and the lower piston parts.

Pistons are available in different types suitable for a specific type of engine. There are many factors that determine the design of a piston head such as the engine type and required performance.

piston skirt

Connecting rod:

A connecting rod is one of the major part of piston most time shortened as 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.

Most piston out there is made with steel as it’s suitable for high-performance engines. Aluminium is used when a lighter weight piston is needed for milder engines.

The function of the connecting rod is to rotate the crankshaft that produces motion that allows the engine to move. This rod contains a bored hole that delivers lubricating oil to the cylinder walls and wrist pin.

Connecting rods is of different design which includes milled joint, crack joint, straight and angled separation rod as well as the parallel and tapered rod design. There is various part in a connecting rod which includes:

  • Small end: it’s the smallest end of the rod that consist of rod eye and piston bushing. This small end links to the piston through a piston pin.
  • Big end: the part is opposite to the small end of the rod. It’s connected to the crankshaft. Finally,
  • Connecting rod beam: this part is between the small and big part of the rod. It is usually a double T construction and may or may not contain an oil passage to convey oil to the cylinder.

set of connecting rod

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Connecting rod bolt:

Another piston parts 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 bearing at the bottom end of the rod bolts. A nut is then used to lock the components down together with the bolt.

The bolt is made from steel, but aluminium is used when lighter weight part is needed. Nickel is also used when the stronger rod is required which is often time needed in heavy-duty vehicles.

The function of the bolts is to secure the connecting rod to the crankshaft, helping the rod to withstand the strain caused by the rotating crankshaft.

The rod would break and affect the working of the engine parts if the bolt is excluded. This rod secures every piston stroke and ensures smooth engine operation.

connecting rod bolts and nuts

Piston bearings:

The bearings are great piston parts that aid the effectiveness of the movement. It’s located at the points the pivotal rotation occurs. These bearings are usually semicircular metal pieces that fit in the bores of these points.

Shells in the big end where the rod is connected to the crankshaft are part of the piston’s bearing. The component is often manufactured from metals like copper, silicon aluminium, etc. It is further coated to enhance hardness and give them the ability to withstand the load of the piston and the connecting movements.

Read: How the automobile engine works

That’s it for this article “Major parts of pistons and their function”. I hope the knowledge is attained, if so, kindly comment, shared and recommend this site to other technical students. Thanks!

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