The piston pin is another term for the gudgeon pin. The piston pin’s job is to transmit force between the piston and the connecting rod by serving as a link between the piston and the tiny end of the rod.
The piston pin is subjected to cyclic shock loads, which perform a swivel motion when working under poor lubrication conditions.
Therefore, the gudgeon pin must have sufficient strength and rigidity, good surface toughness, good wear resistance, and be lightweight.
Piston pins are generally hollow cylinders of low-carbon steel and low-carbon alloy steel.
The outer surface is carburized and quenched to improve hardness and polish after finishing, with high dimensional accuracy and surface finish.
The basic structure of the piston pin is a thick-walled tubular body.
The connection between the gudgeon pin, the piston pin seat hole, and the small end bushing hole of the connecting rod has two ways: full floating connection and semi-floating connection.
Full floating connection means that when the engine is at normal operating temperature, the piston pin can rotate freely in both the piston pin seat hole and the small head sleeve hole connecting rod.
With a full floating connection, the gudgeon pin can bear a large impact load, wear more evenly, and have a long service life, but the assembly process is more complicated.
When assembling the piston and the gudgeon pin, the piston should be heated in water or oil at a temperature of 70-90 ℃ to expand the hole of the piston pin seat, and then the piston pin should be installed.
To prevent the axial rotation of the piston pin, snap rings are also installed at both ends of the pin seat.
A semi-floating connection has one part that is fixed and one that is floating between the piston pin, the piston pin seat hole, and the connecting rod’s small end hole.
The little end of the connecting rod is used to secure the general piston pin. An interference fit holds the gudgeon pin and the connecting rod’s tiny end in place.
Since there is no relative movement between the piston pin and the connecting rod, there is no need for a snap ring to limit the axial position of the piston pin,
that is, the piston pin of the semi-floating connection has no snap ring, and there is no bushing at the small end of the connecting rod.
Semi-floating gudgeon pins can reduce engine noise and eliminate accidents that snap rings may cause.
They are mostly used in light high-speed engines, such as Cherokee, Cheetah, and other cars.
Which Material makes Gudgeon Pin OR Piston Pins
You can be called it a gudgeon pin or piston pin, and it is a pin that holds the piston and the conrod together. What is the material of the piston pin? That is what I will discuss in this article.
In engines with low load, the piston pin is typically made of low carbon steel or low carbon alloy steel in the range of 15, 20, 15Cr, 20Cr, and 20Mn2.
High-quality alloy steel is used to strengthen the engine, such as CrNi3A, 18Cr MnTi2, 20Si MnVB, etc. Sometimes, 45 medium carbon steel is also available.
To make the outer layer of the piston pin hard and wear-resistant, the piston pin needs to be heat treated—Carburizing and quenching the outer surface of the piston pin of mild steel material.
According to the piston pin’s size, the carburized layer’s depth is generally 0.5-2mm.
The piston pin of 45 steel is surface quenched, and the depth of the quenched layer is 1-1.5mm. Note that the piston pin cannot be quenched through; otherwise, the piston pin will become brittle.
The structural shape of the piston pin is very simple, basically a thick-walled hollow cylinder.
The shape of the inner hole is cylindrical, two-section truncated cone and a combined shape.
The cylindrical hole is easy to process, but the mass of the piston pin is large; the mass of the piston pin of the two truncated conical holes is small.
Because the piston pin’s bending moment is the largest in the middle, it is close to the beam of equal strength, but the cone Drilling holes are difficult.
From this explanation, you can see how strong the material of the gudgeon pin is due to the load it is subjected to.