Piston pins
A piston is only as strong as its piston pin
Although piston pins are small and inconspicuous, they still play a crucial role in the distribution of forces within your engine.
We can even say: a piston is only as strong as its piston pin. Here, you will find out what this little part does and why it is so important for tuning.
- 1. How does the piston pin look?
- 2. What is the function of the piston pins?
- 3. Mounting the piston pins
- 4. What damage can occur if you make a mistake installing the piston pins?
- 5. Coating of piston pins
- 6. Do you need help with installation?
- 7. You want to know more about piston rings, piston coating etc.?
What does the piston pin look like?
A piston pin looks like a drilled hollow pin and either has a constant cross-section or is additionally reinforced (like our reinforced turbo piston pin). Especially in motorsport, more and more piston pins can be found that are conical on the inside and therefore very light. The ends of the pins then have a lower wall thickness than the highly stressed center. Pins with chamfers are also very popular, especially in series production. These beveled surfaces on the edges reduce weight, which is not only an advantage in tuning. However, the challenge here is to design the piston pins with sufficient strength.
What is the function of the piston pin?
The piston pin connects the piston to the conrod and thus also transmits the forces between piston and conrod. Gas and mass forces in particular act strongly on the pin, which is why it absolutely must be reinforced as power increases. As a rule, piston pins are ideally designed with a low mass. Most of the time, the piston pin is floating in the small end of the conrod or in the pin bore (or in both) and has little play there. Because the piston pin is subjected to extreme loads, it is manufactured to the highest standards of accuracy. It must be perfectly round, matched to the cylinder shape and dimensionally accurate with regard to its diameter. If the pin were to seize, you would quickly suffer catastrophic engine damage. That is why the pin also plays an important role in tuning. This is precisely where particularly high forces act on the small pin.
Installing the piston pins
First, the conrods are checked for bending and laid out together with the pistons in the installation direction. Then you oil the pin and carefully push it into the small end of the conrod and the piston pin bore of the piston. In some cases (with pins with a tightly toleranced bore), it can be helpful to slightly heat the pistons.
So that the pin does not start to move and damage the cylinder wall, it is fixed in the piston pin bore. This is done using piston pin clips, also called retaining rings, for which there is a groove in the piston pin eye. The ring must snap completely into the groove. You can check whether this is the case by slightly rotating the rings.
The clips must be installed with suitable tools and must under no circumstances be compressed too much. This risks permanent deformation, which results in too little tension on the retaining ring. Make sure that the gap of the clips is always in the stroke direction of the pistons and that pistons and conrods are assembled in the specified installation direction.
What damage can be caused by errors when installing the piston pins?
If pistons and conrods are not properly connected to each other by the piston pin, severe damage can occur. These include, for example
- piston seizure
- erosion at the piston pin bore
- damage to the cylinder bore
- high oil consumption
- loss of power
- overheating
- engine noises
To avoid this damage, you should therefore approach the installation of the pins with a great deal of sensitivity. Remember to replace wear parts such as the retaining rings and not to reuse them.
Coating of piston pins
In order to reduce friction and wear and thus also fuel consumption and emitted pollutants, piston pins are increasingly being coated. Coatings made of carbon such as DLC (Diamond Like Carbon) are suitable for this purpose, for example. These diamond-like carbon layers give the piston pins an extremely hard surface, although the coating is very elastic. This greatly reduces the friction between pin and conrod and improves the emergency running properties.
Do you need help with installation?
You shouldn’t take any risks when installing the bolts. Let our motorsport professionals help you. Simply get in contact with us and arrange an appointment.
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