The piston pin (also called wrist pin or gudgeon pin) is an important component of a diesel engine. While it is smaller than a piston or connecting rod, it is responsible for transferring massive combustion forces whenever the engine starts.
However, despite being a strong component, it can still fail. The reasons can be several. To avoid it, you need to understand why the piston pin fails.
This blog explores how piston pins work, the signs and causes of their failure, and how to prevent them.
What Do Piston Pins Do?
Piston pins connect the piston and connecting rod, allowing the piston to move freely as the rod rotates around the crankshaft. A piston pin can transmit immense force, but it also needs to move smoothly within the piston and connecting rod. For that, it needs proper lubrication, cooling, engine oil pressure, and piston-to-pin and rod bushing clearances.
Some engines use fully floating piston pins while others use a semi-floating design. However, no matter what the design is, any piston pin can fail due to insufficient lubrication and excessive heat.
Signs of Piston Pin Failure
Piston pin failures usually happen quietly. So, it is important to recognize warning signs to prevent complete engine damage.
The signs are
- Excessive piston wear
- Knocking or ticking noise
- Loss of compression
- Scored or galled piston pin
- Complete engine failure
While these signs indicate piston pin failure, they can also be related to connecting rod damage, lubrication issues, or piston damage. Therefore, you should opt for a complete professional inspection to identify the root cause.
Piston Pin Lubrication
Piston pins rely on a very thin oil film to avoid metal-to-metal contact. This lubrication is necessary for them to work properly. In the event of interrupted lubrication, the piston pin and other surfaces begin to rub against one another.
This process causes friction, which leads to heat. As a result, the materials get removed from both surfaces, leaving behind deep scoring or galling. Once it is visible, the damage is already extensive.
What Happens Due to Insufficient Lubrication
When lubrication is not enough, the piston pin cannot rotate properly within the connecting rod and piston. When friction increases, temperature rises, the piston pin starts to score, clearance changes, and the piston can’t travel smoothly through the cylinder.
Once this starts happening, the galling starts. By the time galling becomes visible, the damage is already spread beyond piston pins.
Probable Root Causes
Some possible root causes of insufficient lubrication can include
- Low engine oil pressure
- Worn oil pump
- Contaminated engine oil
- Restricted oil passages
- Improper engine assembly
- Blocked piston cooling jets
- Not priming the lubrication system after an overhaul
Before you replace only the damaged piston, make sure all potential causes are investigated, because replacing parts without addressing the lubrication problem can lead to another failure.
How to Prevent Piston Pin Failure
While you can replace piston pins or even the entire piston assembly, it is usually better to try preventive care to avoid piston pin failure.
For failure prevention, make sure to maintain proper oil level and pressure, replace engine oil and filters as recommended, inspect piston cooling nozzles and lubrication passages, clean all engine components, and prime the lubrication system before starting a newly rebuilt engine.