Abnormal noise of wheel loader and forklift diesel engine——piston knocking

Piston Knocking in Wheel Loaders and Forklifts

Understanding the Issue

Piston knocking is a distinct engine noise characterized by a sharp, metallic sound. It occurs when the piston and cylinder wall clearance exceeds acceptable limits, causing the piston to collide with the cylinder wall during the combustion cycle.

Identifying the Symptoms

1. Cold Engine Noise: The noise is most pronounced when the engine is cold, especially at idle.
2. Warming Trend: As the engine warms up, the noise diminishes or disappears.
3. Oil Injection Test: Injecting oil into the cylinder through the injector seat hole and restarting the engine can temporarily alleviate the noise, confirming piston knocking as the culprit.

Causes and Solutions:

• Excessive Clearance: Wear between the piston and cylinder wall can lead to increased clearance and piston knocking.
• Bent Connecting Rod: A bent connecting rod can misalign the piston and cause it to strike the cylinder wall.
• Detonation: Detonation, or uncontrolled combustion, can generate shock waves that can damage engine components, including pistons and cylinder walls.

Preventive Measures:

• Regular Maintenance: Adhere to the manufacturer's recommended maintenance schedule, including oil changes and filter replacements.
• High-Quality Fuel: Use high-quality fuel to minimize detonation.
• Proper Timing: Ensure accurate ignition timing to prevent detonation.
• Avoid Overheating: Overheating can exacerbate wear and damage to engine components.

By recognizing the symptoms of piston knocking and taking proactive measures, you can prevent serious engine damage and costly repairs.