Fault Diagnosis Column [2]: Severe vibration, unbalanced operation, and noise—what exactly is wrong?

When the engine malfunctions, troubleshooting can be quite difficult. However, among the possible issues listed below, if a similar fault occurs, you can refer to the causes and their solutions.

　　When the engine malfunctions, troubleshooting can be difficult, but for the possible issues listed below, you can refer to the causes and solutions for similar faults.

　　Fault 5

　　Severe engine vibration

　　Possible causes:

　　1. Nut securing the pulley is loose

　　Solution: Tighten the nut.

　　2. Pulley damaged

　　Solution: Install a new pulley.

　　3. Engine base is loose, worn, or damaged

　　Solution: Tighten all mounting bolts. If necessary, install new parts.

　　4. Engine does not ignite or runs unevenly

　　Solution: Refer to the method for Fault 2.

　　5. Fan blades are unbalanced

　　Solution: Loosen or remove the fan drive belt. Vibration occurs at a specific speed; run the engine briefly at this speed. If no vibration occurs, replace the fan assembly.

　　Fault 6

　　Engine runs unevenly

　　Possible causes:

　　1. Low fuel pressure

　　Solution: Ensure there is enough fuel in the tank. Check for leaks in the fuel system. Check for severe bends in the fuel line between the tank and fuel pump. Check for air in the fuel system. Check fuel pressure. At full load speed, check if the fuel delivery pump is functioning properly. Check the pressure difference before and after the fuel filter; if fuel pressure drops, install a new fuel filter element.

　　2. Air in the fuel system

　　Solution: Find and repair leaks in the fuel system. Remove air from the fuel system.

　　3. Fuel line between injection pump and injection valve is missing or broken

　　Solution: Install a new fuel line.

　　4. Incorrect valve clearance

　　Solution: Adjust the valve clearance.

　　Fault 7

　　Mechanical noise (knocking) in the engine

　　Possible causes:

　　1. Connecting rod bearing damaged

　　Solution: Check the connecting rod bearing and crankshaft bearing surfaces. Install new parts if necessary.

　　2. Accessory failure