Symptom: the engine idling operation, the upper part of the cylinder head "flap" light crisp metal percussion, high-speed moving when the sound messy. Driving distance: 100,000 km.
     Failure Analysis and Elimination: Measure the ignition advance angle of 8.5 degrees to adjust it to the normal value of 6 degrees, but abnormal sound still. Check that the oil is normal. Hand oil can feel the oil is too thin, the viscosity is not enough to check the oil pressure, idle than the normal low 60kPa (0.6bar), suspected oil is poor quality, high temperature viscosity is low, resulting in idle lubrication Large, hydraulic tappet can not build enough oil pressure, resulting in abnormal sound. Replace the oil after the test, the sound than the original reduced, after a while after the operation completely disappeared, power also returned to normal.