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Valve noise is one of the factors that deteriorate the signal-to-noise ratio in the detection of combustion knock in spark ignition engines by means of a knock control system with a conventional knock sensor and a higher frequency band-pass filter. It was determined that one of the principal mechanisms of valve noise increase is the eccentricity between the valve seat face and the insert seat face at valve contact in addition to excess valve contact speed. One of the reasons for this eccentricity is the offset between the centers of the valve guide and insert caused by cylinder head distortion due to fastening of the cylinder head and thermal distortion of the insert. Other reasons include excess clearance caused by the abrasion of the valve guide and stem, and valve tilt increase caused by inherent valve spring bend.