Knocking !!! watch out
•Knocking is an abnormal combustion that does not need in the operation. Spark knock or detonation is the other ignition nucleated in front of the normal flame front. Two flame fronts meet, producing a very rapid, and high ,pressure rise. The result is a high-pitch metallic rapping noise called “pinging” (เสียงคล้ายโลหะกระทบกัน-เสียงแหลม).
•Detonation can ruin an engine that heave shocks on the piston put great load on bearings and other parts.