Detonation, also known as “pinging,” can be a problem in any internal-combustion engine. Detonation occurs when the fuel-air mixture ignites as soon as it enters the combustion chamber instead of at the proper moment in the combustion cycle. Detonation is revealed by a loud pinging sound—hence, the term “ping.” Detonation/ pinging is usually caused by too much compression or by using glow plugs that are too hot. If left unchecked, pinging can cause pitting of the piston and sleeve, and it compromises performance. To stop pinging, use a cooler plug or install a 0.002-inch (two-thousandths-inch) shim between the heat-sink head and case to reduce compression.