Detonation occurs when excessive heat and pressure in the combustion chamber enable the air fuel mixture to auto ignite. Instead of a single flame kernel in the combustion chamber there will now be several flame fronts. When these flame fronts cross they produce an explosive force, which constitutes to the pressure within the cylinder rising. This results in shock waves passing through the rod bearings, head gasket, pistons and piston rings that generates overloading and can be heard as a ‘pinking’ noise. Also the chamber itself will sustain damage, shown below, that can induce further detonation due to Pre-Ignition (see bottom of page).
Causes of Detonation :-
· Poor quality fuel.
· Compression ratio too high.
· Ignition timing over advanced.
· Engine overheating.
· Lean fuel mixture.
· Spark plug incorrect.
· Excess carbon deposits in the combustion area.
This damage to the cylinder head will need aluminium welding see right. The chamber port shape will need re-cutting and re-profiling and finally the cylinder head will need to be skimmed.
Pre- ignition is caused by sharp edges in the combustion chamber or on top of a piston. These sharp edges become so hot that they become the source of ignition, causing the fuel to ignite before the spark plug fires. This can be very damaging as the piston receives a force in the opposite direction to which it is travelling. Pre-ignition can contribute or cause detonation problems.