That explains the whole process perfectly.
This is what happens when the fuel mixture burns in a controlled fashion.
The time it takes to burn is a relativly slow process that can be measured so that the complete combustion does occur at or just after tdc.
Pinging is just that, the explosive uncontrolled detonation of the mixture as the piston is still trying to move UP the bore.
As you can imagine, the force of such an event on an upward travelling crank, rod and piston is quite extreme.
Rough castings and sharp edges within the combustion chamber can also cause this to happen as these small obtrusions or sharp edges will start to glow under the heat of the combustion process and cause the incoming mixture to ignite before the spark plug can fire........causing pinging again!!!!!!!!
As this can happen without extreme compression ratios or bad timing settings, people get caught out diagnosing the reasons behind an engine pinging ecause it is being formed by "Hot Spots " within the engine and is unseen.
When building a high compression engine, smooth off all rough castings in the heads, round off any machined square edges on pistons and this will prevent this problem from occuring.
Just some extra info for any Stovebolters' having a similar problem with their vehicles.
