>>> Pre-ignition is an ignition caused by a hot-spot within the combustion chamber, like a sharp edge on the piston, or the head, or carbon deposits. In a spark-ignition engine, it can even be the electrode of the plug.
In a glow engine it is nearly always the glow-plug coil that initiates the ignition. >>>

Is this why it doesn't matter that all of OS's "long" plugs are actually a short reach? These so called long plugs leave lots of threads exposed inside of the head. Being used to gasoline engines, I thought this would lead to preignition or hot spots. But apparently not? I would still prefer that OS's plugs would be a true long reach. They could be tightened more safely in the head. Does anyone have a clue why they are such short reach?

Ernie