Junk Motor

[jeffko]

I may not explain it very well but it occurs when a the flame of the burning air/fuel is interuppted by an explosion of the mixture outside of the flame such as timing is too far advanced and the mixture has not been compressed to the optimum point to where it will all burn evenly. It can very substantialy raise the pressure in the cylinders with the pounding explosion to the point that your pistons wind up in your oil pan. It can be very mechanical sounding like a spark knock, but worse.