I wouldn't believe it either, but I saw it happen at our GASCAR race yesterday. The thing that we believe made it happen is that there is more than 1 head shim and the glow plug is either double shimmed or your using a short and should be running a long. This happened to an OS CV 12. After checking the motor out, we found 2 shims on the glow plug and the plug was to be a long and it was a short. So, YES this can happen. STRANGE, but does happen.