the conrods, whilst running at 40 000 rpm, stretch meaning the little bushings in the hole where it joins onto the crank strech and this will produce movement and this can lead to the piston putting out the glow plug. also due to normal wear they will get weak, and possibly break, this is when u probabley will have to replace the rod,pin,piston,sleave,bearings and even the case if it has been periced by the rod.

Mitchell