In one reply to this thread it says "there is a reason for the delay glow starters".

I would argue that a delayed glow starter may be the reason for this piston failure. I believe that YS users use delay glow igniters to stop the knock or backfire which will accompany trying to start an engine with too much fuel in the cylinder. A powerful starter combined with too much fuel will stress the engine. The crankshaft will twist and eventfully break, probably in the air some flights later. The same with the connecting rod.

When an engine backfires or knocks on starting all the energy is fed back through the starter to your wrist, if it is allowed to backfire in this way most of the energy will be dissipated with less stress on the internal parts of the engine. If the starter is held in place through 'the knock' the stresses inside the engine will be enormous.

The delayed glow drivers have been referred to as 'soft starts' and I would suggest just the opposite happens. Instead of letting the engine dissipate its energy through the backfire (due to too much fuel) you are forcing the engine to turn by building up inertia generated before the glow is switched on which gives the impression that you are avoiding the knock when starting. Not so! The knock will still occur but because of the inertia before igniting the glow plug it will force the engine through TDC putting huge amounts of stress on the connecting rod and crankshaft. The nearer that knock occurs to TDC the more likely the piston will fail as the connecting rod at TDC is at its least vulnerable, but something has to give, in this case the piston.

The only way to 'soft start' or be kind to an engine is to start the process with the glowplug ignited and less than enough fuel in the cylinder to fire, and allow the engine to gradually start as sufficient fuel is made available.

Your thoughts would be appreciated.