[rotorwrench]

My experience with the high compression helicopter engines over the years was interesting on what can happen when the spark retard system doesn't function properly. I've replaced more than a few starters with broken housings and bendix parts. It didn't matter if the starter was turning or not. When they want to kick back, they will and with a vengeance.

At one time, at least one magneto had an impulse coupling to retard the spark but the engine had to be started on just that one mag. After it was running then the switch could be turned to both to get it up to normal ignition function for two mags. Impulse couplings were problematic so most manufacturers recommended replacing them with electronic vibrator types. On the large and high compression engines, an electronic vibrator that functions through a different set of points in the magneto to give a shower of sparks through the magneto coil as long as the retard points were open. The vibrator was connected into the starter circuit so that it only operated as long as the starter was turning. Some of the higher compression engines had to have this system on both magnetos or the engine wouldn't start well when cold. Now days most all engines use electronic stater vibrator systems for piston engines other than the occasional diesel type.

A person would need to find some way to retard the spark enough to prevent kick back. If that can't be done then they should always keep a spare starter around just in case.