Obligatory reference: VH-KBZ
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In a Cessna with an electric starter? Big no-no for starters.
Correct me if I'm wrong but I thought electric starters all had a "Bendix" drive (or whatever it is called) which physically disengages the starter from the engine when the starter is not engaged. This would mean that hand-propping an engine with an electric starter does not have any impact on the starter whatsoever. There may be other considerations, but damage to the starter motor is not one of them.