Things to make it go bang!
Experience (bitter and expensive) from Enstrom (non turbo, high compresssion) which are notorius for shedding ring gear teeth. I assume the R44 uses retard breakers and not impulse coupling.
1) anything to make it fire before the piston reaches top dead centre while the starter is engaged. Check mags to make points are ok, p leads are sound, capacitors are properly grounded, distributers work.
2) check starter vibrator to make sure normal points are inactive whilst starting.
3) check timing of retard points (Enstrom 1/2 degree after TDC)
4)Battery must be good so it has enough momentum to take it over TDC. If the piston is on the way up on compression when you disengage the starter, As soon as the switch goes from start to run the main points are activated. If this happens at the right point of the piston stroke, the cylinder may fire before the starter has dropped out of mesh. If this happens and causes a kick back - no more starter ring/starter motor.
5) Starter motor must not be lazy, for the same reason. I had one with an internal fault which made it slow. It killed the ring gear and smashed the motor casing.
If a cylinder fires before TDC whilst starting, it not only removes teeth from your ring gear but can also smash your starter motor to bits.