My Maule has a placard which says * PROPELLER WILL NOT WINDMILL BELOW 52K (60 MPH). which is pretty self explanatory, but what does this mean while trying to restart in an engine out scenario? Is it a bunch of starter gear crunching during attempted restarts?
Make sure the speed is somewhere above 52 Kts and just blip the starter quickly. This will get the engine past its first compression cycle. From that point on, the momentum of the engine/prop plus the aerodynamic force generated will be enough to get it past the subsequent compression cycles.
I deliberately tested this in the R2160 (O-320 engine, fixed pitch prop) because there is a chance that the prop will stop completely in a 3+ turn spin. With the mixture off, I had to fly below stall speed (through a half-G pushover maneuver) to get the prop to stop windmilling. But it took a dive to about 140 Kts to get the prop to start windmilling again using aerodynamics only.
Word of warning: When you do this stuff, be very, very careful. The chance of shock cooling is very great so be very gentle in building up and taking off the power. Also, when you restore the windmilling through such a dive, make sure the throttle is closed or at best half open. Otherwise you go from zero RPM to overspeed in next to no time.
Also when blipping the starter, do this at a speed and throttle setting which leads to a relatively low RPM afterwards. Otherwise the Bendix might not have time to disengage, leading to a wrecked starter motor (or worse).