T-rex 700N hex starter coupling

Another "engine starting issue" I ran into a while back was the starter coupling, or what I call the hex starter cup. It was cracked about a year ago, but had been working ok after some reinforcement with some metallic epoxy.

I only used one screw to secure the hex adapter to the starter shaft when I built the heli. It never gave any issue, till I got the new starter. With the new starter, even on just 12v, the starter coupling gave way and started spinning on the shaft, rather than with the shaft. This worn out the grub screw and the shaft, which eventually meant that I again, could not start the engine.


Unfortunately, I haven't got my macro lens when the shaft failed, so I was unable to get a decent shot of the wear on the shaft.

New one is cheap, but it was a bitch to get it off. It basically involves taking apart most of the screw below the swash plate, equally, if not, more tedious than on the plastic frame raptor 50. This is because of the design of the starter bearing block and also, the placing of the governor sensor. Because there was no way I could remove the coupling from the shaft to get the clutch bell/pinion assembly out, the coupling had to be drilled out.

I believe the cracking of the starter coupling is not common and the recent failure is a user-error, that is again, relatively uncommon. Still, it was quite frustrating.