Why are MA0097 "Jesus bolts" breaking?

[wnor]

In the past six months I have had three MA0097 "Jesus bolts" break in a Raptor 50V2 with an OS 50 Hyper that runs well. I'm certain of the history of the latest casualty: I bought it three weeks ago, and have put twelve flights on it - nothing fancy, no flip-switching autos from a hover, no hot starts, no crashes, not even any full-throttle forward flight. I found it broken during a post-flight check brought on by paranoia from: The prior bolt separated from the helicopter during the flare of an autorotation (the resulting in-flight explosion of the helicopter was spectacular). I'm less certain about the history of this bolt except that it had about 100 flights on it, also with zero crashes or hot starts, and just garden-variety, mild 3-D flying. The bolt before that was discovered broken after 100-200 flights, also with no crashes or hot starts. During its time in service I had been having a lot of problems with stuck auto-rotation units, so I had attributed the failure to the stress put on the bolt when the auto switch is flipped in a hover with a stuck auto hub. The bolts are failing, not surprisingly, at the junction of the un-threaded and threaded portions of the shank.

I really, honestly do not think I am over-torquing the bolts. I just take up the slack, then give the bolt one final tweak with a Wiha hex driver held loosely. I am not a newbie; this is my fourth machine, and I have had no prior trouble of this kind.

So, has Miniature Aircraft received a defective lot of bolts? Despite on-line advice, is the MA0097 not a good bolt for this machine? The OEM bolt's un-threaded shank is a little longer than that of the MA0097, so perhaps it is better suited to the TT head after all.

Thanks for considering these questions.

[capebob]

I had the same experience with the hardened MA bolt. I never had a bolt break, but following the advice of one of the online shops I installed the MA bolt. It lasted two flights. I think that the MA bolt is too brittle for the J bolt application on the Raptor. I have gone back to a standard M3 shouldered bolt with no further trouble. I do change the bolt from time to time just in case.
Bob