From the manufacturer....
Rather than just relying on the HeliCoil spring tension to retain the insert, is there any way to positively lock the insert into the housing threads?
The following methods are recommended to help secure an insert into the housing...
Apply a light coating of Loctite Thread-Locker compound to the external portion of the coils of the insert prior to threading it into the housing. If this method is used, be sure not to apply too much Loctite and be sure to wipe the internal threads of the HeliCoil insert clean after it is installed so that the fastener does not bond to the insert.
HeliCoil Install
This is simply another one of those commons sense deals. That is to say somewhere out there would be someone that would apply way too much threadlock and not bother to clean out the excess. There's absolutely nothing wrong with using threadlock on helicoil, providing you've got common sense. I swear, 98% of the problems I see posted in forums that go page after page in explanations all stem from lack of common sense....
