Drill? Helicoil? .......
Must be using the cheap ****...
A proper helicoil™ kit uses a tap like this:
Runs through the existing thread and chases through with the insert thread, bugger all effort on an alloy head.
A custom made insert holder using a hollow rod, cross section drilled for the insert tang and a tapped end so a bolt can be threaded in to hold the tang.
When you give the rod a tap to break it off, hold it in place and successfully pop it back out isn't hard to make either.
Even for those deep cop heads... $0.50 of scrap material is an invaluable tool.