5/16 helicoil

I would have thought you could do this without taking the head off, not that I`ve done it myself but if you use a small piece of cloth rammed tight into the bottom of the hole to block off the oilways just beyond the thread and make sure you don`t drill and tap down much further than the length of the helicoil you should then be able to blow out any swarf with an airline or solvent aerosol before picking the cloth out again. Take time to make sure it`s completely clean first though. You can use a small magnetic screwdriver to remove the helicoil tang once you`ve snapped it off. Making sure you don`t drill down into the cloth would be key, a depth stop on the drill would be advisable.

Best regards, Al.

As well as the above put grease on the tap it will collect most of the swarf as you cut the new thread. Apply a couple of turns at a time, keep withdrawing it, wiping it clean and applying fresh grease.

If you get caught out with a stripped plug thread and are not in a position to remove the head the same grease tip can be used when helicoiling a new plug thread. Well it worked for me in the paddock when I stripped the plug thread between races.