Kawi2strokes.com Forum

I wrote this up for Brad's KTOG "Help Desk" and wanted to share it here too.

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Heli Coils are used to replace stripped threads. A Heli Coil kit ( also sold as "STI" -screw thread insert - since heli coil is a brand name ) contains a specialized tap, an insertion device and inserts.

The most accurate way to do the repair is with a drill press or milling machine ( bridgeport type ) but could be done with a hand drill ( you must be careful to stay square / parallel to the original hole )

I'll describe the repair using a drill press. Pick a drill that fits into the hole that will be repaired. Put that drill in the chuck ( do NOT turn on the drill ) and with the quill (spindle ) down, clamp the part in place. ( this will center the part to be repaired ). By moving the spindle up and down, it shouldn't drag the sides.

Put in the correct size drill and drill to the depth needed. ( use of a stop is suggested if too deep could be a problem ). You are only removing a little bit of material from the sides so feed slowly so it doesn't grab. Kerosene works well as a lubricant for aluminum ( and cast iron too ).

Keep the part clamped in position and remove the drill bit and put the heli coil tap in place. DO NOT TURN ON THE DRILL, it would be best to unplug the drill press at this time. Turn the tap by hand by either grabbing the chuck or by putting the chuck key in and get a few turns on the tap.

Tap to depth ( using a lubricant ) and back off every few turns to break the chips. I highly suggest using a tap wrench since it allows you to apply even pressure from both sides. ( unequal pressure pushes the tap to one side causing an oversize thread which isn't as strong )

Clean out the chips and make sure there isn't any chips stuck to the threads. Place the insert on the insertion tool and screw down into the hole. Watch the end of the insert and put it down 1/2-3/4 of a turn below the surface. Remove the insertion tool.

Double check the thread with a bolt and if it's good, remove the bolt. Using a small punch, knock out the driving tab from the bottom of the insert. Get the tab out and your repaired part is ready for reassembly.