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A while back I had repaired a stripped thread on my aluminium timing chain cover with a M6x1.0 Helicoil. This involved:

  • drilling out the damaged thread
  • tapping a slightly larger M8x1.0 internal thread
  • screwing in the M6x1.0 Helicoil

Lately I noticed that the Helicoil had backed out. In an attempt to "fix" this I ended up damaging the new thread.

Short of replacing the timing cover itself, is it possible to recover from this mess I've made?

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up vote 3 down vote accepted

One possible corrective action is to use a key-locking insert (commercial name "KeySert" or "KeenSert").

For an M6x1.0 internal thread, the standard external thread is M10x1.25. The following steps will need to be taken:

  • Enlarge the hole size with to 8.8mm (3.5" drill bit is close enough)
  • Create new thread with an M10x1.25 tap wrench
  • Screw in the locking insert until the head is flush with the surface
  • Press the locks in to lock the insert in place.

Here is a YouTube video demonstrating the steps involved:

Key Locking Inserts

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