Motor Vehicle Maintenance & Repair Stack Exchange is a question and answer site for mechanics and DIY enthusiast owners of cars, trucks, and motorcycles. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

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?

share|improve this question
up vote 5 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 (0.35" 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

share|improve this answer
These also also available under the brand Time-sert. – Roger Mellie Jun 9 at 11:44
I'm not too familiar with the imperial system, but I'm pretty sure that 3.5" is not close to 8.8mm by any standard ;-) – Mels Jun 10 at 5:39
@Mels fixed, thanks – Zaid Jun 12 at 7:18

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.