I have a problem with my spark plug either vibrating loose in the head or shooting right out! I always retighten it but it still does it. My questions are, 1. Does anyone have any experiance with the "Helicoil" Technique and does it work, and 2. Has anyone else heard of this happening i.e. a factory defect of some kind. Thanks in advance!

 

humm Not with mine. That sucks... I would see Honda

 

Helicoils work really well, I've used them on spark plug holes as well. Can't imagine having troubles with the 400EX spark plug. I've owned one since March and checked the spark plug once.

 

First of all, are you sure you are getting the plug tight? Very few sockets (even the one in the tool kit) will tighten the spark plug all the way. I had to modify the one that came in my toolkit in order for it to fit.

If you really have stripped the head, you may as well try a helicoil (yes, they usually work), you have nothing to lose. I'm sure Honda is quite proud of their cylinder heads...