How to repair threads in cylinder head.

[bmwman91]

Alrighty, I had 9 of 15 valve cover bolt holes stripped out.  Don't ask how, I am not some crazy overtightener.  Anyway, I fixed them.  Here's how:

http://bmw.e30tuner.com/articles_vchc.php

Enjoy!

[Zoso]

I've thought about this process in the past.  What actually holds the insert into the hole that you overdrill?  How strong are they?

[bmwman91]

Here is what you do, in a nutshel:
You drill out the old threads, and enlarge the hole a little, to the diameter needed to thread it for the coil insert (the coil manufacturer will tell you what size).  You tap the threads in, that are sized to provide a tight fit with the coils' OD.  You insert the coils.  The coils' ID is the diameter & pitch of the original thread.  Done.

Strength-wise, i have heard that thread inserts like this are nto a whole lot stronger than the original.  There is another type where you waay overdrill and it is a plug, threaded inside & out.  That would be much stronger, BUT you also have to drill the hell out of the original hole, which I do not like.  I just plan on not overtightening these, and hopefully this will solve the problem.  I tightened them all by hand with just the 1/2 drive extension in my hand, and not as tight as I possibly could.  Just so that it felt like it was at its needed tightness.  I prolly should have used a small torque wrench or something, but oh well.

[dave45056]

Great write-up.  This is exactly the kind of fix I would do as well.  The coil inserts really are the best.  And they are stronger than the thick wall types.  Also they resist vibration better.
Thanks for all the tips!