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!