A couple of months ago I removed my exhaust headers while replacing my spark plugs. I was underneath the car yesterday installing a set of Fister modified mufflers and noticed that one of my header bolts was missing.

I distinctly remember using the torque wrench to set the bolts to 17 ft-lbs when installing them. I rechecked the manuals and it does indeed say to set them at 17 ft-lbs.

What could account for this? I guess I'll just order a complete set of replacement bolts. I'm a bit concerned over how one could come out when set to the specified torque level. Am I looking at the wrong section for torque specs on my car? A 2006 C2, base model.

Thanks, Derek

 

Did you put anything on the bolts?

 

Loctite
Threadlocker blue

 

I've heard of people breaking bolts using a thread locker. Thoughts?

The reason I asked was if he put an anti seize compound on - it's possible that the bolt work its way out before engine temperature cycling locked the bolt in place.

I usually just clean up the threads and use new bolts each time.

 

I didn't use grease or anti-seize on the bolts before reinstalling them.

Where's the best place to order new bolts? I've been searching online and haven't found anything yet. I'm sure my local dealer can get them, but I usually order online.

Derek

 

Quick iPhone bolted joint primer. When you torque a fastener it stretches the bolt and acting like a spring applies a preload to the joint. The preload that is applied keeps the two surfaces in contact and generally friction keeps them from slipping. There is a relationship between the torque applied on the head and the preload of the fastener. Many things can effect this relationship. For example a rusty old bolt will generally have less preload for a given torque than a clean bolt. This is because some of the torque goes into overcoming friction in the old rusty threads and thus reduces the preload applied. Conversely it is possible to inadvertently over tighten a fastener by using an antisieze compound as it reduced the friction in the threads. Thus more of a given torque goes into stretching the fastener. Lastly toque wrenches can be inaccurate. By using an uncalibrated torque wrench along with an old fastener you can easily see how things can stack up and you can wind up with a bolted joint without the proper preload. If the preload is too low then the joint can gap under loads (vibration, normal loading, or thermal expansion etc.) and fall out.

 

S&!t Happens

Ok, I'm going with the rusty bolt option. Actually I don't remember how bad the threads were but it seems like the only possibility. The torque wrench is a new cdi/snap-on job and wasn't some el-cheapo.

I guess I'm glad I happened to be looking around under there before my headers fell off!

D