<br /><br />The nylon portion may or may not melt, but will hold the torque even when melted, the remains create a drag effect. It is a use once solution. Being that the flange is further away from the manifold it does have a chance.

 

I replaced the flex pipe with the Walker replacement. I ordered new bolts and gasket for the forward connection. The connection between the front-bank exhaust manifold and the replacement flex pipe.
Now every month or so, the bolts are backing out and the gasket is failing. I have gone through 4 gaskets already and have tried Red Locktite, and slightly deforming the threads on the bolt for a better grip. All to no avail.
Just to verify, the forward gasket is a flat gasket, not a tapered donut looking gasket, right?
I have yet to try 2 gaskets and am considering taking the flex pipe off to verify the mounting flange is not warped. Other than that, I am at a loss. Any suggestions would be helpful.

 

Locktite on exhaust system will not work due to heat.

If the setup is like OEM then make sure you are using the proper Torque.

You can spot weld the bolt head or the nut ... OEM has one of these welded.

You can use double NUT on a single bolt. Tighten the first nut/bolt [unwelded] per spec and then tighten the second nut against the first nut and create tension between the the two nuts. For this set up your bolt may need to be slightly longer [Caution ... longer bolt may tend to snag the floating bags on the streets].

Last of all you can spot weld the free part too. Not my preferred solution, but as a last resort. You will have to chisel off the spot when the system has to be undone.

Also check you engine mounts for play, as excessive movement may be causing more than expected vibrations.

Salim

 

thanks for the info.
The Red Hi-Temp locktite seemed to last longer, but you are right, the heat just kills it.
The welded-on factory nuts are still there so I am using them. Maybe a second nut on top of that.
How about the gasket? Flat or donut?
i will pull the flex pipe and look for warping and re-torque properly.
Do you know the torque number of the top of your head?

 

Here is a pic http://catalog.walkerexhaust.com/catalogPart/partImageDisplay.do?catalogCode=walkerexhaust&loadStatus=ACTIVE&partNumber=31555

36 ft/lbs

 

There are several different types of self-locking nuts, part of a family that is more formally called "prevailing torque fasteners." They are widely used in aircraft applications.

As you have already figured out, do not use nylon-insert or fiber-insert lock nuts in high-temperature service. There are several types of all-metal lock nuts that you should use instead. All of these designs use a more-or-less standard-looking nut that has had its threads carefully deformed in manufacture, which leads to a slight interference fit when assembled onto a bolt or stud.

Try: "Hi-Temp Lock Nut" with Google search