Header/overpipe interface
 

I've been having an ongoing issue with the connection loosening over time.

Do you have a solution?

Thanks in advance

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I've tried Loctite (fail)

Locking washers (fail)

Currently anti seize so that I can apply proper torque

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Maybe the two flanges aren't mating properly, and over time the extra stress if causing the bolts to loosen.

Maybe you could have a muffler shop look at it, maybe cut or bend the tubing to relieve the stress on the flanges?

Any indication as to what is causing the loosening? Is the gasket between the two flanges relaxing and "flowing" under temperature causing a loss in preload? Is it a nut loosening under vibration? Is the bolt stretching after being overloaded?

My guess on solutions for each of the following cases:
Gasket flowing: Make sure you are preloading to the correct value using the correct lubrication and a torque wrench per the manual. I'd replace the gasket at the same time.
Loosening nut under vibration: Use a higher strength/heat resistance loctite if a normal strength loctite isn't working. Or you could look into Nord lock washers.
Stretching bolt: Buy higher yield strength bolts.
Mismatched flanges: Try loosening other parts in the exhaust system to free up some room for compliance. Make up that connection first, then work your way back till everything is tight again.

Hope this helps.

I'm thinking your last suggestion will work...