Weekly. I dont know where they go. Seems each week I replace the exhaust flange gasket and after about 5 days I hear the leak again....and the gasket is dead...eaten through to the metal mesh. I've been using Permatex Copper sealant and NAPA gaskets. I think it might be the weight of the pipe that pulls it apart of the manifold so it might need to be cinched up tighter with something......any suggestions??

Only time that ever happened to me was because I had hand tightened the bolts but had forgotten to go back and cinch them with a wrench before starting the car.

Here's another thought: try loosening up all the tailpipe hangers before tightening the flange bolts on the gasket. It could be that the exhaust pipe isn't able to move enough to allow you tp mate things up flush.

If the mating surfaces are off kilter, it could still feel like the bolts are cinched tight while a seal isn't being created. If the hot exhaust gases can escape through a gap between the flange and the gasket, the gasket will get fried.

I think there could also be an issue if you hook a 225 to a 170 tailpipe. Because of the difference in deck height, this combination might mate up off kilter. This is just a guess, as all my slants are 225s. Other members who've had both could probably validate or shoot down this theory.

Torque spec is 30 foot-pounds.

---Red

I think Red has the problem / caused pretty well defined, the header pipe flange needs to be in contact the manifold's outlet flange evenly so you get full contact / crush on the gasket.

I also see many of the header pipe flanges with the ends bent up, right around the bolt holes. If this happens, the ends with the bolt holes make contact but the thin sections near the middle have no gasket contact / crush allowing the gasket to blow-out. I had one aftermarket pipe make contact with the engine block's oil pan rail before it would close the gap on the gasket.

Disconnect the pipe and do a trial fit-up to see if everything mates-up squarely and with flat contact, adjust as needed to get full and even gasket crush.

I had the same problem on my D150. The head pipe didn't have enough bend at the flange and it was hitting on the pan rail and a boss on the block. I put a dent in the pipe, ground down the block boss and bent the pil pan lip over. Has the same gasket in it for a year now.

Cecil

I had this same problem om my x-wifes 71 Demonand as doc said, the flange was bent up on either side where the bolts go through.
When it came time to do a full exhaust system, I took a flange gasket to my local machine shop and had a new flange machined from 1/2 inch steel(overkill, I know but it never leaked again) and welded a piece 2 inch steel pipe to that, to make a new "collector" for the exhaust outlet.

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Ive got a slanted attitude and a heavy right foot.

Next time you get a flange gasket, ask for one with a "fire ring". It is the same construction as a standard gasket, only with a crushable metal ring around the inside cercumference. I've reused mine before, no leaks.

I also use that type flange gasket...good stuff.


---Red

As stated above, be sure to check the clearance between the pipe & oil pan when bolted up. In the last one I saw that was doing this, the pipe was touching the pan.

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Chuck Rivers, Webmaster