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2001 Exhaust flange gasket leaking... ?

Redsnake

NAXJA Forum User
Location
Tulsa, OK
So I replaced the headers and pre-cats on my '01 XJ about 1 year back... and have had a very slight (now much bigger) leak where the end of the pre-cats meet the crossover pipe under the transmission. There is a flat flange gasket that has 3 bolt holes... and apparently the connection point isn't flat where the pre-cat pipe meets the OE crossover pipe. So my gasket is leaking there.

I'm in need of some suggestions. Are there any thick gaskets for this connection point? Can I double/triple gaskets or will that cause a leak? Any suggestions or help is appreciated as this area where the exhaust leaks is REALLY loud and annoying since it's right under the drivers seat and I'm also pretty sure it's allowing a LOT of heat to be pointed right at my transmission were the exhaust leak is.

It might come down to me loosening up the 2 connectors where the pre-cat's connect to the header and then snugging the collector and crossover pipe before re-tightening the pre-cat to header connection. I'd hate to have to go that route as it's quite hard to get to those 4 collector bolts to loosen/tighten... if you can picture that area.

I appreciate any tips or ideas that I could try.
 
Why not try 2 gaskets -- they're cheap enough...

I had a similar alignment issue in the same spot -- I replaced my Pre-cat down pipe with a replacement from walker

I ended up cutting the crossover pipe underneath the trans -- then slipping a coupling in place where I had cut the pipe -- then I bolted up the 2 flanges with a new gasket

Once all bolted up I welded the coupling and pipe up solid
 
Thx. I guess you're right and I'll just try the double gasket method. I wish I was able to slide the gaskets up in there along w/some high heat silicone to help... but the exhaust pipe has very little give at all so I think adding the silicone to 2 gaskets and trying to slide it up in place would just make a big mess!

I wish I could weld as my first thought was cutting the crossover pipe and putting in some type of flex pipe but I'm not sure there is a 'universal' type pipe I could use w/out being able to weld one or both ends. :)
 
You have to have a friend who can weld -- There is a really nice flex pipe available -- needs to be welded though

In all reality how much could a muffler shop really charge you to weld in a flex pipe?

Even if you bring all the parts to a local welder -- gotta be a way to get it done on the cheap...
 
Probably so... I'm just the type who likes to fix things on my own, if possible. I hate to drop $50 or so just to get a small gasket leak fixed.. On the flip side, I'm thinking I may need to replace my main Catalytic Converter so that would give me the reason to loosen up all those pipes and maybe I could get everything sealed up that way. No doubt doing this would cost more than $50 but with 165K miles on my '01 and the OE Cat in place I should probably just replace it. :)
 
Those bolts on the cat are stubborn for sure -- I had to cut mine with the torch then pound them out

Surprisingly the cat was clean as can be once I was able to look inside -- Sure looked stock but who knows -- 225,000 miles on the clock

That crossover pipe gets easy to move once you detach from cat -- definitely can fix your flange leak then
 
Just ordered a new Catalytic Converter f/ rockauto (they must love me...) and 3 new flange gaskets (just in case I need a spare).

Now to figure out what the actual bolt sizes are and where to get them as I'm pretty confident I'll be breaking or cutting most of those bolts off to swap out the Cat.

Does anyone know the specifics of the bolts/sizes so I could pick them up and have them on hand to replace? I'm not sure what the actual bolt sizes are... but now to do some google and internet forum searches.
 
No need to use the actual pressed in bolts -- Just use regular grade 5 bolts

I have to look but I'm pretty sure I used 7/16th nuts,bolts and lock washers maybe 1 1/2 long but I will confirm later today
 
It does not really matter what you use as long as it works.

3/8" or M10 are generally what's used

Curious that you are replacing the main cat as that is considered a lifetime unit.

The best way to NOT brake the studs is to try to tighten before loosening... preferably with an impact wrench.
 
Thanks... another ? about the bolts, I've read several different opinions on what grade or material the exhaust bolts should be made of, or grade 5, 9, 10.9 metric, Stainless? Or does it really even matter. From my experience bolts used in exhaust parts tend to stain/degrage/rust/heat-weld themselves in short order so knowing what has/hasn't worked for others is appreciated.

Main reason for replacing the main Cat in my case... I had the typical 0331 head crack, which lead to degradation and clogged pre-cats which I replaced last Summer. I'm assuming (yes I know that's not always a good thing) the main Cat was somewhat damaged as well and couple that w/the mis-alignment of the crossover pipe and trying to adjust my exhaust and get it all sealed up... I figured this would be a good time to replace the main cat and realign the rest of the leaking exhaust. That and I'd dare say nothing on a Jeep Cherokee could be really considered 'lifetime' ... :) and the fact I have 166K miles on my '01 I figured it's time to change this out. Maybe even pick up a few mpg's in the process if my OE cat is indeed faulty. Guess we'll see... and thanks for the tips on how to try and not break the bolts!
 
Umm... how exactly does the crossover pipe get misaligned when both ends are flanged?

The most significant improvement in a 2001 I've seen comes from changing the mini-cats.

If you want to know if you have an exhaust restriction test it with one of the vacuum/low pressure gauges. You can probably rent one at the parts store. Temperature changes across the cat can also be recorded.

This whole problem sounds like your mini-cat replacement part was defective and came with a bent flange???
 
I believe it was my error in how I tightened everything up when installing a new header and pre-cat pipe ... I tightened up the 2 x 2 bolts on the header to pre-cat side before snugging up the 3 bolt crossover pipe. The 2 x 2 has more adjustment and can still seal up vs the flat on flat 3 bolt crossover pipe... if that makes sense. Since the crossover pipe was solidly mounted to the main catalytic converter and then when I snugged the co pipe to the pre-cat downpipe it was slightly off. Off enough to allow a small exhaust leak that's now turned into a big and noisy exhaust leak. Could be the Walker Pre-Cat pipe flange isn't flush/flat/bent but when I compared it to the OE bad pre-cat they looked identical and I didn't notice a bent flange. I didn't put a flat edge on it so it could be so I guess I'll find out. :)
 
How was the welding on your walker pre cat assembly -- Mine looked like it was welded by a 6 month old blind monkey -- I ended up re-welding the whole thing with the Tig and stainless wire

I'm going to bet your main cat is fine -- You'll know once you look into it -- Sounds like you had the same problem mine did -- bad head, bad pre-cats

Hope you didn't buy the main cat yet -- It's gonna be fine
 
Welding wasn't really nice, but it appeared to be sealed up and welded good enough to not leak or crack. I didn't mind since I hopefully will never have to look at it again... :)

I already ordered the new main cat and it along w/ 3 new gaskets (1 extra) for the 3-bolt flange locations should be delivered today. Not sure I'll have a chance to get it installed this weekend but I'm going to try. The OE Main Cat very well could be in fine shape but it's going to get replaced...
 
If you can get brass nuts and stainless bolts that is the best combo for maintainability. Should never seize and if it does you can blow the brass nuts off with a torch without harming the bolts. Studebaker used to use (steel, not stainless) studs on their exhaust manifolds, and they used brass nuts to hold the flange up (as well as for the carburetor.) They also used nickel plated bolts for the manifold to head bolts which made them a joy to work on. About the only thing that would fail was the studs, everything else was awesome to deal with.
 
I was able to swap out the main Catalytic Converter this weekend w/a new one from Walker. The OE Cat is much larger in diameter and the piping is much thicker than the new one I put on from Walker. I'd say the OE one was in ok shape, but since I was doing the work I went ahead and swapped them out. I added in some Permatex High Temp Gold silicone on each side of the gasket to help seal the flange. So far so good, but of course I've only driven it about 10 miles post procedure. I could see very easily where the exhaust leak was coming from as the gasket was nearly blown thru where the Pre-Cat Flange meets the crossover pipe flange. That is now hopefully sealed much better. I'd post up the pics but since photobucket suxs these days I'm not sure how to post up pics for a good reference. I also ended up using 5/16-18-2" hex head cap screws and washers/nuts for the flange connection. I was able to get the old nuts off easy enough but since the bolts were basically heat welded to the OE Converter they were useless in the swap. Thanks again for the tips and suggestions.
 
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