Catalytic converter gasket

[moerdogg]

Reader's Digest/ADD version: How do I make sure the catalytic converter gasket seals properly? Hey look, something shiny!

Full version: Last year I pulled my header out to try and fix some heat shield rattling. When I re-installed, gave the flange surfaces at the cat a scrub with a wire brush and then put in a new gasket. Turns out I hadn't cleaned it off nearly well enough, there were exhaust gases pouring out of the joint. I ended up getting in there with a screwdriver and chipping away old gasket chunks. Then I tightened the bejesus out of the bolts and re-used the "new" gasket. That got the leak down to a very low level, but it's still there. I've put up with it for a little while, but I have my inspection coming up and would like to avoid flunking. Plus, I'm kind of anal-retentive. I pulled out the cat this weekend and took a bastard file to both flanges. The faces are clean now, and I purchased new hardware. Any other suggestions for making sure I don't get leaks? I saw one how-to that suggested hi-temp permatex sealant. Anyone use that with success? I have the orange stuff that is pretty robust, but I'm not sure it's rated for exhaust temps. I thought the gaskets themselves should be capable of sealing, but if the flanges are distorted from 20 year of heat/cool cycles, maybe they need a little something extra.

If it helps, the car is a 1992, 1.6L.

[WASABI]

Are you running a stock set up? When I have done it...one of many times (8 or 9), I have found that there is some wiggle room for the gasket. I always try my best to center it with my fingers as I tighten the bolts. I wouldn't use the orange gasket stuff, it's a temporary fix at best, as it will eventually work it's way out...ask me how I know!!!

I know that there are many different types/materials of gaskets, so I would look for one that has some dimension to it that you can squish down as you tighten it up.

Good luck,

-Jim

[psulja]

I think if your flanges are clean and you have a new gasket you should be fine.

I've also heard of using the sealant to make sure you don't get any leaks from a friend and he says it works great. I haven't gotten into a situation where I couldnt get the exhaust to seal with just a new gasket and clean flanges so I haven't had to use it yet.

You can always put it together with the new gasket and cleaned flanges and see if it leaks. If it leaks try again with the silicone sealant.

[psulja]

I know that there are many different types/materials of gaskets, so I would look for one that has some dimension to it that you can squish down as you tighten it up.

I think the oem type gaskets are pretty good, I think they are pretty much a ring that crushes as you tighten to make sure it is fully sealed. I posted a pic of one in my how to thread for an NC muffler. I forget if they are the same/would work. Worth a look.

[moerdogg]

I think the oem type gaskets are pretty good, I think they are pretty much a ring that crushes as you tighten to make sure it is fully sealed. I posted a pic of one in my how to thread for an NC muffler. I forget if they are the same/would work. Worth a look.

Great how-to! The OEM one looks like a spiral-wound gasket, those things are pretty nice. Based on what I pulled out, I am using the same as OEM on the older models, which looks like the dimpled sheet one you didn't like. My exhaust pipes don't have that piloting feature, so it would be very difficult to get the round gasket centered during install. The dimpled sheet I have at least has a ring on the ID. I'll try to take some pics and post up tonight.

Are you running a stock set up? When I have done it...one of many times (8 or 9), I have found that there is some wiggle room for the gasket. I always try my best to center it with my fingers as I tighten the bolts. I wouldn't use the orange gasket stuff, it's a temporary fix at best, as it will eventually work it's way out...ask me how I know!!!

Stock header and muffler, not sure about the cat. I thought it was stock, but the exit end of the cat doesn't quite look like the right diameter for the gasket I got. The gasket is much larger in ID than the pipe. Again, I'll try to take some pics to illustrate.

[psulja]

Great how-to! The OEM one looks like a spiral-wound gasket, those things are pretty nice. Based on what I pulled out, I am using the same as OEM on the older models, which looks like the dimpled sheet one you didn't like. My exhaust pipes don't have that piloting feature, so it would be very difficult to get the round gasket centered during install. The dimpled sheet I have at least has a ring on the ID. I'll try to take some pics and post up tonight.

Oh too bad.. Well I guess you just need to get it centered as much as possible and check for leaks, if you have a minor leak try to loosen, reposition, and retighten. Good luck!

[cjsafski]

On my volvo I just use red rtv by itself. As long as the flanges are fairly flat this seems to work well.

[WASABI]

On my volvo I just use red rtv by itself. As long as the flanges are fairly flat this seems to work well.

It doesn't dry out, crack, and fall out? Mine did! I used in conjunction to the gasket, and after a year or so of hard driving (daily driver) I noticed it getting loud. When I checked on it, I saw the gasket but little sealant left.

-Jim

[cjsafski]

The flanges on my volvo are fairly new so they seal ok on their own. Also I tend to remove the exhaust more than once a year since I keep changing turbo sized on it. So the rtv is always fairly fresh.

[moerdogg]

Okay, so some minor (well, major) frustration at this point. I cleaned up the flanges:

Inlet
DSCN1600.JPG

Outlet


And I cleaned up the mating flanges (not shown)

Added the Gaskets
Inlet


Outlet


The I bolted everything together:
Inlet


Outlet


Aaand, it leaks like a damn sieve. I would have been far better leaving it alone. WTF am I doing wrong here? I got to the point on the outlet flange where I'm moderately sure I stripped the threads on the nut. It doesn't seem like it should be this difficult, but maybe that's the nature of 20-y-o exhaust flanges.

\rant

[moerdogg]

Should have started with: thanks for the great replies, I really appreciate the forum support!

Too frustrated to think straight at the moment.

[WASABI]

Interesting, I encountered a similar situation when I first did mine. The flanges were never really flat, even though they were clean. I ended up grinding/filing them down first, and I believe, at one point I used two gaskets, just so there would be enough mass to take up the void when I squished everything together, tightening it up. Realistically I would love to get a 1/4 inch thick gasket. That would solve the problem.

I have since, bought a new cat, and new header, and since the Borla was pretty new, everything goes together fine now. Good luck with yours.

-Jim

[moerdogg]

Jim - Thanks, I'll give the two-gasket method a try. Throwing wrenches didn't seem to seal any of the leaks

[psulja]

i used to think it does, and then i lost a couple wrenches and sockets and realized it wasn't working.

Goodluck getting it sorted out, I know how frustrating it can be when things just won't seal up.

[— kung fu jesus —]

Those look like the wrong sized gaskets. The first pic looks like the gasket is in the exhaust stream, which it shouldn't. You may want to sand those flanges flat, too, looks like there is still stuff on the mating surfaces.

Sometimes those flanges warp. Pro tip to check: put a sheet of sandpaper on a known flat surface, like a piece of glass or countertop. lay the flange onto the sandpaper flush. move the cat with the flange flat on the sandpaper in a circular or figure 8 pattern. Do this for about a minute. Look at the flange for high/low spots. Continue until the entire suface looks flat, unless you have big low spots on the holes of the flange (warped).