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Ah, interesting. Well since I'm going to take it off in about a week to put on the new gaskets anyway, I'll flip it over so the shield is on the bottom. I feel like all the forums I saw online when I was looking to see if it mattered which way was forward all mentioned "heat shield up". But the truck itself has built-in heat shields over the exhaust, so I'm sure that covers it from above.

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I could use some advice.

I took off the cat so I could install the OEM gaskets, but the gaskets don’t fit. So I put it back together with the cheap gaskets.

This time the front wouldn’t seal. I couldn’t even get the visible gap closed. Worse exhaust leak than before.

Took it apart again today to see what’s wrong, and somehow when I worked it out yesterday, I must have bent the front exhaust pipe opening a bit. It was slightly out of shape. So I managed to get it back to round enough that the cat will slide all the way in, but it seems like in tightening the bolts when it wasn’t going to seat all the way, I must have bent either the exhaust side or cat side of the flange/mating surface. Or both.

This photo shows it. Bolts are as tight as they’ll go, but there’s still a gap, and I can even see the gasket still moving around free in there.




I hammered on the exhaust flange and cat flange to see if I could get that bow out, but I feel like any more hammering on the cat especially and I’ll be buying a new one.

I feel like worst case, I’m buying a new length of front exhaust pipe and another cat.

Before I give up and do that, anyone have ideas? The truck sounds pretty cool and all, but I don’t want an exhaust leak!

Edit...hard to tell because photos can distort things, but looking at the photo, it sure seems like it's the exhaust side that most likely bent, not the cat. Maybe I'll take it apart once more and focus more on hammering the exhaust flange since I felt like there was less change breaking that than the cat.

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Well, best I can tell I need another cat. I heated & hammered the exhaust flange back to what looks like flat, but the cat flange seems warped all out of shape, not just bent in at the ends.

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Nothing to do with my current issue, but for anyone who's been following, Magnaflow answered my question from earlier. They say the heat shield should be on top:

Your question:
Does installation orientation matter? Obviously the heat shield needs to go up, but what about direction of flow? I see no arrow or other markings so I'm assuming it doesn't matter...but I hate to assume.

MagnaFlow's response:
Our converters are designed to be bi-directional meaning they can go in either way as long as the heat shield is on top.

2ToyGuy

Apparently, things changed over the generations. A single, vice 2 "TWC"s as they call them, heat shield up, not down, and so forth. Also, what I'm calling a "heat shield" is a screen like device, wrapped around the bottom of the cat. Maybe what I'm seeing as a "heat shield" is just a cover of some sort.

All could merely be misunderstandings, misnamings, an idiot non-mechanic (me) not calling things by the right names, etc.I'll dig into the FSMs and see what can be seen.
Good luck!
Pat☺

PS: I found the following drawings in the FSMs. First is the 3rd gen, second is the 1st gen. It looks like what I called a heat shield, the screenlike device, on the 1st gen cat is just part of the casing the cat is IN.


3rd Gen FSM drawing

1st Gen FSM drawing
As you can see, the screen-like device I called a "heatshield" is simply a part of the casing of the cat. I apologize for my confusion, and lack of detailed naming convention knowledge.

Pat☺

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I'm starting to think it may be more of a fitment issue than anything else. You can see in the photos how one end of my exhaust extends much farther out from the gasket than the other. This is the side I've been having problems with. The catalytic converter has a thick outer tube, and a thinner inner tube. I'm starting think that inner tube is the same diameter as my exhaust, so there's really no way to get them to slide together. I took a couple photos.
Front (problem side)

Rear



Here's as far as I can get it together.



And for anyone considering this job, check out the difference between OEM and aftermarket gaskets. No comparison. I started the truck but haven't driven around yet. I honestly think the thicker, tighter gasket just might allow a decent seal even with that visible gap. It's a little misleading in the photos, but the cloth-looking OEM fits snug. I had to press it on with my hand, and it was hard to get off. The aftermarket gasket hung loose with a large gap.