Hummer Forums - Enthusiast Forum for Hummer Owners - Replacing both catalytic converters

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Alright. All the bolts came out. Man I was stressed. The rest of the parts will be in tomorrow.

https://cimg1.ibsrv.net/gimg/www.hum...b94f1eba8.jpeg

So I know for tomorrow. I would assume I need to use anti seeze on the stud and nut... do I need to torque the ARP studs or just run them in till they bottom out? What is the torque of the exhaust manafold nuts (ARP) and what is the torque on the converter bolts/nuts?

also can anyone recommend what bolts to get fee the converter to header and converter to muffler? Or do I just go to the local parts store and grab some exhaust bolts?

I reused the lower ones on mine. Bolts into the block need to be properly torqued with a torque wrench. That is what will properly compress the graphite gaskets. The GM eSI system says for a 2005 (my guess is it might be the same for 08/09 models but you might search google to be sure)

"Important

- Tighten the exhaust manifold bolts as specified in the service procedure. Improperly installed and/or leaking exhaust manifold gaskets may affect vehicle emissions and/or On-Board Diagnostics (OBD) II system performance.
- The cylinder head exhaust manifold bolt hole threads must be clean and free of debris or threadlocking material.
- Do not apply sealant to the first three threads of the bolt.
Apply a 5 mm (0.2 in) wide band of threadlock GM P/N 12345493 (Canadian P/N 101953488) or equivalent to the threads of the exhaust manifold bolts.
Install the exhaust manifold, NEW gasket and bolts.
Tighten
1. Tighten the exhaust manifold bolts a first pass to 15 N·m (11 lb ft). Tighten the exhaust manifold bolts beginning with the center two bolts. Alternate from side-to-side, and work toward the outside bolts.
2. Tighten the exhaust manifold bolts a final pass to 25 N·m (18 lb ft). Tighten the exhaust manifold bolts beginning with the center two bolts. Alternate from side-to-side, and work toward the outside bolts."

"Install the exhaust manifold pipe nuts. Tighten the nuts to 50 N·m (37 lb ft)"

What I’m not following is that it’s teferring to the stock bolts and not the ARP studs. Do I need to torque the studs or turn them in till they bottom out? Then I assume I would torque the nut. Also I’m reading some say use anti seeze and some use lock tight. Confusing.

I'm not certain in that case. Might check some of the GR truck forums to see if there are recommendations on using the studs instead of bolts. I say that because the trucks are far far more common and use the exact same engines, etc. I'd guess that the stud would be installed until they bottom out (and probably use some removable loctite) and then torque the nuts (also with removable loctite) to the same torque specs I posted. The final torque specs should be the same regardless of the fastener type as that is required to properly compress the gaskets.

Ok I got the studs in and gaskets on also put the headers back on and I just bolted up the converters. I have an exhaust leak where the passenger side cat attaches to the muffler pipe. Should there be a gasket there? It’s metal to metal... the cat side has a rounded hump and the muffler side has a reseeded hump. I have it pretty tight there. Not sure what to do. I drive over to the parts store and they didn’t know anything about it, and didn’t show any gasket on the computer.

Am I supposed to have one of these? I don’t think I had one before I took it apart. But I could if lost it I guess.
https://cimg9.ibsrv.net/gimg/www.hum...029b31d397.png
https://cimg0.ibsrv.net/gimg/www.hum...0fbc1511fa.png

Kind of stuck. Going to call it a day

I loosened it up and realigned the flange and tightened it all back up and it’s better now. I’ll check the bolts after I drive it for a week. I noticed I have a crack in the seam of my muffler so I’m thinking once I pay off the converters I’ll order a muffler to match.

No no more work for now... I cleared the code. I hope it’s gone for good. p0420