Replacing both catalytic converters
 

Totally replace the gaskets, you only want to go through this once, they are not expensive and the risk of a leak with an old gasket is high.

I used those same SS cats when I did mine 2 years ago. I went ahead and replaced all 4 O2 sensors and it runs like new.

Good Luck!

You'll be lucky if there aren't a couple already broke off,

on the LS I would leave things alone if they aren't leaking as they are known for broken manifold bolts.

If you do decide to tackle the gaskets be prepared to deal with broken bolts.

Neal

If you have headers and plan to replace the header gaskets but good GM gaskets and replace the bolts with these:ARP 4341301 Header Stud Kit for Chevy LS1



Many of us here have used them and I haven't any issues since.

myrddin,

If you don't have any leaks then you may be good. I had a couple that were broken so when I installed headers and cats I did them at that time. Fortunately the 2 broken bolts left enough sticking out to grab with an extractor tool. If and when you do these remove the plastic inner fender wells, takes 5 minutes and makes everything easy to reach.

Good Luck!

My thoughts would be to take advantage of the fact that all the bolt heads are there and replace them and the gaskets now or before a problem comes up.

Good Luck!

If the bolts have been replaced (header install) chances are good you wont have an issue,

the factory bolts are of poor quality and break often, my 08 has 1 broken bolt.

Once replaced with good bolts they rarely fail again,

I would give it a shot and see what happens,

Neal

I ordered the bolts and am about to order the gaskets. Mixman is this the right one?

Remflex 2008 Exhaust Gasket for Chevy V8 Engine, (Set of 2) https://www.amazon.com/dp/B00B2HM5NA/ref=cm_sw_r_oth_api_DAIBBbXN97KD7

I started working on it tonight. I pulled the skid, and was able to unbolt and remove the driver side easy. The passenger side converter bolts are all ate up. I cut off the ones I could get to. I’m down to one bolt on the back side where the converter meets the header. I think I need some kind of socket that will bite into the metal there really isint a lot of flat left on it for me to turn. Ideas? Extractor of some sort?

i can see the manafold bolts better now. I think they are all there but I’m afraid they are also not as flat as they used to be. Once I can get to them I’ll see how the socket feels on them.

I have a bunch bunch of questions. I’m just so beat from being under the Hummer that I’m going to have to ask tomorrow. Sucks getting old!

please let me know on the part number and what ideas you have to get that last bolt out. Thinking extractor set and work it from the top and bottom.

Yeah that was the right gasket set to order. Broken manifold bolts are a pain. Remove the front wheels and black plastic wheel housing liners to make access easier. Well worth the extra 15 minutes... On mine I had 4 broken bolts but ultimately failed to extract all but one. The rear drivers side one just kicked my ass for a few hours... Mine had been broken there for quite some time and I previously already had one of the clamp repair brackets to clamp that one down so I just put that back on with my new headers and it works just fine.

If it comes to it - this is the drivers side rear one (or pass side front).

There is another one that clamps the rear pass or front driver ends.

Kroil is awesome stuff for repeatedly soaking rusted bolts. On mine I soaked the bolts a few times over a prior week. Then just prior to pulling them, while the front end was on jack stands, etc I ran the engine for about 3 minutes to heat things up just a little. Then went at them. 2 more bolts ended up breaking off for a total of 4. Three extracted pretty easily.

No thats not normal but if the particular headers come that close there is not much you can do other than trimming the wheel liner or wrapping the header pipes where they come close. Many strongly recommend against wrapping headers as it traps moisture and will reduce their life dramatically in the long run. Only good option in my opinion is to get ceramic coated headers but that is expensive.

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

1.  
   • 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.
2. 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.
3. Install the exhaust manifold, NEW gasket and bolts.
4. 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)"

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.