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-   -   Replacing both catalytic converters (https://www.hummerforums.com/forum/hummer-h2-8/replacing-both-catalytic-converters-40084/)

myrddin 08-08-2018 12:47 PM

Replacing both catalytic converters
 
I’m having a nagging P0420, and I’m noticing a few other codes that support the need for a cat replacement. The codes as well as a white discolored cat and surrounding pipe. So I figured signs are good that one is failing and I bet the other one is not far behind. So I ordered the SS magniflow cats and will be replacing them over the weekend. I also have short headers and an aftermarket muffler (no idea of brand, was like that when I got it). Anyway on to my question. You folks think I should replace the exhaust manafold gasket while I have the cats off, or no need to? I am not aware of any leaks. But if I were to do it I guess this might be a good time.

Im going to start spraying the bolts today with some PB blaster to help them play nice over the weekend. Any other tips or thoughts?

oceanbrave 08-08-2018 03:01 PM

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.

NoSpoon 08-08-2018 04:16 PM

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!

myrddin 08-08-2018 08:33 PM

Thanks guys. I guess I’m kind of hesitant because I’m afraid a bolt will brake off. Then I would be in trouble.

Thoughts?

legerwn 08-08-2018 09:06 PM

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

myrddin 08-08-2018 09:15 PM

All the bolt heads are there. They have been out at some point because someone put headers on it’ll inspect them closer tomorrow. I’m thinking if they are leaking I’d see black around the head

NoSpoon 08-09-2018 07:40 AM

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 08-09-2018 08:32 AM

NoSpoon. I have them on the list. I’m still trying to decide if I should try to replace them, or the gaskets. I am not aware of a leek, and I have no broken bolts. I’m afraid if I try to remove the bolts to swap gaskets that the bolts will snap and then I’ll be stuck with a how to repair situation. My ICD wants me to replace the bolts and gaskets while I’m in. But my logical thoughts are if it ain’t broke... don’t fix it.

:)

NoSpoon 08-09-2018 08:49 AM

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!

myrddin 08-09-2018 09:05 AM

Thanks buddy! So would you say that if the bolt heads are all there that I should keep as is? And if that’s true would you say to keep an eye on them and if one of the bolt heads break then it’s time to go in and replace all the bolts and gaskets?


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