Exhaust Manifold Replacement - question on pipe to manifold removal

keitho64

Original poster
Member
Mar 27, 2012
21
I am replacing the exhaust manifold on my 09 97x with the 4.2. I had this done on my 04 Trailblazer a long time ago but decided to tackle it myself this time.

I purchased a Dorman manifold which has all the hardware and seems to be a quality part.

So far I have had great success. I removed the air box, windshield washer reservoir, power steering pump, relocated the dipsticks and upper AC hose. This gave me a great access to the manifold.

When I removed the heat shield I could see the crack on number 1 cylinder where the manifold collector is. It appears to be cracked about 3/4 of the way around.

I was able to get all the manifold to head bolts free. I soaked them with Kroil for a while and then used a 3/8" ratchet. ( I am totally sold on Kroil, best penetrating oil I ever found) I worked the bolts back and forth as I was removing them. I did this for all 11 bolts, YES 11. The factory never put a bolt at the bottom of number 6 cylinder. It seems odd it isn't there. I plan to put a new one in.

I tightened all the manifold bolts back down and went underneath to remove the exhaust pipe from the manifold. I cannot seem to get a straight shot to the nuts on the manifold flange. Does anyone have suggestions on routing an extension to get to the nuts? Did you get them from above or below?

I was able to get one free via the wheel well. There are three nuts on the flange and the one closest to the wheel well came free. I can't seem to get the other two.

I am open to suggestions / recommendations on this as I plan to attack it in the morning.

I will post pictures of all this tomorrow.
 

Mounce

Member
Mar 29, 2014
13,667
Tuscaloosa, AL
I don't have any input on your issue unless it's the Trans cross member getting in your way, if that's it, pull her out and use a jack to support the Trans while it's out.

The 12th bolt probably either worked loose and fell out or snapped off on it's own. Try running a bolt in there and see what happens. If it won't go in all the way, it's probably a snapped bolt blocking the way.
 

NJTB

Member
Aug 27, 2012
612
Flemington, NJ
Put a jackstand under the passenger side, crawl under the car with a LONG extension and a deep swivel socket, loosen. It's still a 'poke and hope'.
This part was the biggest pain for me, bolts were rusted and I snapped one off after lots of grunting, but had the new manifold, so I didn't care.
FWIW, the exhaust system will slide back and forth a bit so you can get the flange to line up on the manifold. Don't make the mistake I did and tighten the bolts without it being seated correctly on the flange (damn sure looked like it was in there). Started the car, heard the exhaust leak, crawled back under it, re seated and went on my way.
 

keitho64

Original poster
Member
Mar 27, 2012
21
Thanks for the tips, I am going to head out and try again.
 

keitho64

Original poster
Member
Mar 27, 2012
21
It is out!!! I ended up taking the front wheel off and going in by the tire. I got one from below and the other two from the top. Time to put the new manifold back it. Soon to be quite again. :smile:
 
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keitho64

Original poster
Member
Mar 27, 2012
21
Here is the "Bad Manifold", clean head and the completed project. All in I have 6 hours into the project and I am sure I could have done it faster but I was trying not to break anything.

The one picture of the manifold to pipe connection was taken from inside the wheel well. This made it easier as I only had to do one bolt from below.

The vehicle has just over 63,000 miles and if this replacement lasts like the one on my other Trailblazer I can get 100K out of it. ...hopefully... I had the 04 Trailblazer replaced at 60K and sold the vehicle at 155,00 and it was still going strong.

Thanks everyone. I may write up a how to on this.
 

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redmaro42

Member
Sep 25, 2014
70
yea that was a serious crack there. Good job on getting the job done in 6hrs. Must not have ran into any broken studs that needed to be extracted (pain in the rear!)
 

keitho64

Original poster
Member
Mar 27, 2012
21
I had one broken bolt but was able to get it out. There was more room to work on it than I expected. I probably wasted 1 hour on the exhaust pipe removal, that was the hardest part for me. It was a bit of a pain but I have worked on much worse.

The crack was way larger that on my 04, I couldn't believe how big this was. It was very loud!

Glad it is done, can hardly hear it run again.
 

keitho64

Original poster
Member
Mar 27, 2012
21
So 2 years and 50000 miles later the manifold cracked again. This time it split completely in half.

Thankfully last time I did it I used anti-seize on exerything and soaked all the bolts with Kroil before I started. I managed to get it done in 3 hours this time.

When I put the manifold on I loosely installed it on the head and bolted the exhaust pipe. Once the pipe was tight I torqued the manifold down. My hope is this will reduce the stress on the manifold and hopefully last longer than 2 years or 50000 miles.

I'm attaching a picture of the cracked manifold.

This is the third manifold in the Saab and I did it on my Trailblazer twice. Maybe next time I try to find a header and do a full exhaust.
 

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mrrsm

Lifetime VIP Donor
Supporting Donor
Member
Oct 22, 2015
7,639
Tampa Bay Area
Keith... I've had an uncommon opportunity to study difficulties with the Dorman Exhaust Manifold and as it turns out... The Original GM OEM Exhaust Manifold Attachment Flanges measure out in the range of just under 8 to 9 mm in thickness. The Dorman Flanges, however measure in at around 13 mm in thickness... and this presents you with a very real problem.

Both the GM OEM Exhaust Manifold Fasteners and the New Dorman "Gold" Fasteners consistently measure out to a length of 30mm and the Holes machined into the perimeter of the Exhaust Manifold Ports of the Aluminum Engine Head measure consistently to a depth of 25mm.

In either case... regardless of which of these two fasteners you decide to use to attach the New Dorman Exhaust Manifold... to the Engine Head, you'll find approximately 5mm of Thread Length left inside of each of the Bolt Holes that remain ...unused.

What I discovered here prompted me to obtain After-Market Grade 8 (10.9) Hard Bolts M8 X 1.25 X 35mm Flanged Bolts with a satisfactory length required for the New Dorman Replacement New Exhaust Manifold... but these should NOT be used with any of the GM OEM Exhaust Manifolds.

Five (5) Millimeters might not seem like such an extreme amount of Holding Power. But not having as much holding power and resistance as possible to deny the dynamic stresses of thousands of heating and cooling cycles from failing really can make a very big difference.

I've attached the images of these components so you can see first hand how very different these designs are. I hope this helps if you determine the EM Bolts have begun to loosen up prematurely and decide to make the replacements at least 35 mm in length ...but no longer:

http://s557.photobucket.com/user/60...INEREPAIR/DORMANEXHAUSTMANIFOLD?sort=3&page=1

M8X125X35A.jpg


M8X125X35D.jpg


M8X125X35B.jpg


DSC06760.jpg


DSC06757.jpg


DSC06755.jpg
 
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keitho64

Original poster
Member
Mar 27, 2012
21
Thanks for the information. Last time I did it I bought new bolts from the local hardware store but used the same size as the stock ones. This time I bought new ones from Dorman and they are 35mm in length. I noticed they were longer so I tested them to make sure they didn't bottom out. They fit so I used them.

I stumbled onto this and your explanation makes sense. Hopefully this will last longer.

Your explanation makes sense and gives me hope this repair will last.
 
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