How hard is it to replace the exhaust manifold?

Answer 1

Changing the exhaust manifold on a Chevy trailblazer 4.2 I6 can be done without removing the engine or exhaust pipes. You need a 13 mm socket with a 2" extension for the 11 manifold bolts. 10 mm for the 4 heat shield bolts and nuts that hold the transmit ion and engine oil dip stick brackets. And a 15 mm ½ drive socket with a 2 foot extension for the pipe to manifold nuts

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Remove the air box by losing a hose clamp and the 3 screws holding the box in with a long slotted screw driver. Disconnect the IAT censer by squeezing the connector.

Remove the nut's that holds the oil dip stick brackets and A/C line bracket that mounts to the same stud as the oil dip stick bracket. Remove the other bolt that holds a A/C line bracket at the front of the engine so you can move the line.

You may want to brake the oxygen censer lose at this time or you can remove the heat shield with the O2 censer in place by feeding the wire threw the hole in the shield. The O2 censer is a 22mm or a 7/8 will work and AutoZone will lone the tool to remove it. You can remove the nuts on the 3 exhaust pipe to manifold studs with a 15 mm deep sockets anytime before all the manifold bolts are loosened.

Removing the heat shield it's a tight fit, but it comes out. Spray the 11 bolt and three studs that connect the manifold to engine and exhaust pipe with penetrating oil. You may want to weight for the penetrate to work. If your in a hurry and the engine is cool you can brake the bolts loose, but mechanics brake them off sometimes and you have to pull the engine or the head to drill them out. Once the bolt is broken loose try some more oil. The bolts do have lock tight on them and come out hard all the way. The bolts shaft will twist with 350 in lb of force, and brake after being twisted 1/3 of a turn so once broken loose if the torque seams high and you have a torque wrench that works turning left you may want to check to see if your at 300 in lb or less. If more try more oil and turning the bolt back in and out to work it loose.

The bolt are 8mm x 33mm with 1.25 pitch class 10.9 and are equivalent to a grade 8 bolt. You may want to remove the top radiator hose inlet to get at the front bolt, but it isn't mandatory. If you don't bother; be vary careful to keep the sockets on straight and do not put side lode on the bolt while struggling to turn it out if, you bend it might brake. Try to avoid using a deep socket, it makes it easer to put a bending force on the bolt.

Once all the bolts are removed you can remove the manifold out the top, but you may need to wedge the rest of the exhaust system back a few inches in order to turn the manifold up and out. Clean the exhaust ports on the engine and run a new bolt or tap in and out of the holes. Cutting a grove the long way through the threads of a bolt can help it work like a tap.

Bolts from the hardware store come in 30mm not the 33mm the factory bolts are, but the factory bolts aren't threaded all the way to the tip so the 30 mm should be close enough. If I was to do the job again I might try to find studs and nuts. When I reinstalled new bolts I did not use lock tight I don't think it's necessary, I used antisez on all nuts and bolts. Torque the manifold bolts 220 in lb with a new gasket working from the center out to the ends 3 times,

Unnecessary notes:

Penetrating oil will work it's way through tight fits by capillary action. (2) I torque the bolts a little high to 220 because there was still some old lock tight in the hole. (3) I have never heard of using anything but antiseze used for manifold bolts. I have a manual for a 1991 Dodge 2.2 that was well known for vibration. It says use antiseze on the exhaust and turbo and use lock tight on flex plate bolts ware the parts move.(4) I removed the right front tire to get at a manifold stud. (5) when I installed the new manifold I had the three studs removed so they would not catch on the pipe.( 6) The new manifold is garneted not to crack, but came unpainted. I painted with high temp paint and baked it with a heat gun than with the home oven. If you heat the paint by running the engine to full temp in one shot it can burn off. (7)Don't get confused about bolt grade metric 8.8=grade 5 SAE/ 9.8 is 7.5% stronger/ metric10.9 is 20% stronger than 8.8= grade 8 SAE. It may be hard to find a 10.9 hex bolt and you may have to go to a cap bolt and use a fender washer. (8)I never got the O2 cancer out even with a pipe wrench and about 250 foot pounds of force.