The standard Z22SE exhaust manifold is a cast part that is prone to cracking, particularly at the "Y" junctions. One owner says it was fit for purpose on the Vectra and Astra and simply ended up on the VX as part of the Z22SE package, which also makes standard replacements cheap. This page covers swapping it. For which replacement to buy, see Exhaust manifold options.
Check it is really the manifold
- Symptoms owners reported: a ticking noise on a cold start, which led one owner to replace his as a precaution.
- A broken stud can cause the same thing. One owner who thought his manifold was cracked had it checked by a garage, who found only a broken stud. They drilled it out and kept the same manifold. A replacement 4-1 is big money, so worth checking before you order.
Removal outline (standard manifold)
One owner's summary, in 2017:
- Remove the undertrays.
- Remove the heat shield from the manifold. The nut that holds it can be seized; one owner says only proper penetrating fluid shifted it.
- Remove the exhaust downpipe.
- Remove the head-to-manifold nuts (or nuts and studs together, if they have rusted together).
- The manifold should come out reasonably easily without touching the coolant hoses.
Refitting: separate the nuts from the studs, refit the studs first (before the manifold goes on), fit a new gasket, then the new manifold.
If the old studs won't come out cleanly, one owner used penetrating oil overnight and the double-nut method. See Torque values for tightening figures, though the threads don't give one for these nuts.
Stainless 4-1 manifolds: more work
The outline above is for the standard part. Owners say an aftermarket stainless 4-1 needs more removed:
- A Tullet 4-1: the coolant hoses (the water pipe) have to come off. See Coolant change and bleeding.
- A TMS 4-1: the rear clam has to come off. See Rear clam removal.
Clam on or off?
Owners who did it with the clam on say it is a pig; those who took it off say it saved hours.
- One owner fitted a Tullet with the clam on and the water pipe on. He called it the biggest pain of any job on the car, with skinned knuckles. It took three hours to get three nuts on, and a day and a half in all. A lug caught and damaged about 1 cm of the boot box insulation.
- Another owner says it is much easier to take the clam off, and another removed it "saving hours and loads of pain". A third says it is not too bad if the heat shield comes off easily.
- One owner whose garage was doing the swap told them it can be done with the clam in place, and planned to suggest taking it off if they struggled.
- One owner left the original heat shield off and put Nimbus on the underside of the boot instead.