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[Miggy24]

Hi guys i need to replace the exhaust manifold gasket and want to know the best was to get the manifold off without the bolts snapping off and the threads stuck in the block

[Varche]

I've just done mine on a 12 year old V6 without any snapping. I squirted Plus Gas on them in advance of doing the job.

[Andy H]

Spray the nuts with penetrating oil 3 or 4 days before you start the job.

With time/patience/practice even the worst seized nuts can usually be persuaded to come out in one piece.

If you dont think a nut will come off without shearing the stud then try cutting it in half and prise the bits off the stud. When the manifold is off spray the base of the stud with releasing oil, leave for 3 days and carefully unscrew it.

If all else fails then you need to carefully drill through the centre of the sheared stud with progressively larger drill bits until the remains of the stud can be picked out. Because the stud is steel (hard) and the cylinder head is aluminium (soft) the drill bit will prefer to destroy the thread in the head rather than stay in the centre of the stud.

I have had success using a diamond coated Dremel tool to remove the bits of stud without damaging the aluminium.

The last resort is to drill out the damaged thread and fit a helicoil/recoil insert. (Not a disaster as the stainless steel insert is stronger than the aluminium and the new stud is unlikely to seize in the insert)

[Shackeng]

I always very slightly tighten any fast fixing, either nut/bolt/screw, and also, if felt necessary, give a sharp tap on the head, after soaking in release fluid also. This usually allows relatively easy removal. In some circumstances, but possibly not in this case, it is feasible to take advantage of the different coefficients of expansion of ally vs steel and make an application of heat to expand the surrounding alloy.

PS I'm not trying to teach grandmothers to suck eggs, but speak from a background of an aircraft engineer for 40 years.