Change a CAT

1. Diffuser off (Rearmost part of the undertray)
2. Soak cat nuts in penetrating oil for a few days before hand. Undo nuts from Cat. (15MM), use Loctite Freeze and Release to break the nuts free of rust etc. It really does work. Use of an electric or air impact wrench here is a timesaver for removing the rusted nuts from the cat flanges.
3. Cut off those that won't move, swear profusely.
4. Wiggle the Cat, silencer and flexi until it all comes apart (If necessary remove rubber mount from the flexi)
5. Offer up CRP and fit the new stainless steel bolts in place not forgetting the gaskets
6. Tighten the new stainless steel nuts progressively as your CRP may not be an exact fit
7. Find gaskets on the floor undo the bolts and refit corectly
8. Refit diffuser

Job is a carrot, first time will take hours as the bolts are all rusted, second time is a doddle. While the cat is off press out the studs with a vice and a suitable socket, makes things easier next time.

Note that some grades of SS bolts may seize over time with the extreme temperatures; the only way to remove them is to apply pressure until they shear, then they will need to be renewed (removal will be necessary once a year for MOT if you are fitting a CRP). If fitting a CRP, normal steel bolts will be fine as the constant removal-refitting is enough to keep them from rusting up.

The use of copper grease can help prevent seizure.