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The catalytic convertor is fitted using steel studs, washers and nuts. These become terribly rusted within a short time and, in some extreme cases, must be cut through should you need to remove the cat for any reason.

This guide is based on my own experience in replacing the studs with stainless steel replacements.

You'll need 6 off M10 x 40mm Stainless Steel A4 Bolts, each with 2 washers and 1 nut (all A4 stainless). I got mine from Wessex Fasteners in Swindon, but most decent fastener suppliers should be able to obtain them. Total cost was £3.88.

Step 1: Remove the Cat

The removal of the cat is covered in the Race Exhaust Section, Steps 2 to 5 inclusive. Note that if you still have the original exhaust system fitted you may need to carry out Steps 7 through 12 too (I didn't as I had already fitted the Race Exhaust which gives more room to manouver the cat). You may need to attach several extension bars to the wrench handle in order to get sufficient leverage to undo the rusted bolts, having applied plenty of WD40 first.

Here you can see one end of the cat with the existing studs ...

Step 2: Remove the Cat Studs

Referring to the photo, you can see that a cat stud has a flat end and a threaded end. Don't be tempted to bash the stud out - you may fracture the cat housing!

We'll use a large engineers vice as a press. Screw one of the original nuts onto the stud so that it increases the surface area of the end of the stud (i.e. its only screwed down as far as the thickness of the nut).

Select a socket into which the stud head can be pushed WITHOUT JAMMING (!). Place the socket over the stud head, then put the assembly (socket, stud / cat and nut) between the vice jaws as shown in the graphic below.

Close the vice jaws (you'll need to exert a lot of pressure) until the stud pops out. Repeat for each stud.

Step 3: Replace the Cat

The replacement of the cat is covered in the Race Exhaust Section, Step 8.

Here's a view of the installation and a visual comparison of the stud / bolt fixings.