MGF FAQ

How To...
Fit A Catalyst Bypass-Tube

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Please Note: Although this task is relatively straight forward it can be quite strenuous and require some physical strength.

Before beginning, ask yourself a couple of questions:

  1. Is your F less than 6 months old?
  2. Do you have Mike Satur's KatKit fitted?

If you answer "no" to both questions then I would seriously consider getting someone else to fit the cat bypass for you. The 6 nuts that secure the catalyst are made from mild steel and very quickly corrode due to their exposed location. This makes removing the catalyst EXTREMELY difficult, as these nuts are likely to be rusted into position. In trying to remove these nuts you also run the risk of shearing the threaded studs off of the cat, a potentially expensive problem. A "yes" to either of these questions will make life a lot easier.


To fit a cat bypass, you need to get access to the underside of the car (picture 1).

Step 1: Park the car on a flat, level surface & place the piece of wood in front of the front wheel(s) to prevent it rolling forward (the handbrake only applies to the rear wheels). (Picture 2)

Click images to enlarge
Picture 1
Picture 1
Picture 2
Picture 2

Step 2: Using the jack, jack up the rear of the vehicle and position the axle stands as shown. (Picture 3)

Picture 3
Picture 3

Step 3: Remove the jack and begin to remove the 6 retaining nuts with the ratchet, extension piece and either the 15mm socket (MGF original equipment) or 17mm socket (Mike Satur KatKit) (Pictures 4 & 5). Use the WD40 penetrating oil to help loosen the nuts if necessary.

Picture 4
Picture 4
Picture 5
Picture 5

Step 4: Once all 6 nuts have been removed, prise the exhaust system off of the catalyst's threaded studs and then do the same at the other end, detaching the cat from the car. It is a good idea to replace the 2 metal gaskets with new ones, however, if you inspect the old ones and they appear sound, you can re-use them.

Step 5: The cat bypass should have come with a set of 6 stainless steel nuts and bolts. In my case I replaced the nuts with the KatKit as I find them easier to work with under the car. Offer up the bypass tube, sandwiching a gasket at each end and bolt it into position using the ratchet and 17mm spanner. I always orientate the bolts so that the nuts face outwards as this makes future access easier. Ensure that each nut and bolt is fully tightened. (Picture 6)

Picture 6
Picture 6

Step 6: Jack the car off of the axle stands, remove them and then gently lower the car to the ground. Remove the jack and the piece of wood from the front wheel(s).


Notes:

There are a number of reasons for bypassing the cat, on a 1.8i there is a small power increase, it is likely to aid in engine cooling as you are removing a "blockage" from the exhaust system - thus allowing the hot gasses to escape more easily, the life of the catalyst is prolonged as it is not being worn out and finally, fitment of a cat bypass roughly doubles the volume of the exhaust. The downside to this is that without the cat, the F will fail the MOT emissions test and there are green issues that need to be taken into consideration. I am not going to get into this topic here due to lack of space and this being the wrong forum for my opinions on the subject.

Things to note & Tips:

  • Obviously, do not attempt this if the exhaust system is hot!

  • Removal of the (unbolted) catalyst can be a bit tricky, a tip is to remove the flexi-pipe end first and slide the rear silencer box as far as possible to the right in its rubber mountings. This should make it easier.

  • I have a piece of old carpet which I spread on the ground prior to working under the car. This saves your clothes from getting filthy. Also, a good tip is to use some surgical latex gloves, again, for cleanliness reasons.

  • Storage: The cat should be blanked off with some cardboard both ends (use the old nuts for this) and stored upright in a dry place. (Picture 7)

Picture 7
Picture 7

2nd May 2001, Andy Phillips (AKA: Scarlet Fever)