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Catalytic Converter & Cable ties

Updated: Jan 21, 2019

Fitting the catalytic converter is straightforward and certainly easier than I’d anticipated. When planning for the task I’d expected a fight between the end of the collectors and the catalytic converter however that simple wasn’t the case. Once the 4 collector pipes were aligned with the catalytic converter, the cat simple slid on. A bit of force was required to sit fully home, but nothing excess. I did heat the end of the catalytic converter pipes with a heat gun to expand the metal, but I’m not sure how much benefit it actually had, at the end of the day I used a very small and weak heat gun.

Caterham 7 Catalytic converter
Initial fitment of the catalytic converter

Note, it is important to ensure the sensor plug threaded hole is facing downwards and towards the car.

Whilst fitting the catalytic converter to the end of the collectors is easy, getting the retaining springs on less so. The manual makes reference to using cable ties but doesn’t state how big, or how many. I’d also read a number of other blogs where builders struggled with cable ties breaking. Fortunately I didn’t, and the installation of the springs when reasonably well.

Why? Firstly I feel the size and strength of the cable tie is critical.

You need to compress the spring to its maximum, and it takes some force, so I can see why others might have snapped many cable ties. Additionally you will need 3 cable ties per spring, if not the spring has a habit of bowing and the cable ties slips around.

Caterham 7 exhaust spring
Spring compressed and uncompressed without cable ties.

Assuming you have suitable cable ties installed you should achieve a compressed spring which appears something like the following.

Caterham 7 exhaust spring
Fully compressed, quite a difference from the previous image

Once ready you need to hook the spring loop around the hook end which is bent to 180 degrees and then pull the other end over the end which is bent to a less extent.

I found the curve of the spring to be too small and it prevented the spring loop from sitting fully home. Since the springs are designed to slot over with a mill of clearance, that loss of distance stopped the spring fitting over the second hook. My solution was to use a large flat head screw driver to widened the loop at the end until the first hook sat fully home. This provided just enough to get the other spring loop over. It was an incredibly tight fight and took some effort but it eventually went over.

Of course don't forget to cut and remove the cable ties when installed.

For reference

Cable ties

Heavy Duty Cable Zip Ties 300mm x 7.6mm, EAXER Ultra Strong Plastic Wire Wraps Ties with 50 KG Tensile Strength, Industrial Grade Nylon Ties for Indoor & Outdoor Use, 100 Pcs (50 White & 50 Black)

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