Silencer, clamp and another bobbin

I was in two minds whether to install the exhaust silencer before the rear arches had been fitted, however given the issues I’d faced (yet to be explained) I decided to proceed, mainly to reduce the volume of components cluttering up the house. I’ll just need to be very careful when it comes to adding the arches in future as the driver side is very close to the end of the silencer.


Before installing the silencer you need to fit the mount which is made up of a bracket and bobbin. This is a simple task and one which doesn’t really warrant a separate blog article or any real explanation. I’m mentioning the installation as I opted to swap out the supplied M8x25 hex bolt inserted into the chassis. The supplied bolt just looked cheap and I so I used an M8x25 12.9 hardened steel black cap-head bolt which I’d purchased from Accugroup. I also found the chassis threads were not entirely clean, I suspect from paint or powder coat. I used the replacement bolt to gently screw in and out to clean the threads. I found once I’d passed the first couple of mm the threads were nice and clean.

Bracket installed with M8x25 Black cap-head replacement

The next step was to place the bobbin on top of the bracket and secure below with a washer, spring washer and nut. Since I had some spare A4 stainless nylocs I also swapped the nut for a nyloc and kept both the washer and spring washer, again the stainless just looked better. I appreciate I don’t need a spring washer with the nyloc. but I figured it couldn’t harm. I used the same setup on top of the bobbin to secure the silencer.

Bobbin installed, top nut and washers need to be removed for exhaust to fit over.

Once the bobbin was ready I could install the silencer into the back of the catalytic converter and then place the rear silencer bracket onto the bobbin, easy. Not quite.


The diameters of the catalytic converter and the silencer at the point they interface are pretty much identical, and without some form of adjustment they were never going to fit inside one another.


The interfacing pipe on the silencer is manufactured with cut outs so it can deform inwards to allow fitment, however the strength of the metal is pretty high and it wouldn’t deform inwards by hand. I needed a solution.

Silencer end pipe cut outs

The silencer and cat are sealed together using a robust metal clamp, sorry I’m not sure of its official name, its just referred to as exhaust clamp in the manual. When compressed fully the clamp diameter is just lower than that of the silencer, and so I used the clamp to slightly compress the end of the silencer. I placed the clamp right on the end of the silencer and completely compressed the clamp, then backed it off, and moved the clamp inwards by a few millimetres and re-clamped. I repeated this process until I could just squeeze the end of the silencer inside the cat. Once I’d got an initial 2-3mm of the silencer inside the cat I sprayed a small amount of WD40 on the silencer and gradually rotated backwards and forwards whilst pushing inwards. The silencer worked its way home, far enough for the rear bracket to sit over the bobbin.

The bobbin was then secured with a washer, spring washer and A4 nyloc. Given I'd been using the clamp to reduce the diameter of the pipe it was already fitted around the assembly and so just needed positioning and clamping down, don't forget to fit this before mating the two parts!


The process of clamping, twisting and aligning needs two pairs of hands, which thankfully I had and I would highly recommend.


Since the exhaust system is now fully installed I can torque up the extractor bolts fitted to the block.



I've also fitted the heatshield around the catalytic converter and Lamda probe. I'll follow up with these in a subsequent article.

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Meet Mark
Loves cars, light weight specials, jDM, Lotus, Caterham, Rallying and Trackdays