Heater, Airbox and Horn

Updated: Jan 21, 2019


This weekend, which I believe is weekend 3 I set to work on the Heater, Airbox and Horn amongst other areas. I’ll save the specifics of the Heater for a post later in the week. For now let’s review the Airbox and Horn.


Assembly of the Airbox and Horn again resulted in the now typical Caterham treasure hunt.


So starting with the Airbox.


Before we get onto the specifics of the installation I have to say I am a little disappointed with the quality of the airbox. It’s sadly manufactured from appalling plastics which are thin and hard. The fitment is pretty terrible too, the joint between the two halves its just awful. For such a simple piece it would have been nice to see Caterham spend a little more money on the development. Post IVA I might look for an aftermarket unit from Reverie or similar.


Installation is pretty simple,

  1. Fit the Bobbins on the chassis holes, there are three, finger tight.

  2. Split the Airbox in half, it's shipped with cable ties holding the units two halves together.

  3. Once split apply the supplied trim to the lower half.

  4. Place the bottom half of the box over the bobbins, and fix down with a washer and M5 Nyloc nut

  5. Place the top half over, and secure using the special washers and bolts.

Simple right! Nearly.

So what when wrong. Well to be honest not much but of course issue did occur.


First off, watch the trim to be fitted around the Airbox inlet. The trim has an inner metal structure which makes it stiff and difficult to fit. More importantly my piece had been cut in such a manner it was supplied with quite a nasty metal edge, very sharp if you're not looking. I appreciate the sharp edge is simply due to the nature of the trim, it is incredibly difficult to achieve a clean straight cut. You need to cut the strip to fit the box, so through experience you understand the problems Caterham have.


Fitting the trim is pretty easy, and you should be an expert by now. Just watch the tighter radius at the forward end. Also ensure the trim flares outwards, that's important. Lastly once I'd cut to length and fitted the trim I used some superglue to just hold the joints together.


Any other issues, yep! So the M5 Nyloc nuts used to hold the box down. I'm sure those nuts and washers are somewhere in the kit, could I find them! Hell no! Caterham's guidance is "unmarked bag". Helpful come on guys you need to work on this stuff. It kills the fun of the build.


In true Top Gear fashion I felt a challenge coming on :-)


Which is quicker, a wife going to B&Q or a Caterham builder looking through misc parts.

So I asked my wife to goto B&Q and pick up some M5 Nylocs, I figured the nuts weren't critical in terms of load and thus specification. Any available at B&Q would be acceptable.

Whilst the wife was gone I continued to hunt for the nuts, of course the wife beat me, its probably about 5 miles to B&Q, so 10miles there and back. She returned holding M5s and found me still searching. I gave up and fitted those from B&Q. I already had suitable washers.


In response to this I've ordered a pack of metric Stainless A4 Marine grade Nylocs. I'll hunt to a point, but no further.



Fitting the Horn.


Unfortunately I've yet to complete the installation of the Horn, the reason being more hardware issues. Let me explain.


I've got a 420 R kit with a dry sump and as a result installation of the horn is different to the 270, 310, and 360, although I suspect a 360 with dry sump would be the same.

So what's different, well you need to drill steering rack cross member and mount the horn underneath. It's reasonably well documented in the manual,


Manual Extract

Locating the horns is simple, they're in clearly marked manufacturer packaging, easy.

The bolt, 3 and collar 2 are a different matter entirely, here we go on another treasure hunt, and these aren't available at B&Q.


After plenty of searching I eventually located the following bolt and collar in they're own plastic bag marked only with the Caterham brand. It had to be these.


Bolt and Collar surely.

From the shipping notes I believe the collar is the same as the one installed in the bottom of the suspension strut assembly.


I tried a test fit on the worktop, just to confirm everything looked OK. I quickly found the bolt was too short. as shown in the following images.




There isn't sufficient length, the bolt isn't M8x50 as required. I've measure the bolt at its certainly short, M8x40. I've found an M8x50 in the Coolant fasteners pack and tried that and sure enough the collar and everything else seems to work. At the moment I've chosen not to steal the fixing from the Coolant pack and so the horn is currently sat part assembled in a storage box.


Time to email Derek! Although it's half term and I know he is away on annual leave. I'll need to wait for his return before seeking clarification.


I'll follow up once I have the correct bolt, maybe it's elsewhere, I suspect documenting drill the chassis is also worthwhile.


To follow the heater, and a catch up on the front suspension.

121 views
follow me
  • Twitter Social Icon
  • White YouTube Icon
Meet Mark
Loves cars, light weight specials, jDM, Lotus, Caterham, Rallying and Trackdays