Day 7: Complete front end

But just before completing the front end…

I finished the diff on day 6, but didn’t fill it with the diff oil or LSD additive. I decided that based on the volume, I could probably fill the diff with it in place, and without the drive shafts fitted. I thought that I would take this slowly and fill properly from the drain plug to ensure I got the correct volume of oil in the diff, and lost none from the drive shaft holes!

So this was a really straightforward operation, with the exception of the fact that the diff drain plug is a rather large hex bolt, so I needed to buy a 14 mm allen key socket to remove. I could have filled via either side of the diff, but ultimately I need this socket for regular maintenance and top up purposes.

I used a small funnel and some clear rubber tubing, and attached the funnel to the car with a tie wrap. All very painless. And for reference, you can fill the diff using the whole of the 1 Litre bottle of oil and the LSD additive and it takes the whole lot, but starts dribbling back out of the drain hole in the last few ml, and this is the sign you are looking for to validate its full.

And no oil came out of either side, so this is a job that is good to do at this point, when you have a little better access before the rear suspension goes in.

Water expansion bottle mounting plate

On a 420R, the oil tank for the dry sump kit is attached to the centre top of the cruciform, so you have to move the water expansion bottle off to the right hand side of the car, by attaching a plate to the top of the chassis tubes.

Two minor challenges with this small job are the fact that the plate to attach to the chassis is a rubbish fit. It wouldn’t take much effort for Caterham to create this plate to actually fit the chassis tube angles, but unfortunately they never have. My assumption is that it’s a plate designed for the S3 as the angles of the top tubes may be very slightly different, and they just “made do” for the SV.

The second challenge is that drilling holes into round chassis tubes isn’t fun. Once I decided on the hole location, I used an awl and a punch to gently make 4 big enough marks to attempt with a pilot drill bit. I then gradually moved up to the final 4mm bit size. The shape of the plate meant that not every hole was lined up along the centre line of the tube.

Roll over bar

After the “fraught with danger” expansion bottle bracket mounting, it was time for a really easy job. I attached the rollover bar. My variant is the FIA bar, so that means a thicker stronger tube and two additional mounting points. This has to be completed before the rear coils and dampers are fitted, as in addition to the top mount bolt you can see in the photo below, there is another bolt that goes upwards into the base of the roll bar from where the suspension will be. Its simple, especially when you realise that you can undo the long bolts that will be the top mounts for the suspension from inside the car.

Exhaust system

This is a one man job, but Paul was around to help and it made the job a little easier. He could hold the primaries in position whilst I torqued up the bolts into the block. My primaries were marked up before I sent them off for polishing, and of course when they came back, there were no labels on them.

To be honest, its dead easy to work out which is primary 1,2,3,4 from simply placing them like a jigsaw puzzle on the floor. For an SV, the insertion order is 4-3-2-1, so in effect start from the furthest back on the engine.

In my case, I had already completed the steering, so I had to angle the primaries around the steering rod too, but this was no problem. Primary one goes over the steering rod, and that was actually inserted from the top, rotated a little to get through the hole in the side skin and then rotated back. I used offcuts of bubble wrap to protect the side skin around the exit hole.


Once loosely bolted in place, I attached the collector (catalyst), and its a simple interference fit. A little alignment and a gentle tap or two with a rubber mallet, and it slid on easily. So far so good. The harder piece is attaching the “reverse springs”, of which there are 2, and these ensure that the collector remains tight onto the primaries.

I’d previously read on another blog that this can be made easy with a bunch of tie wraps. So, with the held from my vice and 4 tie wraps per spring, I compressed the springs all the way and the just about slipped over the hooks on the exhaust parts. I still had to use a little copper slip and a gentle bash from a mallet to get the hoops to slip over the hooks.

I imagine that if I didn’t know about this trick, I’d still be in the garage now chasing springs bouncing around!

Finally, the back box and the collector heat guard completed the job. The back box fits more loosely over the rear of the collector, and a bracket is provided to draw these two pieces tightly together.

And then a small L shaped bracket for the rear mount, with a rubber exhaust bobbin and a few nuts to attach and the job is done. The whole exhaust was done in less than an hour, so felt rather pleased, and I love the polished completed exhaust in situ. Of course the moment its been through a heat cycle or two it wont look like this, but in years to come I can reminisce by looking back at this photo! (did I tell you that I’m not a polisher?)

Cowling, ARB, Radiator, Oil Cooler

I’ve previously mentioned that the rear cowling for the radiator needs some rework to enlarge the slots in order that the front ARB will clear the sides of it. I achieved this with a Dremel and a metal file, and although I’m not going to win any metal works awards, I was quite pleased with the end result. Thanks to Dan Smith for sending photos and measurements of his enlarged slots, and here they are for future self-builders:

In effect, this was a relatively simple job, but it’s all about the order of assembly. The manual tells us to fit the inner cowl before the ARB, but as you c an see from the first photo below, there is enough wiggle room to rotate the cowl up and under even if the ARB is in place. The SV has some additional brackets because tis slightly wider than the S3, but the radiators are the same. The manual here is a little poor, and it needs a few good quality photos of the layout.The photos I have taken should really help with “what goes where, and on top of what”.

Everything fitted well, but note that the oil cooler needs its top mounting holes drilling. This is simple from an alignment perspective, just attach to the lower holes first. I did have to gently bend the oil cooler bracket to get it to sit straight, with the bracket mounts aligned vertically up the sides of the radiator. In the final picture you can see that I have attached the oil pipes.

The diagram in the assembly guide is perfect for this, it really simplifies what goes where with respect to the 3 oil pipes you have to attach – sorry no photos here, but it really is simple in terms of what connects where, and the oil hoses are only just long enough to fit, which means that routing is based on shortest distance through the chassis rails.

Oil and Water hoses

This is a picture of how I attached everything. The only item I was missing at this point was the water return pipe for the expansion bottle. Caterham simply hadn’t provided one in the kit, so a quick phone call to Derek and the following day the hose arrived. I cable tied it neatly directly under the top left (from the perspective of this photo) oil hose from the oil tank that you can see in the picture below.


Heater hoses

Fixing the heater pipes requires a Stanley knife for chopping up bits of hose, but other than that it’s simple. What is more of a pain is that the manual is painfully rubbish when it comes to the instructions for the where these hoses terminate. The final picture below shows that the heater inlet (top) is the hose that goes down to the front LHS of the engine,, and the heater outlet (lower), goes around to the rear RHS of the engine, where there is an inlet. It does this via the water temperature submarine and a chopped up J hose, with just the curvy J to double back. The green wire from the loom very close to where the submarine is, is inserted into the temperature sender.


Unfortunately, I have done this slightly wrong in this final photo. The assembly guide does not mention anything about the black and yellow wires that are floating around in the same area. I heard from Simon Calvert, another self-builder, that this is the earth to the submarine, and that if you don’t attach this then the water temperature gauge does not work properly. All of the 420R kits seem to be missing a metal adapter that coverts this black/yellow connector (bottom, middle below) into a hole to attach to the screw thread on the under side of the sender. Nothing in instructions and no part = minor frustration. What this means is that I will move the hoses UNDERNEATH the black plastic plate, not above as you can see here below. This way I get access to the threaded bolt on the sender, which is currently screwed into the plastic plate.


The routing of the water hoses caused me a headache to the point that I knew what the manual meant, but I wanted a little peace of mind and validation. As luck would have it, I’m building my car around the same time time Dan Smith and Simon Calvert are doing theirs. Dan kindly sent me a video of the water hose routing and has kindly allowed me to post this here:

I also completed the heater build by attaching the heater cable from the underside of the dash all the way through to the heater valve, which needed a tiny amount of adjusting to ensure that the valve moves from fully open to fully closed.

At this point I also fitted the throttle cable, but took no photos (I’m almost as bad as the assembly guide, sorry!). This was easy once I worked out that I had to cut the nipple off the throttle peddle end, thread it through the slot and hole, and then secure on the other side. Many other self-builders use the brass inner wire gripper from a standard electrical joining plug (not sure what their proper name is!) I used this method too, and made sure that the throttle pedal movement fully opened and closed the throttle body.

Air box woes, and other misaligned holes…

Now onto what should have been really easy. The air box sits on 3 small rubber bobbins, as per the photo below. What happened with my car is that some bright spark at Caterham decided to use the template for drilling these 3 riv-nut hole from the S3 model. Which means that I am left with 3 holes that are about 4 cm too far “outboard” which means simply that the air box will not fit, the hose doesn’t really reach the throttle body and is a long way offset, and the cold air inlet that should butt up against the bonnet is also outside the car by 4 cm. Its tragic…


See the air box as I can position it:


I am not happy with this, as the suggestion by Caterham is to drill another 3 holes in the horizontal scuttle in the right place. But I paid a lot of money for this kit, and I don’t want 6 holes in the car when I only need 3. Caterham has agreed to rework this scuttle at the Post Build Check, and has apologised for this error.

As a temporary solution, I am going to retain the 3 bobbins in position, and make some metal extension bars that move the air box inboard, imagine like some pieces of Meccano.

And finally, whilst we are on the subject of hole placement, the nose cone badge is supposed to fit on top of the 2 holes pre-drilled in the nose cone. The badge has two fat pins on its underside which locate in the holes.

It looks like the same person responsible for my air box holes has been working on the nose cones too. I posted these pictures on Facebook and the comment that made me laugh most was that its totally fine, just a parallax error and it looks central from a certain angle…

Someone else then posted a load of new bonnets photographed in the factory under my facebook thread. If you zoom in I don’t see one of these bonnets that has central holes.


From a chassis and part engineering quality, the whole kit is top notch and tolerances are fine. Its the final stage simple work such as drilling these air box and bonnet holes that REALLY lets Caterham down in my opinion.

Anyway, even these two little problems aren’t spoiling my enjoyment, and Derek from the factory is extremely good at customer service, and progresses any issues or shortages to my satisfaction.

Day 7 efforts have really moved my build on. I now have the whole front end down, and everything wired up and plumbed in properly. I have yet to fill with fluids (with the exception of the pre-filled gearbox and the diff), but now its time to move rearwards and get my head around the rear suspension and brakes. But that’s for another day!

One thought on “Day 7: Complete front end

  1. Glad my idea re the exhaust springs has helped! I remember chasing springs all around the garage and thinking “This is impossible – there must be a better way!”


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