Day 12: Engine running, rear lights, tidy wiring, prep front wings

I’d been away all week and hadn’t managed to get the engine running before I left because of the problems recording oil pressure. Whilst I was away Derek had sent me a new oil pressure sender as a first attempt at trouble shooting my gauge not showing any pressure

O/P Sender swap

A simple job. I applied PTFE tape to the thread, placed a drip tray underneath, and removed one sender to replace as fast as possible with the new one. I estimate I lost a thimble full of oil in the process, so nothing to worry about.

Of course I immediately tried turning the engine over on the starter motor again to see if it was working, but still nothing.

So in the end I decided it was time to start the car properly. Just for reference, what I had been doing prior to adding any fuel into the car was disconnecting the crank sensor connector block (front RHS engine) to avoid a spark.

I had previously filled with fuel so I also disconnected the Inertia Switch connector, as this shuts off the fuel pump and stops fuel flowing. It’s good that other home builders know what these two connectors do. I favour removing both, as a belt and braces approach. There is no need for fuel flow or spark when cranking for oil pressure.

Starting the engine

There are no two ways about it, this is nerve wracking, more so in my case that I never saw any oil pressure. If you have a dry sump 420R, then seeing oil return and flow around the system means you do have pressure, so don’t panic.

It took 4 or 5 attempts to start the car once I had reconnected the inertia switch and crank position sensor. This is fairly normal, and it would catch and then die almost immediately. Primarily its just getting fuel into the system.

I should have realised when I was adjusting my throttle cable for 0 to 100% open/closed that actually without any air coming in on closed, it was never going to run. I adjusted the screw under the throttle spring enough for the car to stay running once I had let go of the throttle. Its probably running a little fast on idle, but its running, all by itself.

I noticed that my coolant level was very low, and stopped the car to investigate. Turns out that I had a very small coolant leak at the temperature sender, as I hadn’t tightened this up enough. Once fixed, I topped up and started the car again.

I was checking that the engine was running on all cylinders and therefore could also see that the primaries were changing colour at the same rate.

I was also checking for water temperature on the gauge and I aimed to leave it running until the thermostat kicked in, cooled the water and switched off again.

All of this worked beautifully, with one small exception. The damn water temperature gauge is not recording any temp in the same way to O/P gauge records no pressure.

Im going to have a word wit hDerek on Monday, but someone on FaceBook has mentioned that it could be that the gauges themselves are not earthing correctly. I will ask Derek what I am to look for and fiddle with here.

Here is the video of the car running up to temperature and all sounding well. Another magic moment on the journey to completion!

Rear lighting

This job is made all the easier because Caterham pre-drill the large central hole to feed the wires through and the inner lower corner hole for mounting the light block.

The only real challenge is finding a level. My floor was level, but the car was sitting slightly out of level on its axle stands, so I adjusted that, checked again, then felt confident that using a spirit level along the top of the light blocks on either side would get them horizontal.

I simply held each light level whilst drilling with the other hand. I didn’t feel the urge to mark holes before hand, or use masking tape, I just went for it. The holes in the block and the rubber act as a guide and fibreglass is simple to drill through, just follow the guide, removing the bulbs before you go for it!

You have to feed all of the cables through inboard of the body after connecting, and use this inner hole for covering with the grommet attached.

I then attached the number plate light, pulled through excess cable and removed the excess, whilst using my wire strippers to provide me with enough wire to crimp a bullet connector on to the end. I found one in my tool box, so straightforward. Since then I have found a little bag from Caterham with some connectors in it, but I’m happy using my own bullet. You have to remove the little brass sleeves that cover the hoop for connecting the bullet too inside the light. I also filed off a little powder coat on the bracket so that the screw and nuts that attach the light to the bracket are earthed.

I finished off the rear end with the 420R decal, and the end result can be seen in the picture below. I tested all lights and everything works!


Tidying cables

I decided that I would spend the next hour or so just tidying up after myself, and this meant cable ties. Specifically I tidied up the handbrake cables, the speed sensor cable (hopefully leaving enough slack), and the Lambda sensor cable.

In the kit you receive 4 small black cable tie blocks with a hole in the middle of them. Derek informed me that these are to be used by riveting them to the chassis under the drivers side foot box, so that’s what I did.

It was a bit of a pain because of limited access and trying to use a rivet gun whilst lying on the floor is harder work than normal.


The other cables were easier and mine are routed like this, but Caterham may still wish to adjust these at PBC:

Preparing front wings

I then moved on to the front wings and prepped the wing stays first. After fiddling with BigHead mounts (to cable tie the wings in place), I decided that these would slightly raise the height of the wings and I didn’t like that look as much.

So I have decided to simply stick them using Sikaflex. But this means that to do this properly you need to remove the powder coat from the wing stay where it will be glued. I did this easily with 120 grade sand paper, right down to the metal.

And then you have to drill a 4mm hole to the underside of the forward wing stay, as the earth for the side repeater will be attached by rivet here. I had a think about this and decided that drilling a round tube is hard enough, I would drill from above and go through the top and bottom material of the tube. It seemed far easier than drilling from underneath and the wing stay is covered by the wing anyway.


I then prepped the wings by adding IVA rubber all around each edge, only to find that I have not been supplied with enough. I have completed one wing, but I’m about 3 cm short on the second, which is damn annoying. I’m sure Derek won’t mind providing me with another length.

And then I went to B&Q to hunt down a drill bit suitable for drilling out the centre of the 3 holes on each wing to attach the indicator repeaters.

After B&Q advice, I went with a 13mm steel drill bit, which cost me around £15. The guide suggests cutting a hole of 15mm, but with fibre glass disintegrating slightly and the back nodule of the indicator smaller than 15mm, I went with 13mm.

IMG_1941It worked perfectly, copious amounts of masking tape used, and I went up from 6.5mm through 8mm to the final 13mm bit. The trick is to get the drill bit spinning fast and then go for it!

I then placed the wings on the wing stays and chickened out of fixing them because I was unsure of how far forward or backwards they should be placed. Also, as you can see from a dry run photo below, the LHS (right side in photo) wing stay is bent a little upwards so the wing edge doesn’t run horizontal to the ground.


So I gave up work for the day, tidied the garage, spent time with the kids in the back garden, and fell asleep to the monotony of the Hungarian Grand Prix….

There’s always another day!

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