Cracked clutch disc - engine out!

I always had troubles downshifting at high RPM. Always when trying to engage second gear when going into an hairpin I had to struggle until the revs dropped. My upshifts weren't that fast either, but within reason. After consulting lots of people I just couldn't diagnose what the problem was. Everything went smooth when standing still and at normal road driving.

One day I had enough and decided to take the engine out and investigate what the problem was.

Cracked clutch disc. At high RPMs the centrifugal force would make the loose part of the disc move outward and touch the clutch cover, making it not fully disengage.

So what I learned about taking the engine out was:

• Write down and take photos of all connectors and hoses, and where they should be.
• Take your time and have someone to help you!
• You need a crane.
• Be sure that you put the gearbox mount at the right way when the engine is going back in, or you have to take it out again (ask me how I know this).
• There is a way to get the engine out. The exhaust outlet is really in the way, but if you rotate the exhaust so the cat points upwards/forward there is enough room. Take your time to avoid any damage to the body panels. If your exhaust manifold is not welded together it will be much easier because it can be removed completely.
• You have to remove the steering rod.
• Engine oil and coolant will be all over the floor, be sure to drain as much as you can before disconnecting anything.
• You don't have to drain the engine oil if you take the gearbox out with the engine.
• The engine mounts are hard to put back. Small hands would help.

And what a change! The new clutch completely transformed the car. What a relief!

Differential support

There are reports on broken differential mounts on the CSRs, so I have mounted support brackets to avoid a future disaster.  Some say they're not necessary if you have steel spacers on the diff mount, but all race CSRs have support brackets mounted, it is even in the regulations, and if they're not necessary I wonder why it shouldn't be necessary on the road models which are used on the track with sticky tires.

Caterham sell support brackets for race CSRs. Unfortunately they don't fit the road version! The reason is that the race CSR has the differential mounted in the center but the road version has the diff a couple of centimeters to the right. MOG racing also have an adjustable diff support kit but take quite a lot of money for it. Others (Gunnars garage) weld mounts onto the frame and bolt the diff through there.

EDIT 2011-10-11: Caterham now have a road-version of the diff strut available!

The original - doesn't fit

I didn't want to modify the frame so I bought the race support brackets from Caterham and modified them. Since I don't have any tools nor the skills about welding I went to a local firm to and asked them to do the welding for me.

I took the Caterham support brackets and cut the ends off. I let the welder make a L-profile with some angle to the sides. They are bolted on the existing diff cover holes and the seatbelt mounts.

Fitment check, then back to the welder

Removed excessive metal with a grinder, and then some black paint.

In place!

New holes in the trunk-plate.

Thanks to Tyresö Svets.

Mantorp trackday movie

Movie clip from Mantorp this summer. Personal best 1:27.94!

Avon ACB10 tyres
Filmed with a GoPro HD

About using nitrogen in tyres

There are different opinions about using Nitrogen in tyres instead of ordinary air. I did some research and here are my conclusions regarding nitrogen and track driving:

The Ideal gas law says there are no difference between different gases regarding temperture vs pressure relationship. Many people use that as an argument for that air works just as fine as nitrogene.

However, if the gas contains moist, the number of mol of gas changes when the water changes state between liquid and vapor. The Ideal gas law also says pressure is relative to number of mol of gas and the amount of vapor a gas can carry is relative to temperature. So with a gas containing moist, the pressure relationship to temperature is not linear!

Any gas can carry moist, even nitrogen. The difference is that nitrogen is produced by cooling air, removing any possible moist. Diving air is also completely dry for the same reasons.

Air for divers and tyres

So my conclusions are that any dry gas is more predictable than humid air. Dry air works just as good as dry nitrogene. The benefit with a completely dry gas is a linear temperature-pressure relationship. Remember that you have four wheels and the chance you have exactly the same amount of moist in all of them is not very likely.

With that said, I did try nitrogen once instead of my normal gas-station air and couldn't find that much difference, but I tend to drive a handful of laps and then check and re-adjust my tyre pressures over and over. For those who have to start a race with cold tyres I can clearly see the benefit.

To be able to fill a tyre with nitrogen or dry air you must do it several times before all humid air is out. With stiff side-walls and low tyre pressure it not easy to get all out.

Silencer mounting bracket

When I bought my Caterham it was equiped with a big heavy rear silencer. Last winter I decided to remove it and modify the side silencer. After a couple of bad attempts with cracked welds and brackets I once again went to my local garage and extended the exhaust and welded a new mounting bracket. Hope it works this season!

Yes, the red spot is blood from my fingers

In order to decrease the bending force on the welds I have put rubber bushes between the brackets.

Thanks to Stefan Andersson Bil & Plåt

Spark plugs

Finally I changed the spark plugs. About time I'd say!

NGK BR7EFS
Gap 0,64mm
12 Nm