torquing up the wishbone required draining the coolant!

The last week has been spent tidying up odds and ends which needed finessing as I approach the completion of the build. One of the areas I knew needed addressing was the front wishbone bolts, they needed torquing up to specification. The bolts were fitted along with the wishbones very early on in the build, I believe probably one of the first tasks after protecting the chassis. Now Caterham provide very specific instructions on not torquing up the wishbone bolts until the car is complete, the instructions are as follows,

Recommendation from Caterham regarding when to torque the wishbones

So I followed the instructions to the letter. This was a big mistake!


The 420R engine bay is incredibly cramped, particularly on the near side. The presence of the catch can, radiator top hose, dry sump tank, and dry sump lines exclude access to the near side rear lower wishbone bolt. Of course, if you've read my previous blogs, you'll know I'd already expressed concern regarding the design of the catch can and top hose. You can't get the catch can out without removing the top hose. Not good!

Cramped engine bay, no access to the near side lower wishbone

After much pondering, I accepted the situation and decided I had to remove the top hose, then the catch can, only then did I have a chance of reaching the nut and bolt for the wishbone. It's worth commenting the lower wishbone bolts need to be torqued to 81Nm. So you'll need a bit of space to work.


Removing the radiator top hose without draining the system would I assume create a mess. So I decided I had to drain the cooling system, something I could definitely do without. I jacked the car up just high enough to place a high-quality B&Q bucket underneath the radiator drain bolt, and then removed the bolt. To my surprise, no coolant came out. Please remember I'm not massively experienced. Hmm, I briefly considered why this was, and concluded some form of vacum or pressure must be holding the fluid in. I removed the pressure cap from the reservoir, and sure enough the coolant shot out, initially overshooting the bucket.


Coolant drained, and any mess cleared up.

Once the coolant was drained I removed the top hose followed by the catch can and then went to work on the nut and bolt. Sorry I didn't stop to photograph the process, apart from the following, which shows how tight access is, even with the catch can removed.

Limited access even with the catch can removed

Torquing the bolt was incredibly difficult, even without the catch can there wasn't space for my torque wrench, so I had to guestimate 81Nm. Luckily having just done the offside where I could use a torque wrench I had a reasonable idea of the force required. I also used a trick I'd be shown by my mate Mark to extend the length of a tool such as a spanner. The trick involves interlinking the ends of spanners, this was critical as it gave me a tool similar in length to my torque wrench and thus some commonality in the physical strength required to torque the bolt.

Interlinking spanners, clever little trick.

I used a 19mm spanner interlinked on the nut at the front, and a ring spanner at the rear which rested again a lower chassis tube. It was hard and slow work, as the throw wasn't easy, but i got there.


I'm now confident I've torqued the lower bolt up to ~81Nm and with the car on the ground.


If you are building a 420R or any Caterham with a catch tank and limited access I would recommend torquing these bolts as soon as the engine goes in and the suspension is on, so you can get the wishbone level. Ignore Caterham's instructions.

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