Build Session 3 : Tapping a Poorly Threaded Harness Mount





A simple job today… when the car arrived there was an obvious problem with the inboard off side harness bolt. The car is set up for 4-point harnesses and it now seems that Caterham, not only pre-attach the hood and the boot cover, they also pre-drill and set up the attachment points for the harnesses.

Many build blogs talk about the process of unstitching the boot cover at the point where the stiffening aluminium (aluminum) bar sits at the front of the boot cover. The bar has to then be removed and the boot cover has the four holes for the harness bots punched in it. Then people typically glue up the unstitched boot cover.

I have none of that to do as Caterham have done it already and has probably saved me a days work with the hood, hood sticks, harness bolts and boot cover.

However, one of the bolts wasn’t screwed all the way into it’s thread. A quick tweak of the bolt on arrival day showed that it was binding in it’s thread and probably was suffering from some swarf or material in the threads.

Harness bolt sticking out

After pulling out the callipers and tap/die thread gauge it became apparent that I was going to need to order a new tap – the bolt is M11x1.25t/mm. One was ordered on Amazon and arrived today.

It was then a five minute job to tap out the hole and test fit the bolt – another job done, 10 minutes.

Tapping the harness mounting point


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