May the force of the spring be with you

Louise Smyth

The engineers at Jedi Racing Cars in Wellingborough had a recurring problem when servicing their F1000 single seater racing cars: the half shaft CV pot joint they were using, derived from the original Mini, just wasn’t intended for quick removal and often resulted in breakage of the adjacent casting mounted on the differential.

Mike West of Lee Spring explains, “It was John Corbyn, MD at Jedi, who came up with the idea of using a spring to make it easier to get apart and cut the service time down. He knows the old Mini mechanics inside out so called our customer service team and they asked me to give him a call.

Conical concept

“I went to see him and saw the problem first-hand. His idea meant they could separate the joint without having to fully dismantle the drive shaft, by using a compression spring to apply a force between the two surfaces without being too strong to push them apart. When we looked at the dimensions they had about 60mm at one end and 25mm at the other. I knew that putting a standard 25mm compression spring in situ wouldn’t work and would allow too much movement, especially at speed. So I suggested a conical spring would do the job, with a dimension of 55mm at the base and 20mm at the top and an overall height of 30mm. The spring rate was calculated from using a standard compression spring with a wire diameter of 1.4mm and based on the spec of this we determined what was needed for the conical equivalent.”

John Corbyn says: “The spring takes the float out of the drive shaft, and removes the need for a retaining circlip, which sometimes necessitated destroying the bearing housing on the differential to extract the shaft and CV joint. The team at Lee Spring quickly turned around a set of sample springs for test and we have had no problems with the assembly in two seasons since – it has transformed the way we work.”

He adds: “F1000 Championship (formerly Formula Jedi) has provided exciting, cost-effective racing and has established itself as the premier bike-engined, single-seater category in the UK. The cars use a proven ‘slicks and wings’ configuration with excellent handling characteristics and powered by a 1,000cc high-performance motorbike engine, going from 0-60mph in just three seconds and on to 150mph, while revving to around 14,000rpm!”

Speeding up service times

“It is ideal for the novice or serious club racer, for whom it offers a proven and affordable route onto the single-seater ladder from karting. Consequently it is of great importance to keep budgets down and speed up between-race service times, which this innovative and elegant fix from Lee Spring has achieved.”


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