Fuel gauge update and paranoia

Updated: Apr 16, 2019

It's been an interesting couple of weeks since getting the 7 on the road.


I've had a response from Derek Howlett regarding the fuel pump and I've properly let a good dose of paranoia settle in. Plus I've been on a quick blat with a friend and his Westie, also our local version of the Taffia fish n chip run.


So the fuel pump progress, well Derek has requested I further the issue under warranty with Oakmere. Now this isn't an issue, other than it's just inconvenient to have the car stuck at a UK dealer, especially if it needs a part the dealer doesn't have and potentially Caterham can't immediately supply before my return journey to the Isle of Man. I am aware of a fellow owner via the Lotus 7 club website with the identical issue, he has sadly been waiting weeks for a replacement sender. I have expressed this view to Derek and he has offered further support by requesting I photograph the top of the fuel pump to see if it's sat correctly. To do this I'll need a lockring tool to remove the fuel pump lock ring, unfortunately, I don't have one, so the job is on hold until I can source the correct tool. Derek also confirmed all the gauges operate through the tacho, so there is a possibility the tacho could be at fault, rather than a part in the tank or fuel gauge.


Given I've not been able to get the car to a UK Caterham dealer yet and coupled with the fact I built the car any unusual noise has been a cause for concern. The two main areas which have worried me the most is the L.S.D. and an engine noise.


For me the L.S.D. sounded like there was too much backlash, though please consider my relative inexperience in that statement. The amount of noise, a sort of clonk on the initial engagement of torque into the differential is quite pronounced. I appreciate you are sat on top of the differential which is directly mounted to the chassis, however even considering this the amount of noise is still considerable. I've been a co-driver for many years and sat in numerous rally cars with plated diffs, none have been as noisy. The amount of play before takeup between the ring gear and pinion commonly known as backlash is also surprising. I recorded a video of the noise along with the play with one wheel held and sent the video to both Derek and also Simon Lambert at Caterham Cars.

Simon responded acknowledging the noise as normal for the sintered plate setup now used in the BMW differential supplied for the 420 R. Simon also commented the previous Ford ZF differentials were much quieter. While the response has confirmed everything should be OK it still leaves me feeling a little uneasy, I guess I'll just need to recondition my mind to accept that's how it is.


Having exchanged videos with Simon over my differential concerns I also reached out to him regarding noise from the engine. As I'd had numerous unsuccessful idle running cycles trying to get the 7's radiator fan working (see prior blogs) I was concerned excess heat might have caused some damage. Why? well to me there was a noise from the engine's top end which didn't sound right, a very pronounced noise heard above the normal valve train noise. It's difficult to describe, and best heard in the video below.

Simon again responded, and also provided an example video from a new car currently being built in the factory. His explanation stated the noise which caused me concerned is known as 'plenum reverb' and is caused by resonance within the plenum chamber, it's an expected characteristic of the 7 420 design. This is certainly a new concept to me and not something I've experienced on other engines I've own. I suspect the noise is more prevalent due to the bespoke low volume nature for the Caterham plenum being designed for performance only, and without any real consideration for such resonance. That's my personal view and not something Simon offered.


I've kindly asked Simon if he would mind providing additional information about the behaviour so that I may include it here, it's an interesting concept and one worth further expansion. I really hope Simon is able to find time to provide more technical data I can share with you, it is a long shot, if not I may need to do my own research.


The weather last weekend was truly glorious for this time of year and I took the opportunity to meet up with a friend and fellow kit car owner to show off the 7. My friend had bought a Westfield towards the end of last year and with the weather now improving it was an ideal opportunity for us to have run out to Sulby reservoir and beyond. It was a cracking afternoon out, we went further than originally expected and ended up out for 5 hours with a tea stop at the Sound Cafe.

Caterham 7 420R at Sulby reservoir, basking in the sun

The amazing weather has continued through the week too, so last night the wife and I took the 7 out for a posh tea, fish n chips in Port Erin. We parked on the prom and from the comfort of the 7 we watched the sunset with a bag of chips each. Magic times!

Watching the sunset in the 7 with a bag of chips

References

Original blog, https://www.caterham7diaries.com/420r/fuel-gauge-inaccuracy

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