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Costin Walker F3/F4/FJ Imp Rebuild

Mark (smokey mow)

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I like to start my build threads with a little bit of background and history and although this cars history started all the way back in 1968 my knowledge and involvement with it  began much later than that.


Those of you that have seen my other posts and build thread will know that my involvement in single seaters and specifically Johnny Walker's F4 cars began in around 2014 when I bought my first JW4 Formula four car, one of the first 1966 250cc Mk2 chassis.  Walker only made 56 cars of which only 12 were Mk2's and search to find original parts to rebuild my particular car lead me on an unexpected journey which culminated in me obtaining much of the original factory records, drawings and tooling for the JW4.


One car that had always intrigued me during my research was the very last car that Johnny Walker made; the Costin Walker. This car was something quite different to any of his previous F4 chassis and for which Walker had employed the talent's of Aerodynamist Frank Costin to design the chassis and bodywork who was famed for his early work with Lotus cars then later Marcos. More used to working with a wooden monocoque for his chassis construction on previous projects, for this commission his 18th car Frank Costin chose to adopt a space-frame construction and in his words to "carry it to its logical ultimate".  Costin set out to design what was to become one of the stiffest space-frames ever produced for its weight and this very car went on to be displayed at the 1969 Racing Car Show at Olympia.






I will continue the full history in later posts but, the history of the prototype was short lived when in 1971 during an F4 race at Lydden, the car spun striking the bank which caused damage to the front suspension upright and steering rack. 

Rather than rebuilding the car a disillusioned and financially strained Walker sought to sell the car, but it was not to be run again by any of the subsequent owners. 


The last recorded information I had of the car was a magazine cutting from 1991 where then then owner of the remains was seeking information about it's past.  This article was the first breadcrumb in my search to find the whereabouts of the car as I wanted to learn of it's fate.  As luck would have it the owners name in the article was quite unusual and after a session of googling I was able to find somebody with the same name but promisingly working in the motorsports industry.  An enquiring email was sent and luck was again on my side as I had not only found the right person but also they were still the owner of the car having by then had it for nearly 40 years.




I would add that at this time I had no intent in buying the car as my interest was in the researching the history of the marque. I arranged to meet the owner Denis and I was grateful that he was also willing to show me the car and fill in a few blanks about its history and whereabouts over the preceding years.  




Denis had bought the car in 1976, 5 years after its Lydden accident. back then it was in a sorry state having languished in a damp and draughty barn for 5 years and it's original 85bhp imp engine and jack knight gearbox had long since gone. After a period of storage Denis had set out to restore the car and at the time I first saw it in 2016 the car was still in pieces and the only part which had then been restored was painting of the chassis.  


A pleasant afternoon was spent kicking tyres and talking cars then I went on my way back home.  A few more emails were exchanged between us over the next few weeks as I found out more about the cars history and we shared information and then that was it.

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Out of the blue I received an email from Denis at the start of this year explaining that he was thinking of selling.  I wasn't looking for another project as by now I was mid-way through the restoration of my third JW4 but this car meant something to me and these opportunities don't come along everyday.  I'm not sure my partner Dawn entirely understands my passion about old cars or why I would pay quite what it did for a pile of dusty rotten old car parts designed by some slightly famous bloke but I nevertheless did. 




Given the relatively short timeframe in which I bought the car and the fact I was financially crippled in buying it at a time when I was already haemorrhaging money on finishing the restoration of my JW4 together with attempting a garden room build for the house, there was no spare cash or time to make a start.  So nothing more was done other than sorting, labelling and boxing up in readiness for the re-build to begin.  


The car came with an engine, but this also had been stripped into parts so when the time allowed this would be my first challenge to see what was salvageable.  It didn't take long for me to find that the years hadn't been kind to this, and with the head split from the block, moisture had been allowed to get into the bores and the crank was locked solid with the pistons rusted in place.  The head wasn't looking much better either with rust on the camshaft and many of the lobes stuck fast. The carburettor is beyond rebuild.



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The gearbox had faired slightly better, and despite looking like it had spent some time sat outside or in a damp barn, the damage initially appeared limited to an inspection cover which had rusted in a hole but the inside still had a good layer of oil protecting everything and gear selection felt smooth. As I intend to build this car to be raced, the gearbox was duly despatched for a thorough inspection and rebuild to ensure all was working and in good order.





As I worked to finish JW4 which I'm pleased to say is now complete and soon to be on its way to join the home of two of its sister cars in Belgium I only had time for a few small jobs on the Costin Walker, which mainly involved sourcing a few much need parts for the rebuild and for now that almost brings us up to date.  


Realising that the engine was not in a salvageable state I made the decision to strip it for all the parts that were unique to its install in the Costin chassis and then to seek out a replacement. The Costin runs the engine in a near vertical orientation at an angle of approximately 20degrees whereas in the Imp its laid near to flat, this means that all the inlet manifold, exhaust and also the cooling set-up are unique and needed to be swapped over.  An adaptor flange is also mounted between the engine and gearbox to accommodate the different orientation of the engine but also because the box is run inverted in the Costin.





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As mentioned earlier, at this stage I'm just sourcing parts and doing a small amount of trial assembly to check the fit of parts and ease of assembly, although I have some photos and a few of the factory drawings for this car, being a prototype I have a lot less detail and info compared to the JW4's that I'd built before.


One problem I needed to resolve was the uprights both front and rear.  During its development the car ran with two different types of front uprights. Initially Costin at the request of Johnny Walker design the car to use the JW4 magnesium uprights and front drum brakes, which were paired with 10" front wheels. Frank Costin had commented that these weren't perfect but initially worked ok, later on in the development the car was passed to Tony Hilder of Piper Cars to try and tame the handling and he adopted 13" front wheels in lieu of the 10's fitted by Costin and also fitted front disc brakes.




When the car suffered its accident at Lydden in 1971 the Hilder front upright was broken beyond repair. Unbelievably I still have that damage upright amongst the boxes of parts. Not being able to source an identical replacement I was left with the option of either reverting back to the JW4 upright with drum brakes or sourcing a suitable alternative.


Frank Costin in his design for the chassis had considered several different race series including F4, F3, F5000 and Formula Ford and designed the chassis to be able to accept engines for each of these and the suspension parts as series regulations dictated. For Formula Ford the Alford Alder or Triumph upright as its better known was used so this seemed a sensible option as parts are easily available, disc brakes could be fitted and it would fit with 13" wheels.


Once I'd settled on the front suspension the next search would be for suitable wheels. The downside of the using the triumph upright is that the hubs have a PCD or 3-3/4" compared to the Hillman Imp hubs on the rear which are 4" PCD so I'd have to run a miss match front to rear. All the photos and articles I have of the car are are in it's earlier years where it ran JA Pearce Magna wheels so the hunt was on for yet another set. 


Well i didn't have to wait too long until just what I needed appeared on eBay from the same seller who I'd bought the uprights from a month or two before.



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Mark you are mad 😀

Really looking forward to this rebuild. I presume this car is slightly larger than the JW4. 

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Hello ,Mark thanks for sharing,good to see the pictures.........at least you've got a pattern of the inlet manifold..........and some interesting relics,to go with the car.....well done.FW.

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24 minutes ago, Nic (NICO) - Shropshire and Mid-Wales AO said:

Mark you are mad 😀

Really looking forward to this rebuild. I presume this car is slightly larger than the JW4. 

:d thanks Nic, you're not the first to think that! Yes it's a bit better proportioned than the JW4 but would still be snug for some.

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  • 4 weeks later...
  • 3 weeks later...

Thanks for the words.  This last month has been quite slow progress but I did find some time to work through a few more ideas for the suspension and braking.


Having worked out a plan for the front suspension my attention has now turned to the rear.  As mentioned earlier in the thread the original magnesium upright was broken during the Lydden accident and are beyond repair. This had been replaced with a fabricated steel upright of the same geometry as the mag upright to get the car rolling but over time that too had rusted to dust. I'd looked at the options of reverse engineering the Mag upright to make some replacements but after some preliminary enquiries with some suitable companies the costs of 3D scanning and prototyping would have been prohibitive so and early decision has been made to go with fabricated uprights that were used on the slightly earlier JW4 Mk4 .




The JW4 Mk4 was a car that for a short time I owned and this was the prototype for the car engined JW4's when F4 was being developed to move away from the use of Motorcycle engines.  The first prototype which I had was much like the Costin designed for a Hillman Imp engine and ran with unmodified imp drive shafts. As it happens amongst all the factory drawings I have for the earlier cars are the upright drawings for the Mk4 and the details necessary for making new replacements.  The sheet metal parts would be easy to recreate and I'll be getting these laser cut as usual, the hubs and bearing carriers are slightly tricker as these are taken from the Hillman Imp's rear trailing arms and then cut down for repurposing. The uprights are still on the drawing board at the moment so there's no fabrication to show at this time however I have sourced a pair of Imp rear wishbones and cut these down for the bearing carriers that I'll need for the new suspension.








I've also found a pair of rear drums, that have now been stripped down, shot blasted, powder-coated and now reassembled again.







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  • Mark (smokey mow) changed the title to Costin Walker F3/F4/FJ Imp Rebuild

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