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Author: Subject: L7 Series 3 clone - optimum running gear?

posted on 17/12/14 at 01:41 AM Reply With Quote
L7 Series 3 clone - optimum running gear?

Hello folks.

I'm posting here as it covers chassis, running gear, transmission, etc. rather than focusing on a single area.

Some of you have been kind enough to help me with an engine query on one of our existing 7s.

Now we get to my new build.

I'd like to build a Lotus 7 S3/Short-Cockpit Caterham clone, a starter kit for which is sadly no longer available so I shall scratch-build. That is - by taking the information available to us, which I have devoured:

'The books': Locost, Haynes Roadster, Avon and Keith Tanner's version

'The plans': Those from the book, McSorley's and Prince and Cushing's Lotus 7 Chassis drawings, obviously some dimensions are known to be suspect in some Lotus drawings.

'The articles': Wesley Linton's Thesis on the chassis and Cymtriks' Analysis of the chassis - which show how to alter the basic locust design to reduce weight and improve stiffness.

The build manuals: 1988 Westfield SE and the 1988 Caterham manuals, both of which I have.

Plus, and perhaps most importantly, all the forums.

and then tailoring it to produce the car I'd like.

It should certainly have the same silhouette as the Lotus 7 S3/Short-Cockpit Caterham - some body panels will be bought - such as GRP 'Lotus/Caterham' nosecone.

However - to me the first and most important step is to choose the running gear. This will allow me to finish gathering my donor parts and start working on my modified plans for the steelwork. I should point out that I am very comfortable fabricating all the parts myself.

So I have a few choices to make in arms of which units I pick and any help in reaching a decision would be very welcome:


Engine: No issue here, I definitely want to go either X-Flow or I'll use a 1800 Zetec on carbs as a plentiful modern successor to the Lotus Twincam (thank you to those who answered my previous post based on which my Father has decided to switch from X-Flow to Zetec for the same reason). I'll decide on this later on in the build.

Gearbox: No question: Semi-close 3-rail, 4 speed/2000e

Rear axle: QUESTION: The Caterham build manual covers in detail why they switched from Mk 2 Escort to Morris Marina/Ital. They say supply and parts (were) more plentiful and tat the latter was lighter. They also say that the Morris unit has to be strengthened prior to fitment. But, given that both are thin on the ground, which is the superior unit? I look for strength and reliability. I realise the English is not as strong as some others but should be plenty for my application.

Front uprights: QUESTION I've just bought a set from a mk4 Cortina, but I also have a lot of Triumph spares. The Caterham build manual uses the Triumph Spitfire mk IV. Though I've heard of people 'upgrading' from Triumph to Ford. Again, which is the superior unit - does one give more adjustment or better geometry than the other? I'm happy to create wishbones to suit either.

Steering: QUESTION The front end of a Lotus/Caterham is narrower than a Locost and I intended to loose this width by shortening a mk2 Escort steering rack. Is this sensible?

If I can answer the above then I'll nip away for a couple of months while I finish gathering the parts and work up my modified chassis drawings.

Really appreciate your help, there is a significant amount of knowledge on this site and I'd lot to tie something back by uploading the chassis plans once finalised.

[Edited on 17/12/14 by gasket999]

[Edited on 17/12/14 by gasket999]

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posted on 17/12/14 at 02:02 AM Reply With Quote
To clarify - my short term aims are:

1) To decide on the donor parts, source and put these into storage. Trying to follow the Lotus spirit/recipe, but using superior units where appropriate.

2) Compile all the known Series 3 plans in order to remove any inconsistencies (checking against a real Series 3). Incorporate any obvious design improvements to improve the chassis.

3) Produce a one-off reproduction Lotus 7 Series 3 'starter kit'

That will be enough for the coming year. I'll probably assemble the vehicle once I've got my breath back.

Even though I've allowed a good budget for the project, I'll still aim to follow the Locost principals of cost savings and aftermarket parts will not be used unless necessary.

Thanks again.

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posted on 17/12/14 at 02:44 AM Reply With Quote
Just a follow-up in case anyone else is thinking about this. The "DSK Blueprints" are available online and detail period improvements to the chassis to handle increased power and grip. These should be read in conjunction with the Prince and Cushing plans, along with the background info on the DSK pages here

There is also a superb set of (possibly factory) drawings of unknown origin (Lotus? Caterham? A.N. Other kit car manufacturer?) that detail the allegedly Lotus plans - though I have not yet studied them in detail to see how they compare to the known Prince and Cushing plans - see here. I would be comfortable working with these drawings.

From background reading (now I know what to search for) it would appear that the triumph geometry is superior to the Cortina, though the lower Trunion on the OEM uprights is a weak point. Modern replacements have this replaced with a ball joint but are expensive, even more so if you include the cost of altering the hubs to match the rears - does this sound like a reasonable summary?

So standard Triumph vs Cortina = performance vs reliability?

Assuming I can produce a good Series 3 chassis I suppose I have a chose of including Locost/Westfield suspension mounts - plus the Ron Champion wishbones we all know (Cortina) or using a standard chassis and trying to recreate the Lotus wishbones. OR use a standard chassis and spend a lot of money at Caterham to buy their improved upright kit.

[Edited on 17/12/14 by gasket999]

[Edited on 17/12/14 by gasket999]

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posted on 17/12/14 at 10:22 AM Reply With Quote
I would have thought the spares availability and up grade options on the ford axle would be better.

If I remember right the BMC axle had a problem with weak half shafts even when used in a Morris 1000 as standard.

I seem to remember going out to several when I was an apprentice where the owners had parked on a hill, rolled back to pull out of a parking space and as the pulled away the shaft snapped at the splines in the diff. An absolute pig to get the broken bits out.

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posted on 17/12/14 at 12:41 PM Reply With Quote
Just been having a chat with my father about this - he's pointing out that I'm effectively trying to decide between building an early and later Pre-litigation Westfield. I don't want to buy an old one and restore it tho.

Early pre litigation - "an accurate replica of the early Lotus Seven, with all-alloy bodywork (except for GRP wings and nosecone), Triumph front uprights and Spridget or Ford engine/gearbox/axle. Total production 132"

Later pre-lit Westfield SE (like my Dad's) "was a cheaper update with more GRP (all-in-one GRP rear bodywork and wings, for example)and all-Ford running gear. Robinshaw and Bouckley reckon '605 Seven SE kits were sold from Spring '86 until production was brought to a premature halt in early 1988 as a result of the litigation with Caterham Cars.' "

I'm leaning towards the later mechanicals due to slightly better availability, strength and simplicity of build but still open to suggestions.

The triumph uprights are my ideal but these would require reverse-engineering of the caterham wishbones and roll bar, dealing with trunions (or spending to se the later ball-point Caterham version) plus machining a hub to take ford PCD (assuming I go escort back axle).

The nose of the car and the bodywork around the wishbones are where I think the really special Sevens stand out. I'd be aiming for a finish similar to this:

[Edited on 17/12/14 by gasket999]

[Edited on 17/12/14 by gasket999]

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posted on 17/12/14 at 12:50 PM Reply With Quote
Mechanically I'm leaning towards the same 1800 Zetec on carbs as we've been discussing for my Father's car, complete with the lovely BDA style rocker cover from Burton.

This should effectively give me a simplified version of the Lotus Seven Twin-Cam SS but with Westfield SE suspension geometry. In terms of aesthetics I'd be aiming for the early Series 3 Lotus 7 look compete with steel wheels and chrome hub caps.

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posted on 17/12/14 at 02:45 PM Reply With Quote
can i ask why you want the old 4 speed box?

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posted on 17/12/14 at 03:49 PM Reply With Quote
Let me start by saying, been there done that, though I used a Toyota 4AG and T50 gearbox. In regards to the various chassis drawings, unless you're trying to achieve a 100% accurate chassis, don't worry too much about the discrepancies in dimensions. Even the real chassis that I've measured aren't all the same.

In regards to the mechanical bits, use an English axle, don't bother wasting time with the Triumph based axle. The Triumph front uprights can be modified to accept the spherical bearing that the current Cateringvans use, but the trunnion style lower mounting does work to some degree (was even used in F1). The steering rack will need to be modified regardless of what rack you choose. The original Lotus Seven rack was a Morris Minor/early Spridget rack, then switched to the more common Triumph Herald/Spitfire based rack, and finally Caterham switched to the Mini based rack. The bonus of the Triumph or Mini rack is the tie rod ends match the Triumph uprights (note: the mini rack requires the Spitfire TRE, the rack uses the same 1/2" UNF thread).

Good luck with your build,


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posted on 24/12/16 at 03:33 PM Reply With Quote
Found this thread on a search. It's something i'm considering / debating in my mind.

Does anybody know if caterham drawings are available anywhere as the links above appear to be dead.


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posted on 24/12/16 at 05:11 PM Reply With Quote
First of all welcome and great you have a good idea of where you are heading and therefore have a good head start on most.

Assuming you are looking to road register this through IVA then....

Couple of points - 1800 zetec on carbs - engine will need to be pre-1995 engine otherwise you will need injection and a cat to pass the IVA emissions test, this goes for any engine and you will need to get a manufacturers proof of age letter. Worth reading the IVA manual before you do anything to make sure you build it to comply, at a guess a true s3 replica would fail on a number of points.

As for the zetec being the natural successor to the twink I would possibly disagree, I think the zetec se (sigma, Yamaha designed) engine is more like it -all alloy (zetec has an iron block), likes to rev, arp rod bolts and hd springs will give you 8k (zetec revs ok but not like the se), and in stock with a good exhaust and injection will give you a 1600 engine with around 140hp. (1.6 also has standard spigot bearing cavity). But the exhaust is on the drivers side like the pinto, not the zetec/xflow which is on the passenger.

This zetec se engine is stock in the caterham (zetec wasn't from the factory) currently so many parts available, search shawspeed, oc motorsport and lightening motorsport (lms) to see what can be done.

I originally fitted a type 9 with alloy bell housing (non standard whereas the zetec is ford standard bolt pattern) that should fit in a locost chassis but have moved on to an rx8 6 speed so have the bellhousing and type 9 spare.

I have a stock 1.7 puma zetec se in my Anglia as I think this is pretty close to a tricked up twink (1700 with injection and exhaust should be around 155hp at 6250rpm). But compared to the twink if I blow an engine it is 100 (don't ask me how I know!) from the scrappers to replace not an arm and a leg to refurb.

But as said 4age is a good shout, well supported (raw who make the striker 7 type car supply/fit them) as this was a copy of the bda engine iirc.

So, depending on the depth of your pockets I would go for a 1.6 zetec se on dcoe throttle bodies (could even use the new Jenveys ones that look like carbs) and an emerald ecu with a long first type 9 running an English rear axle and atb diff, discs front, drums rear. That would make a very handy and light road car.

Just a few thoughts, all the best.

1968 Ford Anglia 105e, 1.7 Zetec SE, Mk2 Escort Workd Cup front end, 5 link rear
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