Out of interest, I have recently been checking the internet for Lotus Sevens that are listed for sale, or were listed and are now sold. I have recorded the Lotus Factory assigned chassis numbers along with descriptions of each vehicle.
For some clarity, Wikipedia provides the following information: “A vehicle frame also historically known as its chassis, is the main load bearing supporting structure of a motor vehicle on which the body is mounted, and to which all components are attached” (Definition of ‘chassis’ and ‘vehicle frame’ combined by me).
In the case of the Seven, Lotus sourced the mild steel space frame from one contractor, and the riveted aluminium and steel body cladding from another. Lotus – according to Graham Arnold *(1) – called the combined structures “units”.
Note: Where a number appears between brackets with an asterisk – *( ), credit to the relevant book and author is noted at the end of this article.
Similarly, Arch Motor and Manufacturing Ltd (Arch), when they provided complete frames and bodies post 1973 to Caterham for their 7, called the assemblies ‘Chassis Body Units’ or ‘CBUs’.
John Watson on his Lotus Seven Registry refers to the scribed or punched Lotus chassis plate number only. The frame number is kept secret by J.W. and many owners in an effort to stop cloning of cars and for security reasons (e.g. identification of a stolen car).
The contractors’ frame number and the Lotus designated chassis number do not coincide with each other in the majority of cases. I have only seen one instance when the frame number and the chassis number were the same.
The following is from the Lotus Seven Owners Manual, 3rd. Edition:
(Note: published post 1965).
SECTION A
1—General.
Date of commencement of manufacture Series I cars – February, 1958.
Date of commencement of manufacture Series II cars – July, 1960.
Series II cars (including America and Super models) carry prefix SB on chassis number plate commencing SB 1000. Left-hand drive vehicles have their own ranges of chassis numbers; SB 1500-1550, SB 1750-1799, cars produced after October, 1963 also have prefix “L” e.g. LSB 1999. After all the numbers in the two ranges have been allocated, both LHD and RHD cars will use the same range of numbers the only indication of a LHD car being the prefix “L”.
Lotus Contractors.
Contractors who manufactured the mild steel frame, and formed and attached the bodywork on the Lotus Seven are as follows:
| Frame Contractor | Bodywork Contractor | |
| Series 1 | Progress Chassis | Williams and Pritchard |
| Series 2 | Progress Chassis | Williams and Pritchard |
| Series 2 | Universal Radiators | Alert Motor Works |
| Series 3 | Universal Radiators | Alert Motor Works |
| Series 2-1/2 | Arch Motor | J.W. Eve and Alert + ? |
| Series 3 | Arch Motor | J.W. Eve and Alert + ? |
| Series 4 | Arch Motor | Lotus in-house (fibreglass) |
| Series 4 | Griston Engineering | Lotus in-house (fibreglass) |
If anyone has evidence of other frame and body contractors that Lotus used to build the Seven, please advise, and I will add the name(s) to the above list.
My own 1969 registered Lotus Seven Series 3, fully assembled by Lotus in Norwich, England in October 1968 (I’m the third owner), had a Universal Radiator fusion welded frame. It was fitted with the two lower wing stay brackets welded onto the frame in the engine bay, a carry-over from the early Series 2 cars that used the cycle wings. My car had the clamshells. The bonnet was fitted with a carburretor half-scoop on the left-hand-side, as used for clearance of the Weber carb bell-mouths on the pre-crossflow engines (and possibly SUs on other engines?). It also had the fibrerglass scoop on the top of the bonnet providing clearance for the downdraught Weber 32 DFM of the 1600 cc Crossflow 225E/2737E engine the car came equipped with.
It would seem natural that Lotus would use up all of the body components and frames on the Series 3 that had been produced over the years for the Series 2. The Universal Radiators top clamshell/cycle wing brackets had extra reinforcing plates welded onto them which Arch did not carry over onto their frames. Likewise, Arch did not install the lower wing stay brackets, as cycle wings had not been an option for quite some time.
A number of years ago, I was fortunate to receive the records from a Lotus Seven Registry that had been started by two Lotus Seven owners in the U.S. A newsletter had also been produced, but the two publishers had more pressing business, so decided to fold the register and kindly passed all of the information they had gathered to me.
I found six Lotus Sevens in their records that were either on sale, or had been sold on the ‘Bring A Trailer’ (BAT) web site, and noticed that some of the cars in the records had a different letter identifying the frame build number. In a few cases the frame identification for Universal Radiators frames started with a ‘U’, not a ‘B’, as I had originally noted on this site.
Arch used the letters ‘AM’ with three numbers following. The highest Arch replacement frame number I found was in the early two-hundreds (AM2XX- in 1992).
As John Watson and I have kept in touch over the years, I wrote to him recently inquiring about frame numbers and Lotus chassis numbers, providing him with the list of cars that I had found on the internet.
In the early 1990s John had been permitted to copy all of the remains of the Lotus Seven factory ‘build card’ records at his cost at the factory.
John’s information shows how the cars came equipped (as built) from the factory including colour, fittings, engine specifications etc. The list of Canadian and U.S. owned Lotus Sevens that I have is not necessarily how they originally came from the factory, but how they had been modified, repainted, or repaired up until 1992.
John advised me some time ago that he doesn’t have all of the records, and would still like to gather as much information on any ‘missing’ cars as possible. I would highly recommend John’s Lotus Seven Register web site to any potential Seven purchaser, or even current owner, as it provides a lot of very interesting facts regarding the cars from Series 1 to 4. All information provided to John is kept strictly confidential.
Following is John Watson’s take on the Lotus Seven chassis numbers:
- SERIES ONE (Hornsey) – Mk.7/400 to Mk.7/499 – circa September 1957 to circa June 1959
- SERIES ONE (Cheshunt) – Mk.7/750 to Mk.7/892 – circa July 1959 to circa June 1960
- SERIES TWO (Cheshunt then Hethel) 7/B or ‘SB’ to distinguish the Seven from the Type 14 Elite which used ‘EB’ (so Seven Body/Elite Body).
- 1000 to 2310 – circa July 1960 to August 1968
- SERIES THREE (Hethel) SB2311 to SB2649a, b, and c with 13 Twin-Cam cars using the ‘SC’ prefix instead – circa August 1968 to December 1969
My note: In a couple of the books on the Lotus Seven – *(2) and *(3), the Twin-Cam cars are noted to have the chassis numbers SC2564 to SC2576. John Watson advised me some time ago that one of the cars with the ‘SC’ chassis number was a LHD car, and did not come fitted with a Twin-Cam engine from the factory, having a Crossflow fitted instead. Also later, another RHD car that had been factory fitted with a Twin-Cam reverted back to a Crossflow engine.
SERIES IV (Hethel) S4/2650 to S4/3315 (the highest number that John has on record) At this point it should be noted that after mid-1971 (S4/2953), Lotus Components was wound up and Lotus Cars took over and the records stopped! So circa January 1970 to circa mid 1973 when Caterham Cars took over.
Further information from John Watson:
“With regards to FRAME # (stampings):-
- Progress Co. Used just numbers. They made frames for all SERIES ONE and early SERIES TWO.
- Universal Radiator used both ‘U’ and ‘B’ prefixes. They made frames for most SERIES TWO and some SERIES THREE.
- Arch Motor(s) used ‘AM’ prefixes. They made frames for some SERIES THREE and most SERIES IV.
- Griston Engineering used ‘GE’ prefixes. They made a few SERIES IV chassis frames.
Two points:
- ‘U’ prefixes were on home market cars as well as North American.
- One of the ways of telling the difference between a Universal and an Arch Motor frame is that AM always missed the lower cycle wing bracket!
The books on Lotus Sevens that I regard as the most reliable are:-
- The two (yellow and red) by Jeremy Coulter – this was the recommendation of the late Graham Nearn to me.
- The book by Tony Weale.
- The Series 2/3 Lotus Seven Owners Manual.”
My note. In one book, *(2) and *(3), the author notes that the prototype Series 2 car was given the number 999, was the first LHD Seven, and was fitted with an ‘A’ series Sprite engine. Seven Series 2 chassis SB1000 was given the Lotus factory assigned registration ‘7 TPE’, and was later modified with a ‘boat tail’ rear body, and exported to the U.S., where it then made its way to New Zealand possibly sans the ‘boat tail’? *(5).
Lotus Seven Build Numbers.
The 1992 North American registry that I was given consists of the following numbers of Lotus Sevens and includes registrations from my local Motor Vehicle Branch:
- Series 1. – 10 of
- Series 2. – 81 of
- Series 3. – 16 of
- Series 4. – 7 of
- Early Caterham 7 – 16 of
It is definitely not my intention to query or criticize the writers of the various books dedicated to the Lotus Seven where their statistics vary. The information they were provided with to write their books came from credible sources, and was as accurate as memory and perhaps documentation could provide at the time. Graham Arnold advised that Lotus (Colin Chapman) was not one to be tied down with numbers. In some ways it was to confuse the tax man regarding just how many cars they were constructing and selling.
The total number of Series 1 cars built is estimated at 242 plus or minus.
Graham Arnold, Sales Director at Lotus from 1963 to 1971 and then again from 1977 to 1981, calculated in his book *(1) that approximately:
– 1370 Series 2 cars, and
– 350 Series 3 cars were built and sold.
= 1720 Total.
Other estimates consider: 1648 total for S2 and S3 as a good estimate (Lotus Seven Register U.K.); 1576 total *(2) and *(3); 1350 Series 2 cars *(4) with no mention of Series 3 numbers; 1362 Series 2 *(5); and 240 to 250 Series 1, 1350-1370 Series 2, and 260 to 350 Series 3 – including at least 13 SS twin-cam cars *(6).
Totals for Series 4 are 1000 *(1); 588 to 887 (includes 37 Caterham built cars) *(6); 587 *(2) and *(3).
Dennis Ortenburger in his book *(7) attempted to solve the gaps between production numbers and also the possible disagreements between numbers assigned to LHD and RHD cars, but gave up describing it as a ‘mystery’. Likewise, Graham Arnold *(1a) noted that “Lotus’ numbering system and subsequent claims have a greater place in ‘Alice in Wonderland’ than any other publication”!
It could be assumed that as a number of Lotus Sevens were used solely for racing, spills could occur resulting in a severely damaged frame and body requiring a replacement. Also, road traffic collisions could result in an insurance write-off. Once all of the Universal frames and bodies (plus bonnets) had been exhausted by Lotus, then Arch manufactured frames would presumably be used unless an original frame was repairable.
Bruce Robinson of Arch advised me some time ago that he has the original invoice for the first Series 2 frame that was built by Arch. This was in January 1968. Arch then went on to build the car called the Series 2-1/2, which had the Ford 225E/2737E 1600 Crossflow engine, but was still fitted with the Standard Triumph rear axle as on other Series 2 cars. This was until approximately August 1968 when Lotus introduced the Series 3. The bodies for Arch built frames were produced by Alert, E.W. Eve, and one other company that Bruce could not recall. All of the Arch Lotus Seven frames were gas flux bronze/braze welded together, as opposed to the fusion welding method used by Universal Radiators.
When Caterham started manufacturing their own version of the 7 post 1973, Arch began manufacturing both the frames and bodies for the cars. In the early to late 1960s, Arch was not in a position to manufacture frames for the Seven due to their commitment(s) to build racing frames for Lotus and others. They did however manufacture suspension parts and various brackets for the Lotus Seven.
Universal Radiators Limited.
This company has received mention in name only in the various Lotus Seven books as the main contractors for building the Seven Series 2 and 3 frames. At least four of the books detailing the Lotus Seven Series 2 and 3 have noted that Universal Radiator was based in Northampton, U.K.
I checked with the Northampton Archives, and was advised that there is no evidence the company ever existed in this location. British business listings similarly have no record of this company in Northampton.
A major supplier to Lotus located in Northampton was Cosworth Engineering. Cosworth under the ownership of Mike Costin and Keith Duckworth (who both worked for Lotus at one time), supplied engines and parts to Lotus for the Seven Series 2, plus other Lotus sports racing cars. Cosworth later went on to supply engines to other racing formulas especially Formula 1 for Lotus and other F1 companies. Possibly due to the Northampton connection, sources who provided information to the various book authors mistakenly placed Universal Radiators in the same location?
I then contacted a U.K. forum, and a number of very helpful members provided information on Universal Radiators. Universal Radiators was owned by Maurice Emil Deen, who also owned 275 Blue Star Garages located throughout the U.K., Silvertown Plating, battery factories, and was a franchisee for Coronet Engineering. (Coronet produced a three-wheeler sporty looking road car which could be registered as a motorcycle in the U.K.).
Another forum member sent me the following from the Biggleswade Chronicle dated 12th. and 19th. February 1960:
“Required Immediately
Sheet Metal Workers
accustomed to flat aluminium body work on Sports Car body
assembly; also Motor Radiator Repairs. Top Rates of Pay: Apply for Interview.
UNIVERSAL RADIATORS LIMTED
147 London Road, Biggleswade
Telephone: Biggleswade 3355
Open Saturday Mornings”
A small cutting from the Ampthill News of 28 August 1956 noted:
“Approval was given by Biggleswade Urban council last week to proposals for a petrol filling station and radiator factory for Universal Radiators Ltd., at the former Chocolat Menier factory in London Road, Biggleswade”
Biggleswade is located in Bedfordshire, England, and is approximately 42 miles south and east of Northampton or 1 hour by road.
Another item regarding the ‘Ogle 1.5’ car in Autocar 23 June 1961 noted that: “John Tojeiro built the first of the chassis frames, welded by Universal Radiators of Biggleswade.”
‘John Tojeiro was an engineer and racing car designer whose innovations helped to revolutionise car design in the 1950s and 1960s.’ (Wikipedia quote).
An article in ‘The Sport’ – Autocar 29 October 1965, notes the following:
“JOHN BERRY, Home Sales Manager of Lotus, has won the Lotus Seven Trophy. Second, and winner of the Universal Radiators Cup, was last year’s winner, Michael Crabtree. Berry is also runner-up in the Guards Trophy, which has its final round at Brands Hatch on Boxing Day.”
Universal Radiators had a few different addresses as follows:
Universal Radiators Ltd., Back Lane Hampstead N.W.3 (The Light Car edition of 8/1948)
It also mentions the company ‘has opened a further branch at Dartford [Kent] in order to cope with the volume of work in hand.’
One forum member posted the following:
“The 1959 edition of ‘Who’s who in the Motor Industry’ (which later morphed into the Guild of Motoring Writers Yearbook) has a listing for Universal Radiators Ltd. – ‘Manufacturers of radiators, cooling elements, fuel tanks, and tubular manipulations.’ Their Head Office is given as 40 High Street, Hampstead, London N.W.3 (not that far from Hornsey). Chairman and Managing Director: M.E. Deen, Director and General Manager: E.J. Boother M.I.M.I.”
By 1968 they had an address of Argyll Works, 71 Priory Road, Hornsey, London N.8, which a forum member advised was almost next door to Lotus.
Mr. Maurice Deen died in January of 1971, and the last posting that I found on the internet came from his son, John Deen, who in 2017 responded to a forum post regarding Blue Star Garages as follows:
“Blue Star Garages started by my father Maurice Deen in early 1930s. We had 275 garages nationwide, plus battery factories, Coronet Cars at one moment and many other companies. My dad dies in 1971 and to satisfy his ‘young’ wife, the company was sold half to Texaco, and the rest otherwise all against my wishes. I bought 3 sites for redevelopment. Today even a reduced chain would be worth over L400 million [U.K. Pounds Sterling] but that’s life! John DEEN” (from ‘rumcars.org forum with their permission.)
John Deen passed away in July 2020.
I tried to calculate how many frames Universal Radiators had constructed for the Seven, and came up with what I considered to be a suitable number. I wrote to John Watson inquiring if he knew the total, and John came up with the figure of approximately 1200, produced over a ten year period at probably 2.5 frames per week. Unfortunately, I had failed to consider the number of Series 2 frames constructed initially by Progress Chassis, and also the final amount of frames built by Arch Motor. John was very diplomatic, and did not point out the glaring error with my calculation. Thank you John..
When I first commenced rebuilding my damaged Seven (unavoidable road construction collision with a raised manhole cover!), I purchased as many books as I could that featured the car. Prices back then were very reasonable, and a couple of books were secondhand, and in good condition. Now (2025), prices for some of the books are at a ridiculously high level. It is hoped that they can be republished, but this may never happen. If you can source any of the books below, they will make good reading.
Recommended Books featuring the Lotus Seven.
*(1) ’Illustrated Lotus Buyer’s Guide’ by Graham Arnold
ISBN 0-87938-217-1 Published by Motorbooks International.
Although the Seven is one of many 1960s to 1980s Lotus cars featured in this soft cover booklet, Mr. Arnold provides a deep dive into Lotus (and his personal dealings with Colin Chapman) in his role as Lotus Sales Director.
*(1.a) ’Lotus Seven Super Profile’ by Graham Arnold
ISBN 0 85429 385 X Published by Haynes.
This book covers all of the Sevens, Series 1 to 4. Unfortunately, Mr. Arnold contradicts himself providing different build numbers for all of the Seven Series in two separate chapters. Some good colour photos of Sevens, and advice on purchasing a Seven.
*(2) ’Lotus Seven A Collector’s Guide’ by Jeremy Coulter
ISBN 0-947981-71-3
*(3) ’The Lotus and Caterham Sevens Collector’s Guide’ by Jeremy Coulter
ISBN 0 947981 06 3. Motor Racing Publications Ltd.
Both books cover the Lotus Seven in great detail, and the latter adds the Caterham story. Both highly recommended.
*(4) ’Caterham Sevens’ by Chris Rees
ISBN 0947981977 Mine published 1996 by Motor Racing Publications.
Provides the history of the Lotus Seven, then concentrates mostly on the Caterham version of the 7.
Informative book, especially regarding Caterhams’ involvement with Lotus.
*(5) ’Lotus and Caterham Seven’ Racers for the Road’ by John Tipler
ISBN 1 85223 858 5. Crowood Press Ltd.
Another very detailed book by an author who has done his homework. John (Johnny) Tipler has been very helpful to me in the past, and is currently assisting my research into a U.K. Lotus contractor. Again, the Caterham 7 features heavily in the book, but the Lotus version is given full coverage. Contractors for the Caterham 7 are covered in detail.
*(6) ’Lotus Seven Restoration-Preparation-Maintenance’ by Tony Weale.
ISBN 1-85532-153-X Osprey Publishing Ltd.
In my opinion, the ‘bible’ regarding the Lotus and Caterham Seven. Good line drawings plus history, advice, specifications, part numbers etc., etc.
Tony Weale knows the Lotus and Caterham 7 inside and out. This book is commanding ridiculous prices on the ‘e-market’ and book sellers’ sites, but it may be worth it, as it can almost be compared to a workshop manual.
*(7). ‘Legend of the Lotus Seven by Dennis Ortenburger’
ISBN 0-85045-411-5 Osprey Publishing
or
ISBN 0-930880-06-04 Newport Press.
One of the first books I discovered on the Lotus Seven. I almost wore the first one out referring to it so many times. A few slightly more unusual Sevens are featured in the book along with various Seven copies. Lots of photos and line drawings. Not a build manual as such, but a guide to how the car is constructed, and advice on how to improve deficiencies in the original construction of the frame. A good read.
One other recommended publication for the Lotus Seven Series of cars (only for the Series 2, 3 and 4) is the Lotus Seven Owners Manual produced by Caterham Cars many years ago. It has the full Series 2 manual, and adds the Series 3 supplement, followed by the full parts and build details for the Series 4/IV. There is no ISBN assigned. The details are as originally supplied by Lotus in the form of workshop manuals and parts catalogues. Again available from e-market sites and possibly second-hand book sellers.
Note: A recent reply to my email sent to Caterham (Oct/2025), advised that as far as the company knew, all of the original Lotus Seven and early Caterham 7 cars’ information (under the original ownership of Messrs Nearn and Wakefield), had been passed on to the Historic Lotus Register or possibly the Lotus Seven Register.
Lotus Seven Frame Building and Repair Companies
Mike Brotherwood, Calne, Wiltshire U.K.
Lotus 6 and Seven S1 frames, plus Coventry Climax parts and some parts for Seven S2 and 3.
F. and L. Fairman Bodmin, Cornwall U.K.
Lotus 6 and Seven S1 frames and bodies.
Arch Motor and Manufacturing Co., Ltd,
Redwongs Way, Huntingdon, U.K.
Lotus Seven Series 2 and 3 frames, bodies, and suspension, and Series 4 frames. Plus Caterham 7 frame, body and suspension variations when Caterham was still owned by Messrs. Nearn and Wakefield.
Club Lotus New Zealand, Auckland N.Z.,
Held the jigs and molds for the Series 4 after purchasing them from Steel Brothers N.Z. An email will determine if they are still able to produce frame and body parts for this car.
Companies Who Once Repaired or Constructed Lotus Seven Frames
‘Curtis Unlimited’ – Bert and Fay Curtis, Kneeland, California, U.S.A.
Curtis Unlimited would repair or reproduce Seven frames (among others), either fusion welded or bronze welded according to the preference of the customer.
DSK Cars Inc., David S. Kaplan, Marblehead, Massachusetts, U.S.A.
DSK repaired Seven frames, and also produced their own frame and body for their ‘Turbo 7’.
Prince Race Car Engineering, Pat Prince, Sterling, Illinois, U.S.A.
Repaired Sevens, and also produced frames, bodywork, and complete Lotus Seven copies.
Xtra Special Sevens, Mick Beveridge, Exeter, Devon, U.K.
Repair of Lotus Seven frames. Constructor of Lotus Seven Series 2 and 3 copies, plus numerous frame brackets and spare parts.
Please advise if you know of other sources of frame and body repair for the Lotus Seven Series 1 to 4.
Postscript
John Watson’s ‘Lotus Seven Register’ has a couple of photographs that show the possible locations where the frame identification is stamped by the frame contractor. They are shown by clicking on the ‘register page’ and scrolling down.
John does advise that the frame identifier letter/number can be found in various locations depending on when the frame was constructed. Lotus fitters seem to have riveted the Lotus aluminium chassis plate in different orientations to fit beside the heater for example, but in all of the photos I have seen it is shown on the flat horizontal aluminium panel in front of the scuttle. Which side of the flat panel would depend on whether the car was l.h.d or r.h.d.
It appears that the 1” x 1” angled mild steel bracket (the front mounting of the Ford cast aluminium bracket that holds the brake and clutch master cylinders and pedals), was the location used by Universal Radiators to stamp their frames, but John also shows another location on older Seven frames that were produced by Progress Chassis.
Lastly, to throw another bit of confusion into the mix, John advised me that the last three Lotus Seven Series 3s to be produced were given chassis plates SB2649a, b, and c. I queried this with him, but it seems that as Lotus was at the end of Series 3 production, someone at the factory stipulated that the Series 4 (or IV) should start with the Lotus chassis number of 2650. So, with three Series 3s awaiting completion, they were given the chassis serial numbers of SB2649a, SB2649b, and SB2649c. Not sure how this was viewed by the U.K. vehicle licensing office, but it was accepted, and all three were registered for the road. John has the factory build records for all three.
My appreciation to:
The Autosport Forums members who provided information.
The Lotus Seven Register and Registrar.
Rumcars Forum.
