The Anglo-Canadian Corner
Lotus Seven Research and Musings by William Fayers

Lotus Seven Parts and Repair
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Fuel Filler Hose:

I somehow misplaced the rubber fuel filler hose that connects between the metal fuel filler neck (with chrome gas cap attached) and the gas tank on my Series 3 Seven. The car has been completely dismantled for longer than I care to admit, and I wanted to complete an inventory to see what parts would be required. I purchased a new hose from Redline, but on receipt of the part, it was noted that it was longer, had a smaller inside diameter, and was molded at a 45 degree angle. I am not sure if heating would correct the angle to 90 degrees as per the original as it may cause the rubber to crush in the middle when bent to a full 90. The part number from Redline and Caterham is the same, although the hose illustrated in the "Caterham Cars Parts Catalogue for cars 1973 onwards" looks the same as my old one. I checked my various catalogues, and Burton U.K. and Mocal U.K. sell rubber fuel tank hoses of various internal diameters in imperial measurements. A 90 degree rubber elbow looks to be the correct shape, but I can more accurately advise if it is suitable when I receive it.

Toggle Switches

On my 1969 Lotus Seven Series 3, (factory authentication letter from 1973 none of the original toggle switches were supplied by Lucas. They were manufactured by a British company called 'Radiospares'. They are 12 m.m. or 1/2" diameter. I am not sure if this company was a forerunner to 'Radio Shack' but they sold very similar items for almost everything electrical (electronic). The Lucas switches are 14.5 m.m. or +/- 5/8" diameter. Holden advertise a line of Lucas look-alike switches that are described as 'a quality switch with a Lucas lever' of 12 m.m. or 1/2" diameter.

It would be a good idea to check the make and diameter of switch on your car fitted as original, and replace with similar. A smaller dia. switch in a larger hole can easily vibrate loose, and cause problems (shorts etc.) The only other alternative would be to use a round crush washer (aluminum?) of 12 m.m. i.d. and 14.5 m.m. o.d. to centre and securely hold the switch in place on the dash, or perhaps a ring of copper which will squash fairly flat once bolted up.

Stop/Tail Lights

The rear brake/tail lights for the Series 1, 2 and 3 Lotus Seven are becoming harder to find. The Wingard lights used on the Series 1 and 2 were a dual filament light manufactured for aftermarket use on vehicles such as boat, utility, and travel trailers. They appear at irregular intervals on e-bay, but often the price is very high even for lights that have scratched or off-color lenses, and are covered in paint. If you happen to lose the countersunk screw(s) that hold the red reflector on to the metal base, you may have difficulty finding a suitable replacement.

I have determined via a U.K. screw and bolt supplier that the thread is a 3 B.A. (British Association), and I still have a few left from a previous order if anyone requires spares.

Lotus Sevens post 1965, both Series 2 and 3, received rear brake/tail lights manufactured for aftermarket use by a company named Thorpe. I do not recall ever seeing these for sale on e-bay, although I have only checked for them periodically. It is a possibility that production of this type of rear light was taken over by the well known lamp and accessory manufacturer Britax, but a check of their web site did not mention these lights as far as I could determine. I have recently purchased a pair of these "Thorpe" lights (new, old stock) from a company in the U.S., and they were in Britax boxes. There was no part number on either box, or positive proof that the lights actually belonged in the Britax boxes. However, both the boxes and lights are as brand new, so it may be worth checking with Britax U.K. or Germany to see if in fact they still produce this model.

Repairs to Aluminium Panels

While sourcing aluminum to replace a damaged undertray and some other body parts on my Seven, I found these descriptions in the Lotus Seven Series 2 and 3 manual as follows:

"Undertray: Aluminium Sheet 20G. (hard) - 610B, L72 or equivalent. Not Weldable. Heat destroys condition." and, "Other alloy panels: Aluminium sheet 20G. (half hard) - B.A. 60. Softened by welding."

I went to my local friendly aluminum supplier and gave him a copy of these descriptions, and he gave me a blank stare. He had obviously never heard of them. In North America (including Canada), sheet, plate, bar, rod, tube and anything else aluminum are classified with four digits followed by a letter and number(s) e.g. 6061-T6, 3003-H14 etc. The actual specifications of the various types of aluminum are available in numerous books (see "Metal Fabricator's Handbook" by Ron Fournier or the excellent books by the late Carroll Smith e.g. "Engineer to Win"). In order to obtain the correct or near correct alloy, I went on- line for a search of available resources.

Alcoa, U.K. was extremely helpful, and advised the following:

610B and (3)L72 are old British Department of Transport/ British Aerospace series specifications that have been replaced with newer specifications. The equivalent of 610B and L72 in North American terms would be 2014 in the T3 temper. For the undertray, 2024-T3 would be ideal, although it is believed to be more expensive than 6061-T6, but worth the extra cost according to Carroll Smith. He preferred 2024 in structure over 6061.

B.A. 60 refers to alloy 3103 and the North American near equivalent would be 3003 - H14. (H14 is the condition and hardness - in this case half hard. It has good strength and is relatively easy to form with excellent welding characteristics according to Ron Fournier).

With regard to the 20G measurement, the Alcoa representative suspected it referred to the old British Standard Wire Gauge measurements, in this case 20G = 0.036". If you wish to use a slightly thicker sheet, the length of the 'pop' rivets may have to be increased accordingly. Just prior to Alcoa contacting me, I talked to Arch Motors regarding my order of some small parts. In conversation with the manager at Arch, I was advised that they use NS4 for the undertray which corresponds to 5251-H24 or H34. For the body, they use NS3 which corresponds to 3103 as per the information from Alcoa.

'Pop' Rivets. Arch use aluminum 'pop' rivets of 5/32" diameter, with a length of 10 m.m. (3/8") when gripping 3 layers (e.g. undertray, body side, 18 gauge chassis rail), and 8 m.m. (5/16") when gripping 2 layers. It should be noted that in the Lotus Seven manual, Lotus recommend Monel rivets. Checking my trusty welding/metallurgy book, Monel is described as a natural alloy, made by smelting a nickel-copper ore which is mined in the Sudbury basin, in Ontario, Canada. It is composed of 67% nickel, and 28% copper, with the remainder made up of manganese, iron, cobalt, and silicon. It is stronger and harder than either copper or nickel in their pure states, and possesses a strong resistance to corrosion, except in the presence of hydrochloric or sulphuric acids (hopefully there is no spillage from the battery on any parts of your car!). As the pop rivets on a Lotus Seven are joining aluminum and steel, Lotus no doubt chose Monel to help prevent galvanic corrosion. Carroll Smith makes the following recommendations: "If you find yourself in the position of needing to perform structural repairs, and hardware store rivets are all that is available, use the Monel rivets with steel mandrels. They are a lot harder to drill out than their aluminum cousins, but are about a third stronger in shear."

Carroll Smith also advises to use a new, slightly smaller diameter drill than the pop rivet to drill out old rivets, and use a sharp drill bit for the following replacement rivet sizes:

#30 (0.1285") for 1/8 in. (0.1250") diameter rivets, #20 (0.1610") for 5/32 in. (0.1562") , and #10 (0.1935") for 3/16 in. (0.1875") except for Avex rivets that require #29, #21 and #8 drill bits respectively. (See Chapter 9 of Carroll Smith's - "Nuts, Bolts, Fasteners and Plumbing Handbook" published by Motor Books International.) If you are able to manually pull them, closed-end, solid core rivets are the best way to go for a Seven, providing a good seal if installed with a little bit of Loctite, and higher shear value than a hollow core rivet.

Removing paint or corrosion from chassis tubes.

A suggestion from Peter Egan (Road and Track Magazine) and other sources that I have read, suggests that the safest blasting medium seems to be ground walnut shells when trying to remove paint or corrosion from steel frame tubes. Glass beads and silica can work-harden some surfaces making them brittle or hard to shape. Sandblasting aluminum can expand and deform the metal causing sine waves in the surface.

If there are open rivet holes, the chassis tubes may become full of blasting medium. If this happens and you also want to remove unwanted rivets from the 1" square main top and bottom tubes, the only answer may be to drill a 1/2" hole in the blanking plates on these tubes at the very front of the chassis. By elevating the chassis so that the rear of the car is much higher than the front (this is supposing that the engine and transmission etc. have been removed so that you can in fact hoist up the rear of the chassis), the medium and rivets should tumble down to the open holes. A strong suction workshop vacuum cleaner will then suck out any loose rivets and medium. I did this on my old chassis and it worked like a charm. As the top and bottom main rails are connected to the open 3/4" tubes on the rear of the chassis, any rivets from that area will also tumble down to the front with the help of a side to side tilt. The front tubes can then be plugged up by brazing or fusion welding a thin steel plate on the end. Obviously there is no reason to perform this operation if none, or very few of the rivets have been removed, and there is no place for the medium to work its way into.

Legal Warning:

As I am not a qualified engineer, I cannot safely advise which alloy(s) would be best for structure or bodywork on a Seven. I can only attempt to demystify the specifications in the Lotus Manual and provide information which may or may not apply in North America. Your local racing shop, aluminum supplier, Institute of Technology or air frame technician is way better qualified than I to suggest alternative materials. It is not my intention to suggest that you invest in a certain alloy listed above, pop rivet it on to your Lotus Seven, and then find out it is/was totally unsuitable for the purpose. Your own research can often provide you with better peace of mind, plus save you money and a lot of grief.

Space frame restoration.

If planning any repairs to your Lotus 7 chassis, it would pay dividends to determine who the constructor of the frame was, and how it was welded together. There were two factory approved constructors of the mild steel Series 2 and 3 chassis, Arch Motors, and Universal Radiator. Arch Motors preceded their chassis number with the letters A/M. Universal Radiator used the letter 'B' (possibly followed by an 'L' if the chassis was left hand drive) with four numerals for the chassis number. This letter/number combination was normally stamped on the angular steel bracket that held the front mounting of the master cylinder bracket. It should not be confused with the actual vehicle serial number (V.I.N.) such as SB XXXX or LSBXXXX.

The reason for mentioning these two manufacturers of the 7 Series 2/3 chassis, (there was also another company who built chassis for the 7 Series 1) is that both these companies used different welding techniques to construct the mild steel chassis. Arch Motors were one of the original race car constructors to use a technique called gas flux bronze welding. This method of welding uses an oxy/acetylene set-up whereby the liquid flux is contained in a separate metal bottle and mixes with the acetylene gas, emitting from the torch tip in a greenish flame. A bare nickel bronze or manganese bronze rod is applied to the joint, and there is little or no flux residue remaining. The weld has a similar appearance to a fusion welded joint as there is a full bead of filler applied in the same manner as a fusion weld. It is claimed that in some cases, the joint can be stronger than if it were fusion welded. This would depend of course on the quality of the rod, the skill of the welder, and the fit of the joint prior to welding.

Universal Radiator on the other hand, fusion welded their chassis using an oxy/acetylene set-up with the filler rod the same as, or similar to, the metal to be joined.

It should be mentioned that many of the wishbones fitted to the front suspensions of numerous Lotus road and racing cars of the 60s and early 70s, including the road-going Seven, had the joints on these wishbones bronze welded rather than fusion welded. When I revealed to Don Gadd of Arch Motors in 1975 that the government where I lived strictly prohibited (i.e. banned) the use of any suspension components on a vehicle that had been brazed or bronze welded, I believe soon after that, some of the wishbones made for Sevens abroad were fusion (mig) welded. My replacement wishbones shipped to North America certainly were.

Colin Chapman apparently approved of bronze welding on many of his later designs of Lotus space frame chassis, making production of this type of chassis quicker, cheaper and easier to fabricate and repair. Also, due to the lower temperature range required for bronze welding, there is less chance of distortion to the materials being joined.

Note: I use the term bronze welding and braze welding synonymously. Another term sometimes used is fillet brazing. In all three cases, a large fillet or bead of low melting point filler alloy is deposited on the metals to be joined, at a temperature well below the melting point of these metals. (Perhaps a somewhat poor analogy, but bronze welding is more like 'gluing' the parts together, as opposed to actually fusing them together).

When repairing a Seven chassis that has been bronze welded, mig, tig, or oxy/acetylene welding should not occur too close to a bronze welded joint. If too much heat is applied near a braze welded joint, intergranular penetration of the braze material into the surface of the steel can occur, which not only makes a brittle joint, but at the same time considerably weakens the affected steel component. It is best to repair the chassis using the same method as used in its original build if possible. The joints to be braze welded have to be clean of any paint, rust, oils or other contaminants. After making sure the area has been thoroughly cleansed of all the above, a good wiping with MEK (methyl ethyl ketone) will assist in keeping the area clean for bronze welding to take place.

With a chassis built by Universal Radiator that has been fusion welded, mig or tig welding is most appropriate. However, this does not rule out a weld using bronze welding techniques.

Bronze welding can be accomplished quite easily on top of a fusion welded joint as long as the same precautions of cleanliness are carried out as above. There should be no detritus in or around the area to be welded. If you have to fusion weld (mig or tig) close to a bronze weld be careful not to point the tig welding torch or mig welding gun directly at the bronze welded joint. The force of the shielding gas from either system can literally blow out the bronze filler material, plus can cause the above noted intergranular penetration.

I have noted some welding techniques illustrated in Dennis Ortenburger's book "Legend of the Lotus Seven". A section of the book under 'Chassis Restoration' illustrated a Seven owner's attempts at further strengthening his/her chassis with extra 'triangulating' members. It appears from the photographs that the body panels were not removed, so I would doubt that a complete weld bead was achieved around the tubes in question. This could allow moisture into the tubes. Further, the additional chassis tubes did not provide full triangulation in the technical sense, as some of the tubes formed a trapezoid which, my old math/ science teacher would tell me, is not as strong as a true triangle. All the extra metal, in some cases double the amount of tubing required for strength purposes, would make the car considerably heavier - especially so if some of the tubes were full of water as road/racing cars do get wet! Lastly, I have to wonder how the driver got in and out of the car, as it appears from a couple of the photographs that the driver and passengers' cockpit area had extra tubes welded inside.

Unfortunately, even the professionals - Lotus and Arch - have sometimes forgotten the rules regarding correct triangulation and the proper construction (read layout) of multi-tube joints. These errors were to save time and money presumably.

Many years ago, when I first became interested in the Lotus 7, I hung around with a crowd of enthusiasts that entered slaloms with their road cars at a local disused airfield. A husband and wife team owned a Series 3, which they both shared for occasional slalom competitions, and invited me over to their house to look the car over. I noticed straight away that the inside metal cockpit panels had been completely removed. These interior panels, which are an essential structural component of the chassis, are made of galvanized sheet metal covered with vinyl that has been bonded to it during manufacture, known as "Lamiplate" or "skin plate". By removing these interior chassis "stiffeners", the chassis sides become considerably weakened. (Standard Series 2 and 3 models never received triangulation until late in Series 3 production - i.e. the SS and subsequent models). The weight saved is hardly worth the breakage that may occur. There have been a few books written that include paragraphs regarding Seven frame failures. Also, there is an excellent link on (soon to be available again) which provides owners' comments with diagrams relating to certain common failures. This information should really be enough evidence for any owner contemplating permanent panel removal, that professional advice should probably be sought to avoid problems in the future. I have noted in a number of photographs of Sevens used solely for competition (racing, slalom, sprints etc.), that the inside panels have been removed, but proper triangulation has been installed to make up for the loss of these structural panels. As Lotus included both on the 7 SS and subsequent chassis, perhaps there is a message here that these panels and the extra triangulation are both essential to the integrity of the space frame. Lotus welded steel panels on the outside of the prototype SS7, and also on the Series IV chassis. The fact that the vinyl clad steel inner cockpit panels of the Series 2 and 3 are riveted, should not be considered as inferior to welded panels of the same thickness. Riveting makes removal and replacement of the panels easier for repair, and provides almost the same strength. It would be even better practice if these panels were riveted with solid core rivets rather than the hollow core type used by Lotus and Arch for reasons noted previously.

If you examine pictures of the Series 1 chassis, there was far better triangulation in the frame, with tubing where it was required to be to prevent frame failure. The Series 1 had a very creditable hill climb and racing history, and the slightly extra weight of the chassis, fitted with a side valve engine far less powerful than some of the engines fitted in the Series 2, did not seem to impair the success of this car. Some of these necessary tubes were not carried over for the Series 2 build (the early Series 3 space frames were actually Series 2 chassis with a few extra brackets welded on, so essentially experience the same problems). Although purists do not recommend adding any more tubing to the Series 2 and early Series 3 for authenticity reasons, unless some of the problem areas are addressed, the car will always be prone to breakage in one area or another. If extra tubing is added to a replacement chassis in the cockpit sides for example, no one except the owner is going to know it is there, as it is covered on both sides by metal (vinyl clad steel on one side, aluminum on the other). Of course, it is ultimately up to the owner to decide how authentic his or her car should be.

Universal Radiator used a loose sleeve (distance piece) in the two vertical 1" square tubes located just to the rear of the steering rack mounts on either side of the chassis, and immediately in front of the engine, for attachment of the rear mounting of the front lower wishbone. The use of non-welded distance pieces is very poor engineering practice, and was presumably done for cheapness. These tubes often suffer from the attachment holes becoming oval with consequent tearing of the thin gauge tube. If the 1/2" suspension bolts are not maintained in a very tight state at all times, the suspension geometry can alter as excessive movement of the wishbone causes further wear to the tubes. Repair is not that simple, as prior to welding a replacement sleeve in place, the suspension geometry should be correctly set to factory specifications. The Lotus Seven can only be adjusted for toe-in and toe-out, as camber and caster settings were preset by Colin Chapman during the initial design of the car. Shims may be of help, but there may be limited space to install them.