Recreating the XJ13 – Old Technology meets New

Where did Jaguar source components in period? 

Although Jaguar were able to raid their “parts bin” for some components of their XJ13 Le Mans Prototype, most of the car’s major items were custom-made. “Off-the-Shelf” components used in period included things such as Lightweight E-Type (LWE) front suspension & steering rack (albeit modified), instruments, lighting and front wheels (as also used on the rears of LWE racers). However, major components used for the car’s rear wheels, drivetrain, power-unit, braking systems and rear suspension had to be custom made in period.

The engine and associated castings such as bellhousing and rear hub carriers were, of course, designed in-house by Jaguar. The prime architect of the mighty quad-cam engine was Claude Baily under the direction of William Heynes. These major components were drawn up within Jaguar’s Drawing Office, signed off by Baily and casting carried out by The West Yorkshire Foundry. Final finishing of items such as engine blocks and heads was entrusted to Coventry Climax before being returned to Jaguar for final assembly.

The “old skills”

In the mid-1960s design was pretty much a “pen-and-paper” exercise drawing on the designer’s skills, knowledge and hard-won experience. These drawings were translated into real-world components using intermediaries such as wooden patterns (for casting) and wooden bucks/formers for things such as body shapes and some suspension components. “Fettling” and finishing of the final items relied on the manual skills and experience of Jaguar’s engineers.

As well as creating the engineering drawings themselves, the skill needed to produce things such as wooden patterns should not be underestimated. For example, wooden casting patterns need to be made slightly larger than the finished item to take account of shrinkage of molten metals – different metals need different degrees of compensation. Wooden patterns also need to include “draft” and “fillets” such that they can be satisfactorily removed from the casting sand.

The following drawings show these first steps in producing a finished component – in this case, the front upright (hub-carrier) as used in our re-creations.

Jaguar XJ13, Building The Legend, Jaguar, 3D Engineers, 3D Engineering, Neville Swales
Example engineering drawing for Lightweight E-Type front upright (hub-carrier)
Critical dimensions have been deliberately blurred for the web.
© Building The Legend Limited
Jaguar XJ13, Building The Legend, Jaguar, 3D Engineers, 3D Engineering, Neville Swales
Notes for pattern-maker and machinist included on engineering drawing
© Building The Legend Limited

Wooden patterns made from the above drawings could be similar to those pictured below:

Jaguar XJ13, Building The Legend, Jaguar, 3D Engineers, 3D Engineering, Neville Swales
Wooden patterns produced from engineering drawings above.
© Building The Legend Limited

These wooden patterns could then be used to sand-cast final components in the traditional manner. In the case of items such as these uprights, and in the days before metallurgy was advanced enough to be able to produce castings with similar properties to forgings, the engineering drawings could be translated into dyes for use in the forging process.

The skills of those who could design, draw and create such components in the days before Computer Assisted Design (CAD) and techniques such as 3D-Printing were quite remarkable. Don’t forget they didn’t just produce the components but also produced components which were fit for purpose and able to take the designed stresses placed on them. The skills extended from the designers, through those casting/forging the components, to the final machinists.

In particular, the skills of people such as the late Malcolm Sayer when translating his complex body shapes into wooden bucks were quite outstanding. Sayer worked with a precursor of today’s computerised 3D techniques – in his case, the complex maths was arrived at manually using log-tables with typical accuracies of four-figures and more. Nowadays, we have the luxury of computers which greatly assist the process.

In with the new

Today, we are able to design and, in some cases, produce a finished component entirely within a computerised environment. In addition, it is possible to investigate the performance of a component in a completely virtual environment – seeing how the component will respond to various stresses, how it will perform in concert with other virtual components as well as basics such as finished component weight, centre of gravity etc. All this can be done before the component is actually manufactured in real life.

SolidWorks is the CAD programme favoured by Building The Legend Limited. It lends itself to reproducing complex components such as cylinder heads and is preferred to 3D-Scanning for such items. For example, the following pictures show our digital recreations of a 6-cylinder “XK” head as well as a SOHC V12 head. These models were produced as a precursor to a separate project where we are producing quad-cam V12 engines of our own.

Jaguar XJ13, Building The Legend, Jaguar, 3D Engineers, 3D Engineering, Neville Swales
Digital representation of 6-cylinder XK engine
© Building The Legend Limited
Jaguar XJ13, Building The Legend, Jaguar, 3D Engineers, 3D Engineering, Neville Swales
Digital representation of V12 SOHC “A-Bank” Head
© Building The Legend Limited

Going back to the example of Jaguar’s LWE upright (used in the original XJ13 and not now available “off-the-shelf”), CAD and 3D-Printing was used to create the various moulds used to cast the finished component. Those of you familiar with this component will see it has been modified slightly to enable the use of modern “sealed-for-life” lower ball-joints.

The material used was EN-GJS-500-7 – a spheroidal graphite cast iron which approaches the strength of equivalent forgings. The following pictures show the finished items.

Jaguar XJ13, Building The Legend, Jaguar, 3D Engineers, 3D Engineering, Neville Swales
Front Uprights
© Building The Legend Limited
Jaguar XJ13, Building The Legend, Jaguar, 3D Engineers, 3D Engineering, Neville Swales
Finished machined Front Uprights
© Building The Legend Limited

We were able to use this marriage of old and new techniques to produce items for the project such as bellhousings (both for the prototype DOHC engine as well as later SOHC engines). In the case of the later SOHC bellhousings, “traditional” casting was carried out at a traditional foundry in Nuneaton, close to Coventry. The first stage was for us to design the bellhousings using CAD. The aim was to end up with something cosmetically similar to the original XJ13 item but suitable for use with the later SOHC V12 blocks (5.3, 6.0-litre and larger).  The SOHC bellhousing is sized to accommodate either single- or multi-plate clutches (XJ13 used a twin-plate racing clutch as is the case with our prototype-engined car).

We also took the opportunity to “beef-up” the design to cope with the way the drivetrain is stressed in its unique XJ13 application. Derek White of Jaguar designed the engine as a stressed member in the XJ13. Colin Chapman didn’t come up with this concept until his Lotus 49 of 1967 which means Jaguar would have been first to use this configuration if they had raced in 1965 or 1966.

Here are some pictures of the finished CAD SOHC bellhousing model:

Jaguar XJ13, Building The Legend, Jaguar, 3D Engineers, 3D Engineering, Neville Swales
SOHC Bellhousing
© Building The Legend Limited
Jaguar XJ13, Building The Legend, Jaguar, 3D Engineers, 3D Engineering, Neville Swales
SOHC Bellhousing
© Building The Legend Limited
Jaguar XJ13, Building The Legend, Jaguar, 3D Engineers, 3D Engineering, Neville Swales
Building The Legend’s SOHC Bellhousing attached to modified Quaife ZF Transaxle
© Building The Legend Limited

These CAD models were then used to produce the various molds needed for traditional sand-casting.

Jaguar XJ13, Building The Legend, Jaguar, 3D Engineers, 3D Engineering, Neville Swales
SOHC Bellhousing Mold
© Building The Legend Limited
Jaguar XJ13, Building The Legend, Jaguar, 3D Engineers, 3D Engineering, Neville Swales
SOHC Bellhousing Mold
© Building The Legend Limited
Jaguar XJ13, Building The Legend, Jaguar, 3D Engineers, 3D Engineering, Neville Swales
SOHC Bellhousing Mold
© Building The Legend Limited

The actual molds were produced using a combination of 3D-Printing and CNC-Machining. The following video shows them being used to cast the finished items in the traditional way. I was joined on the day by ex-Jaguar Peter Wilson (ex-Competition Department and author) and Nigel Boycott (ex-Jaguar Service Department). The process was described to us by Malcolm Hammersley of GPD Developments.

The bellhousings ended up as follows:

Jaguar XJ13, Building The Legend, Jaguar, 3D Engineers, 3D Engineering, Neville Swales
Cast SOHC bellhousing
© Building The Legend Limited
Jaguar XJ13, Building The Legend, Jaguar, 3D Engineers, 3D Engineering, Neville Swales
Cast SOHC bellhousing
© Building The Legend Limited
Jaguar XJ13, Building The Legend, Jaguar, 3D Engineers, 3D Engineering, Neville Swales
Cast SOHC bellhousing
© Building The Legend Limited

The runners etc were then removed:

Jaguar XJ13, Building The Legend, Jaguar, 3D Engineers, 3D Engineering, Neville Swales
Cast SOHC bellhousing
© Building The Legend Limited

We then machined the bellhousings as shown in the following video:

Similar techniques are being used to replicate other items such as rear hub carriers (unique to the XJ13 and certainly not available “off-the-shelf”!):

Jaguar XJ13, Building The Legend, Jaguar, 3D Engineers, 3D Engineering, Neville Swales
SOHC Rear Suspension
© Building The Legend Limited
Jaguar XJ13, Building The Legend, Jaguar, 3D Engineers, 3D Engineering, Neville Swales
SOHC Rear Hub Carrier and Dunlop-Style Brakes
© Building The Legend Limited

The words Jaguar, Jaguar XJ13, XJ13 are used in a historical/descriptive context and in no way suggest our recreations/replicas are approved by Jaguar. It is widely known that there was only ever one Jaguar XJ13 and any others can only ever be replicas, facsimilies, tributes, recreations, toolroom copies or similar.

Leave a Reply

Your email address will not be published. Required fields are marked *