Background

Looking back at building up the chassis/monocoque of my recreation of the 1966 Jaguar XJ13 - a "snapshot" of the car as it was in 1966 before it was crashed and modified. Almost 18 months of painstaking and exhaustive research revealed details of the original 1966 car which allowed me to recreate the car as Malcolm Sayer intended - without the later "1970's" modifications/enhancements.

Research is still ongoing and takes advantage of recent, previously-unpublished, documentary finds as well as details revealed in Peter Wilson's book - the definitive story of the XJ13 and the quad-cam engine that powered it.

Peter Wilson book - "XJ13".

Piecing together details of the original car was an exhaustive and a very time-consuming process. Originally centred around the relatively few original documents that have survived as part of Jaguar Heritage's archive, research was supplemented by face-to-face and written communication with surviving ex-Jaguar employees. Chief amongst these is Peter Wilson (Jaguar Competition Department 1961 - 1966). Since leaving Jaguar, he has worked in a number of prominent and senior positions in the automotive industry including time spent Brico Engineering, Cummins Diesel Engines and British Leyland. Since his retirement in 1999 he has written the definitive work on the Competitions Department between 1961 and 1966 including not only the XJ13, but a significant era in the racing and development of the E-Type. I can heartily recommend Peter's book "Cat Out of the Bag" which is available from Paul Skilleter books at  www.paulskilleterbooks.co.uk. Others have included the Jaguar automotive electrician Brian Martin who actually wired up the original car and applied all those "temporary" red dynatape stickers (which still "grace" the car almost 50 years later ...).

Another invaluable resource was Norman Dewis himself - not only from his numerous recorded interviews and recollections but face-to-face discussions at Jaguar Heritage. I am the proud owner of a personally signed copy of Norman's autobiography "Norman Dewis - Developing the Legend" which contains some facts about the XJ13 - the whole book is a fascinating read.

Norman Dewis' Autobiography - "Developing the Legend".

The work of creating my first car was been entrusted to North Devon Metalcraft - a long-established family-run company manufacturing high quality, complete steel and aluminium motor bodies and replacement panels. ND Metalcraft was founded over thirty years ago by the father of John and Paul Evans who run the company today. Their late father was a time-served craftsman with experience stretching back to the 1950's. As well as being a Freeman of the City of Coventry he handbuilt the first London Black Cab. He passed his skills on to his sons Paul and John and now ND Metalcraft are best known for their body/chassis work on the Shelby Cobra, Jaguar, Aston and Triumph TR. The quality of their work is beyond reproach and I was confident in their ability to deliver an absolutely authentic 1966 XJ13 copy.

North Devon Metalcraft.

North Devon Metalcraft - XJ13 monocoque buck in the company of an Aston and Triumph.

As I researched the original XJ13 it very soon became apparent that there is no such thing as an original XJ13 blueprint, construction plans or drawings. To make matters worse, Jaguar have never allowed anyone close enough to the XJ13 to take detailed measurements for the purposes of manufacturing a replica. Replica manufacturers who claim they have had privileged access to the XJ13 are not being truthful. Others who say they have copies of original manufacturing plans are telling lies. Testament to this are the number of inaccurate XJ13 replicas currently in existence - to be truthful, I have yet to see a replica that accurately replicates the current car - and I have seen lots!

The detailed information needed to reconstruct the original 1966 XJ13 had to be pieced together from original drawing fragments, original Malcolm Sayer 3D measurement data, period photographs and the surviving remains of the original car.

Very early photo of the 1966 XJ13 clearly showing original lines of front and rear wheelarches.

It has to be remembered that the car currently in the Jaguar Heritage Collection differs in many respects from the 1966 original. Although many components such as the engine, instruments, chassis/monocoque, bonnet lid etc survived the crash intact, it is unlikely that original components such as the windscreen would actually fit the rebuilt car's body and there are numerous differences in the body form - some subtle and others rather more substantial (such as later 1970's flared wheelarches and the overall length and height of the car).

Crashed XJ13.

However Jaguar's XJ13 does provide clues to be able to "peel back" changes made in 1972/73 and reveal many features of the original car. For example, evidence of where the crumpled remains of the original body was cut away from the monocoque and how the new body/outer-sills were attached can be seen in the following sequence of pictures:

The following original 1965/66 photograph (reproduced with permission) shows the original sill in place in the car. The TIG weld and breather(?) holes are highlighted in yellow.

Photo of original 1965/66 monocoque. (The more eagle-eyed of you may notice the dash panel instrument layout differs to that in the current rebuilt car as well as their E-Type origins).

A separate panel is riveted to the floorplan (highlighted below) and meets the folded-over sill along the TIG weld. I suspect this panel had to be separate because a row of rivets attaching it to the floorplan can clearly be seen when the car is viewed from underneath (it would not have been possible to place these rivets if the sill/floor was formed from a single sheet of aluminium and folded back over itself to meet the floor).

Photo of original 1965/66 monocoque.

The car suffered substantial damage to its sills during its crash in 1971. Indeed, Norman Dewis' account of the crash suggests a sill may have made contact with a sand-filled oil drum. The following photo of the rebuilt car gives evidence that the outer sill was replaced and joined to the upper sill cover at its outer edge. The join was masked by the door rubber sealing trim and was roughly pop-rivetted into place.

Sill detail - rebuilt car.

Use of 3D Reverse-Engineering

A major contributor to the project was the use of 3D Engineering. Without these cutting-edge reverse-engineering techniques, the ability to produce an absolutely authentic and accurate replica would have been severely compromised.

What is 3D Engineering?

In simple terms, 3D scanning is a fast and supremely accurate method of putting physical measurements of an object onto the computer in an organised manner, resulting in what is commonly called 3D scan data. Typically, the 3D scan data is represented with a scale digital model or a 3D graphical rendering. Once the scan data is on the computer, all of the dimensions of the physical object can be taken, such as length, width, height, volume, feature size, feature location, surface area, etc. This even extends to being able to calculate things such as centre-of-gravity, suspension clearances, how well various components such as radiators etc will fit in the final car etc.

Components that are known to have been used in the original XJ13 can be scanned in this way and added to the 3D scan data. This includes things such as the windscreen (made using original tooling), E-Type rear light clusters and front suspension components.

In general, a device that captures 3D information from a physical object is referred to as a 3D scanner. There are many different methods for capturing the 3D measurements of a physical part and thus, many different types of scanners. We made use of various scanners including an OptiNum 3D optical scanner.

Because the 1966 XJ13 doesn't exist in its original form it was been necessary to supplement the digital scan data with data from other sources. Even if Jaguar made the rebuilt XJ13 available to us for scanning (unlikely in the extreme!)it would be of little value to us because it differs from the original 1966 car. One of the major sources of this 3D data for the 1966 XJ13 are documents containing measurements made in 3D space originally by Jaguar - possibly Malcolm Sayer himself. As Peter Wilson describes in his book "Cat Out of the Bag", Bob Blake built the original XJ13 by starting with a baseboard marked out with 10" squares. Malcolm Sayer's design was translated into 3D measurements by recording various points in 3D space relative to the baseboard markings. For example, the left-hand steering rack inner ball joint was defined as being 24.330" from the zero line on the baseboard, 17.320" perpendicularly up from this and 14.740" from the baseboad centreline.

Location of left-hand steering rack inner ball joint in 3D space.

I obtained a large number of original key measurements such as this which precisely identify the location of key components such as front and rear suspension, monocoque/chassis dimensions etc. All of these critical measurements were incorporated into the digital representation of the car.

The first task was to recreate the 1966 monocoque chassis - as was the case when Bob Blake picked up his first piece of aluminium and pondered Malcolm Sayer's measurements in 1965. The following picture shows the original XJ13 monocoque in the process of construction in 1965/66. If you look very closely at the bottom right of the picture it is possible to make out the 10" x 10" squares drawn on the baseboard.

Original 1966 XJ13 - chassis/monocoque construction detail - reproduced with permission.

This second picture is a representation of what the finished monocoque/chassis looks like. I own the original drawing of this which was produced for "Motor Magazine".

Representation of original XJ13 monocoque/chassis.

I decided to produce two major buck/formers for my recreation - one for the chassis/monocoque and a second for the body itself. The following pictures show a digital representation of the chassis/monocoque buck followed by its full-size version. The central section and bulkheads are removable and were replaced by the body buck when the chassis/monocoque was complete and we were ready to start work on the body. The plan was to first build a basic monocoque using sheet steel before committing ourselves to a full monocoque built using original-specification aluminium. 

According to Peter Wilson,

" ... the monocoque was constructed almost entirely from NS4 2 percent magnesium and 2 percent manganese, half-hard alloy sheet, mostly of 18 swg thickness (0.048 inches), together with some sheet steel pressings in areas of high and concentrated stress, such as the main engine mountings and front suspension attachment areas."

The modern equivalent, Aluminium 5251 (NS4), is available and was used for the recreation along with steel pressings where appropriate. This attention to detail extended to the choice of aviation-quality Avdel rivets as original (I have seen too many oversize rivets used in replicas!)

Chassis/Monocoque - digital image.

Chassis/Monocoque buck.

The XJ13 used E-Type front suspension using coil-over shocks in place of torsion bars, vented discs and specially-manufactured calipers. All of these components were be used with modifications as per original. I had to cast and machine my own components as needed.

Paul (ND Metalcraft) identifying data points on bulkhead from original Jaguar XJ13 data.

The front of the sills/floor. A "trial monocoque" was constructed using sheet steel. Once we were happy with the details we worked using the rather more expensive original-spec sheet aluminium. I ended up with a complete surplus steel monocoque before we began building the final aluminium version. The steel monocoque was destroyed/recycled.

Rear view. The cross-hatched section was removed.

"Trial" Chassis/Monocoque - side view.