A bit of cam-timing …

Building The Legend, Quad-Cam, tera-, V12

A bit of cam-timing on our own full-race, quad-cam V12 ……

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.

How many quad-cam V12s were built and where are they now?

XJ13 Original Quad-Cam V12

A question often asked of me is,

“How many prototype V12 quad-cam engines were built by Jaguar and where are they now?”

As I reported on this blog back in May 2010, the answer is SIX. Of this six, only three progressed beyond test-bed stage and were installed in cars. A seventh engine was assembled as a 60° V8 and run on Jaguar’s test bed. The V12 block for this engine was converted into a V8 using a special crankshaft with throws for only eight of the twelve cylinders. There were plans to assemble an eighth engine but it never reached the test bed stage.

The above has now been confirmed by XJ13-expert Peter Wilson in an excerpt from his forthcoming book which appears in the November 2011 issue of “Jaguar World”. I can now add further confirmation of these facts from a collection of previously unknown and unpublished original documentation. These documents were in the personal collection of the late Claude Baily – the architect of Jaguar’s quad-cam V12, their legendary XK engine and quad-cam 90° 8 litre V8 amongst others.

XJ13 - Building the Legend
Claude Baily

Claude Baily joined the SS Jaguar drawing office during the second World War and his engineering talents were soon exploited by Jaguar. Baily became intimately involved in Jaguar’s plans to replace their pre-war engine designs with a new generation of engines designed to power their latest saloons. He is perhaps best known for his part in the design of the legendary XK twin-cam engine.

XJ13 - Building the Legend
Claud Baily’s appointment letter.
© Copyright Tony Bailey (WPO Communications) – not to be reproduced without permission.

Spending long war-time nights fire-watching in a small office above the assembly tracks in Coventry, in the company of William Lyons, William Heynes and Walter Hassan, the architecture of the world-beating XK engine was laid down. The new engine was required to reliably provide a minimum of 160bhp, have a long service life and be refined in operation. Before the end of the war, a number of experimental single-cylinder and full engines were evaluated. The following original document from 1941 is likely to relate to one such experimental engine. J.A.Prestwich was better known by its initials “J.A.P.” whose engines were used in many famous motorcycle marques and early aeroplanes. Customers included Morgan, Triumph, Brough Superior, AJS and HRD.

XJ13 - Building the Legend
12th December 1941 – letter to SS Cars referring to experimental engine.
© Copyright image – not to be reproduced without permission.

4, 6, 8 and 12 cylinder configurations were all considered at this very early stage but it was the 4 and 6 cylinder versions that were finally adopted. It has to be said that the BMW 328 engine played an important part in formulating the architecture of these engines. Indeed, Heynes was great friends with an owner of a 328, Leslie Johnson, who loaned his 328 to SS Cars for evaluation.  Johnson was a British racing driver who competed in rallies, hill climbs, sports car races and Grand Prix races. Johnson’s car was highly developed and had raced pre-war. In my opinion, the styling of the XK120 owes much to the BMW. A BMW saloon was also acquired by SS during the war and was fitted with one of the early experimental engines (the “XG”). Walter Hassan used this car as his own personal transport for an extended period for evaluation. One of Jaguar’s own 2.5 litre SS Saloons was also used for testing the prototype engines although most of the development work was carried out on the test bed.

XJ13 - Building the Legend
3.5 litre experimental XK engine – drawing produced to calculate compression ration.
© Copyright image – not to be reproduced without permission.
XJ13 - Building the Legend

Left to right – Walter Hassan, William Heynes, Claude Baily.
© Copyright image – not to be reproduced without permission.

Heynes and Baily applied all their thoughts on engine design to the XK engine although they later commissioned Henry “Harry” Weslake to help optimise their design. Jaguar already had a long association with Weslake, a cylinder head specialist who had been instrumental in modifying the side valve standard engine used in the first SS sports car. He also worked on the larger SS engine. It is believed he was involved in the design of every Jaguar engine up to and including the V12 of the early 1970s.

XJ13 - Building the Legend
Harry Weslake – © Copyright image – not to be reproduced without permission.

The following Weslake report gives a fascinating insight into his evaluation methods and his closing summary bears testament to the soundness of the XK basic design. Weslake concludes:

“…. The engine has stood up remarkably well through these series of tests. The valve gear has remained quiet throughout, there has been no sign of variation in oil pressure and the engine improves in power out-put the longer it runs. The tests have been very severe, particularly the distribution ones, but never once was any mechanical trouble experienced. It is suggested that some breather attachment should be developed in order to keep a small depression in the crankcase so that oil corrosion can be minimised and this would also help to stop oil leaks, particularly in the valve chest covers …”

XJ13 - Building the Legend

© Copyright image – not to be reproduced without permission.
XJ13 - Building the Legend
© Copyright image – not to be reproduced without permission.
XJ13 - Building the Legend
© Copyright image – not to be reproduced without permission.
XJ13 - Building the Legend


© Copyright image – not to be reproduced without permission.

XJ13 - Building the Legend
© Copyright image – not to be reproduced without permission.
XJ13 - Building the Legend
© Copyright image – not to be reproduced without permission.
XJ13 - Building the Legend
© Copyright image – not to be reproduced without permission.

The camshaft drive was by duplex roller chain – an arrangement that was carried forward to the quad-cam V12 prototype engines. This arrangement was used in the first engine installed in the XJ13 as well as the second engine built and tested in a Mk.10 Jaguar. The “genetics” of the XK engine could clearly be seen in the later quad-cam V12. The following page of sketches (made by Claude Baily around 1949/50) clearly show how he was formulating a suitable cam drive for a quad-cam engine. It is believed the sketches were produced as a precursor to designing and building a quad-cam 8-litre 90° V8 engine for a post-war military application. A similar architecture found its way into Baily’s quad-cam V12.

XJ13 - Building the Legend
Baily’s drawings showing his ideas for a quad-cam duplex chain drive
© Copyright image – not to be reproduced without permission.

Claude Baily had been working on a quad-cam 60° since 1949/50 – perhaps earlier. By the February of 1951 a fully-working engine may have been running on the test bed. This 12-cylinder engine was later developed as an 8-cylinder variant for military use. The following quad-cam V12 performance data was recorded on the 19th February 1951.

XJ13 - Building the Legend
Claud Baily’s 1950/51 60° quad-cam 8-litre V12 engine performance data.
© Copyright image – not to be reproduced without permission.

The following picture shows Baily’s data in his own hand. Was this an estimate/conjecture or are they figures actually recorded on the test bed?

XJ13 - Building the Legend
Claud Baily’s 1950/51 notes.
© Copyright image – not to be reproduced without permission.

In 1962, Baily was given the go-ahead to develop his design as a 5 litre V12 to challenge at Le Mans. Although primarily designed for racing, consideration was also given to using the engine in production cars. At least two years before the go-ahead, Baily’s 60° V12 engine was being proposed as a future Jaguar engine with a range of possible capacities as the following memo from Claude Baily to William Heynes demonstrates:

XJ13 - Building the Legend
5th December 1960 memo – “POSSIBLE FUTURE RANGE”.
© Copyright image – not to be reproduced without permission.

The quad-cam V12 engine project was given the code “XJ6” – not to be confused with the saloon of the same name. “XJ6” followed on from “XJ5” which was the code name given to the Mk10 replacement (eventually to become the 420G). Two Mk.10 cars (XJ5/4 and XJ5/5) were to become mules for the production variant of the “XJ6” racing engine. The following memo confirms that six prototype engines were being developed.

XJ13 - Building the Legend

25th November 1964 memo – “12 CYLINDER ENGINES”.
© Copyright image – not to be reproduced without permission.

The first two engines (XJ6/1 & XJ6/2) were first assembled to almost identical specifications which included dry-sump lubrication and Lucas mechanical fuel injection. In April 1966 XJ6/1 was installed in the XJ13. The second engine, XJ6/2, was installed in a Mk10 Jaguar (XJ5/5 – manual gearbox) on 14th April 1965. It was converted to wet-sump lubrication although its Lucas fuel injection system remained. After six months of testing in the Mk.10, XJ6/2 was removed from the car and reunited with a dry sump for further test bed development. In March 1966 it’s dry sump was again converted to enable fitment in a second Mk.10 (XJ5/4 – automatic gearbox). By this time it had acquired a sextet of SU carburettors. It ran for almost 35,000 miles in this car before it was removed and replaced in XJ5/5. It was finally removed from the latter car and placed on the test bed for further development/testing until it was put into store in March of 1969. It remained as a complete engine until I acquired it in 2010. It is now being rebuilt to its original specification and will be placed in my replica of the 1966 XJ13.

So, to answer the question “How many quad-cam V12s were built and where are they now?” SIX quad-cam V12 engines were built.


  • XJ6/1 The first quad-cam V12 built but only the second to leave the test-bed and be installed in a car (XJ4/1).  Damaged in 1967 and retained as a spare by Jaguar. 
  • XJ6/2 The second quad-cam V12 built and the first to be installed in a car (XJ5/5) Survived as a complete engine and sold by Jaguar in the mid 1970s. Currently under restoration to original specification (same build spec as XJ6/1).
  • XJ6/3 Only ever ran on the test bed in a variety of configurations. Has not survived.
  • XJ6/4 Built using cast iron block and ran on test bed. Has not survived.
  • XJ6/5 Internally modified to run as a V8. Ran on test bed for a short while in 1965. Surviving components are with a collector in the US.
  • XJ6/6 No records exist. It is believed this engine was never actually assembled.
  • XJ6/7 Built to trial a die-cast “open-deck” engine block.  Installed in XJ4/1 (XJ13) to replace its original engine when damaged in 1967. Remains in the car to this day.
  • XJ6/8 Built to competition spec with ultimate development of cylinder heads but never left the test bed. Cannibalised whilst in storage in 1969. Cylinder heads placed on XJ6/2 which remain with it until today. The engine block found its way into an XJ13 replica built by Bryam Wingfield for the collector Walter Hill. 

It is interesting to note that Jaguar’s XJ13 currently has a die-cast block that differs from its original XJ6/1. This die-casting process is used to reduce costs and will have been more relevant for a production as opposed to competition engine. The following letter indicates the target casting weight of a V12 block (OXW 5620 is an experimental part number current at the time of quad-cam testing)

XJ13 - Building the Legend
XJ13 - Building the Legend
Die Casting Quote.
© Copyright image – not to be reproduced without permission.

The XJ13’s rather poor power to weight ratio when compared with its likely Le Mans competitors may have contributed to this attempt to lighten its weight?

As Mike Kimberley recorded after a test of the XJ13 at Silverstone in 1967:

BHP per lb weight

  • Ferrari P4/ .210
  • Lola Chev/ .207
  • Ford Mk4/ .206
  • XJ13/ .177

It is also interesting to note that the engine currently installed in the XJ13 has a single OPUS 12 cylinder distributor. Its original engine, XJ6/1, as well as XJ6/2 were fitted with twin 6-cylinder distributors.

XJ13 - Building the Legend

XJ6/2 Original twin distributors as originally fitted to XJ6/1.
© Neville Swales.
XJ13 - Building the Legend
XJ13 single 12-cylinder distributor on XJ6/7 engine.
© Neville Swales.

The rebuilt XJ6/2 will, of course, be built using its original twin distributors. In 1966 Claude Baily was charged with pricing the OPUS system. The following letters give an interesting insight – comparing the various options under consideration.

XJ13 - Building the Legend
© Copyright image – not to be reproduced without permission.
XJ13 - Building the Legend
© Copyright image – not to be reproduced without permission.
XJ13 - Building the Legend
© Copyright image – not to be reproduced without permission.

There are other differences between the XJ13’s original engine (XJ6/1) and the one currently installed in the car (XJ6/7). One is the inlet manifold throttle bodies. The first photo shows the original (1967) arrangement with dual throttle bodies (and separate mounting plates – coloured yellow) and the second shows the current arrangement (photo taken 1973) with individual throttle bodies and a single mounting plate on each head. Note also the different cam cover treatment – the earlier engine has the “trademark” polished cam covers wheras the currently-installed engine has a crackle-black finish.

XJ13 - Building the Legend

1967 (original car)
© Copyright image – not to be reproduced without permission.
XJ13 - Building the Legend
1973 (rebuilt car)
© Copyright image – not to be reproduced without permission

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.