The time has come to consider the specification for the rebuild of the quad-cam V12 engine. The first important thing to consider was the means of driving the four camshafts.

As stated previously on this blog, the intention is to recreate an EXACT copy of the XJ13 as it was in its heyday in 1966/67 - WITHOUT its subsequent modifications which include its "delightful" 1970s-style flared wheelarches, alloy wheels and gear-drive to the cams. Contrary to common belief, gear-driven cams were not installed in the car until 1978 - a good 11 years after the project had been allowed to die. The XJ13 NEVER ran with gear drive to the cams in period - the cams were always driven by duplex chains. My original engine has duplex chain drive to the cams - as was the case with both engines originally installed in the XJ13.

This "gear-driven cam" myth became widespread by the publication of cutaway drawings such as the ones shown below. Indeed, Jaguar themselves began to believe their own myth.

Cutaway drawing of engine fitted to XJ13 in 1978.

Detail of partial gear drive to cams - part chain and part gears.

The confirmation that the XJ13 never ran with gear-driven cams in period can be found in Jaguar's own archive. The archive contains a series of engine test logs - a log for each of the six prototype engines assembled as quad-cam V12s. Of these six original engines, only three survived as complete units(although a fourth was subsequently built up from new and used parts left over at the end of the project and used by Bryan Wingfield in a XJ13 copy for the late Walter Hill). Two of the three engines remained with the XJ13 and I have the third. As well as these engine logs, a number of original reports and other documents have survived. The facts recorded in these documents can be used to accurately chart the progress of these engines. A good 45 years have elapsed since the project commenced and people's recollections of events all those years ago may be a little hazy - even those who were directly involved at the time. It is for this reason that I base my conclusions purely on the documentary evidence.

The logs confirm the XJ13 never ran with gear-driven cams in period as follows:

1. Only two of the six prototype engines have ever been installed in the XJ13. These are recorded as "No.1" and No.7".

2. The first engine to be installed in the XJ13 was "No.1". This unit was NOT built to competition spec and did NOT have geared cam drive.

3. After a spell of testing on the test-bed (conducted by Mr J Eastick) "No.1" was installed in the car in April 1966 - " ... engine handed to Mr Brookes for installation in XJ13 rear engined car..."

4. In the meantime, "No.7" engine was being developed on the test bed. This engine - No.7 - HAD been assembled with gear-drive to the cams. " ... 12/8/65 ... built to competition specification ...". Later that year, in December while the engine was still on the test bed, the timing gear on "No.7" engine was replaced by the timing gear from the "No.4" engine. " ... timing chain brackets, chains, sprockets, dampers from No.4 ...". "No.4" engine was the only V12 engine with a cast-iron block (the other engines were all alloy). "No.4" was not built to competition specification and had duplex chain drive to its cams. "No.4" may have been subsequently smashed up and has not survived.

5. For the remainder of 1966 and the start of 1967, the XJ13 continued its development powered by the chain-driven "No.1" engine. Meanwhile, "No.7"'s development continued on Jaguar's test bed with numerous references to the cam chain drive in its testing log.

6. On the 23rd April 1967 disaster struck! Norman Dewis missed a gear change at MIRA whilst testing - " ... unable to test for extended period. Dewis missed gear. Suspect bent valves ..." The XJ13's engine ("No.1") suffered extensive damage after the missed gear change. The "No.7" engine, still with chain-driven cams, was hurriedly prepared for installation in the car. On the 10th May 1967 "No.7" was removed from the test bed - still with chain-driven cams. Installation of "No.7" in the XJ13 commenced on 11th May 1967. "No.7" was recorded as still being in the car as late as July 1973 " ... engine in car for Silverstone demonstration run on 14/7/73 ...".

7. Meanwhile, "No.1" was returned to the test bed for further development/testing where it remained until 1978. In July of 1967, gear-driven cams were added to "No.1" while it was still on the test bed.

8. During this time, my engine, "No.2" continued to be developed both on the road and on the test bed. Indeed, it remained under development long after the other V12s had been removed/dismantled for storage. Development of "No.2" continued until 1969 when it was used to carry out comparisons with the road-car single overhead cam engine. It has the distinction of being the very first Jaguar V12 ever to run on the road and may have been the only engine to have reached the 502bhp @ 7500rpm falsely claimed for the engines installed in the XJ13. It is likely the maximum power developed by engines fitted to the XJ13 was a much lower 438bhp.

9. In 1978 disaster struck again ... " ... 3/7/78 (No.7) removed from XJ13 car after damage to 'A' bank cylinder head during warm-up for demonstration run at Daily Express March meeting. Engine known to have over-revved during missed gear change, would appear to be broken tappets or tappet guides, No.6 exhaust valve head broken off and jammed in seat ...". It was at this point, as late as 1978, the XJ13 was fitted with gear-driven cams for the first time - long after the project was dead, after its crash and after it had been "modified" for a life of demonstration runs only.

"No.1" engine remains with the XJ13 to this day.