In January of 2011, on a very cold January morning, the restoration of my quad-cam V12 began in earnest with a total stripdown and detailed examination. The task of rebuilding this important engine has been entrusted to David Butcher.
David can draw on his vast experience gained from many years of rebuilding Jaguar engines from the 1960s to date. He has had a long involvement with Jaguar engines since his days working alongside the late Ron Beaty at Forward Engineering. Although in "semi-retirement", David's skills are very much in demand today - particularly by racers and enthusiasts. David has worked on all variants of Jaguar's classic engines including the Group C and prototype Le Mans racers.
David Butcher starting work on the prototype V12.We were privileged to be joined at the initial engine stripdown by Peter Wilson and Jim Eastick. Both Peter and Jim worked at Jaguar on projects associated with the XJ13 - Peter on the car itself and Jim on the prototype's V12 engines.
From left to right - Peter Wilson, David Butcher and Jim Eastick.I was fascinated to learn from Jim Eastick that my engine has a direct connection with the legendary Ron Beaty as it was Ron who actually ran and optimised my engine on the Jaguar test bed. Beaty joined Jaguar and made his way up to being one of the all time greats at the works. He worked in the former competition dept and was experimental engineer for the V12. In the late 1960's Ron Beaty formed the company Forward Engineering which made him a household name in the Jaguar world, creating power units for British and world water speed records, Lister Jaguars (Beaty created the original Lister XJS with Brian Lister) as well as many track records both here and abroad. The original TWR XJS's were also "Forward " powered as were many small volume constructors like Panther. David Butcher worked alongside Ron Beaty at Forward Engineering and played an important role in some of Forward Engineering's various projects. Other notable "Forward Engineering Graduates" were Rob Beere and Carl Taylor of Rob Beere Racing.
While David worked on the engine, I was treated to an accompanying dialogue of recollections of life at Jaguar at the time of the project between Peter, David and Jim - memories sparked by details of the engine revealed as the stripdown progressed - recollections not only of the engine itself but also the many individuals involved at the time. Sadly many of these individuals are no longer with us. Jim also brought with him his personal notebook containing notes made while the prototype engines were actually being run on Jaguar's Test Beds - a book he kept very close to his chest!
Jim Eastick consulting notes made during prototype engine testing.My engine was the second engine assembled and is believed to be one of only three engines surviving having left Jaguar as complete engines. Two of the three engines remain with the XJ13. There is a fourth engine which was assembled from a collection of new and used parts left over at the end of the project and installed in a replica for the late collector Walter Hill by Bryan Wingfield. As the stripdown progressed it soon became clear that the engine was not only complete internally but was in quite remarkable condition despite its 40+ years of storage.
Head removal.Jaguar's habit of liberally applying "Wellseal" to gasket surfaces was very much in evidence! Having removed the heads, the condition of the bores and pistons became apparent. Although there is slight surface oxidation on the crowns of the cast alloy pistons, this is to be expected on an engine that has been stored for this period of time. It does confirm that the engine has spent its last 40 years undercover and in dry conditions. The slight oxide buildup was only present on the pent-roof piston crowns and the remainder of the pistons was found to be in quite remarkably good and usable condition. The lack of any significant carbon buildup does tie up with the original testing logs which indicate the engine was only run for a short time on Jaguar's test bed before being removed for storage in December of 1969. The final bout of testing was for emmision comparisons with the SOHC production engine.
The cylinder block is a L.M.8 sand casting and has a sump face on the crankshaft centre line. This is in contrast with the later SOHC V12 which had a much longer "skirt" which helped increase block stiffness. The prototype engine is a solid casting as opposed to the die-cast "open deck" design of the later engine. This makes it a rather heavy engine which is difficult to manouevre by hand - ask me how I know!
Cylinder heads showing "tin" gaskets. In the foreground can be seen the original twin distributors. Twin distributors were used in the original 1966 XJ13 and were only replaced with a single "modern" V12 distributor during the car's rebuild in 1972/73.
Hemispherical combustion chambers.The V12 cylinder head design is very similar to the 6-cylinder XK engine in basics such as valve operation with a few significant differences. In an attempt to arrive at a more compact and efficient combustion chamber, the chamber depth was reduced to 1.03" (from the XK's 1.30") and the included valve angle was reduced.
As explained by Jim Eastick, the V12 prototype engine has equal firing impulses along each bank and can be carburetted as an in-line 6 cylinder. The bore and stroke is 87mm x 70mm giving a displacement of 4991cc.
All prototype engines were fitted with twin 6-cylinder distributors. One of the many changes made when Jaguar rebuilt the XJ13 after its crash in 1971 was their replacement by a single 12-cylinder distributor. One of the two distributors, the "master", contained two sets of contact-breakers plus a centrifugal advance mechanism that served both distributors. The second distributor, the "slave", was simply a distributor for the H.T. current. My engine will be rebuilt with both distributors as original.
Jim Eastick explaining how he had added extra springs to the "master" distributor in an attempt to reduce points bounce during testing.The heads on my engine are numbered 18 and 19. This confirms them as the ultimate development of the prototype cylinder head having an optimum subtended angle of 41 degrees to the valve axis with camshaft centres raised by 0.25". The cylinder heads remaining with the XJ13 may have never achieved the widely-reported maximum power of 502 bhp at 7,600 rpm achieved by an engine with this design of head.
The following picture shows the modified sump fitted to my engine. Although it is the engine's original racing dry sump, it was considerably modified in period to enable its fitment in the two Mk10 Jaguar "mules" for testing. The original gear scavenge/pressure in-sump gear pump was found to be in place but modified so that drive was transferred to a rear "wet-sump" pickup. The welded-up position of the original scavenge/pressure outlets can be seen at the front of the sump. The plan is to return the original sump to dry-sump specification.
Modified dry sump.The four studs on the skirt of the block are used to not only mount the engine but also to provide a location for the rear trailing arms. There will be a corresponding pair of locating studs on the final sump. The engine/transaxle in the XJ13 supports the entire rear suspension.
Seen here is part of the duplex chain cam-drive arrangement - incidentally, as originally fitted to the XJ13 engines and not gear-drive as widely thought.
Chain-drive to cams.The next few pictures show the sump being removed - revealing components not seen since the engine was assembled in Coventry in the late 1960s.
Preparing to remove the sump under the watchful eye of Jim Eastick.
Sump removed revealing combined scavenge/pressure pump and shaft used to transfer drive to the rear oil pickup. As with the later SOHC engines, a steel plate extends the full length of the crank.
Oil pump detail.
Chain drive to oil pump.
The engine has seven 3" diameter main bearings which means the later shells can be used (perhaps with slight modification to oil-holes). The big ends are unique which may cause some problems in finding replacements. When Jaguar recently rebuilt the XJ13's engine they found it necessary to increase the diameter of the conrod big ends to accept "off-the-shelf" bearing shells. This avoided a cost of something in excess of £20,000 to tool up for the prototype's unique bearing size. However, we have yet to fully explore whether or not the original size shells can be found. The crank pins are 2.187" diameter and are 1.20" wide to accept the side-by-side conrods. The conrods are offset 0.75" bank-to-bank. The crankshaft is made from forged steel and is lubricated using an end-to-end feed from grooves in the main bearings. The same sludge trap system as used on the earlier 6-cylinder XK engine was used with transverse oil feed holes. Although we have yet to confirm whether or not the crank was nitrided it is known that Jaguar used a EN 40 nitrided crankshaft in the competition V12.
David then began to remove the timing-chain cover so that pistons and crank could be removed.
Preparing to remove timing cover.
Timing cover removed.The following picture shows detail of the lower two chains (four separate chains in total). One chain drives the oil pump while a second takes drive to intermediate sprockets - one for each head. Another sprocket is used to drive the twin distributors and Lucas fuel injection metering unit via a "Jackshaft". A hydraulic chain tensioner can be seen towards the bottom of the picture. The two top chains (driving the cams) are tensioned by an external nut applying pressure to a slipper.
The complexity of this chain layout was a factor in deciding to go with a SOHC layout for the production engine. The weight and cost could be reduced using a single chain drive with four sprockets compared to the prototype's four chains and twelve sprockets. Also, the noise level of the quad-cam layout was unacceptably high for a production engine. However, for racing purposes the quad-cam layout was preferred.
Timing chain detail.
Drive removed from oil pump.
Steel cover plate and scavenge/pressure pump removed.
Referring to original notes .....
Oil pump.
Removing slave distributor drive.
Distributor drive "jackshaft"
Piston sees light of day after 40 years.
All bearing shells were in remarkably good condition - confirming the engine's short time on Jaguar's test bed before the engine was removed for storage.
Journals also in good condition.
"Yours Truly" lends a hand.
Connecting rod still polished and shiny after all these years.
Preparing to remove crankshaft.
Jim Eastick remembering modifications to oiling system.
Detail showing "grooves" around oil holes on alternate big ends.
Slip-fit dry liners.
Crankshaft removed. Bearing shells were all in excellent condition.Now that the engine has been stripped it can be given a detailed examination/measurement in readiness for its rebuild. As a matter of course things such as valve springs and (probably) valves will be replaced. After standing for more than 40 years it makes sense to replace items such as this - the thought of a detached valve in the rebuilt engine doesn't bear thinking about! Fortunately, we are well-blessed in the UK with skills and expertise to be able to build an engine such as this.
To be continued ...
