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The Manufacturing Facilities.Perhaps this is time to look at how the XK was made. It is fairly common knowledge that (Sir) William Lyons bought the machinery on which the XK engine was to be produced from Sir John Black of Standard Cars in circumstances in which it was thought prudent to whizz the payment cheque round before Black could change his mind.
So, an engine of advanced design was to be made on second hand machinery. An astute person can profit from such a situation if the machinery is good enough, but problems arise if the machinery wears out and can no longer maintain accuracy. I doubt if it was even considered that much of this same machinery would still be in use 30 years and more later although of course some of it had to be renewed.
In fact the XK engine was never a true mass produced engine - it was selectively assembled with various grades for cylinder bores, pistons, and even gudgeon pins. The cost of skilled labour increased with time, whilst the ability of the machinery to produce accurate components declined as it wore out, so by the 1970s the poor old XK really had its back to the wall. Who would want to invest in new machinery to keep a near 30 year old engine going? - certainly not British Leyland, who then had control - and would a wise man advise otherwise? Of course, BL was never awash with money and Jaguar was probably regarded as having a need for substantial investment which they were not in a position to provide. In more recent times I am sure Ford were unpleasantly surprised to find how much it was going to cost to get Jaguar up to date. Perhaps it was easier for BL to just let it sink or swim and apply pressure to keep production up at all costs in the interests of desperately needed short term cash flow, regardless of any effect on future sales. It is easy to blame BL for Jaguars ills, but in fairness BL did not have a total monopoly on bad decision making. If you doubt that just consider the bland and unimaginative body colours offered by Jaguar in the 1970s.
What comes next?Of course, an XK replacement should have been initiated at a much earlier date, but the intended V8 derivative of the V12 was just not good enough, neither were the 2 and 4 valve slant six prototypes based on one cylinder bank. Had this been known at the time it is quite possible the V12 would never have made it to production. Actually one could easily look at the now defunct 2.9 variant of the AJ6 engine and imagine that it descended from the V12 and Slant Six, but in fact the AJ6 evolved from a late 1970s four valve engine based on the XK block (fig 7). The existing head stud pattern necessitated the curious feature of having the head bolts passing through the camshaft caps which carried over onto the AJ6 and later AJ16 engines. As the project progressed the cylinder bore spacing was increased to be the same as the V12 so that the May head could be more easily adapted for the 2.9.
70s Decline.As the 70s progressed so the shortcomings of the poor XK became more exposed and it began to wilt. Bore grades were reduced in number, as were piston grades, so piston/cylinder fits considered too sloppy to be acceptable in the 1950s became OK for the 1970s. Piston slap from cold became noticeable, as did "little end knock" which, strangely, could be best heard by standing a few yards in front of the car. Most engines were not too bad but the worst were getting to be a bit clanky for a "Quality Car".
Around this time the sump was altered and this introduced further problems. To meet the ever tightening exhaust emission regulations in the U.S.A. the XK was equipped, as we saw earlier, with L Jetronic fuel injection and a three-way catalytic converter, which needed to be placed nearer to the engine than had been the case with the earlier oxidising catalyst. The only way the catalyst could be accomodated was by cutting off the "ear" of the sump which was in the way. Somebody said "why not cut both ears off the sump, simplify the casting and just raise the oil level" - so that was done. Sometime after that it was noticed that if a car was left idling on a hill then one of the crank throws would hit the oil and make a noise easily confused with "big end" knock. Just to compound the problem an epidemic of real big end failures started around the same time. Spates of big end troubles were not unknown on the XK but the outbreak in 1978 was the worst by far.
A situation now existed in which production engines could display several faults:- piston slap, little end knock, oil slap, and big end knock. The latter was further complicated by variability in the surface finish from the crank grinding process and because some engines were not noisy but could suffer sudden bearing failure, whilst others knocked quite audibly but did not fail. Around the same time it had been decided to relax the interference fit of the tappet guides, which seemed all right for a while until they started working loose in service. (This problem gave graphic proof of the quality of Jaguars chill cast camshafts which could happily bash a loose tappet and guide to smithereens without suffering in any way.) Even the well proven skew gear drive to the distributor began to fail following a minor modification. Another change was that the block settling time was cut from, I think, 6 months to 3, referring to the practice of leaving castings outside to stabilise and for stresses to be relieved naturally before machining. There is no such thing as a totally rigid engine and it was known that deflections of as much as 0.010" could take place around the centre bearing structure of the XK block under high speed loads, which gives some idea of the stresses generated even in normal use. The reduction of settling time for the block may well have contributed to the formation of cracks between bores which now became common with the slightest overheating provocation. The so-called slotted block mentioned earlier made its appearance around this time to simplify production. A shaft carrying a gang of circular cutters machined transverse slots between each pair of head studs to create coolant passages between bores without need for liners. For some reason a few of the early slotted block engines burnt oil heavily whilst others were fine - by XK standards - although no XK ever set records in this respect.
Really, apart from the 2.8 situation, most of the problems were largely the consequence of the XKs age and the state of the tooling with which it was made - not to mention a dispirited workforce aggravated by myopic management from on high. The exception was the bearing trouble - and to find the origin of that we need to go back in time - to THE Mk X SALOON.
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