Jaguar XJ-S. Manual — part 7

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Victor Naumann recommends Publication #S-58, XJ-S Engine Performance. “It has photos and diagrams of ignition
and fuel systems, all the controls and switches and a good section on maintenance procedures, setting throttle plates and
linkage and checking the potentiometer etc.”

Jaguar XJS Gold Portfolio 1975-1988, compiled by R. M. Clarke, is a collection of road tests, specifications,
comparisons, and reports on racing and other modifications. It is published by Brooklands Book Distribution Ltd.,
“Holmerise”, Seven Hills Road, Cobham, Surrey, UK.

John T. Horner suggests “There is a brochure type booklet written by Jaguar when the V12 was introduced and which
is sometimes still available: Genesis of the Jaguar V12. It has a good official summary of the history and
specifications as well as beautiful color overlay drawings of an engine cutaway. I think Bookspeed in the UK may still
offer it.” This author has acquired a copy of this book; it isn’t much from a maintenance standpoint, but it cannot be
beat for instilling an appreciation of one of the finest automotive engines ever designed, providing a concise history and
background of the engine’s development. From an XJ-S owner’s standpoint, the worst thing about the book is that it
truly applies to the original Jaguar V12 introduced in the Series III E-type; many of the details changed by the time
most XJ-S’s were built. The engine shown in the book has carburetors, a canister-type oil filter mounted under the
front end of the sump, an oil-to-coolant oil cooler, an oil pan that is no wider than the bottom of the block, an alternator
mounted backwards so it sticks out the front of the engine, etc.

Bookspeed’s address is on page 720. Genesis of the Jaguar V12 is also available from Classic Motorbooks, page 720.

Lawrence Buja recommends Jaguar Driver Technical Tips by Bob Bate, ©1990, R.G. Bate Publishing, 501 Cleveland
St., Birkenhead, Merseyside, England. “Technical Tips is a huge collection of tech articles published in the Jaguar
Driver Club magazine by a professional Jaguar mechanic. It is about 500 pages long and covers an immense range of
topics all related to the real-world operation, diagnosis and repair of Jaguar automobiles.” Makoto Honjo adds, “Bob
does advertise on the JDC, whose flier I sought for a lead. Well, turns out that Jaguar Driver Technical Tips is his
private and is available through him at GBP40 (hey, you've got to pay for quality). You can call him at phone +44-151-
653-6765 for a copy.”

TECHNICAL PAPERS: In the US the Society of Automotive Engineers (SAE) maintains a collection of technical
papers. Paper #720163, by Walter T. F. Hassan of Jaguar Cars Ltd., Div., British Leyland Motor Corp., is a quite
detailed engineering study of the development of the Jaguar V12. Of course, the paper predates such later
developments as the H.E. Bob Weisickle points out that SAE papers can be ordered from:

http://www.sae.org/

but note that they only offer recent papers online; older papers don’t even show up in a search! You’ll have to call SAE
at +1 (724) 776-4970 Monday through Friday, 8:00 a.m. to 5:00 p.m. Eastern time to get older publications.

In the UK there is a similar paper titled “Jaguar V12 Engine - Its Design and Background”, also by Hassan, from the
Technical, Administrative and Supervisory Section of the Amalgamated Union of Engineering Workers
(AUEW-TASS), Onslow Hall, Little Green, Richmond, Surrey.

Roger Bywater says “there is also a similar Institute of Mechanical Engineers paper by Harry Mundy from about the
same time (1972).”

SERVICE RECORDS: Chad Bolles: “...just go to any dealer’s service dept., give them the serial no. of your car; they
can pull it up on the computer and give you the available history.”

FUEL ECONOMY: Keeping an eye on fuel consumption is an excellent way to monitor your car’s condition. Since
EPA ratings are generally unreliable in the real world, it is helpful to know what kind of fuel consumption the XJ-S
should have:

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miles/US

gal miles/Imp.

gal. litres/100km

XJ-S H.E.:

everyday: 16-18

19-22

13-15

highway: 18-20

21-24

12-13

Pre-H.E.:

everyday: 9-12

11-14

20-26

6.0:

everyday: 12

14

20

highway: 16-18

19-22

13-15

For those who like to do their own converting, there are 0.83267 Imperial gallons in a US gallon, 3.7854 litres in a US
gallon, and 1.609344 kilometers in a mile.

The values for the pre-H.E. are based on fewer reports, but those reports were fairly consistent; apparently the H.E.
really was a huge improvement in fuel efficiency over the previous design! Note that reportedly the difference only
occurs under light (street) use; with harder running or racing the economy difference diminishes.

The values for the 6.0 are likewise based on fewer reports but the reports were consistent; since the cars are of more
recent vintage and have electronic controls less subject to variation or misadjustment, you’d expect them to be
consistent. It’s perhaps surprising that these cars don’t get better economy than they do, especially considering the
improved transmission and the longer stroke engine. Perhaps the 6.0 drivers have their foot in it more than the 5.3
drivers!

Of course, the standard disclaimer: “Your mileage may vary.” But you know if you are driving harder or under worse
conditions than the average driver, and if you think your fuel mileage is worse than it should be you should
immediately investigate the causes. Many of the common causes also result in major engine damage if left uncorrected.

Jim Isbell was doubtful, but now is a believer: “The O

2

sensors were changed. The results were fantastic. The around

town mileage has increased from 12 MPG (US gallon) to 17 MPG on the first tank after the change.”

Unfortunately, there is one other reported reason for bad city mileage. “B emission” (UK and Europe spec) H.E.’s have
a timer that disables the vacuum advance for 15 minutes after startup if the coolant was below 45°C when started. If
you drive 15 minutes to work, park there 8 hours, and drive 15 minutes home, you are always operating on retarded
timing and will get something around 12 mpg. See page 134.

Note also that some areas require the use of “oxygenated fuels”, sometimes just during particular seasons. Oxygenated
fuels result in far worse fuel consumption in any car.

THREADS: The British invented the inch/foot system of measurement, so most of the fasteners on the pre-1984 XJ-S
are English fine thread (UNF or National Fine), available in any hardware store in the US. Jaguar and other British cars
extensively use fine threads, as opposed to the coarse threads (SAE or National Coarse) normally used on American
cars. Coarse threads are sometimes used in aluminum parts, because aluminum is too soft for effective use of fine
threads.

In 1984, many of the fasteners within the engine itself changed to metric sizes. Notably, just about every 5/16” stud
appears to have changed to M8, according to David Johnson. Many of the 1/4” threads changed to M6.

Thanks to a continuing effort towards metric standards, there are metric fasteners in other parts of the car as well --
even in the pre-1984. Many of the subcomponents, such as the alternator, air conditioner compressor, and stereo are
made with metric threads. Later cars seem to have more and more metric threads. Mike Morrin says, “The nuts
holding the wiper blades are the only metric fasteners I have found on my 1975 car.”

WHITWORTH/BSF: There are, unfortunately, a couple of places where obsolete British standards such as BSF or
Whitworth are found on the XJ-S. See the discussions on the crank damper retaining bolt on page 88, the surge tank

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vent connection on page 253, the main power terminals on the firewall on page 556, and the battery terminals and hold-
down nuts on page 583. Also note that page 12 of the Haynes manual lists wrench sizes for such oddities. Most of the
BSF/Whitworth wrench sizes don’t correspond to anything in SAE or metric sizes; supposedly, Mr. Whitworth decided
to size his bolt heads so that the length of a flat on one side of the hex was some nice even number.

Keep in mind that BSF and Whitworth wrench sizes are the diameter of the bolt, not the dimension across the flats on
the head. And, for some reason, the wrench that fits a BSF bolt seems to fit the next smaller size bolt in Whitworth.

To learn more about British non-standard standards, David Littlefield suggests visiting these WWW sites:

http://www.team.net/sol/tech/whitworth-hist.html

http://home.sol.no/~karne/threads/threads.htm

Craig Sawyers: “At least here in the UK you can get spanners and sockets from the local tool store that are correct.”
Actually, you can obtain Whitworth tools in the US and presumably other countries; it just takes more looking. Jeb
Boyd says Snap-On has Whitworth tools. David Littlefield suggests British Tools and Fasteners; see page 707. A
search of the WWW should turn up an assortment of mail-order sources.

Note: with the exception of the crank bolt (for which wrench options are discussed on page 88), all of the
Whitworth/BSF wrench sizes used in the XJ-S seem to be the same size: 1/4” Whitworth/5/16” BSF. Hence, it might
be good advice for the XJ-S owner/mechanic to obtain one wrench. The entire Whitworth set is not needed.

TORQUE UNITS: Torque, or twisting force, is specified as an amount of force applied at a radius. In the English
system of measurement force is typically given in pounds or ounces, and radius (distance) in either feet or inches. The
first point of confusion arises because units of mass are also called pounds. As a result, it is increasingly preferred to
speak of pounds force or pounds mass instead of simply pounds. The abbreviation for pounds force is “lbf.” The f
does not stand for feet, and lbf. does not stand for foot-pounds. Readers are encouraged to beat this into their hard
skulls until it sinks in; reading “lbf.” and thinking “foot-pounds” is a good recipe for disaster with this car and this
ROM.

The torque value is the amount of force applied times the radius. Twenty pounds applied at a radius of 18 inches is 360
inch-pounds or thirty foot-pounds. Hence, the terms for force and the terms for distance are written sequentially
(doesn’t matter which order, really). Sometimes a hyphen is used, which in this author’s opinion makes things clearer,
but as expected that means that Jaguar chooses not to use a hyphen. In the XJ-S ROM, foot-pounds are written as “lbf.
ft” and inch-pounds are written as “lbf. in” That last one, if you’re not paying attention, looks like foot-pounds
followed by the word “in” -- especially if it’s word-wrapped and the “in” is at the beginning of the next line. If you
make a mistake here, you will overtighten something by a factor of 12.

Lacking a hyphen may be confusing, but at least it’s technically correct. Putting a slash between the terms, such as
lbf./ft or lbf./in indicates pounds force divided by feet or inches, and this is most definitely incorrect when used to
indicate units of torque; lbf./ft or lbf./in are units of spring rate, not torque. Unfortunately, Jaguar is reportedly guilty of
this error -- not just once or twice, but throughout entire manuals. The XJ-S ROM uses correct terms, but Peter Cohen
reports “I don't have the ROM. I have the 4 volume service manual. They use the term "lbf/in".” Loudon Seth says,
“The SIII ROM uses (incorrectly) the form lbf/in or lbf/ft throughout.”

STUDS: Jaguar studs sometimes have fine threads on both ends, and are therefore difficult to find locally. Most studs
in the US have coarse threads on one end and fine on the other. You can, of course, order studs from a Jag mail order
outfit -- sometimes they’re even reasonably priced. If you want to get on with the job and not wait on the mail,
however, you can find a very long stud or bolt at your local auto parts store on which the fine threaded end by itself is
longer than the entire Jaguar stud (many Jaguar studs are rather short). Simply cut the end off and dress up the threads.
Thread the sawn end into the part, leaving the factory-made threads for assembly.

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SPIRAL GROOVE WASHERS: The V12 engine is covered with an unusual type of 5/16” washer, C30075/2, that has
a spiral serration pattern on it and is slightly dished. This washer serves the purposes of both a flat washer and a lock
washer. While the serrations may help prevent nuts and bolts from unscrewing, the real locking feature is the dishing; it
makes the washer springy, keeping tension on the fastener.

David Johnson found an acceptable substitute for the spiral groove washers: “I found at Pep Boys an 8MM spring
washer. It's part number is 153-0800. They are in the racks of boxed hardware.” Note these washers don’t look much
like the spiral groove washers; they have no serrations and are sprung the other way -- they’re not dished, they’re wavy.
They are dirt cheap, though. If you find an auto parts store with a Dorman hardware case, Dorman sells essentially the
same type wavy 8mm washer as part number 436-008. They are also available at Lowe’s as Pik-A-Nut part number
792694. Nobody seems to sell wavy spring washers in SAE sizes, but 8mm will fit perfectly on 5/16” bolts.

The V12 also uses a few 1/4” spriral groove washers. A 6mm wavy spring washer (153-0600 at Pep Boys, 436-006 in
a Dorman case) will fit a 1/4” bolt perfectly and serve well.

Note that it is always recommended to use some sort of flat washer whenever a bolt head or nut tightens down onto
aluminum. If you find any places on your engine where a fastener is tightened onto aluminum without a flat washer, it
is recommended that you provide a flat washer.

Conversely, lock washers are only required in certain places. For example, the head studs require no locking feature
because the tension on the stud is carefully applied with a torque wrench and the designers have ensured that the
assembly will never allow the stud to become untensioned in operation. As a general rule, lock washers are required on
short bolts or studs but not required on longer ones because the longer fasteners provide enough stretch to absorb
vibrations and thermal transients without ever going completely slack.

PHILLIPS? THINK AGAIN!: Greg Meboe says, “All Phillips-looking screws on English cars are Pozidriv screws.
(The Japanese radios do use real Phillips screws.) The two standards are different, and once I bought a set of Pozidriv
screwdrivers I found life much easier. The practical difference is quite noticeable. The impressed angle, impression
depth and drive spline widths are different between a Pozidriv and Phillips head design. Using the correct Pozidriv
screwdrivers, I've even had consistent luck removing Pozidriv screws which appeared nearly rounded due to years of
Phillips-buggering by misinformed mechanics.

“A Pozidriv screwdriver will not fit in or drive a Phillips screw. The drive lugs are generally too wide.

“Snap-On, Mac and others sell Pozidriv screwdrivers, but most Americans don't know they exist (I didn't for many
years). I've found Pozidriv #2 bits for the cordless screwdriver at Home Depot for a few bucks. Most Pozidriv screws
on our cars are #2, while door striker mounts and seat mounts are #3.” The big flush-head screws at the back end of the
diagonal struts in the engine compartment are Pozidriv #4.

Peter Cohen adds, “From the look of several Pozidriv screws on my car (removed only by Jaguar dealer personnel,
while under warranty), the dealer tool is a chisel.”

You can learn all about Pozidriv at

http://www.phillips-screw.com/

.

Sometimes Phillips screwdriver bits are marked “No.2” or “P2” while Pozidrive bits are marked “PZ.2” (using size 2 as
the example). Other companies mark their Phillips as “#2” and their Pozidriv as “P2”. The marking on the packaging
can be similarly confusing; the popular idea is to indicate tip types with a little symbol within a circle, but some
companies show the Phillips with a + within a circle and the Pozidriv as an 8-point symbol within a circle while others
show the Phillips as the + within a circle and the Pozidriv as an × within a circle -- basically the same as the Phillips
symbol only rotated 45º. Forget about the markings and simply look for the telltale ridges down the center of each
flute, which may be difficult to make out through the bubble packaging.

Apparently, Phillips Screw has the name “Pozidriv” trademarked, so some other toolmakers make tools to fit Pozidriv
screws while carefully avoiding the illegal use of the name. Easypower Corporation of Chicago makes screwdriver bits
described as “Positive Drive Phillips”, and in fine print says “will fit Pozidriv screws”. Easypower also makes
screwdriver bits called “Octo Driv”, apparently their own trademark, but indiscernable from Pozidriv. All of
Easypower’s bits that fit Pozidriv screws are marked “EZP.1”, “EZP.2”, or “EZP.3”.