in a Book
H.E. VS. NON-H.E.: The H.E.
(High Efficiency) engine, with 11.5:1 compression (12.5:1
outside the US) and a swirl combustion head designed by
Porsche expert Michael May, was introduced in July 1981 and
indicated by the letters "H.E." on the back of the car in
place of the former "V12" emblem. In 1986, the H.E. emblem
was unceremoniously dropped and a V12 emblem was used once
again, but the car still has the H.E. engine.
If you have an engine laying around and need to know
which it is, the trick is to look at the spark plugs. The
plugs on the pre-H.E. are vertical, and relatively easy to
replace. The plugs on the H.E. tilt toward the center just
enough to make them a real pain to get a socket on. Also,
the pre-H.E. plugs use a normal 13/16" spark plug socket,
while the H.E. plugs have the smaller 5/8" or 16mm hex.
ENGINE NUMBERS: The
engine number is stamped on the top rear center of the block
just forward of the joint with the GM400 transmission
bellhousing, but it is typically hard to find because it is
covered with grime. Paul Hackbart sends this tip: "Take your
oil dipstick out and get on the passenger side of car. You
can stick it through near the oil pressure sender and
scratch away until you see it. Just make certain you clean
it off afterwards."
The XK's Unlimited catalog includes a guide of engine
numbers for the XK 6-cylinder and the V12. It provides the
following info on the V12:
E-type Series III
XJ12 Series I
XJ12 Series II
XJ12 Series II
XJ12 Series III
up to 1980
For more detail on XJ-S engines, Richard Mansell sends
this helpful data from "The XJ-S Collectors Guide":
Canister type oil filter introduced
Modified fuel pump
Stronger manual trans selector shafts
Modified air filter box to stop blowing
Ignition amplifier re-located
Twin V groove water pump pulley introduced
Digital P injection introduced
Sump plug relocated
Most changes after this are listed by VIN number but the
following are listed too:
Metric threaded cylinder heads
Piston spec modified
Inlet manifold modified to remove holes for cold
Modified drive plate
Spark plugs changed from B6EFS to BR7EFS
Sump oil baffle plate changed
Water pump bearing size increased
Full flow oil cooling replaces relief flow
GM400 revalved, modified sump pan
5.3 vs. 6.0 LITER: The
Jaguar V12, from its introduction in the E-type MkIII up to
1993, has been a 5.3 liter engine (326 c.i.), with a bore of
90 mm and a stroke of 70 mm.
Engines are often described by the relationship of bore
to stroke. When the bore equals the stroke, the engine is
described as "square". Early gasoline engines tended to have
long strokes and small bores, described as "under-square".
Racing engines have evolved to having the bore larger than
the stroke, or "over-square." The Jaguar V12 was designed to
reestablish Jaguar's eminence as a world-beater in the
racing community (and prior to the fuel crisis of the early
70's), hence the considerably over-square design. It was
quite successful in this regard, still winning LeMans races
in the late 80's.
The popularity of over-square engines in racing is
actually somewhat artificial. Most racing programs divide
competition into classes based on engine displacement. An
over-square design provides the most power for a given
displacement, since it permits higher RPM and provides room
for large valves. However, these priorities do not translate
well to street use. Over-square engines tend to be heavy for
their displacement; a larger displacement engine of
comparable size and weight can be constructed with a nearly
square configuration. The over-square layout also results in
larger surface areas in the combustion chamber, which absorb
combustion heat and reduce fuel efficiency. And while the
design provides excellent power at high RPM, it tends to
lack torque at lower RPM; since people like their engines to
be turning slowly when cruising on the freeway, an
over-square engine can seem anemic under these operating
Ford suspended production of the V12 for 1993, and
reintroduced it in 1994 as a 6.0 liter (366 c.i.). More than
merely an engine enlargement, the change made the V12 much
less over-square, since the change was entirely an increase
in stroke; the new engine has a 90 mm bore and a 78.5 mm
stroke. This would tend to make the engine much more
suitable for street use. It remains more over-square than
most engines, and hence can provide excellent performance at
high RPM, but is more tolerant of stop-and-go driving
conditions and tall final drive ratios. The Michael
May-designed H.E. combustion chambers remain in use in the
larger engine, while the compression ratio has been reduced
Tom Walkinshaw Racing (TWR) was offering 6.0 litre
engines much earlier. According to Richard Mansell, "TWR
started making ësporty' XJ-S's in 1984. One of the
options then was a 6.0 litre engine." John Goodman reports
that TWR also made 6.2 and 6.4 litre versions, and maybe
even a 6.7.
Later on the JaguarSport XJR-S also had a 6.0. Mansell:
"When JaguarSport officially started producing the XJR-S in
1988 only a 5.3 litre engine was available. It was not until
mid-89 that the 6.0 litre was introduced as standard. This
was then discontinued in 1993 as by then the standard XJ-S
now had a 6.0 litre engine."
Note, however, that the 1993-on updated engine has a lot
of other features these earlier engines lacked, such as a
revised bolt pattern for connecting the GM400
WHAT'S IN A
REDLINE?: Some people, probably
accustomed to American pushrod V8's, feel that the 6500 RPM
redline marked on the tach is really aggessive and far too
high for an engine this big for everyday use. Nothing could
be farther from the truth; this is not an American
pushrod V8, it's an OHC V12 with an unusually short stroke.
Roger Bywater, who worked in the engine development
department at Jaguar when this engine was designed, provides
a more realistic understanding of just what that 6500 RPM
redline is all about: "6500 r.p.m. is certainly safe and
7000 would not be a cause for concern. In fact I know of
basically standard 5.3 V12s cobbled together with second
hand bits being taken to near 8000 in race cars without
suffering any problems at all. On the other hand an elderly
engine does deserve a certain amount of respect. I expect
the one thing that would result is that the timing chain and
tensioner would start to show signs of distress a bit sooner
if subjected to continual high r.p.m. In reality, there is
not much point in revving a standard V12 beyond 6000 because
it will be running out of breath anyway and therefore won't
be making much power.
"The real problem taking these engines to 6000 and above
is that the GM 400 torque converter distorts under
centrifugal loads so that the blading can make contact
creating fine metallic particles which then cause
accelerated wear of the transmission. A way around this is
to use a furnace braized converter which is more rigid and
able to tolerate the higher r.p.m. without distorting so
END OF AN ERA: The final Jaguar
V12 engine was built April 17, 1997.
HOT SHUTDOWNS: It is never
a good idea to shut down an engine immediately after running
it hard; it is always better to run it at reduced power for
a few minutes first to let it "cool down". This has nothing
to do with the temperature reading of the coolant; the
problem lies with parts within the engine that get much
hotter at full load than at low load, and can be subjected
to high thermal stresses if the transition from high load to
off is too sudden.
This problem is especially serious in the case of the
Jaguar XJ-S. Several problems the car seems to have,
including vapor locks, distributor seizings, and ignition
amplifier failures, may be exacerbated by hot shutdowns. The
underhood temperatures may skyrocket after a hot shutdown,
and Jaguar is known to have had underhood temperature
problems during development of this car.
Whenever you are driving the car hard, always drive the
car leisurely for a few minutes before shutting it off. If
you are forced to shut the engine off after running hard --
having a mechanical problem, for example -- at least open
the bonnet to allow the heat to rise out of the engine
compartment, providing some convective cooling.
Tips on improving post-shutdown
cooling are in the section on Cooling System
Regardless of what you call that sound, it ain't good for an
engine. A brief description of what's going on: When an
engine is running properly, the fuel/air mixture within the
cylinder is ignited by the spark plug and the flame front
grows continuously and spreads throughout the combustion
chamber until the entire charge has been burned. However,
while this is going on, the piston is moving upwards towards
the head, compressing the charge and thereby heating it. In
the most severe cases of knocking, the compression causes
the charge to self-ignite before the spark plug even fires.
The result is that the entire charge ignites at once, rather
than the gradual ignition of the flame front moving through
the charge. This "explosion" has been likened to hitting the
piston with a hammer. It can damage the piston, connecting
rods, and the bearings in both ends of the con rod.
What usually happens is less severe, however. The spark
plug fires well before the piston reaches the top of its
stroke, so the flame front has begun its travel while the
compression is still in progress. Since the burning charge
is expanding, it is compressing the unburned charge into the
far corners of the combustion chamber. The combined effects
of the piston rising and the flame-induced pressure causes
the remaining portions of the charge to self-ignite. The
actual amount of charge exploded in this fashion can vary
anywhere from a tiny portion to the entire charge, so
knocking can be either severe or barely detectable.
There are many factors that contribute to knocking. The
most notorious is compression ratio; the higher the
compression ratio, the more likely it is for the charge to
be detonated. Another key issue is the octane of the fuel,
which is a measure of how hot it must be before it
self-ignites; the higher the octane, the hotter the mixture
must get before it will burn. And the timing is critical,
since lighting the mixture too early will cause too much of
the charge to be burned before the piston gets to TDC and
the high pressures will cause detonation.
Other factors include the intake air temperature, the
fuel temperature, and cylinder wall and head temperatures.
EGR, which puts some inert gases into the mixture, makes it
harder to ignite and therefore reduces the tendency to
knock. Also, there are some minor details that can
complicate the issue; sharp edges in the combustion chamber
can act as "glow plugs" and ignite the charge prematurely.
Carbon deposits can increase the compression ratio, as well
as provide glowing embers to preignite the charge.
Knocking can be difficult to detect on the Jaguar V12.
All those little cylinders mean that each knock is small,
and all that sound deadening built into the car keeps the
driver from hearing much of anything in the engine
compartment. Basically, if you can hear it at all, you might
need to be concerned. On the other hand, Mike Wilson
reports: "I asked the local Jaguar rep and he had the
audacity to say that "All Marelli cars ping". He said it was
even in the owners manual! So, I came home and read mine and
sure enough, there it was in black and white! It said that a
small amount of pinging was normal and if it happens on flat
roads under no load, to see your dealer for further
If something needs to be done about pinging, the usual
reactions include changing to better octane fuel or
retarding the timing. On the later XJ-S with Marelli
ignition, you can't adjust the timing by just rotating the
distributor, so a jumper was provided that can be pulled to
put the system onto a more retarded map when needed. Even if
we try to buy good fuel, occasionally we always seem to get
a tankful of real crap, and this jumper is a handy fix to
get us to the next fillup.
Joe Ziehl shares some experience: "My mechanic told me to
first try a higher octane fuel because while retarding the
timing may help, the preignition might be caused by
something other than sparkplugs, such as carbon in cylinders
or on pistons. He also recommended that I treat the gasoline
and run the car hard for a few days. This made a significant
improvement in the pinging."
Jeff Elmore reports: "I had been getting some slight
pinging under medium acceleration after the car had warmed
up. I had tried many things, including checking the timing,
high octane gas, etc. Then I tried the temperature at the
thermostats. It was 213†F on one side and 203†F on the
other. I just changed the thermostats and topped off the
coolant (almost half a gallon low), and the pinging is gone.
The car now runs better as a result, with my guess being
that a lower CWT sensor means more fuel and power."
UNLEADED FUEL: XJ-S owners in
the US have been using unleaded fuel for decades, but many
owners in other countries are only recently facing the
prospect of leaded fuel being no longer available. Since
some of their owner's manuals specify the use of "Four Star"
leaded fuel only, they are understandably concerned.
Addressing this concern, Roger Bywater of AJ6 Engineering
(and formerly with Jaguar Engine Development) wrote an
excellent article for Jaguar World magazine, Vol 10 No 3,
January/February 1998, page 42. Some of the high points are
There are two reasons for concern regarding the use of
unleaded fuel: octane and valve seat lubrication. Valve seat
lubrication is simply not an issue in the Jaguar XJ-S: every
engine the car has ever been built with has an aluminum head
with hardened valve seat inserts, and the part numbers for
these parts are the same for US-spec models always intended
to run on unleaded fuel. If you have shoehorned in a Chevy
engine old enough to have a cast iron head with no inserts
and designed to require leaded fuel, well, shame on you.
Octane is another story. The US-spec engines have lower
compression ratios to run on lower octane fuel. To be able
to run the high compression engines on lower octane fuel,
either the compression ratio will need to be lowered or the
timing will need to be retarded. If the engine is being
rebuilt anyway, lowering the compression ratio (different
pistons, thicker head gaskets, machining the combustion
chamber, whatever) may be workable, but most people will
prefer to simply retard the timing. Bywater suggests that
there's very little difference between a high compression
engine with retarded timing and a low compression engine
with advanced timing anyway.
With the Lucas ignition systems, retarding the timing is
simply a matter of turning the distributor to a new setting.
Bywater says that for the 95 octane unleaded that will be
available in the UK and Europe, about three degrees should
do it, although as many as five may be necessary for older
cars with a lot of carbon buildup. On Marelli ignition cars,
retarding the timing only requires pulling a jumper to
switch the ignition ECU to a more retarded timing map.
If you own an early (ë83-87) AJ6-engined car with
the Lucas 8CU EFI, you can retard your timing by simply
turning the distributor. However, if you have a later
(ë87-on) 3.6 with the 9CU engine control system, the
ignition timing is controlled electronically and not so easy
to change. According to Bywater's article, there are two
options: you can remount the crankshaft position sensor
using the mount from the later 4.0 AJ6 engine, or you can
remove the crank pulley and reposition the toothed rotor by
drilling new mounting holes.
MISFIRE: With 12 cylinders,
some people might not even detect a misfire. An easy way to
check -- as well as to tell which bank is acting up -- is to
fold a dollar bill in half and hold it over an exhaust pipe
outlet and listen to the flapping that results; a misfire is
usually obvious. Steven Draper adds, "According to the most
recent Jaguar Repair Information Periodical, the official
procedure is to use a one hundred dollar bill and send it to
the dealer for evaluation. Unfortunately, the bill cannot be
LEAKY GASKETS: One of the
improvements Ford made to the Jaguar product line after they
purchased the company was that they "Fordified" the gaskets
and seals for the V12. While all of the old style gaskets
look like plain paper of various thicknesses, the new
gaskets are often "Gortex" sandwiched around metal or some
Redesigned gaskets, along with the new part numbers:
Oil Filter Housing
Oil Pan Gasket
Cam Cover Gasket, Right C29428
Cam Cover Gasket, Left C29429
Thermostat Housing, Right EAC7048
Thermostat Housing, Left EAC7047
Sandwich Plate Gasket
Coolant Manifold Gaskets
Exhaust Manifold Gaskets C33921
Throttle Body Gaskets
In addition, the 12 individual intake manifold gaskets
C43354 or AJM687 were replaced with two gaskets; each serves
all six ports on one bank. The part number is NNA-3020BA.
The original gaskets were either a very hard thick cardboard
or an embossed metal piece, and the new gaskets are a really
thick, soft cardboard.
The original exhaust manifold gaskets are sort of a
metal/asbestos/metal sandwich with dimpled surfaces, and the
new ones are the same stuff except that they have added a
collar around the center opening.
The original valley cover gasket was a piece of thin
paper, and the new one is a piece of thin Gortex -- black on
one side, red on the other, but it doesn't seem to matter
which way you install it; it's really flexible, it even
comes all crumpled up in a bag.
I would like someone to tell me what's updated about the
thermostat housing gaskets; they look like normal paper
gaskets to me. They are black paper and kinda thin, while
the older style is thicker red paper. The only other
difference I can see is that the outside edge of the newer
3-bolt cover gasket lacks the bulge at one corner, so it can
fit on in any of three positions.
The original coolant manifold gaskets were apparently
very thin paper and later versions were really thick paper;
the EBC 9634 gaskets are Gortex/metal sandwiches, and are
pretty thin. There are 12 used on the engine, although
because some are used under the coolant headers and others
are used under blank-off plates they may be listed in
catalogs as 8 needed in one place and 4 in another. Note
that the steel blank-off plates tend to distort with stress
and time, especially if they've been holding down the thick
paper gaskets; prior to reinstalling, it'd be a good idea to
run a flat file across the bottom to make the surface flat
The same gasket is used on both sides of the throttle
body, between the air filter housing and the throttle body
and between the throttle body and the intake manifold, so
you need a total of four. The EBC 9635 gasket is a
Gortex/metal sandwich and has 7 bolt holes in it; four in a
rectangular pattern, two more at 10 and 4 o'clock for the
hidden bolts that hold the throttle body to the intake
manifold, and a single loop that can either point straight
up or straight down depending on which way you flip it. This
last feature serves no purpose on the '83, and can either be
cut off or left in place to hang out the edge of the
Most of the new gaskets are only moderately expensive,
but the cam cover gaskets are obscenely expensive.
Apparently as a result, some of the mail order places
continue to stock the old paper versions.
The new gaskets should be widely available. Be sure to
check the part number or description of the gasket as some
parts people will try to give you the old style to get rid
of old stock.
Michael Neal, a Jaguar-certified mechanic who apparently
spends a lot of his time fixing oil leaks, provides a great
deal of input here:
Even using the new gaskets, Neal recommends the following
procedure for the cam covers: "After much trial and error
and the monitoring of some cars for several years I have
come up with some leak-proof techniques. Only use silicone
on the rear of the gaskets. Use Hylosil (British-made white
silicone) to seal the end. Use a lot. Coat the half moon
seal all the way around. Also coat the ends of the gaskets
on both sides and one inch toward the front. Assemble and
wipe off the excess silicone. Let it set up overnight! Over
time, the half moon seal shrinks and the silicone retains
the oil proof seal.
"Be sure to replace the intake manifold gaskets, even if
they look OK. These gaskets can flake away, especially on
reuse, and cause an intake leak that may be overlooked. This
is a sure way to drop a valve seat!
"The absolute best cam cover gaskets are available from
Worldpac, if you know a shop that buys from them, give them
a try! They are thicker than the oem stuff and don't stick
like the oem crap either."
Neal also reports that some of the aftermarket half moon
seals shrink a lot after only a matter of months and create
a leak, while the genuine Jaguar half moon seals don't
shrink enough to cause a leak if installed as described
When installing the intake manifold gaskets, Chad Bolles
suggests "Though you do not really have to seal the intake
gaskets, I do anyway. I use a non-hardening sealer that I
get from a GM dealer, part no. 1050026. I have spent almost
30 years racing automobiles and have found that this sealer
really does not get hard. On my race engine I have even used
the intake gaskets over again, cause they just peeled right
off with no tearing. I am sure somebody will say use
silicone, but I have found that removing it is a pain in the
Regarding sealants, Roger Homer says, "I use some stuff
from Caterpillar (The engine variety, not the garden
variety!). I'm not sure of it's official name/number but out
here I just go into the local Caterpillar dealer and ask for
a tin of Cat Red. This stuff isn't cheap, but it works well,
it will seal the gasket joints but not weld itself like glue
to either surface; if the gasket needs replacing later Cat
Red virtually peels off both surfaces."
CAM COVER BOLTS:
Regarding the cam cover gaskets, Michael Neal says "New
bolts are also necessary. They use an 8mm head with a built
in washer. Unfortunately these parts are only carried by the
dealer." Note: 8mm is essentially the same as 5/16", so this
isn't necessarily an example of metrification. The part
number for the new bolts is FS-106251/J.
The replacement of the bolts may not be as much due to
the excellence of the new bolts as to the lousiness of the
old bolts. The original bolts have a "triangulated" thread
that presumably helps it to drive into the aluminum housing,
but probably is also very effective at boogering the
aluminum threads up.
If you'd rather not pay Jaguar prices here and seek other
sources for bolts, note that 7/16" hex heads will not do,
you can't get a wrench on it; either 3/8" (or smaller) hex
head, socket head (allen wrench drive) or Torx drive bolts
will be necessary. And you might want to look at the access
before you select bolt head styles, since you may want to
retorque them a while after replacement. Of course, buying
el cheapo grade-zilch bolts (like most slotted head screws)
is not a good idea; not only will they rust pretty badly,
they may not hold enough tension to prevent the cam cover
gasket from leaking.
An alternative bolt that would work was found at a Home
Depot in their "specialty fasteners" rack. It is called a
"serrated flange bolt"; it has a 3/8" hex with a washer
face, and a row of serrations around the bottom of that
washer face. The biggest problem will be finding enough of
them to do the job; often such racks in hardware stores only
contain a half dozen or so.
Another alternative: this author bought a box of 1-1/4"
"alloy steel" 1/4"-20 "socket head cap screws" from a local
industrial fastener supplier -- less than $20 for a box of
100. These fasteners are jet black. Strength is not a
problem, alloy steel cap screws are stronger than
The original bolts were 1" long, so replacing them with
1-1/4" bolts provides enough length for some washers under
the heads (and perhaps for thicker gaskets, if you find
something non-OEM). There's no problem with bolts being too
long, since the end just comes out the back side of the
flange on the tappet block. With these socket head cap
screws, the author used split ring lock washers and
As noted in the section on General
Maintenance, flat washers are always recommended
when a bolt head or nut sits on aluminum. This author found
some very suitable flat washers on a bubble card in a
Wal-Mart: they are size 12, also known as 3/16". If you ask
for 1/4" flat washers, you get washers that fit so loosely
on the screw that it looks like a socket head might pull
through the hole! Also, the OD of the standard 1/4" washers
are bigger than the flat area on the cam covers, so you'd
have to cut them down to get them in. Conversely, these #12
washers fit perfectly on a 1/4" bolt and are the correct OD
for the cam cover flats. Make sure you find cheap #12
washers; better quality ones might have closer tolerances
and not fit a 1/4" bolt.
You can buy enough flat washers and lock washers to do
this job for less than two bucks total.
Another type washer that will work on the cam covers is
the 1/4" spiral groove washer used in a couple other places
on the V12 -- if you can find a supply of them. These
washers serve as both a flat washer and lock washer in one.
Also, the 6mm wavy spring washers mentioned in the section
on General Maintenance
as a substitute for the spiral groove washers will work
As always, be sure to use anti-seize compound on the
threads when assembling.
LEAKY OIL DRAIN PLUG: In
general, soft copper drain plug washers should not be
reused, as the copper gets hard and fails to seal. Fiber
washers seem to work fine as long as you don't use those
quick-oil-change shops, where the gorillas will tighten the
drain plug with a power tool and break the fiber washer.
Michael Neal suggests "The drain plug washer for the S3
XJ6 and XJ-S can be replaced with the transmission cooler
line banjo bolt seal from an XJ40, EBC4896. This is a
neoprene-lined washer that is reusable, life is about a year
LEAKY O-RINGS: The
O-rings available at your local parts store are probably as
good as the Jaguar originals -- which is to say, not worth a
damn. Whenever an O-ring is encountered during disassembly
of the V12, it invariably is hard and brittle and has long
since ceased sealing properly. It has been suggested that
Viton O-rings would serve better, although you will need to
visit a good industrial supply place to find them. They can
be ordered in various colors, but basic Viton O-rings are
black so they cannot be distinguished from regular O-rings
on sight. The price is a giveaway, though; they cost several
times as much. Andy Hutchinson reports: "Looked at my book
today. It would seem the choice of "elastomers" (posh for
rubber) is Nitrile, Flurocarbon or Flurosilicon. Viton is
Flurocarbon. Excellent hot and chem resistant. Not so good
cold. Flurosilicon is good at both ends but not very tough
(fixed surfaces only). Nirtrile is a good all rounder and I
suspect the standard material. Rubber, silicone, neoprene,
etc. are dogs." As long as you're not building Space Shuttle
solid rocket boosters, that lack of cold performance of
Viton may be acceptable; on the Jag V12, it'd be preferable
to leak only in freezing weather than to leak all the
BANJO FITTINGS: The copper
washers used to seal the banjo fittings at the back end of
the tappet blocks are really thin, only about .010" thick.
Each fitting requires two washers. If your local auto parts
store has a rack of red cards titled "Help!", it probably
has a package of sealing washers that are the correct
diameter for these fittings but a lot thicker: part
number 66272, labelled "Brake Hose Bolt Washer". It says
they are ID 25/64" and OD 5/8".
However, Craig Sawyers pointed out that the alignment of
the oil feed hole in the banjo bolt doesn't line up with the
feed channel in the fitting as well as might be hoped -- see
Figure 1. The fitting
is about 13/32" thick, with the feed channel right in the
middle, but the feed hole in the bolt is located only about
5/32" from the underside of the head -- and the thickness of
the sealing washer between the bolt head and the fitting
makes the alignment even worse (the drawing at left includes
a 1/16" thick copper washer, and the two passages barely
overlap). The fix is pretty easy, though. Using a Dremel or
some such, provide a chamfered edge on the oil feed hole in
the bolt in the direction of the threaded end only
(it's already chamfered a little, just enlarge it). This may
help the oil flow to the camshafts even if the original
thickness washers are used.
Now that you're practiced at this modification, do the
same thing to the
banjo bolt at the top right of the radiator.
When tightening banjo bolts, be sure to hold the fitting
still. Failure to do so will allow the turning of the bolt
to twist the fitting and bend the tubes.
PRESSURE SENDER CONNECTIONS: The
connection at the block at the rear center of the V is a
larger banjo bolt. For this fitting, Help! number 66265,
"Brake Hose Bolt Washers" are a perfect fit. They are
described on the package as ID = 33/64", OD = 45/64". These
same seals fit the bolts that hold the heat shields to the
The seal on the oil pressure sending unit itself is not
the same as the banjo fitting. The sending unit fitting is
the same diameter as many common oil drain plugs, though, so
it is easy to find a suitable seal in an auto parts store.
Note, however, that if you're buying a new sending unit, it
will usually come with a new sealing washer
LEAKY OIL PRESSURE
SENDER: When searching for sources of oil leaks, don't
overlook the oil pressure sending unit itself. The unit can
fail internally and oil comes seeping out of the electrical
connector, a sure sign of trouble since there isn't supposed
to be any oil within the electrical components in this unit.
The author's car had this problem, and the gauge was still
working just fine. Only solution is to replace it. C46272 is
the part number.
I'd like to be able to tell you what commonly available
sending unit can be used for a substitute, but I can't. The
Jaguar V12 uses a 100 psi oil pressure gauge while most
other cars (including Jaguar 6-cylinders) use an 80 psi
gauge. The threads on the bottom of the gauge are BSPP (see
the section on the radiator
drain plug), but of course you could buy a BSPP fitting
and plumb a line to a remotely-mounted sensor -- or just opt
to replace the entire pedestal. And we haven't even gotten
into the sender's electrical characteristics. Your best
option may be to shop around the mail order places for the
correct part, since prices on this item seem to vary widely
and it sometimes can be found quite reasonable.
LEAKY OIL PRESSURE
SWITCH: The oil pressure switch, which operates the
warning light, is right next to the oil pressure sender --
and is even more notorious for leaking oil out through the
electrical connection. The only solution is to replace it,
but that's not difficult because the thread is standard and
there are lots of cars that use very similar pressure
switches. David Johnson says, "I screwed one from a Chevy
in. The new one was a two wire type, so I simply connected
one side to ground and it works fine."
OIL LEAKS AT FILTER
HEAD ASSEMBLY: Peter Smith says "The oil would gather
around the top of the filter less than a minute after
starting the engine. I eventually took the head assembly off
and found a blanking bolt fitted to the rear which had a
failed fibre sealing washer. Replaced it with a copper
washer -- no more leaks. I had to take the head assembly off
to see the bolt but when you know it's there it may be
possible by feel."
OIL IN AIR INTAKES:
Robert Dingli explains the oil that always seems to collect
in the air filter housings and around the butterflies: "What
you are noticing is probably a mixture of a small amount of
engine oil that has been forced out as a vapour from the
crankcase by blowby gas which has then condensed within the
inlet manifold. You may also get some residual fuel (usually
the heavier fractions) leaving an oily film. This is normal
even for new engines but will tend to get worse as the
"On engines which have the inlet manifold sloping down
from the head, there is usually quite a puddle sitting in
the plenum. The first time I noticed this was when one of
the vacuum lines became blocked. It turned out to be the
line which connects to the underside of the plenum. I have
since re-routed that line and plugged the connection.
Whenever I remove the plug, a thick deep red oily mess
dribbles out. The red colour is obviously the remnants of
petrol (leaded petrol in Australia is coloured red) which
has run down into the plenum after the engine has been
stopped. The lighter fractions tend to evaporate when the
engine is next heated.
"Very occasionally, I have been known to pour a small
amount of petrol into the plenum to dissolve the goo and
then drain from the lowest point."
REMOVAL: The crankcase bottom is actually two pieces, a
pan and a sandwich plate. The pan, which exists only at the
rear of the engine, comes off easily enough. However, any
hope that this will get you anywhere is quickly shattered.
The crankcase is fully baffled (necessary to prevent
foaming, reduce heat buildup and power loss, and insure
proper oil flow to the pickup in a high RPM engine), and
there is one baffle the length of the engine that cannot be
removed without removing the sandwich plate.
Contrary to the manual, the sandwich plate can be removed
without pulling either the front suspension assembly or the
engine out of the car. It's a real pain, though, so you
might still consider one of those options. To remove the
1. Unbolt the steering rack without
disconnecting hoses, steering column or tie rods. Lower
the rack a few inches and let it hang there.
2. Remove the fan to allow the engine to be raised
without hitting the shroud.
3. Remove the nuts from the two main engine mounts,
and use a hoist to lift the front of the engine as far as
With all this done, the sandwich plate will just barely
come out rearward. Putting it back in, with new gasket in
place, will also be a lot of laughs.
While you're in there, replace all the O-rings you can
find, such as those in each end of each oil tube. If they
leak, they just leak into the crankcase, but each leak
reduces oil flow to the engine.
First, a brief description of how to properly perform a
compression check on any car: The battery and starter must
be in good condition. All of the spark plugs should
be removed. Power to the ignition system should be
disconnected, since an electronic ignition system may be
damaged trying to fire with the spark plugs disconnected.
And the throttle should be held at least part way open,
usually by jamming something in the linkage. On a car with
EFI, it would also be helpful to disconnect the power to the
EFI system or fuel pump to prevent fuel flow. With a
compression gauge fitted to one spark plug hole, the engine
should be turned on the starter through several compression
strokes, until the reading stabilizes at a peak value.
On the XJ-S, it would be most helpful to have the type of
compression gauge that screws into the spark plug hole and
has a lengthy hose. Trying to hold the press-in-place type
on this engine is not easy. Also, since the A/C compressor
usually has to be removed to get at the front plugs, you
will probably have to run the test with a dangling drive
belt; try to position it so there is no tension on it, and
the crank pulley can turn within it without driving it.
On the US-spec pre-H.E. engine, the readings typically
will be about 130-150 psi. The US-spec 5.3 liter H.E. engine
has 11.5:1 compression, and will read about 200-220 psi.
Note that readings will be lower at high elevations.
Keep in mind, however, that the absolute values are not
as important as the relationship between them. There are
dozens of factors that could affect the absolute values
(including the calibration of your gauge), so if your
readings are all a little higher or lower than the above,
don't worry about it. But they should all be nearly the
same; one significantly lower than the others is not a good
If one cylinder reads low, it is customary to add a
couple tablespoons of motor oil into that spark plug hole
and test it again. In theory, the oil will temporarily seal
bad piston rings but won't seal a burned valve, so this test
may indicate the level of disassembly needed. Of course, the
oil probably won't seal a burned piston or a hole in a
cylinder liner, so the results are best taken with a grain
of salt. Either way, the head has to come off.
LEAKDOWN TEST: The leakdown
test is gaining in popularity among mechanics, who feel that
it gives a better indication of the actual quality of the
sealing of the compression chamber than the compression
check. To perform a leakdown test, compressed air at a known
pressure (usually 100 psig) is fed through device with an
orifice in it and into a cylinder via the spark plug hole.
The pressure downstream of the orifice is measured, and the
leakdown rate is calculated as the percent which the
pressure dropped across the orifice. If the leakage out of
the cylinder is very low, the pressure after the orifice
will be very close to the pressure before the orifice, and
the percent of pressure lost will be low. If the compression
chamber has big gaping openings in it, the main restriction
in the flow will be the orifice itself, and the pressure
after the orifice will be closer to ambient -- and therefore
the percentage lost will be much higher.
Note that, when doing such a test on the Jaguar V12, it'd
be a good idea to take the oil filler cap off the left cam
cover. We wouldn't want a well-sealed crankcase (hah!) to
cause unwarranted favorable readings. Also, just in case
there's a leak in a head gasket, the radiator cap should be
removed to prevent pressure buildup in the cooling
Kyle Chatman points out that if the leakdown test finds
excessive leakage in a cylinder, it might be possible
to determine whether the leakage is from the rings, the
exhaust valve, or the intake valve by listening closely at
the oil filler cap, the air intakes, or the exhaust pipe
outlets. And a bad head gasket might cause bubbles in the
coolant (especially if it's the center cap that was removed)
or other motion in the coolant level.
It's entirely possible that the leakdown test is highly
regarded simply because it gives results in percent. It
should be pointed out, however, that the percent has no real
basis and is entirely dependent upon the size of the orifice
in the test device -- and Randy Wilson says "and there is no
such thing as a standard orifice size." In order to be able
to compare the results of one leakdown test against another,
it would be necessary to confirm that the orifices used were
the same size and had exactly the same flow characteristics
and that the same air pressure was used for the tests.
Wilson adds: "Next question is: how much air leakage is
acceptable? This all depends on how big the cylinder is. The
bigger the bore, the more ring area there is to leak by.
Typically, the valves are bigger, too. Here we could really
use a percent of leakage vs. base volume, but our tester is
effectively measuring finite volume of flow."
There are other concerns involving leakdown tests. For
one thing, since the engine does not turn during the test,
it really only gives an indication of the leakage at one
piston position. While this is usually adequate, it may fail
to identify certain types of problems such as localized
damage on a cylinder wall. Perhaps the careful mechanic
could slowly turn the engine over by hand while doing the
leakdown test, and watch the gauge for variance in the
The leakdown test does have the advantage, however, that
if a mechanic is using the same leakdown tester at the same
pressure all the time, he can get a real good idea of
just what condition cars are in. While compression readings
will always vary from car to car, the percentage readings
from his trusty leakdown tester should give very consistent
indications on cars in similar condition regardless of
compression ratio or other variables.
HEAD GASKET CHECK: Michael
Neal suggests two methods of checking the integrity of the
head gaskets. First, remove the rubber hood that connects
the PCV system to the engine just forward of the oil filler
cap, and look inside it. Milky deposits are an indication
that water is getting into the oil, usually a sign of
For a more definite check, Neal recommends removing the
spark plugs, pressurizing the cooling system to 15 psi, and
leaving it overnight. Then have someone turn the starter
while watching the spark plug holes. Mist (or worse, a solid
stream of water) coming out of a plug hole means it's time
for engine work.
Of course, pressurizing the cooling system usually calls
for a special tool. It basically is an adapter radiator cap
and a hand pressure pump; Stant is the common manufacturer
and it runs $60 to $70. In a pinch you could tee into the
small hose on the center fill pipe and apply pressure.
COVER WORK: If you
need to get down to the cam covers or beyond, Victor Naumann
sends this awesome tip: Remove the PCV crossover manifold,
fuel rail and injectors, air injection manifolds, both fuel
pressure regulators, the ignition amplifier, the intake
manifold crossover pipe, both butterfly housings, and both
intake manifolds as one piece. Be sure to disconnect
the butterfly return springs before lifting.
OFF?: If you remove the cam covers off for any reason
that is not intended to include further disassembly of the
engine, it cannot be reiterated too many times that every
bolt, nut, tool, or whatever that is in this vicinity should
have a string tied to it with the other end tied to your
finger. If a metal part falls down into the timing cover
while you're fiddling around, see the section on timing
cover removal. Peter Smith suggests "I shove a big rag
down the timing cover on each side to catch the bolts if
they fall. I find this to be a nerve racking part of the job
-- if the damned things fall in it can really test your
sense of humour!"
The repair manuals provide complete instructions for
timing chain disengagement and camshaft removal, except they
neglect to remind you that you might want to measure the
valve clearances before disconnecting the timing
chain and removing the cams. The assembly must be together
to make the measurements, so measuring before disassembly
will save you having to slap it back together to measure it
later. Of course, if you plan on reseating valves and the
like, the measurements won't do you any good anyway.
MANIFOLD CROSSOVER PIPE
HOSES: On the author's '83, the intake manifold
crossover pipe is connected to the manifolds with a short,
straight piece of 1" hose at each side. However, sometime
before '89, the assembly was changed so that pieces of hose
with 45† bends are required. If you have the earlier
straight hoses and need to replace them, it's obviously
pretty easy to find pieces of 1" hose. As for the later
parts, Jeff Elmore says, "The dealer quoted me $22 apiece
for these three inch long, 7/8-1" diam hoses with a 45
degree bend in it. Bennett Auto Supply had a Goodyear
coolant bypass hose that fit perfectly for $2.62 apiece.
Part number #gyy 63064."
Whatever you fit, note that the vacuum inside these parts
is considerable, and long unsupported sections of rubber
hose will be sucked flat. With the earlier design with
straight hoses, it appears to be sufficient to merely be
sure to insert the hoses far enough onto the fittings that
there is only a short area of hose that doesn't have
fittings within it. If you must have longer sections, you
may need to insert a piece of wire coiled like a spring to
hold the hose round, or perhaps just a short section of
CRANKSHAFT PULLEY REMOVAL:
First note that, contrary to the repair manuals, it is
not necessary to remove the crank pulley to get the
water pump off.
To loosen and retighten the large bolt holding the
crankshaft pulley on, it is necessary to hold the crank
still. Here we have a veritable cornucopia of suggestions.
You can remove the starter to jam the flywheel, but that is
definitely the hard way. An easier way would be to use the
access hole on the left side of the engine, the one with a
rubber plug and intended to provide access to the torque
convertor mounting bolts. Michael Neal provides an even
simpler access: just remove the cover from the bottom of the
torque convertor housing.
Matthias Fouquet-Lapar suggests "You don't need to jam
the flywheel. Once you have removed the upper part of the
pulley (the one which drives 3 belts), you can easily use
its 2 screws to attach a home-made bar on the damper."
Mike Cogswell suggests "you can weld a short length of
rod to the end of an old spark plug. Use it to replace a
plug, hand rotate the engine (breaker bar on that bolt
you're trying to remove) until the piston is up against the
rod. Now it's locked for sure. Just make sure you disable
the starter and hang a red tag so it can't get turned over
with the rod in it. You do need to be very careful
about valves. Obviously if the rod interferes with the
valves you could easily damage a valve and create a lot of
work for yourself." Some suggest this method risks damaging
the piston, plug threads or other engine parts if the torque
necessary to remove that bolt is too high; to minimize this
concern, the device should be long enough to obstruct the
piston a good ways below TDC, since near TDC the leverage is
not favorable for this job. This method does have the
advantage that the same tool may be usable for calibrating
the timing marks on the bottom of the engine -- see the
section on ignition
Jeffrey Gram (who doesn't care for the above suggestion)
writes: "To fill a cylinder with concrete works well also,
but oil is better..."
Ryan Border says "I always thought the trick for this was
to fill the cylinder with nylon rope through the spark-plug
hole. Soft enough not to damage anything, but "rigid" enough
(when it's all bunched up by the piston) to work some
serious force against." Note: make real sure you're
on the compression or power stroke and not on an intake or
exhaust stroke -- having open valves can bend them.
Shane Mantoszko says "use a good long handled
socket/torsion wrench, put it on the front crank nut, brace
it on a strong part of the engine bay, disconnect the coil,
and then turn your ignition key for a few quick bursts, and
viola, the crank nut will be loose...hard part is then
re-tightening it, but a ratchet gun worked for me."
Dale Knaus says, "To remove the nut on the end of the
crank I used what we call a "slug wrench". It is a box end
wrench made extra heavy with a striking pad on the other
end. It is made to hit with a hammer to tighten and remove
nuts. By paying careful attention to how much impact it took
to break loose the nut, I had some idea how hard to hit it
to tighten the nut back at reassembly. I would have much
preferred to use a torque wrench, but couldn't figure out
how to keep the motor from turning over. I tried not to
overtighten the nut, didn't want to strip it. Used
lock-tight on it to help keep it on there if it isn't
torqued enough. If I ever need to put in a front seal, I'll
use the slug wrench again. I borrowed the tool from the
industrial plant where I work, they are probably available
from industrial tool supply companies."
Of course, on my car I can just put it in 5th gear
with the emergency brake on!
PULLEY -- WOODRUFF KEY PROBLEMS: Paul
Konitshek and Michael Neal report that the woodruff keys
that aligns the crankshaft damper/pulley are a known problem
area. The keys may become worn or totally sheared, allowing
the pulley to reposition itself around the crank. This
becomes only too apparent when trying to set the ignition
timing according to the marks on the pulley.
Note that there are two keys used. There is a "split
cone" that is similar to those used on industrial pulleys.
The pulley fits onto the outside tapered surface of the cone
and is aligned with one key. The cone slides over the crank
and is aligned with another key. When the bolt securing the
pulley is tightened to specification, the split cone
compresses securely onto the crank like a collet in a
Neal reports: "The woodruff keys on the crank pulley do
have a bad history. It almost never gets to the point where
the pulley comes loose. It seems only to happen if water has
gotten into the nosecone on the crank. The area is always
very rusty when the front pulley is removed. The woodruff
key is either broken or eroded away from the rust. In some
cases the slot in the crank is widened a bit but a new key
usually secures it substantially. By the way, I have never
seen the rubber dampeners on the pulley on either the XJ-S
or the XJ6 fail."
The other problem is a key that won't come out, notably
on the key on the crank itself. Suggestions include using a
pair of angle cutters to grab it and walk it upwards, and
using a suitable chisel to cut under the key to pry it out.
The suitable chisel needs to be a hair narrower than the
key, and can be made from old lathe bits or "cut nails". Cut
nails are made from flat stock, giving them a sort of
trapezoidal shape, and are really hard for pounding into
masonry. Greg Guillaume: "Here's what I did: get a 1"
chisel, lay it on the crank, perpendicular to the crank, up
against the key. Then whack away with a hammer on the
opposite side of the chisel. The shape of the chisel is just
right so it bites into the key, the 1" width hangs over the
end of the crank, and you get a lot of room to swing the
hammer. Of course, the chisel is a little beat up, but it
CRANKSHAFT PULLEY -- SPLIT CONE
PROBLEMS: Dan Jensen says, "The split cone was broken in
three places. Rather than pay $$ for a replacement, I just
stuck it back into the damper/pulley with Hylomar sealant
and gently replaced it. It centered properly and has worked
great for 35K miles."
FRONT OIL SEAL REPLACEMENT:
Peter Cohen points out that the Jaguar repair manual's
procedure for replacing the front oil seal involves removing
the radiator -- which, in turn, supposedly requires
depressurizing the A/C freon circuit. Boy, I hope you read
this first! Depressurizing the freon circuit is totally
unnecessary to get
the radiator out, and if you don't mind working in tight
quarters, taking the radiator out is unnecessary to change
the front oil seal. Matthias Fouquet-Lapar says, "I've done
this in my garage without pulling the radiator. Once all the
belt-driven hardware is removed, there is enough space. I
did not even take out the fan shroud." Brian Sherwood says,
"I replaced mine without pulling the radiator -- not very
convenient, but possible. The most difficult parts were: 1.
removing the old seal (finally had to prick a small hole in
it, and screwed in a sheet metal screw to pull on), and 2.
getting the pulley bolts thru the lock plate, pulley, and
into the crank damper -- can't see these at all, have to do
When you buy the front seal from Jaguar, you get the seal
and the spacer sleeve it rides on in one box; this may be a
recent development, apparently a new part number has been
issued. Matthias Fouquet-Lapar says, "The new part at least
includes the spacer. The part number is JLM 10613." However,
if you buy a generic seal somewhere else (or maybe older
stock from Jaguar), you'll probably get just the seal. You
can look at the condition of your sleeve and see if you
think this will cause a problem. Peter Smith says, "If the
spacer appears worn it can simply be reversed on refitting
because the seal does not ride at the half way point. The
new seal will then ride on an unworn part of the spacer."
Whatever, you will want to take the sleeve out, because the
proper order of assembly is to install the seal and
then install the sleeve.
You might also consider putting some sealant between the
crank and the spacer prior to installation to absolutely
prevent oil from travelling between the crank and the sleeve
and leaking out the splits in the split cone under the
pulley. There are no reports of leaks this way, but if it
did leak people would think it was the front seal, so who
knows? Maybe it's a common leak!
Cohen adds, "Oh, and by the way, although the old spacer
slid off, the new one had to be driven on. The dealer tells
me they are all like that, and that they loosen up after
time..." Who knows, maybe the new seal comes with a coating
on the inside to seal it, the sealant goes away with time,
and that's why Jaguars leak!
Also of note, illustrations in the repair manual indicate
that the sleeve has a keyway, but according to Alex Dorne
they lie; "The sleeve is not keyed."
TENSIONER ACCESS COVER: Before going any farther, please
read the warning about having the cam
covers off: the same warning applies here.
The access to the timing chain tensioner latch is via an
opening on the timing chain cover, forward of the right bank
and just above the support for the belt-driven fan. The
purpose of this access is for locking or releasing the
tensioner during overhauls; there is no need for periodic
adjustment, as the tensioner is self-adjusting.
The rubber plug always seems to get hard and crumbly.
People with the new one in hand sometimes assume there has
been a material change, since the new one is soft and
pliable while the old one appears to be Bakelite. Looking at
the ears on the new one can also lead one to believe that
it's a push-and-turn type of cover, like a radiator cap. No
such luck; it's a simple round hole, and the ears are
supposed to be flexed to get it in and out. The old one will
probably have to be removed in pieces. If a piece or two
fall down inside, don't worry about it, they're too soft to
do any serious damage. They'll probably just come out in the
next oil change; it's definitely not worth further
Note that this is an opening into the crankcase and
should be fairly well sealed to prevent oil vapor leakage
and keep the PCV system working properly; Chad Bolles
suggests "...apply a thin coat of GM Gasket Sealing Compound
part no. 1050026 (stuff never gets hard) and press in the
new plug and you are good to go."
Jim Isbell didn't like how much grief was required
getting the plug out after it had dried up, and determined
it wouldn't happen again. "I have cut the tabs off of the
rubber plug that fills the adjustment hole for the chain
tensioner. I have made a simple aluminum "L" shaped piece
that fits under a water pump bolt and holds the plug so it
wont fall out."
If desired, the opening may be plugged with a
compressible rubber type freeze plug. This may even be
preferable to the original plug, since it will make an
airtight seal. Be sure that the plug does not interfere with
the timing chain or the operation of the tensioner.
If you have access to a lathe, it shouldn't be too
difficult to make an aluminum plug for this hole with
provision for fitting an O-ring for sealing.
TIMING CHAIN TENSIONER:
There are few design features of the Jaguar V12 as poorly
conceived as the material the arch of the timing chain
tensioner is made of. If you manage, on your first try, to
retract the tensioner and reengage it successfully without
breaking this arch, you should consider yourself lucky. The
arch apparently works well when new but gets brittle with
age or heat, and an old one can be broken very easily.
Michael Neal, who works on Jaguars every day, says "I've
become so paranoid of old tensioners, my failure rate has
been very high as of late. I'm not too surprised though,
most of the cars have been approaching ten years old. I've
been as careful as possible, knowing exactly what I was
doing, and have watched the damn thing crack on one of the
pivots." Obviously, if you have the timing cover off for
other reasons and the tensioner is intact but has a few
years on it, it may be advisable to replace it anyway.
Other engines have arched timing chain tensioners in
which the arch itself is made of spring steel. It would seem
a simple matter to design a replacement arch for the Jaguar
V12 tensioner made of spring steel, thereby eliminating the
fracture problems permanently; if noise or wear is a
concern, the spring steel arch could be faced with Teflon or
some such. However, despite more than two decades of trouble
with this piece of junk, apparently neither Jaguar nor any
aftermarket companies have opted to offer an improved
I will first attempt a description of the tensioner,
since it is well hidden and its configuration may not be
apparent until it is too late. Basically, the tensioner
consists of a plastic arch that the timing chain slides over
top of on its way from the crankshaft sprocket to the right
side cam sprocket. This is the slack side of the chain, so
it's the proper place to put the tensioner. Between the legs
of this arch is a spring that pulls the legs together,
making the arch steeper and taller and therefore taking up
slack in the chain. The end of the arch nearest the
crankshaft is located by a pin on the block, while the end
near the cam sprocket has a steel foot attached that is free
to slide up and down on the inside of the housing as the
arch changes shape.
Alongside the spring is a latching assembly that consists
of a rod that is attached near the pinned end of the arch
and passes through a hole in a rocking latch attached to the
steel foot on the other end of the arch. The aforementioned
spring is actually attached to this rocking latch, slightly
off center, so that it not only applies tension to the chain
but also causes the latch to rock in the CW direction (as
viewed from the front of the car facing rearward). This
assembly serves two purposes: First, the rod going through
the hole in the rocking latch makes a very effective one-way
lock; the rod can easily slide in the direction that allows
the tensioner to take up slack, but it cannot back up
and allow more slack. Second, when the mechanic has manually
retracted the tensioner, a step at the end of the rod
provides a catch for holding the tensioner in retracted mode
while working on the car.
When removing the camshafts or the heads, the tension on
the chain must be disengaged. However, the chain is not
removed; the sprockets are simply unbolted from the
camshafts and supported in place by special brackets
provided for the purpose. The heads are removed in this
state, leaving the chain and sprockets hanging there in
Before proceeding, please reread the warning on having
the cam covers off.
To retract the tensioner requires two tools, collectively
known as Jaguar tool JD.50. One tool is inserted from the
top of the engine where the cam cover has been removed,
underneath the cam sprocket, and hooks onto a hole in the
steel foot at the top end of the tensioner; this tool is for
pulling the tensioner back to the disengaged position, and
has a lever handle shaped to rest against the top of the
sprocket. The other tool is inserted through an access hole
in the front of the timing cover and is used to manipulate
the rocking latch. The rocking latch has a slot in it, 3/16"
wide by a little over 1/2" long and roughly parallel to the
chain line, for inserting this tool.
Improvising both tools is fairly easy. For the first
tool, a sturdy hook is required; a standard battery
hold-down bolt may be a good place to start, but you'll need
to trim the hook as shown in
2 in order for it to fit the hole in the tensioner
properly. Adding a lever that rests on top of the sprocket
isn't too hard, you can even make it out of wood; just drill
a 1/2" hole near the center of a 1" x 2" board about a foot
long, insert the battery hold-down bolt through it, and put
a fender washer and a wing nut on the end. The hole needs to
be about 1/2" to allow the battery hold-down bolt to tilt
relative to the board.
Alternatively, Thomas E. Alberts says "I tried the lever
style tool like the manuals show and didn't like it much. I
made one with a long 3/8" bolt (~12in) and a steel tube
(~1.5in dia). I formed a hook by grinding away most of the
bolt head, padded one end of the tube and put it against the
valve cover mating surface and with a washer and a nut on
the threaded end and the bolt running through the tube and
into the chain tensioner, I was able to gently apply the
required tension. It worked well."
For the rocking latch tool, it appears that a common
screwdriver may be used if you can get it in there. A better
idea may be a standard "brake tool", the lever used to turn
the star wheel on self-adjusting drum brakes. You might also
check to see what you have in tire irons, especially those
intended for bicycles. And of course, one of those
right-angle screwdrivers might work, especially if you can
find a large one. You should note, however, that while these
items may get the job done, none of them are likely to work
smoothly enough for you to get a good idea of what you are
doing to that tensioner by feel.
You can easily make a more suitable tool: Buy a piece of
strip steel 1/8" thick x 1/2" wide (commonly available at
hardware stores), and cut off a piece about 7" long. Then,
about 2" from one end, make a sharp bend of something less
than 90 degrees -- see Figure
2. Then cut away one side of the tool -- the side
that will be pointed toward the cam cover opening -- about
3/16" as shown. This is because as you retract the
tensioner, the latch moves upward with it and this side of
the tool will contact the edge of the access hole. This
contact confuses the "feel" and can leave you wondering if
the tensioner is fully retracted or not.
Of course, you could avoid having to cut away the side of
the lever by simply making it out of 3/8" wide strip steel
to begin with. However, this is not recommended. The portion
of the rocking latch above the slot is not very thick, so
having a lever a full 1/2" wide to insert in the slot
ensures that the tool contacts the rocking latch near the
ends of the slot. If a narrower tool is used, applying
torque to the lever can cause one edge of the tool to push
up on this thin portion of the rocking latch near the center
of the span rather than near the edge, greatly increasing
the chances of actually breaking the rocking latch. Breaking
this portion off doesn't really affect the normal operation
of the latch, but it will make it even harder to release,
and if that broken portion falls down into the crankcase
you're gonna be upset about it.
The other feature shown in Figure
2 is a small pin sticking 1/8" up from the surface
of the lever. The purpose of this little pin is to prevent
insertion of the tool farther than 1/4" into the rocking
latch, where it may get involved with other parts. A tiny
roll pin could be used here, or perhaps a small screw. You
can even omit this feature, if you are careful not to jam
that lever in farther than it needs to go.
The actual operation of disengaging the tensioner
requires using both tools simultaneously. To begin with, I
suggest using the latch tool by itself to try rocking the
latch CCW just to get the feel of it. It will not rock very
far, but it shouldn't take too much force to rock it, and
you should be able to feel the spring. Old tensioners always
seem to have bent or damaged rods or latches, and it's
difficult to imagine how the damage occurs other than people
applying great force to this rocking action. You
should also note that, if everything is working properly,
rocking this latch alone will have no discernible effect --
no clicks, pops, clangs, or anything else.
Don't bother testing the other tool by itself. Trust me,
you won't be able to move the tensioner toward the retracted
position without simultaneously rocking the latch CCW --
unless, of course, the tensioner is already broken.
Now, to actually retract the tensioner: First, rock the
latch CCW and hold it rocked; it doesn't need to be held
hard CCW, just so that it is prevented from returning to the
CW position. With the latch so held, pull up on the
retracting tool; you should feel it smoothly moving against
a fairly stiff spring tension. In order to lock the
tensioner in the retracted position, you will need to pull
as far as it will go. At this point, it should suddenly
become possible to rock the latch much farther in the CCW
direction. While holding the latch firmly in this full CCW
position, carefully release your pull; it should lock in
that position. Once it does, you can rest assured it won't
move by itself; you can go on and do other things.
When it comes time to reengage the tensioner, do not
simply trip the latch to restore the tension; the tensioner
will shatter like a dried twig, and you will need several
bottles of high-octane elixir to get over it (see the
section on timing cover removal, below). Use the special
tools to gradually release the tensioner into its normal
position. Pull on the tensioner while rocking the latch in
the CW direction, and gradually release the pull; it may
take a couple tries before the latch is successfully
released and the tensioner starts moving. Once it does, you
may quit fiddling with the rocker altogether, it'll take
care of itself, but continue to use the puller tool to
gradually allow the tensioner to assume its final
Now, on to a suggestion for disaster avoidance. Jaguar
designed the latch so that the tensioner must be retracted
as far as it can possibly go before it can be locked in the
disengaged position. This bends the plastic arch, normally
fairly curved, into a nearly straight shape -- and therefore
stresses it far beyond what it normally sees. For several
operations on the engine (such as camshaft removal), it
doesn't matter how much slack is available, only that the
tension is gone. If this is the case, retracting the
tensioner only part way would suffice -- if there was a way
to hold it there. If the right side tappet block is not to
be removed, this may in fact be fairly easy. Whatever
homemade tool is used to retract the tensioner can also be
fashioned to hold it retracted, possibly by providing a
small block of wood with a hole in it that sits over the
opening and using threaded rod to make the hook.
If the tappet block must be removed, obviously a little
more ingenuity would be required. At this point, your only
option may be to use the latching mechanism as intended and
hope for the best.
TIMING COVER REMOVAL: If
you want to remove the timing cover to replace the front oil
seal, don't waste your time. The front oil seal presses in
from the outside, and Jaguar even provided some prying slots
for removing the old one.
If you do need to remove the timing cover, Section
12.65.01 of the Jaguar "Repair Operation Manual" lists 13
steps, the first two of which are as follows:
1. Remove engine and gearbox assembly from the
2. Remove cylinder heads from the engine.
Fortunately, there is an alternate method. To remove the
timing cover with the engine still in the car and the heads
in place, proceed as follows:
1. Remove the belts, fan and its mounting
bracket, A/C compressor front bracket, and all the other
ancillary stuff in the way.
2. Remove the front crank pulley. NOTE: What looks
like a bolt head in the center of the crank pulley is
actually a hex fixture for turning the engine by hand.
Two smaller bolts must be removed to remove this hex, and
the real pulley retaining bolt is underneath.
3. There are three studs threaded into the timing
cover that protrude upward through the front edge of each
head. Remove the nuts and washers, then grab the studs
with a pair of Vice-Grip pliers and unscrew them. NOTE:
some of the studs are trapped and cannot be removed; once
these are unscrewed, merely retain them (with duct tape)
in a raised position while the cover is being removed.
Once the cover is off, they can be removed.
4. Remove the retaining bolts holding the timing cover
to the block.
5. The timing cover is essentially pinched between the
heads and the sandwich plate. Michael Neal, who is a
Jaguar mechanic and uses this method regularly, says "I
loosen as many of the sandwich plate bolts near the front
as possible. I believe it works out to about 4 or 5 back,
going between the subframe and the motor. I then use a
Snap-On medium sized ladyfoot prybar and go in the hole
where the oil cooler adapter bolts onto the sandwich
plate. I pry against the bottom of the tube that the
adapter goes into and the inside of the sandwich plate.
This pulls down the right front corner of the sandwich
plate and allows some space for the timing cover to move.
The prybar over-centers and locates itself while holding
the plate down. It is very important not to pull down too
far. The bolt holes are very prone to cracking and the
break will spread out toward the center of the sandwich
plate." See this section if you
wish to remove the sandwich plate entirely.
6. REASSEMBLY: Since your studs were all boogered up
by the Vice-Grips, buy new studs with the same threads
but longer. Saw or grind them off until they are 1/4"
longer then the originals. Then, grind flats on this 1/4"
to ease the reinstallation and any future disassembly. Be
sure to clean up the threads so the nuts go on easily.
Remember to slide the trapped studs in place before
installing the timing cover. Be sure to use anti-seize
compound on all studs.
7. Before reassembly, carefully trim the timing cover
gaskets flush with the upper corner of the timing
8. Since the head gaskets are not being replaced, it
is a good idea to apply some sealant to the bottom of
them to help them seal against the timing cover. The only
stress on this portion of the head gasket is a slight
crankcase vacuum; the integrity of the head/block seal is
unaffected. Make sure to apply sealant in the corner of
the two mating surfaces.
9. Neal provides this tip for getting the timing cover
back in between the heads and sandwich plate: "On
reassembly I use sheets of .003" shim stock on the upper
surface of the sandwich plate gasket and the underside of
the front of the head gaskets. You have to trim the stuff
to clear, but it prevents damage to the gaskets and lets
the timing cover slide back in easily. The head gaskets
are...very prone to wrinkling if you don't use the shim
stock pieces to slide the cover back in."
10. When threading the new timing cover-to-head studs
into place, remember there is no reason to tighten them
into the timing cover. As long as they have been threaded
in several turns, the nuts will torque properly.
Tightening the studs into the timing cover merely makes
them harder to remove next time.
11. During reassembly, progressively tighten the
timing cover bolts along with the nuts on the studs. The
cover must be brought up against the heads as it's being
pulled against the block. Tightening one set before the
others will cause leaks.
Note that if the engine is still in the car but the heads
are off for some other reason, the timing cover should be
removable without too much additional trouble, basically
following the rest of the steps in the repair manual and
skipping step 5 above. Hence, you might consider going ahead
with removing it, replacing the chain and tensioner,
checking out the oil pump, etc., depending on the age and
wear on the engine. You might also consider installing the
longer studs as described in step 6 above while you're
TIMING CHAIN DAMPENERS:
These are the steel plates mounted alongside the chain along
several of the straight sections between sprockets. The
repair manual suggests using quick-drying paint to mark
their locations before removal. Failing this, the use of an
elaborate (and undoubtedly expensive) special tool is
required to properly position them.
You already moved them? Sorry, at present I can offer no
help. I am including this section to describe what they are
and how they work.
A roller chain is a fairly decent and reliable drive
mechanism at low speed. However, 6500 RPM is another story;
at higher speeds, chains can whip, flutter, buzz, and
otherwise dance around their path around the sprockets. At
certain resonances, a chain whipping back and forth can
cause very high tension stresses, resulting in damage to the
chain, sprockets, camshaft bearings and tensioner.
These plates are designed to prevent this. If the chain
is moving smoothly and along a straight line like it should,
it shouldn't even touch the plates. But if it starts to
whip, it hits a plate -- which absorbs the energy of the
whip, and allows the chain to return to a calm motion.
Based on this theory, it would be logical to assume we
could just bolt the plates on so that they are immediately
adjacent to the chain without touching it. There are a
couple problems with this plan. First, if you follow the
official Jaguar assembly order, the plates must be installed
and the timing cover bolted up before the heads are
installed, so having the chain in place -- meaning the
tappet blocks, camshafts, and camshaft drive sprockets in
position -- is not possible. Of course, you could always
trial fit the heads, tappet blocks, camshafts, sprockets,
and timing chain in order to set the plate positions, then
tear it all apart again.
Elsewhere I describe how to remove
the timing cover with the heads on and therefore there
may be an opportunity to adjust the dampers with the chain
in place -- although it may be a rare case when the plates
need to be positioned but the heads don't need to
The second problem is that I'm really not providing
enough information for proper positioning. I'm only
providing the theory; presumably, during development of this
engine, the optimum positions of these plates were precisely
determined, and they may be far more critical than simply
"close to the chain without touching it." Improper
positioning of these damper plates could be catastrophic,
causing a broken timing chain which in turn causes pistons
to impact valves in open position. You see, the real purpose
of this section is not to save you effort; it's to
discourage you from assuming the position of these plates is
unimportant, skipping important steps, and causing yourself
a great deal of heartache down the road.
REPLACEMENT: The timing chain in the Jaguar V12 is a
conventional double-row roller chain. Typically, the wear on
chains of this type is much more significant than on the
sprockets, and usually the chain can be replaced without
replacing the sprockets. This is in sharp contrast to the
"silent" timing chains used in many American V-8's, where it
is customary to replace the timing chain and sprockets as a
Another characteristic of typical roller chains is that
wear on the sprockets increases with the use of worn chains;
if the chain is renewed regularly, the sprockets can last
almost indefinitely. The Jaguar timing chain is so cheap
that it is recommended that it be replaced whenever the
engine is disassembled far enough to do so. The sprockets
are so expensive that you will want to do whatever it takes
to keep from having to replace them.
In general, the sprockets don't need replacing unless an
inspection shows signs of serious wear -- one side of each
tooth looks different than the other side.
Per Jan Wikström, "According to a Reynolds chain
handbook that I mislaid some time back in the seventies, so
my memory may be slightly off here, the way to determine
whether a sprocket warrants replacement is to hang the new
chain over the sprocket and apply a strong pull (that's an
Imperial strong pull, not a US strong pull!) in the normal
drive direction. If more than three links ride up noticeably
on the teeth, the sprocket is too worn."
Supposedly, it may be possible to replace the chain
itself by removing only the right side cam cover and without
bothering the timing cover at all. Retract the tensioner,
then break the chain on the top of the cam sprocket and
connect the new chain to the end of the old one. Have
someone turn the crankshaft slowly while you feed the new
chain in and the old chain out, being sure to keep the cam
sprocket engaged at all times. When you reach the other end
of the old chain, disconnect it and connect the new chain
back to itself. You may wish to ask if the new chain has a
master link prior to buying it to make this job easier;
supposedly, some do and some don't.
REMOVAL: The V12 has a cute little bracket just forward
of the camshaft sprockets that holds the sprockets (and
timing chain) in place during removal of the heads or
camshafts. The sprocket hubs have little stubs to sit on
these brackets, and grooves for a clip to secure the
sprocket on the bracket.
The clip, also known as tool JD.40, can obviously be
improvised with sheet metal or even a normal 1/4" E-clip,
perhaps with a 5/16" flat washer behind it. Note: The size
of an E-clip is the size of the shaft it typically fits,
not the diameter at the bottom of the groove it fits
in. The diameter at the bottom of an E-clip groove on a 1/4"
shaft is about 3/16", so that's the ID of a 1/4" E-clip. The
stubs on the front of the cam sprockets at 5/16", but they
have exceptionally deep grooves and the OD at the bottom of
the groove is about 3/16", so 1/4" is the correct E-clip
CAMSHAFT TIMING: The
repair manual describes how to adjust the camshaft timing;
this is just some clarification. To adjust the camshaft
timing, obviously the chain can be moved over one tooth on
the sprocket -- an extremely coarse adjustment. The camshaft
sprockets have a splined inner hub that contains the four
mounting holes. A circlip can be removed, allowing the
separation of the inner hub from the sprocket, and the hub
can be moved over one spline -- a fairly fine adjustment.
However, the hub has an odd number of splines, so rotating
the hub 90ƒ, 180ƒ, or 270ƒ will effectively relocate the
four bolt holes in 1/4-spline increments -- an extremely
The engine is designed so that the crankshaft and the
camshaft can be located where desired, the timing chain put
in place and the tensioner activated, and then the mechanic
can fiddle around with the sprocket hubs until the bolt
holes line up. Jaguar provides an alignment notch on each
camshaft and a special tool for setting the camshaft
position. This special tool, C3993, costs under $20 and is
not easily improvised. It is recommended that anyone who has
an engine apart far enough to use one have it on hand.
If the engine in question has a few miles on it, it may
even be a good idea to go through the procedure of setting
the camshaft timing while there. Wear in the timing chain
will cause the camshaft timing to gradually move. What's
worse, the timing of the right camshaft will move more than
Maintenance is Continued...