of the Engine
The front of the engine: Here we are into the engine
itself, the timing chains. There are both an upper and a
lower timing chain. These items are so inexpensive that I
have a new set on the shelf ready to use if I ever need
them. This will probably protect me from ever having to
replace them. Murphy's law always says that the part you
don't have or can't get or is most expensive is the one that
will break. These are cheap and easy to get.
The first indication that you have a problem will be a
noise from the front of the engine. If the tensioner becomes
worn or becomes dysfunctional you will hear the chain
slapping around. If it gets loose enough the valve timing
will be affected such that the car does not run
The head: One of the weak points of the 6 cyl engine is
that the valve tappet followers will eventually loosen up so
that they do not stay seated in the head. It is an easy fix
and should be done before they start slipping around.
If the tappet follower comes loose there is a ticking
noise from under the cam covers. The sound can be likened to
the sound of a sewing machine. Oddly enough I have heard
people say, "Its so smooth, it sounds like a sewing
machine." In this case, that is not good. A loose follower
can cause all kinds of damage to the engine, mostly in the
Many XJ6s have had the stakedown kit installed already
and you can tell if yours has one by reaching your finger
deep into the oil filler hole on the cam cover and if it is
there you can feel it. I must admit I could not find it when
I felt, but a mechanic friend of mine felt and assured me it
was there. By the way, don't try this if the engine is
A stakedown kit will run about $300(US) installed at 1995
prices. It is a cheap piece of insurance. If it hasn't been
done, do it before you trash your engine!!!
While we are on the subject of the heads, there is alot
of work that can be done here to improve the performance of
the XJ6, especially the series 1 and series 2 versions. By
the time the series 3 came out the head had been very much
improved from the MK VII head from which it evolved.
I have heard it said that you can gain 50HP just on head
From Julio Loza I received the following advice on
removing the head when it is stuck.
"While rebuilding the cylinder head ( it was warped and
leaking water to the cylinders) I found the studs frozen in
place. No matter how hard I tried I could not pull the head
off with the studs on. I tried soaking them in various
solvents to dissolve the rust but to no avail. At the
suggestion of the local Jaguar shop, I tried an impact
wrench to 'loosen' the studs but this did not work. Here is
what a friend suggested and worked:
1. Buy a few of nuts that fit the studs. ( I got mine at
2. Take two nuts and tighten them on one of the frozen
3. When they are both in far enough, take two wrenches
and try to undo the bottom one while tightening the top one.
You are basically compressing the two nuts against one
4. Once they are as tight as they will get, try undoing
the bottom one only. This may require a long pipe to get
enough torque. If the nuts are tight enough the frozen stud
should begin to turn. If the top nut begins to turn instead,
tighten them more.
5. This procedure took all of the studs off and none were
damaged. After a couple of uses, the nuts will begin to
strip and need to be replace with new ones. This procedure
will only take an hour or so and will make the removal of
your cylinder head a lot easier."
I had a head stick on a 1968 420. We took all the nuts
off then squirted WD40 into every nook and cranny. Then we
hooked a hoist to the head as though we were going to remove
the engine. We lifted the car so that the front wheels were
2" off the ground and let it hang. Every day we would squirt
in more WD40. After three days the head slipped off and the
car came down with a thump.
The exhaust side of the XJ6 head is just about as good as
you need it to be no mater how radical you get on improving
the engine. Some of the D-type heads had huge exhaust valves
by comparison, but they are not necessary. There is little
to be gained on the exhaust side, so spend your money on the
intake side where it can use some help.
The first thing you want to do is the porting and
polishing. You do this first so that the crap and dust that
it creates will be washed away after the machine shop does
their job. You don't want it getting into the new valve
guides and other goodies you will be adding later.
Porting and polishing will make the biggest single
difference on the heads of an XJ6.
You have two levels that you can aspire to in porting and
polishing. The first level is to just smooth out the intake
ports so that they are smooth and without lumps and casting
imperfections in the walls. Finish the job with 80 to 100
grit sanding drums. This is probably all you will want to do
for a strictly street machine. Enlarging the ports on a
street machine just hurts the low end performance.
If you are into racing you may want to enlarge the ports
to just under the size of the gasket openings. You can do
this by placing a gasket against the head and marking the
openings on the head. Then enlarge the ports to about 1/16"
smaller than the gasket openings. Be careful though as there
are water passages in the head and they are closer to the
surface as you approach the valve seats and if you cut too
deep you could be in big trouble. The cut is mostly at the
port and should taper off quickly toward the valve seat to
Polishing is probably not done on a street machine, but
if you are into racing then you want to polish the ports
down to a 1200 sand paper. They should be almost a mirror
finish when done. This has to be done gradually from the 80
grit in the first step to the 1200.
Now we come to improvements of the head. There are
several improvements that can be made by the machine shop
that cost very little. First, the valve guides that stick
out into the gas flow can be smoothed flush with the port
wall. This will improve the gas flow immeasurably.
Having the heads "cc'd" will make the engine smoother and
there may be an increase in power. You can do it yourself.
Place the head on its back with the spark plugs installed
and the valves installed Then make sure the mating surface
where the head meets the block is level. Now fill the
depressions in the head at each cylinder with light oil till
it is level with the gasket surface. Use a syringe to remove
the oil from each depression and measure what you take out
very carefully in a graduated container. Write down the
number for each cylinder. What you want to do now is to take
your Dremel tool and sand away enough material from the
inside of the head so that all the cavities are as large as
the one that held the most oil. Do not grind on the one that
was the biggest! You should remove the material evenly
around each cylinder head. When they are all the same size
you are done. Your head has been "cc'd." With all combustion
chambers the same size the engine will run smoother.
The racing engine should have the heads glasspeened to
relieve stress. You can do it on any engine and it is
Increased size on the intake valves can improve even a
street car, and they are almost mandatory for a car that
will be raced seriously. The intake valve size on a series 3
XJ6 is 1 7/8". This is a good size for street use and the
valves are stock Jaguar items so are easy to get. The early
XJ6 had 1 3/4" intake valves and increasing to the 1 7/8"
series 3 intake valves will improve these engines. It is
possible to increase the valve size to 1 15/16" without
changing the size of the spark plug. If you go to a 2"
intake valve you will have to change to a 10mm spark plug.
You should not go to a 2" valve unless you are seriously
racing the car.
Remember though that with the stock dual carburetors you
will gain nothing with the big intake valves. The big intake
valves require more breathing room, like 45DCOE Webers.
The best compromise for a street car is the 1 7/8" valves
of the series 3 with improved carburation. In the series 3
of course, there is nothing to do as it already has this
capability and the EFI to feed it.
While you are doing this valve work, plan on replacing
all the valve springs. You will be putting in a hotter cam
and the stock valve springs will float at 5500 RPM. There is
no reason to do this much work and then scrimp on costs. The
new valve springs won't cost that much. Use a stronger set
of racing springs and you will then be able to use a hotter
cam without valve float.
If you are racing the engine you will want to replace the
stock steel valve spring retainers with the lighter weight
alloy retainers. On a street head, these will do nothing for
you, but at high revs, 6000 up they will make a
Replace all the valve guides. You don't want to waste all
this time then find that you have to replace a valve guide
in the near future. The head is off, so replace the guides
now. Use bronze valve guides as they lubricate the valve
stems better and will last longer for that reason.
Considering the cost vs the improvement, one of the
cheapest things you can do is to have the shop cut "triple
angle" valve seats when they install the new valve seats and
The new valve seats should be "hardened" seats so they
can withstand the rigors of unleaded gasoline. Even if
unleaded is not mandatory where you live now, it probably
will be someday so get a head start on it now.
I recommend that you do your own valve lapping, the last
step in this head restoration/improvement. The shop will not
spend the necessary time to do it right and you will because
you know that its your money down the drain a year from now
when you have a burned valve and your compression is
From Gregory Andrachuk I received the following advice on
"The faulty or fault-prone coils are not he LUCAS coils,
but the DUCELLIER coils made in France. My 82, in fact, has
a DUCELLIER coil, which I presume is original, and it
operates perfectly, with no leaking of oil. I think the
failure is an oil seal failure to begin with. My coil has an
internal ballast resistor, or so I assume, since there is
resistor mounted beside it as on other cars I have seen.
I believe that the DLC 102 coil used as a replacement
requires an EXTERNAL resistor, but the sales reps don't seem
clear about this. I think one should suspect coil trouble
with sudden engine misbehavior, but replacing perfectly
good coils seems unnecessary."
The first piston and cylinder. There is not alot to say
here except to praise the quality of the XJ6 bottom end. The
main and rod bearings are very tough and will last forever.
It is a testament to their strength when you consider how
many horsepower can be coaxed out of this engine without any
change in the bottom end at all.
Jaguars are often asked to run with low oil supplies
(they leak the stuff out) and on turning corners it is not
unusual to see the oil pressure light flicker. This is not
good and should be attended to, but it never seems to damage
the bottom end of the engine to have these temporary losses
You may have heard that Jaguar considered going into the
manufacturer of refrigerators at the end of the second world
war but they changed their mind when they couldn't figure
out how to make them leak oil....8-)
Some owners will try to get more horsepower from their
engines by increasing the compression ratio by using hi
compression pistons. This is not really necessary and it
makes it hard to run on the fuels available at the pump
without causing damage to the engine. Here is where you can
damage the bottom end. If your compression ratio is too high
and the car "pings" you may not notice it and it will be
beating your crank and bearings to death.
You can gain more at lower cost by reworking the head and
changing the cams and you will do it with less possibility
of causing damage to the engine.
The distributor and the oil pressure sender and the oil
pan. All of these have peculiarities worth mentioning.
The oil pressure sender is infamous for its inaccurate
readings. This item is a very expensive sender at the
dealer. After my first edition of this book hit the stands I
recieved a phone call from one of the dealers listed at the
back of the book telling me he could supply it for 60% of
the price the Jaguar dealer was asking, so look around.
Inside the housing is a wire wound resistor that has a wiper
connected to it from a diaphragm that measures the pressure.
The diaphragm is moved by a piston that can get stuck with
crap from dirty oil. If this happens you may get a flat
topped reading that hits a peak and goes no higher or it may
get stuck so that there is a reading of pressure when the
engine is not turning. Sometimes cleaning out the input end
with a blast of pressurized air will make a difference, but
usually it wont.
The wire on the wire wound resistor will wear and after
many miles will either break or will begin sliding around on
the form. When this happens you will get very quirky
readings, sometimes high, sometimes low. If you start
getting low pressure readings and the idiot light is not
confirming the low pressure, this may be the problem.
If you go to the parts house and they tell you they have
a pressure sender for your jag and it seems cheap, they are
talking about the pressure sender for the idiot light. It is
cheap, but it wont work in the gauge. You can tell the two
apart as the light sender is only about 1" in diameter and
1.5" tall. The pressure sender for the gauge is about 3" in
diameter and 3" tall and looks like a small tuna can fitted
to a piece of pipe with an electrical connector on the other
This item is expensive and not readily repaired so the
only alternative is to bite the bullet and get one from
Jaguar or one of the suppliers in the back of this book. The
one consolation is that it will probably last another 70
One of these days I am going to attempt a repair on one
that has had the wire break. I will report the results in
this book, but I doubt that it will be economical, it will
just be to see if I can do it.
The oil pan is another place where things go wrong. Being
of cast alloy it is soft and many a PO (Previous Owner) has
tightened an oil pan plug too tight and stripped out the
threads. One car I bought, the PO had used epoxy glue to
glue the plug in place and then he changed oil using a pump.
Of course he neglected to tell me this when I bought the
There are several ways to solve this problem. All have
their advantages. All are relatively inexpensive and all of
I have already mentioned the pump thing so I will skip
it. Besides, I don't see any real advantage to that one. The
next possibility is to put a helicoil into the old threads
to rebuild the threads to accept the old drain plug. This
works sometimes, if there is enough material around the hole
to do the repair. It usually requires removing the oil pan
which on an XJ6 requires removing the engine from the
The second method is to drill out the hole to a larger
size and retread it. Again this requires removing the oil
pan since you want to be able to remove any metal chips so
they don't get swept into the engine oil passages.
There are rubber stoppers that expand into the threads
when a bolt is tightened they are sometimes available in the
parts stores. I don't like this solution since oil and
rubber don't really mix and I would be suspicious of how
long the rubber could handle the heat of the engine oil.
The best solution I have found is to install one of those
"quick drain" plugs. The ones with either a remote trigger
or with a lever on the plug that allows you to drain the oil
without removing the plug. This way you can put a good grade
epoxy glue on the plug when you install it to glue it in
permanently and yet you can still drain the oil when the
time comes. I like the remote trigger type and consider
installing those even if I didn't have a problem to begin
with. Its alot more pleasant to change the oil if you don't
have to crawl under the car, not to mention, alot safer,
since a Jag is so low you have to jack it up to change the
The distributor is just a standard points and condenser
type of distributor on the series 1. (the series 2 and 3
used contactless electronic ignition) It is adjusted in the
normal way with a screw driver to loosen the arm and to pry
the points apart or together and a feeler gauge to measure
It needs to be lubricated on the pivot post, through the
base plate opening at the cam and on the center screw with a
dab of engine oil. On the cam it should be lubricated with
grease or Vaseline.
There is a vacuum advance diaphragm on the side. The most
common failure of this part is the rubber vacuum hose that
connects to the advance diaphragm. The rubber deteriorates
with age and starts to leak so that there is no advance as
the engine reaches cruise speed. This can cause overheating
and loss of economy by running the engine in a constantly
retarded condition. If the hose is OK you can check the
advance by putting the end of the hose in your mouth and
sucking. This should cause the distributor points plate to
rotate slightly as you watch it with the distributor cap
removed. If it doesn't rotate and the hose is good then
there is a bad diaphragm in the advance mechanism and it
needs to be replaced.
The coarse timing is set in the usual way by first
removing the #6 (the front cylinder) spark plug and turning
the engine by hand until the compression stroke can be
detected by the pressure escaping around your thumb as it is
held over the spark plug hole. Now continue rotating the
engine in the same direction until the appropriate timing
mark is in alignment with the timing cover pointer. The
correct direction to rotate the engine can be easily
determined by looking at the fan blades. The engine rotates
such as to make the fan suck air through the radiator, i.e.
the fan rotates so that the leading edge of the blades are
the edge to the front of the car toward the radiator. Now
set the vernier screw to the center of its position. Then
loosen the distributor clamp so that the distributor can be
turned stiffly. Set the distributor timing as close as you
can get it while using a light across the points to detect
the opening of the points. You want the points to just open.
Clamp the distributor in this position. The car should now
run well enough that you can continue with the fine
The fine timing adjustment is a knurled nut on the
opposite side of the distributor from the advance diaphragm.
To adjust the fine timing a timing light (strobe) is held on
the crankshaft damper timing marks and while watching the
alignment of the marks with the timing cover pointer the
knob can be adjusted to fine tune the spark timing.
On to the