Experience
in a Book
Lucas
Ignition (to 1989)
IGNITION SYSTEM DESIGN: An ignition coil requires
a certain amount of time to build up enough energy to
produce a spark. The faster an engine is turning, the less
time there is between sparks, so the output of an ignition
coil starts to drop off. It is also apparent that the more
cylinders there are, the less time there is between sparks,
and the output of the ignition coil drops off even
faster.
Another lesson in physics is that the higher the
compression, the more resistance there is for electricity to
jump a spark gap, so higher voltage is required.
The Jaguar V12 H.E. has 12 cylinders, turns at 6500 RPM,
and has 11.5:1 compression, making it one of the biggest
challenges for an ignition system in production automobiles.
To cope with this, Jaguar has incorporated some
sophisticated ignition technology. Also, Jaguar uses a spark
plug gap of only .025" to make it easier for the electricity
to jump the gap.
TROUBLESHOOTING: Jan Wikström sends this
procedure: "This is the Gum Tree Garage test for a V12
ignition when it cranks but refuses to start:
1. Pull the lead from coil to distributor out of the
distributor and jam it under a fuel pipe so there's a gap of
about 1 mm (.04in) between the brass and the nearest engine
part.
2. Crank the engine. Do you get fat, blue sparks in the
gap? Then the ignition is OK and you need to troubleshoot
the injection system. If not, continue:
3. Pull the spade connector off the coil terminal marked
(+). Turn the ignition on, then test the power with a spare
light bulb between the connector and engine bare metal (this
is better than a voltmeter, because it will reveal a poor
contact with insufficient current carrying capacity). Is the
lamp bright? Then continue; if there's no voltage, check the
ignition switch and all its wiring including the ballast
resistor.
4. Touch the connector quickly several times to the
terminal. Do you get a spark now? Then the pickup coil in
the distributor or its wiring, or (less likely) the
amplifier, may be faulty. If there's no spark, turn the
ignition off and continue:
5. Get a test lead with alligator clips. Clip one end to
bare metal on the engine, pull the tubular connector off the
(-) terminal of the coil and clip the other end to that
terminal.
6. Repeat test 4. If you get a spark now, the amplifier
or its wiring is faulty. If you get no spark, the coil is
dead."
IGNITION TIMING: The proper
advance setting is indicated on a decal in the engine
compartment. If it differs from the manual, believe the
decal.
The next thing to confirm is that the woodruff keys that
align the front pulley with the crankshaft are in good
condition. They are a known
problem, and clearly if the pulley is allowed to
reposition itself on the crank, use of the timing marks will
be worthless.
On the Jaguar V12, the timing indicator itself is
adjustable. If there is any chance it has been tampered with
(the oil pan and sandwich plate have been removed), then the
position of the indicator must be calibrated before checking
the timing.
The official method for setting this indicator is to do
it when the right side (A bank) head is off. A dial position
indicator can be set up to determine when the 1A or 6A
piston is at TDC. If a position indicator that will fit
through a spark plug hole is available, this same method can
be used with the head in place by removing the spark plug
from either cylinder 1A or 6A. Once TDC is determined,
loosen the two sandwich plate bolts that hold the timing
indicator plate in place, and slide the plate on its slotted
holes until 0ƒ lines up with the mark on the pulley.
There is an alternate method to set the timing indicator
that doesn't require the position indicator or removing the
head. All that is required is a device that will obstruct
the motion of the piston near the top of its stroke. Such a
device can be made from an old spark plug by breaking the
ceramic out of it and installing a bolt through the middle.
Ideally, the length of the bolt into the combustion chamber
should be just enough for the piston to hit it only a few
degrees from TDC. If you make this device strong enough, it
might also come in handy for removing the crankshaft
pulley someday although for that purpose it would be
better if it hit the piston farther away from TDC.
Turn the engine a ways past TDC, and then screw this
obstructing device into the spark plug hole of either 1A or
6A cylinder. Then turn the engine backwards until the piston
hits the device and you can't go any farther. Note the
reading from the timing marks. Then turn the engine forward
through one complete revolution until the piston hits the
device again, and note the reading of the timing marks. The
two readings should be exactly the same amount before and
after TDC. If they are different, loosen the sandwich plate
bolts holding the indicator plate and move it an amount
corresponding to one half the difference between the two
readings.
The ignition timing on the V12 is checked with the engine
held at 3000 RPM. Although a pain, this method insures the
timing is accurate at operating speed rather than at idle,
where timing is less critical. However, proper timing by
this method requires that the tachometer be at least
reasonably accurate. It's not very critical, since it would
have to be in error by about 300 RPM to cause an error of 1ƒ
in the timing. Nevertheless, if one ever finds his car
hooked up to one of those fancy, super-accurate computerized
engine analysis machines, it is suggested that the location
of the tachometer needle be noted when the engine is running
at a real 3000 RPM. That point can then be held whenever the
timing is checked in the future.
When checking the ignition timing on the V12, the vacuum
line to the distributor vacuum advance must be
disconnected and plugged. The vacuum advance capsule is at
the bottom rear of the distributor, making it quite
difficult to get to this line (the larger hoses connecting
to the distributor cap itself are for the distributor
ventilation system, and do not affect timing). Do yourself a
favor and cut the vacuum line somewhere convenient, and
reconnect it with a small piece of tubing. From then on, all
you have to do is disconnect it at the break and plug it
when checking the timing.
Since the battery is in the trunk, connecting the power
leads of the timing light requires ingenuity. The ground
lead can be connected anywhere on the car. The positive lead
must go to 12V, which exists at any solid brown wire. There
are two terminals on the firewall adjacent to the valve
covers, and a terminal on the back of the alternator -- all
difficult to get at. Another solution is to use a pair of
jumper cables from the battery in the trunk. Peter Smith: "I
connect my timing light to the 12V power source at the
headlights fuse box."
Since disconnecting the plug wire from cylinder 1A is
difficult, disconnect the wire from the distributor cap
instead; make a small jumper from an old ignition wire to
use to connect the timing light. Or, just buy an inductive
timing light. If it's more convenient, you can also check
the timing using the signal from cylinder 6A.
Since you must crawl under the front of the car while an
assistant holds the engine at 3000 RPM to read the timing,
it is suggested you put an extra long ignition lead on your
timing light so you can route it around the fender rather
than feeding it through the engine compartment. Interference
with moving parts at 3000 RPM would be memorable. Cheap
ignition wire with metal conductor works well for making a
long timing light ignition lead, and is available by the
foot.
The Jaguar V12 design eliminates most wear items that
would normally cause ignition timing to vary, such as
ignition points or sloppy camshaft drive systems. The only
remaining reason for the timing to change would be wear in
the timing chain itself, and the Jaguar timing chain
normally wears so slowly as to be insignificant. If the
timing in your car is way off, it is highly recommended you
determine why rather than simply readjust it. For
example: if your centrifugal advance unit seizes in the idle
position, then when the car is revved to 3000 RPM the timing
will be retarded by 15 degrees or more. If you merely adjust
the timing rather than correcting the problem, then the
timing will be 15 dfegrees too far advanced at idle!
Timing is normally adjusted using a long screwdriver to
turn a small eccentric cam on the side of the distributor
underneath the cruise control actuator. If your eccentric
timing adjustment won't go far enough, the distributor base
must be repositioned. Remove the distributor cap and insert
a long allen wrench to loosen the three mounting bolts at
the very bottom of the unit. Rotate the entire distributor
housing in the direction needed, then retighten. Please
remember that this much adjustment should never be
necessary, and causes should be investigated.
HOLDING A HIGH RPM: Michael Minglin sends a tip:
"Every time I went to check the timing, alternator, etc. the
book says to set the rpm to such and such. Reaching down to
that auxilary air valve when the engine is hot is not my
idea of fun. What I did was to weld a nut on top of a short
bolt. Threading a longer bolt into this nut gave me a "T"
with a long top and short leg. The short bolt goes into the
RHD throttle cable bracket (not used for anything on my '84
XJ-S), Then I use the long bolt to adjust the bell crank to
the rpm I want. To make it even easier, I forced a short
piece of vacuum hose onto the long bolt, at the head. This
makes it easy to adjust the bolt with your fingers." This
plan will work on either LHD or RHD cars, simply using
whichever cable bracket is unused.
CENTRIFUGAL AND VACUUM ADVANCE DATA: When checking
distributor advance versus tables, make sure you are looking
at the H.E. or pre-H.E. tables, as appropriate. The H.E.
system develops less advance in the centrifugal mechanism
and more advance in the vacuum mechanism than the
pre-H.E..
The data on the pre-H.E. is inconsistent. Page 05-1 of
the XJ-S Repair Operation Manual, ©1975, lists data for
the centrifugal and vacuum advance mechanisms and Section
86.35.29/4 of the same book lists data for bench-checking
the distributor, but the centrifugal advance data doesn't
agree. Values listed in distributor degrees and distributor
RPM should be exactly half of the engine readings, since the
distributor turns at ‡ crankshaft speed. Page 05-1 of the
Supplement to the Repair Operation Manual, ©1982, lists
the same values as page 05-1 of the repair manual itself,
but carefully-taken measurements of the distributors from
John Nuttall's 1977 and 1979 cars indicates that the actual
advance curves match the values indicated in Section
86.35.29/4.
Note that all of these charts are referring to how much
the advances change, not to absolute values read from
the scale at the front pulley. For example, if it says the
centrifugal advance mechanism should provide no advance at
idle, that does not mean you can set the timing at 0ƒ
at idle. It means that the advance mechanism has not yet
begun to move, so the timing at idle should be the same as
the static timing. And, if it says the centrifugal mechanism
provides 18ƒ to 22ƒ advance at 4000 RPM, it doesn't mean to
set the timing at 18ƒ to 22ƒ; it means the timing should be
18ƒ to 22ƒ more advanced than it is at idle.
Regarding the charts for pre-H.E. advance, Mike Morrin
says, "I suspect the service manual only has data for one of
the distributor variants fitted (probably C44663). The parts
book shows that there were 5 different models of distributor
fitted to pre-HE XJ-Ss, and I think that the only difference
was the advance curves.
C.43735 Australia (this is the one with the
peculiar vacuum retard system).
C.44663 California to car 2W54183
C.43735 California from car 2W54184
C.44663 CDN/USA to engine 8S5461 (ie the 4460th engine
what year??)
All other countries to engine 8S5202
C.46173 CDN/USA from engine 8S5462
All other countries from engine 8S5203
DAC1609 California from engine 8S11161 and
Australia from 8S11800
DAC1380 All other countries from 8S11262
"Note that my parts book does not cover the
[pre-H.E.] Digital-P cars, so there are probably 2
more I have not counted.
"On reflection, I am surprised that there is not a
clearly different distributor model (advance curve) for 8:1
and 9:1 compression engines. As far as I can see, the
distributor seems to change according to degree of emission
control, not compression. For example: Australia (9:1) and
California (8:1) get the DAC1609, all other countries
presumably including the UK (9:1) and the rest of the USA
(8:1) get the DAC1380."
For our information, Morrin also provides part numbers
for the distributors on the Series III E-Type:
C33148 up to engine 7S4663 (emission control) or
7S4879 (no emission control)
C37443 from above.
"The carburetted distributors of course have no FI
trigger assembly."
VACUUM ADVANCE MODULE: On most cars, it is a
simple matter to determine if the vacuum advance module is
intact: connect a hose and, using your mouth, suck and watch
the mechanism move. While in advanced position, put your
tongue over the end of the hose, and test to see if it holds
vacuum and stays in position.
On most cars, but not on the XJ-S! On the H.E., there is
a vacuum regulator in the line to the vacuum advance module,
and such regulators cannot be depended on to work properly
with no flow. Therefore, the vacuum advance module on the
XJ-S has a deliberate bleed hole, so the module will not
hold a vacuum even when in perfect condition.
According to Michael Neal, "The vacuum retention ability
of the vacuum unit is dependent on the type of unit. The
early units have a limiting adjuster on the end of the
module. The common replacement unit has no adjuster and will
bleed down slowly. The early units hold vacuum. The adjuster
seems to simply limit the travel of the diaphragm."
Roger Bywater says, "Of course the high temperature
situation also gives the vacuum capsule a hard time and they
usually need replacing every couple of years or so but a lot
of so-called mechanics seem to miss that one."
Note that a vacuum advance module that isn't leaking may
still need replacement. Val Danilov says, "My diaphragm was
fried rock hard, I broke it trying to test the rod movement
(CRRRACK!), so I think it wasn't leaking."
VACUUM ADVANCE MODULE REPAIR: The following
procedure for rebuilding a vacuum advance module is credited
to John Napoli and Val Danilov.
Before removing the vacuum advance module from the
engine, you might want to take note of the best position for
the vacuum line connection when it is reassembled. And after
removing the vacuum advance module but prior to taking it
apart, it is suggested that you first carefully measure the
distance which the actuator rod extends out of the unit.
Also, push the rod back into the unit (fully retracted
position) and measure that as well.
Raw material is a generic replacement vacuum advance from
a Chevy V8 -- dirt cheap at any auto parts store. Take the
Chevy unit apart by prying open the case; Napoli suggests it
may be easier to open the case by grinding the case all
around its periphery to weaken the metal, but be careful not
to get it too hot and damage the diaphragm. What you want to
get ahold of is the diaphragm/rod assembly.
Open up the stock Jag vacuum advance by prying around the
crimped-on case. In this case, you'd like to reuse
everything except the diaphragm/flat link assembly,
so try to do as little damage as possible to the casing; if
you'll read ahead to understand how you'll be reassembling
it, you may decide to simply cut or grind the lip off the
edge to avoid mangling the dome itself. Even though the
diaphragm/flat link won't be reused, keep it on hand for
taking measurements.
Cut the rod from the Chevy diaphragm/rod assembly to the
same length as the Jag original, then set it down on an
anvil or something and pound a flat spot at the end with a
hammer. No problem -- it's a Chevy part, remember?
Reassemble the vacuum advance unit using the new
diaphragm/shaft assembly and all the old Jag parts. If the
casing wasn't damaged when disassembled, you may be able to
simply clamp the unit togeher and gently bend/hammer the
dome shut. This works but the cannister will become
work-hardened so you will never be able to do this repair
this way again.
If the edges were too mangled (or you cut them off),
drill the body and dome for eight fasteners; Napoli suggests
3/4" long 3-48 fillister head screws and nuts, but notes
that the exact sizes aren't critical. Sandwich the body,
diaphragm (poke a hole through for the screws with a
needle), spring, and dome, and bolt it all together, being
careful that the flattened section of the rod is aligned
properly. This method has the distinct advantage that it
permits repeated repairs later -- important, since the heat
in the valley of the V12 will eventually bake the Chevy
diaphragm as assuredly as it did the original.
Check that the unit responds to vacuum and pulls the
shaft in.
Measure carefully the extended length of the rod, mark,
and drill a hole in the flattened area the same size as the
hole on the original part. Check the retracted length as
well, and if there is an adjustment screw on the dome adjust
it to provide the same total travel (if your extended length
was off a little bit, make the retracted length off by the
same amount; the variance can then be corrected by setting
the timing normally). If you don't have an adjustment screw,
don't worry about it, the total travel will probably be
close enough.
Reinstall on the distributor. Be sure to check the
timing; the timing procedure requires that the vacuum be
disconnected, but the module still has an effect -- you
might not have gotten that extended length as perfect as you
thought you did.
Note that the original diaphragm may have had a tiny
orifice built into it to provide a deliberate leak. This
will usually be evident as a tiny hole through the metal
disks on either side of the rubber diaphragm itself. The
vacuum advance plumbing includes a vacuum regulator and such
regulators don't work reliably when there is no flow, so the
orifice is in there to provide a little flow. It appears
that this orifice may not be necessary, since some genuine
Jaguar replacement vacuum advance modules reportedly don't
have it. If having an orifice proves to be necessary, it can
be added anywhere in that branch of the vacuum advance
plumbing; you might wanna make the hole in the dome rather
than in the diaphragm itself. It might make more hiss, but
you can seal it later if you decide to with a small piece of
aluminum tape. Or you may be able to fit a separate device
with an orifice with a tee connection into the vacuum line.
You could, for example, take a piece of brass tubing, drill
a tiny hole in the side, and connect it in the line
to the vacuum advance module.
If, for some reason, you are unable to reuse other parts
of the original Jaguar vacuum advance unit, you may be able
to use the corresponding parts from the Chevy unit. Note,
however, that doing so may result in differences in the
advance curve and/or limits. Use of a different spring will
change the advance rate. Use of a different dome with a
different depth, and therefore a different place where the
spring seats, will also affect the advance rate. And use of
a different dome may also affect the retracted length,
allowing the diaphragm to travel too far or preventing it
from travelling far enough.
If the Chevy dome happens to include a limit adjusting
screw, you may be able to adjust the full-retract position
after assembly to make sure it is the same as the original
was. If there is no adjusting screw, you might actually be
able to add one, being careful to seal it when done to avoid
vacuum leaks. If the Chevy dome is shorter and compresses
the spring too much, you may want to add a spacer ring
between the diaphragm and the dome to space the dome back.
If the Chevy dome is taller and compresses the spring less,
you might want to insert something within the dome for the
spring to sit on.
Napoli adds, "I have seen in this month's Jeg's catalog
that Accel manufactures a replacement Chevy vacuum advance
that is adjustable. The ad copy states that the unit is
adjustable for total advance and rate. It comes with
instructions. The unit looks just like the generic
replacement I used, so the same repair approach should
work." This fancy aftermarket Chevy part is still
cheaper than the stock Jaguar vacuum advance module by a
long shot.
If you tore things apart and then read the
suggestions to take measurements first, Napoli sends some
reference measurements from a junk unit he had laying
around: "For reference, the measurements were taken with
1/16" of the adjusting screw exposed. That is, from the face
of the adjusting nut to the top of the unmolested screw is
1/16". Also, this is a stock '88 V12 advance (non-Marelli)
from my donor engine and the unit does not operate (won't
build vacuum). With the unit relaxed, the length from the
end of the housing to the center of the hole in the
actuating rod is exactly 2 inches. Full compression of the
rod reduces the length by 5/16" (i.e., 5/16" maximum
travel)."
VACUUM ADVANCE MODULE -- PRE-H.E.: Mike O'Neill
noticed that the vacuum advance module from an MGB will fit
the pre-H.E. distributor. However, John Nuttall found that
the MGB advance unit -- as well as some units for Triumphs
-- look similar and will fit, but provide differing amounts
of advance at different vacuum levels. So, if your engine is
largely stock and you want to keep it that way, you probably
should seek a Jaguar advance unit. On the other hand, if
your engine is not stock and you need to provide nonstandard
amounts of vacuum advance, this provides some places to
look. Also, these units might provide materials for
rebuilding your old vacuum advance module in much the same
way Napoli used a Chevy part in the procedure described
above.
VACUUM RETARD: Ian Macfarlane, regarding his 1985
XJ-S: "In Australia the distributor has a retard connection
on the vacuum module which is supposed to operate for about
15 min. after starting via a solenoid valve. But the wire
leading to the solenoid valve had been cut (as had the wire
to the solenoid air switch). Thus, even though the
distributor timing was correct with the vacuum tubes
disconnected, the engine ran at about 6 deg retarded under
normal conditions.
"Although this would not exactly apply to other emission
systems it is another option for those with an overheating
problem - if the vacuum system was not working properly it
is feasible that overheating could occur due to
retardation."
CENTRIFUGAL ADVANCE - SEIZING:
At this point in this book, I used to report how the
pre-Marelli Jaguar V12 centrifugal advance was highly prone
to seizing. However, with more and more readers reporting
back, I can say with relative certainty: Unless your
distributor has been overhauled, it is seized right
now. Period. This has proven to be a 100% failure rate,
every time, every car, there simply is no doubt anymore. And
a seized advance unit results in low power, overheating and
major engine damage if not corrected. If you are not
absolutely positive that your distributor has been
overhauled already, it is imperative that you schedule an
overhaul as soon as possible -- and drive the car very
gently or not at all until it's done.
Folks, this is probably the single most important item in
this book. Centrifugal advance seizure may be the cause
behind most of the problems the Jaguar V12 has --
overheating, dropped valve seats, etc. -- and the reason
behind most owner dissatisfaction, low resale value, Chevy
engine swaps, you name it. Is there any way I can convince
you, the XJ-S owner, to take action now? If it'll
make you feel better, give me a call, I'll tell you in
person: overhaul the distributor NOW.
Sad to say, reports are that this failure mode --
notorious as it is -- is not widely known among
Jaguar dealers and mechanics. Despite the frequency of
charging customers $10K for a new engine, it has never
occurred to many of these shops that the engine failures
were preventable. Some people have reported that their
Jaguar dealer overhauled or replaced several unrelated
components before finally figuring out that the centrifugal
advance was seized. Others never figured it out.
Perhaps their fancy diagnostic computers don't blink
"centrifugal advance seized". Perhaps they just like
collecting those fees for new engines. Whatever, keep in
mind that just because you have had your car "checked out"
by the dealer doesn't mean you don't have the problem. It's
not even a certainty that the advance is OK if you
specifically asked them to check it; some of these mechanics
don't even know how to check it. For those who have
mechanical abilities, it is highly recommended that you
check your centrifugal advance yourself, or better yet
simply go ahead and overhaul it. If you aren't the type to
get your hands dirty, it probably would be money well spent
to have an independent shop confirm the first shop's
conclusions.
John Napoli confirms this: "I know or deal with about a
half-dozen repair shops. Some are run by friends (no
chicanery ever) and the others, including my local Jag
dealer, are pure business relationships. None of them ever
heard anything about the chronic Jag problem of seized
centrifugal weights. Not even the Jag dealer, although maybe
they do know and don't tell. I'll go further and say that no
Jag owner I've encountered has ever heard of it, either. You
get these strange looks when you bring it up ("If I don't
know, then it can't hurt me."). I find it hard to believe,
but it looks like a lot of the information regarding the
idiosyncrasies of these cars never reaches the people who
can use it most. Perhaps this is part of the reason why so
many Jag owners have bad experiences with repair shops."
The usual indications of a seized advance mechanism are
an XJ-S that lacks power at higher RPM and a nasty tendency
to overheat. In some cases, when the throttle is backed off
suddenly there is a brief power surge before decelerating.
If your car doesn't have the performance at higher RPM that
it should, check the advance mechanism immediately; a
distributor seizure is easily fixed, but warped blocks,
dropped valve seats and burned pistons are much more
expensive and are the inevitable outcome of continued
operation.
To confirm for yourself that your advance unit is seized,
remove the distributor cap. Attempt to turn the rotor
counterclockwise. If operating properly, you can easily turn
it about 11ƒ (H.E.) or about 18ƒ (non-H.E.) against a
spring. Note that this thing should feel really loose, and
when you twist it and let go it should snap back with a
metallic clink; if at all sticky or gummy-feeling when
turned, time to overhaul. The forces that move this thing
are balanced against each other, so a very slight difference
is supposed to make it move; even a slight amount of drag or
stickiness is enough to keep it from moving as it should. It
may be movable by hand but not as far as it should or not as
freely as it should. Of course, if totally seized, you
cannot turn it at all except for backlash in the
drivetrain.
Another method of checking for a seized distributor is to
compare the timing (with the vacuum line to the distributor
disconnected and plugged) at 2000 RPM with the timing at
idle (under 900 RPM). The two readings should differ by at
least 12 degrees (H.E.) or at least 22 degrees (non-H.E.).
If they are the same or very close, the centrifugal advance
is seized.
OK, SO IT'S SEIZED -- NOW WHAT? To prevent/correct
a seized centrifugal advance mechanism, it's necessary to
overhaul the distributor, clean out all of the original
lubricant, clean up the parts, and reassemble with a
reliable lubricant. Roger Bywater says, "Most of them
probably run for years without the cap being lifted so by
the time anyone does get round to it the spindle is likely
to be running dry and getting built up with debris. Adding
lube at that stage may well loosen the debris and aggravate
the situation so really it needs complete stripping to
ensure that it will not jam at some future time." Bywater,
having worked for Jaguar, can be expected to blame the
seizures on poor maintenance -- and perhaps he's correct. I
personally suspect the original lubricant used at assembly
was lousy, based on what the stuff looked like when I got my
distributor apart! It really doesn't matter what the cause;
either way, the distributor has to come apart.
Of course, you don't have time for overhauling. You will
probably want to try the easy fix: remove the distributor
cap and rotor, and put some penetrating oil down the center
and see if you can work it loose. If you are successful, it
is recommended that you check its operation regularly -- or
better yet, just go ahead and overhaul it when you get the
chance. The results of operation with a seized centrifugal
advance are simply too costly to ignore.
This is one place where getting a new part will
probably not help. There is little wear in the distributor,
and an overhauled and properly lubricated used part can be
expected to last the life of the car. But a new
distributor may have the same problem as the original
distributor did. It is recommended that even a brand new
in-the-box distributor be overhauled prior to installation
(to get that lousy lubricant outta there).
The good news: the reported incidence of centrifugal
advances seizing after they have been overhauled is
nil. This may be because the original grease is the problem,
and once it's removed the problem goes away. It may simply
be because once the overhaul has been done the owner
understands what's going on and lubricates it regularly.
Whatever, once the distributor has been overhauled, there is
apparently no reason to expect to ever have to do it
again.
Randy K. Wilson points out that the problems with seized
centrifugal advances on pre-H.E. engines may actually be
different in nature. "From what I've seen the gummy advance
problem is unique to the V12 H.E. distributor. Earlier
distributors also had a problem with seizing, but these
galled from a total lack of lubrication." Of course, this
could mean that the H.E. only gets hot enough inside the
distributor to turn the lubricant to varnish while the
pre-H.E. got hot enough to burn the lubricant away entirely.
Or, it could mean that Jaguar added grease to the assembly
in response to the dry seizures, and the grease caused its
own seizures.
DISTRIBUTOR REMOVAL: If the centrifugal advance is
seized, or if you wish to prevent seizure in the future, the
distributor should be removed and disassembled. It's not
difficult, but it will help to read the following sections
before tackling the job.
Before removal, care must be taken to ensure the
distributor can be reinstalled with the gears meshed
correctly so the rotor faces the same direction as before.
If the crankshaft is not to be disturbed, this is very
simple: note the position of the rotor prior to removal, so
you can be sure it is in the same position when reinstalled.
It's a gear mesh and one tooth off would be obvious, so just
note the position well enough you can make sure you are on
the same tooth when reassembled.
Note: if you have the older Lucas Opus ignition system,
you are advised to position the engine at TDC on cylinder
1A, which is where the timing marks on the crank pulley line
up and the rotor is pointing at the front left
headlight. If the rotor is pointing at the right side door,
you need to turn the engine around one full turn. The reason
that this is important is that the Opus has a wheel within
the distributor that has three slotted holes that line up
with the distributor mounting bolts in this position. Even
if you can get it off without moving to TDC (by busting up
the plastic wheel, for example) you're still gonna be in a
pickle putting the rebuilt distributor back on without
tearing it back apart or doing some of the fiddling
mentioned below.
If you turn the crankshaft while the distributor is off,
you face additional problems. The distributor turns once
every time the crankshaft turns twice, and therefore the
distributor must not only be lined up facing 1A while the
engine is at 10ƒ Before Top Dead Center (BTDC) but it must
be on the correct stroke. If not, the spark plugs will fire
at the end of the exhaust stroke instead of the compression
stroke, and the motor will not run.
To get the setting right, cylinder 1A must be on the
compression stroke when the distributor is installed
pointing to 1A on the cap. If you know in advance you may be
turning the engine, it is easy enough to avoid problems.
While the distributor cap is off and the rotor is pointing
at 1A and the crankshaft is at 10ƒ BTDC, remove the oil
filler cap. Reach beyond the front edge of the chain and
mark the camshaft gear itself (the camshaft gear turns at
the same rate as the distributor). You can use a dab of
paint, or stake it, or whatever will give you a clear
indication.
You might also want to mark the position of the base of
the distributor, since it mounts on slotted holes. Ideally,
the base should be mounted so the correct timing is near the
center of the range of the eccentric adjuster, but to begin
with it will be easier to put it back where it came from.
Peter Smith: "I find that using typist's white out to paint
across components can be helpful. It can be applied over
slightly greasy surfaces and if precise alignment is
necessary I can draw on it with a biro."
You can insert an allen wrench through the openings in
the distributor and undo three screws and remove the
distributor as a unit. However, for the purposes of doing
the marking mentioned above, it may be preferable to proceed
with the disassembly described below with the distributor
still on the engine until you've removed enough parts to be
able to mark the bottom of the housing on the inside.
DISTRIBUTOR DISASSEMBLY: Remove the rotor arm.
Right off the bat, this is likely to be somewhat difficult,
since it seems to jam. All you can do is twist, rock, and
pull, and hope you get lucky and don't break it. Or just
have a spare on hand. If the rotor carrier shaft seems to
want to come upward with it (the retainer is broken), then
you might want to try to hold it down by inserting a
screwdriver through an opening in the anti-flash shield or
some such. Pulling upward on the rotor carrier shaft may
distort the centrifugal advance springs far below.
Remove the EFI trigger board or anti-flash shield
(whichever). The biggest problem with removing the
anti-flash shield will be dropping the tiny screws and
washers, but the trigger board causes more trouble. It is
mounted with four tiny plastic screws, and Jan Wikström
reports that the screws get stuck to the metal; "On my own
experience of three distributors, you can expect to get two
out intact. If you're very careful." He also reports
that he has used metal screws in a pinch with no apparent
problems. When installing the plastic screws, maybe it would
be a good idea to use anti-seize compound, even though it
looks silly on tiny plastic screws.
Next, remove whatever is used to trigger the ignition; on
1982-89 cars, you need to remove a C-clip, then slide off a
wavy washer, then pry out a U-shaped pin. Finally, you need
to slide off the iron star-shaped inductor rotor, being
careful not to damage it or deform the points. Even more
importantly, don't just pull upward on a sticky star rotor,
because you may stretch the springs in the centrifugal
advance mechanism underneath. Here's a method that seems to
work: Lift gently on the star rotor a little bit and insert
the claw of a claw hammer under the star rotor. Rest the
head of the hammer on the edge of the distributor housing,
but do not pry. While holding the star rotor in its
slightly elevated position with the claw hammer, tap
downward on the center of the rotor carrier shaft with a
plastic-surfaced hammer. Once the end of the rotor carrier
shaft is flush with the surface of the star rotor, if it
still won't simply slide off you can position a small socket
with an OD slightly smaller than the rotor carrier shaft on
top and continue tapping.
On the pre-1982 cars, a plastic disk with 12 ferrite
inserts was used; according to Jan Wikström, "Its hub
is about an inch long (estimated; I've never seen an intact
one) and all beneath the disk. It's a tight fit on the
spindle and in its keyway. And the disk, which is all you
have to apply force to, is about 3/16 in thick near the hub.
On an old car like mine, the only way to get the disk out
would be by breaking it up."
Fortunately, John Nuttall found a better way: "I
discovered a technique for removing the circular plastic
timing rotor which, according to Jan W in your book, often
breaks under extraction. The idea is to undo the three
screws which hold the movable part of the distributor body
to the base. This can be done with the rotor in place. These
screws have springs on them to allow the body to rotate when
the vernier is turned. It is then possible to push upwards
on the rotor with the body with the force being applied
uniformly very close to the central shaft of the rotor -
much better than pulling at the edge."
Unfortunately, Wikström counters: "It's better than
fingers, although it still bears on the thin part of the
disk outside the hub. But sure, it's worth trying before you
break the disk up. One hitch: if you don't have the
distributor with the little screw inside the top of the
shaft, lifting the micro housing (charming name, isn't it?)
will pull the centrifugal advance mechanism apart without
shifting the disk." And stretch your advance springs beyond
recognition. If you can't rely on the retainer to hold the
rotor carrier shaft still, you must press down on the center
shaft with your thumbs while pulling up on the housing to
get the disk off.
Whichever distributor you have, you must remove the three
screws with springs and lift off the movable portion of the
base to gain access to the centrifugal mechanism below. You
could leave the pickup assembly in place, but on the 1982-89
it's in the way for getting to one of the screws with
springs; since it's only two screws to remove the pickup
assembly, that's the easy solution. Of course, it's a good
idea to inspect the vacuum advance mechanism as well as the
pickup module while you're there.
Disconnect the springs from the centrifugal weights,
noting how they are installed. Yes, the two springs are
different, but it doesn't matter which one goes on which
weight.
Remove the felt from the top of the rotor carrier (if
there is any) and observe the retainer underneath. This is a
possible cause of trouble. The early cars had a screw there,
but on later cars there's a nylon clip instead. The nylon
clip is usually brittle and cracked, sometimes allowing the
rotor carrier to rise on the distributor shaft and possibly
causing interference damage down in the advance mechanism.
If you don't have a screw, the procedure for removing the
rotor carrier is to yank, which usually results in breaking
the nylon clip.
Normally the rotor carrier shaft would slide off the
distributor shaft at this point, but if it is seized some
Liquid Wrench or other measures may be called for. Please
try not to bend the distributor shaft -- it is remarkably
thin within the rotor carrier. Once apart, clean all the
crud off the bearing surfaces. Decide for yourself whether
Bywater or I am right, whether it seized due to lack of
lubrication (dry) or a lousy lubricant (gummed or
varnished).
DISTRIBUTOR SERVICE KIT: A distributor service
kit, part number DZB105, is available; it is often called an
"anti-flash shield kit" since the anti-flash shield is the
most obvious part in the bag. The kit contains parts usable
on all pre-Marelli distributors.
The mail order catalogs may not list what parts are
supplied in this kit, so the list is provided here:
Clear plastic anti-flash shield (used on 1982-89
only)
Screws and washers for anti-flash shield (4 ea)
Ignition pickup mounting screws (2 ea - used on 1982-89
only)
Distributor cap gasket
U-pin for reluctor positioning (used on 1982-89 only)
Reluctor retaining clip and wavy spring washer
Replacement carbon contact for distributor cap, with
spring
O-ring for distributor-to-engine joint
Nylon rotor retaining clip (see note under Distributor
Disassembly above)
Note that it may not be at all necessary to obtain this
kit to perform a distributor overhaul. The existing
anti-flash shield, screws, cap gasket, U-pin, retaining
clip, wavy washer, and carbon contact may all be reusable.
The O-ring can easily be purchased locally, and you'd be
well advised to find a Viton one. And the rotor retaining
clip, while not likely to survive disassembly, can be
replaced with a small washer and tiny O-ring -- see
CENTRIFUGAL ADVANCE
REASSEMBLY below.
DISTRIBUTOR SHAFT SEAL: The
Jaguar V12 distributor has had two common problems,
centrifugal advance seizing and cracking distributor caps.
Both of these problems have been attributed to crankcase
vapors entering the distributor between the shaft and the
housing. Supposedly the vapors condense into the type of
varnish found inside engines, seizing the advance mechanism.
Vapors collecting within the cap are ignited by the arcing
of the distributor and cause an explosion which cracks the
cap.
Both causes are in question. Hard deposits that seize the
advance may very well be the original lubricant exposed to
too much heat. And Jaguar's reported reason for venting the
later distributor caps was to deal with high temperatures
that caused the caps to crack, although clearly the vent
system could also remove collecting vapors. It is noteworthy
that the later, vented distributors are still prone to
advance mechanism seizing, and the still later Marelli
distributors are vented even though they have no advance
mechanisms to seize.
There is a seal between the shaft and the distributor
housing, but it gets hard and brittle, probably due to the
heat in this area. If the distributor is being worked on, it
might be a good idea to replace this seal. Note that
removing the distributor drive gear retaining pin requires
some grinding, and reinstalling the pin requires a tack weld
to hold it in place. There's a bearing in there, too, you
might wanna renew it while you're there.
THINGY: Highly technical term
referring to a specially-shaped plastic thrust washer at the
bottom of the rotor carrier shaft, just below the
centrifugal advance weights. It has ears on it that appear
to provide an inner stop for the centrifugal weights,
apparently to reduce noise but effectively limiting how
retarded the timing moves at idle. It's also a British
non-metallic part, so it may be cracked or broken.
If you're lucky enough to have an intact thingy, you need
to take care to reinstall it properly during reassembly. If
you just look at it and line up the notches with the "wings"
on the cam plate on the bottom of the rotor carrier shaft,
there's a better than even chance you will have installed it
wrong. There is a pair of pins on the thingy that hold it in
position relative to the cam plate, and the correct position
of these pins is shown in
Figure
6. Note that for clarity the thingy itself is not
shown, only its pins.
If your thingy is toast, bad news: this part is
apparently unobtainable. It's not included in the DZB105
kit. One frustrated owner reported: "I phoned Lucas
Aftermarket Operations, Parts and Service. Apparently, they
have routine service parts which are readily available at
most dealers, other service parts which they can provide
part numbers for and which are often available, and then
there are non-service parts which of course the thingy and
the seal fall under. The parts did not show up on his
drawings although he did have DZB105. He could see the shaft
bearings in the drawing, but no seal and no plastic thingy.
I asked what happens to parts that are not on their drawings
anymore. I was advised that once it is not profitable to
sell replacement parts, they are removed from the
aftermarket listing and so, to Lucas Aftermarket the part
numbers are no longer available. He told me that the part
numbers could only be obtained from the factory drawings
once they were declared non-service parts. He also advised
that they factory would not talk to me about this because
that is what Lucas Aftermarket is for. So, Lucas Aftermarket
is apparently the only information source Lucas has for part
numbers and they do not have these parts listed
anymore."
You're screwed. The only option -- and it's a perfectly
workable one -- is to install a generic 5/16" ID flat thrust
washer in place of this thingy. Val Danilov adds "I wouldnt
use any washer there larger than 0.5in OD, as it may
interfere with the weights." The thrust washer also needs to
be at least .060" thick, although if thinner you could
merely stack two in there; the ideal thickness is around
.078", but you could probably install anything up to about
.120" without any problem. The loss of the inner stops for
the centrifugal weights will evidently allow the timing to
retard a fraction of a degree more at idle than before
(timing is set at 3000 RPM, well out of the influence of
this thingy, so timing anywhere except idle will be
unaffected). There also might be some noise at idle with the
weights hitting the metal shaft instead of the plastic
stops, although how you would ever hear it above the general
din of the engine idling is beyond me.
Plastic, brass or bronze will work nicely; steel might
gall against the other steel parts, and aluminum or copper
may be too soft and wear quickly. Danilov doesn't like the
idea of plastic, since this is the type of application where
choosing the wrong plastic will result in a part that gets
hard and cracks with age; he found a porous bronze thrust
washer at an Ace hardware store with the 1/2" OD and was
able to drill out the ID to the correct size. This sintered
bronze bearing material is ideal, since the entire purpose
of the material is for use as a bearing between steel parts.
Another idea would be to buy a 5/16" ID - 1/2" OD bronze
sleeve bushing and slice a suitable ring off one end of it
(if you find a place that sells them, you might want to pick
up a couple more such bushings; see the section on throttle
linkage bushing replacement).
CENTRIFUGAL
ADVANCE REASSEMBLY: Do not grease the sleeve
bearing area between the rotor carrier shaft and the
distributor shaft before reassembly; this bearing should be
lubricated with synthetic engine oil only. Find a light,
high-temp grease (such as distributor grease) for the other
moving parts of the centrifugal advance assembly, such as
the pivots for the weights, the ends of the springs, and all
the way around the cam plate on the bottom of the rotor
carrier shaft.
Finding a replacement nylon clip apparently requires
buying the entire service kit (see above), which you might
want to consider anyway. However, considering the clip's
failure tendencies, you may decide not to use it. It has
been found that an excellent method to retain the rotor
carrier is to insert a small metal washer that fits within
the carrier but around the top of the shaft, followed by a
tiny, chubby O-ring. Snap the O-ring into the groove on the
top of the shaft so that it retains the washer in place,
which in turn retains the carrier. David Johnson says, "I
found a #61 O-Ring at Home Depot was a perfect fit in the
groove. It has the following dimensions: 9/32" x 5/32" x
1/16". The O-Ring has a slightly smaller diameter than the
top of the shaft. When you get it on it seems to stretch
until it is a perfect fit for the groove." It might even be
a good idea to try to find a Viton O-ring in this size,
although since sealing isn't the issue and you'd be willing
to buy a new O-ring whenever you take the distributor apart
perhaps you don't care if it gets hard and brittle. The
washer needs to have an OD less than 13/32" (10.3mm) but
larger than 5/16" (7.9mm), and the ID needs to be at least
3/16" (4.8mm). If these parts are installed properly the
carrier should have a slight amount of up and down play, but
if excessive it might be a good idea to install two washers
or more; you don't want the rotor carrier shaft to be able
to slide up far enough to disengage the pins on the thingy
down below.
Another suggestion: Roger Bywater says, "Pulling the
spindle apart invariably destroys the plastic retainer at
the top but we find a small push on trim lock washer works
just as well."
If there is no felt plug in the top of the rotor carrier
shaft, install one -- or just jam a cotton ball in there.
Something needs to hold some oil.
DISTRIBUTOR OVERHAUL -- PAY SOMEONE ELSE VERSION:
Jeff Elmore points out that British Car Service will
overhaul your distributor for you. "I called them and they
said that they do the whole seals, bushings and new springs.
They said that they have an assortment of springs and they
keep trying until they get the right advance curve."
DISTRIBUTOR INSTALLATION: Since you read this book
first and marked the parts correctly, installation is a
snap. If the crankshaft has not been disturbed, reinstall
the distributor with the rotor pointing in the same
direction it was before removal (note: correcting a seized
advance mechanism may make the rotor point slightly
differently, but it's real close. You'll know if you miss by
one tooth on the drive gear). If the crankshaft was turned,
remove the oil filler cap, turn the engine until 10ƒ BTDC
and the mark you made on the sprocket is showing, and
install the distributor with the rotor pointing towards the
1A contact on the cap.
If you didn't plan ahead and the engine has been turned,
it is not so easy. If you just take a blind shot at this you
only have a 50/50 chance of getting it right. There is a
mark on the jackshaft, but the jackshaft turns at the same
rate as the crankshaft, twice the rate of the distributor,
so that mark is of no help.
To ensure correct positioning, the 1A spark plug can be
removed and the engine turned over with a thumb over the
hole; the compression stroke can easily be determined.
However, getting the 1A plug out and a thumb over the hole
is difficult on the H.E. (it's much easier on the pre-H.E.);
alternatively you can check for compression on cylinder 6A
(right rear cylinder). This cylinder fires exactly one
complete crankshaft rotation before and after 1A. Therefore,
you can find the top of the compression stroke on 6A and
then turn the crankshaft through one complete turn. Or, you
can leave it there and install the distributor such that the
rotor points to the 6A contact instead, exactly opposite the
1A contact.
To place the distributor housing in the right place on
the slotted holes so the vernier adjustment has a usable
range, merely align it with the marks you made before you
took it out. You didn't mark it? Tsk, tsk. Read on.
Michael Neal claims, after working on these cars daily,
that the optimum location of the distributor body on the
three slotted holes is always the same. The correct position
"is with the distributor body set at 3.5 degrees retarded at
the adjuster. The centerline of the rotor will be 75% past
the No. 1 line on the inner shield. The slots for the
holddown allen bolts will be 2/3 past the allen heads. The
tooth on the pickup will be roughly 5 degrees past the
center of the pickup point. Note that the distributor turns
anti-clockwise. This setting will give you near perfect
timing almost every time with adjustments both ways. Other
settings tend to give too much retard or advance with no
adjustment."
PREVENTING THE DAMN THING FROM SEIZING AGAIN:
After you've overhauled the distributor and fixed the
seized advance, the rotor carrier/distributor shaft
interface must be lubricated regularly; the Lubrication
Chart in the Repair Operation Manual says two or three drops
of clean engine oil in the felt under the rotor every 6,000
miles (every oil change - no, Quickie Lube is not
likely to be doing this!). This is not easy, as it requires
removing the distributor cap, which in turn requires
removing the cruise control unit and all the ignition wires.
This lubrication procedure is obviously very important; it
is recommended that owners do it themselves, or make very
sure their mechanic isn't skipping this part of the
maintenance. Jan Wikström suggests installing a new
felt pad, then taking it in for service. If the pad is dry
when checked afterward, cease doing business with that shop.
Perhaps good advice, but has a significant probability of
eliminating every shop in the area from consideration!
Note that many XJ-S distributors don't seem to have any
felt. Considering the known problems here, it'd probably be
a good idea to put some in. Or, just a wad of cotton.
Since the seizing appears to be caused by the lubricant
getting baked, normal "clean engine oil" might not be the
best idea. I recommend that a synthetic engine oil be used,
since it won't tend to varnish or sludge and withstands
higher temperatures without breaking down. Soak the felt or
cotton thoroughly every time you're in there, and make sure
you're in there often enough. It might not need to be as
often as every 6,000 miles -- especially if you're using
synthetic motor oil -- but it's better to be safe than sorry
here, so make sure you do it often until you personally have
confidence that you can go longer between oilings without
the thing drying out or gumming up.
It is suggested that spray lubricants of the flammable
variety be avoided within the distributor. When running,
there are sparks between the rotor and the electrodes in the
cap; vapors will be ignited upon starting, ruining your
day.
DISTRIBUTOR CAP REPLACEMENT: Randy Wilson has a
low opinion of the aftermarket products, and recommends
buying only the genuine Lucas parts: "The last time I
checked, there was only one aftermarket cap available. I
ordered in a lot of them... and every single one was
defective in one way or another. Missing center buttons,
missing vent tubes, pre-cracked, molded oval... Flimsy
pieces. They're about 1/3 the price of the Lucas pieces...
and not worth it." Note that the author has also purchased
one of these aftermarket items, and in fact had trouble with
the vent tubes simply falling off. Rendering it usable
required careful application of JB Weld.
DISTRIBUTOR CAP VENTING: The
82-89 distributor cap has two fittings for a positive
ventilation system. Air is drawn through a small filter,
through the distributor, and into the engine side of the air
filter housing. The filter is normally found laying against
the left wing at the crossbrace attachment, and sometimes
concerns owners because it appears to have been disconnected
from somewhere.
Reportedly this system was incorporated because the
earlier distributor caps were cracking due to excessive
heat, although some suspect removal of flammable vapors was
the real reason -- see the DISTRIBUTOR
SHAFT SEAL comments above.
The connection to the air filter housing is not actually
to the housing directly, but rather to a hose between the
housing and the supplemental air valve. This is therefore a
special molded hose with provision for a tiny fitting. The
fitting itself is a plastic elbow, and is often found to be
broken. It is not to difficult to find a suitable
replacement, though, and you might even find a brass one.
Or, you can forget the whole thing and install a generic
piece of hose between the air filter housing and the
supplemental air valve, and install a small fitting right
onto the inner side of the air fliter housing for connecting
the hose from the distributor.
The filter itself is no more complicated than it looks.
Any suitable fuel filter will serve as a replacement.
If you would like to help this system out, reroute the
intake filter to somewhere in front of the radiator. This
will draw cooler air, and will also draw more air since this
is a high pressure area. The cooler air should also help the
electronic ignition pickup last longer.
It's possible that this ventilation scheme was
retrofitted to earlier cars; SICP lists a "ventilated" cap
for these systems. It may also be possible to drill the
older cap and fashion suitable fittings, one in the side for
an inlet and one out the top for an outlet. A few pieces of
hose, a fuel filter, and a connection to the engine side of
an air filter housing and it's done.
Lucas
Opus Mark 2 (pre-1982)
LUCAS "OPUS" MARK 2 IGNITION -- DESCRIPTION: This
is a brief description of how the pre-1982 ignition system
works, based on the more detailed description in SAE paper
720163 on the development of the engine. It is not
applicable to the 1982-on systems.
The pickup within the distributor consists of an E-shaped
transformer with one input coil and two output coils. The
input coil is on the center leg of the E and is fed a 600KHz
input signal from the amplifier. The two output coils are on
the outer legs of the E and are wired in series so that
their outputs cancel -- provided the two sides of the
transformer are equal.
When one of the ferrite inserts built into the plastic
rotor in the distributor aligns itself with one side of this
transformer, it magnetically completes the circle on one
side of the E. Since the output coil on this side is now
more closely coupled with the input coil than the other
output coil, its output is greater -- and the two no longer
cancel each other. A transistor in the amp is toggled by the
resultant output signal, triggering a spark.
OPUS IGNITION AMPLIFIER
RELOCATION: If you have a 1982 or older XJ-S, the
original ignition amplifier is a finned aluminum block
mounted down within the galley between the cam covers. It
gets cooked, primarily after the engine is shut off and all
that heat from the block rises. Dick Russell says that
intermittent failures characterized by the tach reading zero
even when the engine is still turning are a sure sign the
amp has failed.
Jaguar makes a kit to relocate this amplifier to the
plate across the top of the radiator so it stays cooler. The
kit includes a new amplifier and a new pickup for inside the
distributor, and costs over $300.
It is possible Jaguar includes the amplifier and pickup
simply because the only time their mechanics get a call to
relocate the unit is after the original unit has fried. On
the other hand, perhaps the reason the unit was originally
located in such a sorry place was because the wiring needed
to be as short as possible, and the replacement amp and
pickup have updated circuitry necessary for the longer
wires. According to Jan Wikström, the plugs and wires
used on the replacement kit are different than the original,
indicating you're supposed to replace the amp and pickup
together. However, he simply spliced wires and used his old
pickup, and it worked fine. He notes, however, that the wire
color codes changed; it is necessary to open the amp and
verify where the wires go to ensure they are connected
correctly.
Clearly, crosstalk between the 600 KHz input signal and
the output wire back to the amp would be detrimental to
operation, and such crosstalk could be easily caused by the
wires merely being located too close to each other for too
great a distance. Also, the output wire picking up any
other signals -- such as interference from the
ignition wires -- would be ungood.
Reportedly, some owners have relocated their original
amps by simply lengthening the wires, and have been
successful. Others have not been successful. At least
one owner reports that the official Jaguar relocation kit
caused the wires to pick up so much interference from the
spark plug wires that the car wouldn't run, and he couldn't
get the system to work until he shortened the wires
back to the length of the original.
Russell recommends that ribbon wire with five or more
conductors be used to relocate the amp. By using every other
conductor, the unused conductors in between provide adequate
spacing between the active conductors to prevent crosstalk
and interference.
Russell also recommends relocating the amp to the
firewall rather than the top of the radiator. In his car,
the amp was affected by water and crud thrown up from cars
in front of him. Fortunately, he was able to repair it by
resoldering some connections inside.
Perhaps another solution is to leave the amp in the
valley and attempt to keep it cool there. Fashioning a heat
shield from sheet aluminum for underneath it will help.
Also, see the suggestion about cutting
a hole in the A/C compressor mounting plate.
British Auto/USA claims to have "reinvented" this amp
using modern electronics. The amp they offer, part number
JLM368/R, looks exactly like the original and is supposedly
durable enough that it may be located within the V;
apparently some concours judges (yes, these cars are getting
old enough to be considered classics) will subtract points
if the amp isn't in its original location.
If you have a 1982-89 car with a black plastic amplifier
mounted on top of the left intake manifold, you have no
problem. Although close to the engine, this is actually a
comparatively cool location and there is no significant
history of heat-related failure.
IGNITION AMPLIFIER -- REPAIR: Referring to the
Opus finned aluminum ignition amp, Jan Wikström says:
"As for the amplifier itself, there is precious little
pottery involved. I opened up the suspect one (four small
hex-head screws underneath) and found that while there's a
silicon blob at the cable entry and a silicon slurp for a
seal around the lid, the inside is empty and there is
complete access to PC board and power transistor. No need to
$pend up on a new one if it goes belly up; this unit is
eminently repairable."
PICKUP WIRING: Wikström warns: "One problem
I've had on both cars is an intermittent break in one of the
three ignition trigger wires coming out the front of the
distributor, right in the moulded grommet. This seems
inherent to the design, as the big, heavy three-pin
connector flops around on loose wires and should cause metal
fatigue as the wire bends back and forth. I have replaced
the wires on the XJC (solder joints inside the distributor)
and applied spade connectors instead of the three-pin job. I
am about to apply the same cure to the XJ12L, which suffers
from the same problem."
PICKUP CLEARANCE: Mike Morrin says "My car
suffered for years from an internittantly rough idle. An
oscilloscope connected to the ignition showed that at idle,
one particular cylinder only sparked about half the time. It
turned out that due to wear or some other marginal
condition, the clearance between the pickup transformer and
the rotating disk in the distributor needed reducing from
0.55mm to 0.50mm (both figures within specified range)."
TACHOMETER WIRING: Wikström reports: "the
circuit diagram in the workshop manual is wrong in one
particular: it shows the rev counter take-off from the top
terminal of the ballast resistor unit; this doesn't work, as
that terminal is at direct B+ (I tested). The rev counter is
wired to the neg terminal of the coil on both my cars (with
a resistor in series for whatever purpose)." Although
Wikström's car is an XJ12C, this correction applies to
the diagram in the XJ-S repair manual as well; there is a
power wire and a ground wire, and the third wire (WS/U) is
shown connected to a line from terminal 5 on the ignition
switch to the ballast resistor. This would do no good at
all, just supplying a constant 12V with no RPM signal.
On cars with the later ignition system, the tach wire --
still WS/U -- is connected to the ignition amplifier, and is
shown correctly in the supplement to the repair manual.
OPUS IGNITION SYSTEM REPLACEMENT: Derek Hibbs
reports: "My ign amp died as a result of convected heat last
year. A reliable replacement unit was not available so the
workshop installed a Crane Cams unit. The unit itself is
located on the RHS air cleaner and it came with replacement
pieces for the distributor because it uses an optical pickup
as against the original magnetic pickup."
Bernie Embden came to the same conclusion. "A better
solution is to use an aftermarket brand, which has wires
long enough to locate the amplifier in a more friendly
environment. I installed an Allison optical unit several
years ago, mounting the amplifier inside the passenger
compartment behind the glove box. This has worked
flawlessly, and is significantly cheaper than the original
Jaguar unit."
Welsh Enterprises offers two different Lumenition
ignition systems for the Jaguar V12.
Note: Lucas designed the plastic wheel within the Opus
distributor with three slotted holes that enable the
mechanic to insert an Allen wrench, loosen the three screws
at the very bottom, and remove the distributor as a unit. On
the Lucas CEI (below) this isn't even an issue, since the
star wheel used isn't large enough in diameter to impede
access to the screws. However, if you install some sort of
aftermarket system, you might want to consider whether or
not you will be able to get that Allen wrench past or
through whatever is used to trigger the pickup. Of course,
it might not be your highest priority; you could always
simply disassemble the distributor in place far enough to
remove the wheel to gain access to the screws.
Lucas
Constant Energy ignition (1982-89)
BENEFITS: Roger Bywater describes the reasoning
Jaguar adopted the Constant Energy Ignition system: "The
12.5:1 compression of the H.E. was too much for OPUS to fire
and in any case it was getting to be a bit primitive by that
time as it had no means of current control other than via
the ballast resistor. The Constant Energy system has a
"timed turn on" feature which maximises the coil charging
time at high speeds whilst at lower speeds it limits current
to a predetermined level. This makes possible the use of
more powerful coils with lower primary resistance. At the
time of the H.E. introduction very low resistance coils were
not readily available so the unique dual coil arrangement
was adopted to achieve the necessary spark power for high
speeds.
TROUBLESHOOTING: Randy Wilson sends this
procedure: "With the engine cranking, check for:
- Power to the ballast source
- Power to the coil + post
- Ground switching on coil - post (if so, you should
have spark)
- Ground to amplifier case
"If everything passes except the ground switching on the
coil, then it's in the amplifier or its wiring.
"A scope put on the pickup leads should give a modified
sine wave pattern typical of magnetic induction sensor. At
crank speed, I think it's around 1.5V peak-to-peak.
No scope pattern is a bad pickup."
"I've never personally seen the pickup go bad, but have
run into cracked wires in the pickup harness. Quite often
jiggling the harness will cause the problem to "correct"
itself; sometimes for many years. Everything working fine
after doing the scope check is bad pickup wires."
IGNITION AMPLIFIER -- REPAIR: The Lucas Constant
Energy ignition amplifier is a black plastic box mounted on
top of the left intake manifold. This unit is clearly
labeled "Lucas" and "Made in UK". The mail-order catalogs
call for a part number DAB106, and want serious $$$ for
it.
If you unbolt this unit from the intake manifold, turn it
over, remove four tiny screws and remove the cover, you will
see four components inside. The most predominant component
is a GM High Energy Ignition (HEI) module. This unit is so
common that you can find it on a bubble card hanging from a
hook in any department store with an automotive section --
for around $20.
The other components include a fairly standard condenser
and a zener diode. It is probable that this amplifier can be
repaired by simply replacing the GM HEI module for
considerably less than the cost of replacing the whole
unit.
Richard Mansell found the following warning referring to
his ignition amp:
WARNING: THE
AMPLIFIER IS A SEALED UNIT CONTAINING BERYLIA. THIS
SUBSTANCE IS EXTREMELY DANGEROUS IF HANDLED. DO NOT
ATTEMPT TO OPEN THE AMPLIFIER MODULE.
Apparently, berylia is an ingredient used in a type of
ceramic used to mount electrical parts. This ceramic
conducts heat very well, helping keep the part cool.
Unfortunately, berylia is really as dangerous as indicated,
possibly worse. If you choose to replace the GM HEI ignition
module within your amp, just unbolt it and bolt in the new
one; don't go grinding or chipping away at things or sawing
anything open, the dust created can
kill you.
ELECTRONIC IGNITION PICKUP: The electronic pickup
used in the Lucas Constant Energy distributor involves a
magnet that is mounted with two screws. Be careful
tightening these screws; the ceramic magnet is much more
brittle than metal items, and can easily crack. If already
cracked (notably around one of the screw holes), do not be
concerned, it will not affect operation. However, be sure
not to leave any loose or small parts inside that could come
loose and move around within the distributor. It is better
to discard small bits of the magnet that have broken
away.
CONNECTORS: Mark Whitnell reports, "For the last
several months the only way I could get it started was to
use starting fluid. I checked out the spark since that was
an area recommended by Kirby. The spark was very small and I
suspect that the small spark could not ignite the gas but
could ignite the ether (lower vapor pressure).
"I checked the distributor pick-up coil for the proper
resistance according to Haynes (2.2K to 4.8K). I checked at
the connector attaching to the ig amp first...very high
megohms. Then I pulled the connector apart at the
distributor. Checked the continuity of the wiring to the ig
amp...checked ok. Then measured the resistance at the
connector to the distributor...high resistance. Looking at
the two prong connector...visually it looked fine. I went
ahead an cut off the connector and measured resistance of
the two wires to the distributor pick-up. Measured
resistance... 3000 ohms within the range described in
Haynes. Replaced the connector. Voila, starting problem
solved.. good spark, etc."
COILS: The Lucas Constant Energy ignition uses two
conventional ignition coils wired in parallel. The
high-tension lead of the secondary coil is sealed off, and
only the lead from the main coil is connected to the
distributor. Between firings, energy is built up in both
coils. When the 12V supply is broken ("the points open" in
the lingo of the pre-electronic age), the energy stored in
the secondary coil cannot escape through the high tension
lead because it is sealed off, so the energy comes back
through the 12V leads instead. The primary coil then not
only has to release the energy it has stored itself, but
also the energy coming back from the secondary coil. These
two energies add to produce a powerful output at the high
tension lead on the primary coil.
The secondary coil, located in front of the radiator, is
not a spare or a backup; it is designed into the
system for producing a good spark. If either coil goes bad,
the performance will suffer. The secondary coil is not
special, however, and can be replaced with a conventional
coil provided the high tension connection is covered so that
it cannot arc to ground.
Since mid-1989, XJ-S's have gone to a Marelli ignition
system that also uses two coils. However, these two coils
are totally separate; each one fires only six cylinders.
According to Alan Jenks, "Jaguar now recommends replacing
both coils with a single "solid" (not oil filled) coil (#DAC
6093) that fits in place of the main coil. The aux coil and
wiring is removed." Roger Bywater says, "The best coil to
use on Lucas HE V12s is DAC 6093 (Ducelier coil - 0.62 ohms
primary); only one needed and works well in place of earlier
twin coil set up. If you can find another coil with primary
winding resistance of 0.5 - 0.6 ohms maybe it is worth a
try. If the resistance is any more than that it will not be
able to build up enough coil energy to fire a spark at the
higher end of the rev range when the coil "on time" is very
short (about 1.4 milliseconds at 6000 revs). It might also
struggle around the peak torque point. Although the V12
constant energy ignition module is fairly tolerant (it runs
OK with the blanked second coil removed - albeit with a loss
of spark energy) I have encountered some that behave very
oddly if the coil is not the correct load match. The DAC
6093 might be a bit expensive but it does the job..."
He adds that the original parallel coil arrangement was
"conceived when coils of sufficiently low resistance were
not available."
John Goodman defends the earlier parallel coil setup:
"The only difference (between the two coils) is the HT
socket is sealed on the aux coil, and is no longer stocked
by Lucas. The primary coil is still available from a Lucas
distributor and is cheaper than the universal coil Jaguar
sells to replace the two V12 coils. I am experiencing
coil/ignition related problems on my car and have tried a
few of these Ducelier coils (original equip on the XJR-S). I
am convinced it is the coil causing intermittent starting
and cutting out problems, thinking of resorting to the early
twin Lucas coil system which never gave any trouble on
previous cars."
Jim Isbell: "By the way, if you measure the primary, be
careful because when you remove the meter the secondary
sparks and it can really make you jump; also, when the field
collapses you can feel the bite on the primary as well."
On to the
Marelli
Ignition
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