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XJ-S Ignition

// JagWeb // XJ-S Help // Contents //

 

XJ-S Ignition System

Spark Plugs

A quick survey of a group of Jaguar experts clearly indicates that NGK is the plug to use. The study may have been unscientific and the reasons may have varied, but the consensus was clear and overwhelming.

The H.E. engine uses taper seal plugs; the pre-H.E. engine uses washer-seal plugs. For the H.E., NGK makes at least two plugs, TR5 and BPR6EFS. Both are resistor type, but the TR5 is a "V-Power" plug with a little notch cut in the center electrode.

Notched Plugs

There are many gimmicks used to sell spark plugs these days. There is one common feature that may be of some benefit: it is easier for a spark to jump to an edge or point than to a flat surface. This is why lightning rods are pointed. Many of the cute configurations of spark plugs result in there being more edges on the electrodes, instead of flat surfaces. The notch in the center electrode of the NGK V-Power plug is such a feature.

Resistor plugs

There is no appreciable disadvantage to using resistor plugs. The resistance limits the current flow, which in turn reduces spark plug wear and radio interference. Prior to the actual spark, there is no current flow so the resistance has no effect on the voltage available at the electrodes.

Plug Gap

Note that the pre-Marelli ignition H.E. engine generally calls for a 0.025" gap (check decal on underside of hood). Plugs come out of the box with a 0.032"-0.035" gap. The gaps need to be adjusted prior to installation.

Spark Plug Replacement

Ain't nuthin' easy about this job. Using normal tools, it generally requires removing the cruise control actuator and unbolting the A/C compressor to replace the 1A and 1B plugs. However, according to Chad Bolles, the plug wrench that comes in the XJ-S tool kit can be used to replace these plugs without removing the compressor. If you don't have this tool (CAC5368) it can be purchased from Jaguar for about US$71!

Special Tools

First problem is getting the plug wires off -- and back on later. Jan Wikström:

I've made up a pair of "pusher" tongs out of a bent piece of 4 mm hightensile fence wire. Same idea as the common barbecue tool, but the jaws originated as a short piece of 9 mm copper pipe split lengthwise and brazed to the wire. This gets a good grip on the cable just above the rubber cap on the terminal. This tool needs to be bent to a slight angle above the jaws.

Cleaning

If you have access to a wet/dry vacuum cleaner, use the hose with no attachments to clean around the plugs before removing them. Just poke the hose over the end of the plug. Compressed air can also be used.

As long as you're going to the effort of taking the plugs out, it wouldn't be a bad idea to go ahead and perform a compression check. It's a good way to keep a watchful eye on engine condition.

Plug Threads

Before installing the new plugs, it is recommended the time be taken to carefully inspect the threads. Competition is fierce among the plug manufacturers and they generally cannot afford to spend a lot of time and effort making perfect threads every time. One small burr on a steel spark plug can wreak havoc on the threads in the aluminum head.

Anti-Seize

Be sure to use anti-seize compound on the threads. Do not use normal grease, as this may hamper proper grounding of the plug, and it also may get hot and form a crust that makes it even harder to remove the plugs. And do not use a graphite-based lubricant, as graphite may react with the aluminum and weaken it.

Tightening

When installing spark plugs, it is helpful to use a piece of 3/8" hose to get them started. Press the hose firmly over the top of the plug and use the hose to feed them into place and thread them in finger tight. Then the hose can be pulled off and a socket used for final tightening.

There are warnings not to tighten the plugs past 8 ft-lb. of torque. 8 ft-lb. is not enough to turn the plugs loosely in the threads unless they have been recently cleaned and chased, but the point is well taken. It is an aluminum head, and tightening "three grunts" is both unnecessary and costly. Just tighten until you feel them seat, make sure they're snug, and quit.

Stripped Plug Threads

Since you have read this book, use anti-seize compound on the spark plug threads, and don't overtighten, you will never strip spark plug threads. However, the guy who owned the car before you (affectionately referred to as the PO for Previous Owner) or the idiot you've been taking the car to for service may not be so careful and leave you with plugs that simply won't come out without bringing the threads with them. Aaargh!

The official Jaguar fix involves recessing, drilling and tapping the holes for larger threads, installing an insert, and installing a small pin to prevent the insert from unscrewing. Note that the inserts will be different for H.E. and pre-H.E. engines, since the pre-H.E. used washer seal plugs while the H.E. uses taper seal plugs. Generic inserts may work fine, but regardless of insert used the head surface should be recessed prior to installation to ensure that the tip of the plug will be positioned at the same level as before. If the surface is not recessed, the plug will seat in a slightly retracted position and result in a lower compression ratio on that cylinder as well as possible effects on the swirl pattern in the H.E.

H.E. Spark Plug Indexing

Does "anal-retentive" have a hyphen? If you answered yes, you may be interested in knowing that "indexing" spark plugs may improve performance in the H.E. engine. In the H.E. combustion chamber, the compression stroke squeezes the fuel/air mixture out of the area over the inlet valve and into the area over the exhaust valve, causing a swirl. This fuel/air mixture is swirling when the spark occurs. If the ground electrode on the spark plug happens to point away from the swirl, then the spark is partially hidden from the fuel/air flow, possibly hindering proper ignition.

To avoid this, mark the side of each spark plug with an indelible magic marker to indicate where the electrode is. Check the engine configuration to determine where the exhaust valve is in relation to the spark plug. All valves are in a straight line directly under the camshaft, and the spark plugs are above and between them. The exhaust valves are in front of the inlet valves in the front six cylinders, and behind them in the back six. Then, when installing the plugs, check the alignment of the electrode when the plug is in and tight. If the back side of the electrode faces the exhaust valve (outward and forward on the front six cylinders, outward and rearward on the back six), then exchange that plug with another.

Please do not use a lead pencil to mark the plugs. Graphite conducts electricity, and will cause "tracking" down the side of the ceramic and short out the spark plug. Your engine will run much worse than before you indexed the plugs.

Spark Plug Wires

If your ignition wires need replacing, there's really no reason to buy the Lucas originals; you should be able to purchase two 6-cyl or 8-cyl sets of high-quality ignition wire sets from any auto parts store and combine them into a set for the V-12. Here are some tips:

You can get anything from a roll of wire and a package of connectors all the way to completed, ready-to-install sets; I suggest a "semi-tailored" set -- one end of each wire comes with the spark plug connector attached, but you cut the other end to length and attach the distributor cap connector yourself. The wires on the V-12 are shorter than most, and this permits the right length so you don't have lots of excess wire laying around.

Another feature to look for is the angle of the spark plug connector. Some are straight, some are 90 degree, a few are 45 degree. What the V-12 needs is a slight bend; the ideal kit has connectors that are straight to begin with but can be bent to whatever angle is needed. This allows providing different bends at different cylinders -- working on these plugs, you need all the help you can get!

Of course, silicone wires are a must.

There is also the choice between 7mm and 8mm wires. Ideally, one would choose 8mm wires, since the Jaguar ignition system is really hot. However, I couldn't find an 8mm set that had the type connectors to fit this distributor cap; the 8mm sets all fit caps that the connectors look like the top half of a spark plug rather than holes. So I ended up with a 7mm set. Another option would have been to fashion adapters for the cap, possibly from an old set of spark plugs. Maybe there are suitable 8mm sets available that I didn't find.

All aftermarket kits seem to be bright colors. Deal with it.

The sets I ended up with were made by Auto-Tune and sold by AutoZone as part number 2300. Since each set has enough wires for a V-8, I got four plug wires and one coil wire to spare.

All that said, it should be noted that the original Lucas wires are usually not very expensive; the only valid reasons for using aftermarket wires are availability, a need for a dash of color, and a healthy contempt for all things Lucas.

Ignition Systems

Three ingition systems have been used on the Jaguar XJ-S: the Lucas Opus Mark 2 system on non-H.E. engines prior to 1982; the Lucas ignition on H.E. engines 1982 to 1989; and finally the Marelli ignition on post-1989 cars.

Ignition Design Overview

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.

Troubleshooting

Randy Wilson sends this procedure for troubleshooting the Lucas ignition system:

With the engine cranking, check for:

  • Power to the ballast source
  • Power to the coil + (positive) post
  • Ground switching on coil - (negative) 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.

Jan Wikström sends this procedure:

This is the Gum Tree Garage test for a V-12 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 (0.04in) 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 Jaguar V-12 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 3,000 rpm the timing will be retarded by 25° or so. If you merely adjust the timing rather than correcting the problem, then the timing will be 25° too far advanced at idle!

Front Pulley Position

First, confirm 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. The woodruff key problem is discussed in the section covering the V-12 Engine.

Timing Indicator Adjustment

On the Jaguar V-12, 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 0° lines up with the mark on the pulley.

Alternative Method

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.

Connecting the Timing Light

The battery is in the trunk, so 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. Perhaps the easiest solution is to use a pair of jumper cables from the battery in the trunk. Peter Smith connects his 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.

You must crawl under the front of the car while an assistant holds the engine at 3,000 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 3,000 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.

Centrifugal and Vacuum Advance Data

Page 05-1 of the XJ-S Repair Operation Manual, ©1975, lists data for the centrifugal and vacuum advance mechanisms. This data is valid for the pre-H.E. engine only, as the H.E. system develops less advance in the centrifugal mechanism and more advance in the vacuum mechanism. Section 86.35.29/4 of the same book lists data for bench-checking the distributor, but the centrifugal advance data is in error. Values listed in distributor degrees and distributor rpm should be exactly half of the engine readings, since the distributor turns at 1/2 crankshaft speed.

Page 05-1 of the Supplement to the Repair Operation Manual, ©1982, lists the correct advance values for both non-H.E. and H.E. engines.

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 0° 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 distributor provides 18° to 22° advance at 4,000 rpm, it doesn't mean to set the timing at 18° to 22°; it means the timing should be 18° to 22° more advanced than it is at idle.

Timing Adjustment

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.

Advance Settings

The proper advance setting is indicated on a decal in the engine compartment. If it differs from the manual, believe the decal.

Correct Engine Speed

The ignition timing on the V-12 is checked with the engine held at 3,000 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 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 1° 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 3,000 rpm. That point can then be held whenever the timing is checked in the future.

Disconnect the Vacuum Advance Line

When checking the ignition timing on the V-12, 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.

Centrifugal Advance Seizing

At this point in this book, I used to report how the pre-1987 Jaguar V-12 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 since new, 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 V-12 has, 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.

Indications of Seizure

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 11° (H.E.) or about 18° (non-H.E.) against a spring. Note that this thing should feel really loose, and move with a metallic clink; if at all sticky or gummy-feeling when turned, time to overhaul. If partially seized, it may be movable but not as far as it should or not as freely as it should. 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 2,000 rpm with the timing at idle (under 900 rpm). The two readings should differ by at least 12° (H.E.) or at least 22° (non-H.E.). If they are the same or very close, the centrifugal advance is seized.

Quick Repair

Once you accept the fact that your centrifugal advance is seized, 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.

Prevention and Maintenance

To prevent seizing, it appears to be necessary to overhaul the distributor and clean out all of the original lubricant. However, even after such an overhaul, 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!

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 motor oil be used, since it won't tend to varnish or sludge and withstands higher temperatures without breaking down.

It is suggested that spray lubricants of the flammable variety be avoided within the distributor. There are sparks between the rotor and the electrodes in the cap; vapors will be ignited upon starting, ruining your day.

Distributor

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.

Position

Before removal, care must be taken to ensure the distributor can be reinstalled facing the correct direction. 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.

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 10° 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 10° 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.

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.

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-on cars, it is fairly simple to pry off the iron star-shaped inductor rotor, but be careful not to damage it or deform the points.

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.

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. Of course, it's a good idea to inspect the vacuum advance mechanism within this assembly as well as the pickup module while you're there.

Disconnect the springs from the centrifugal weights, noting how they are installed. Remove the felt from the top of the rotor carrier 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. Remove the retention, even if it involves breaking the nylon clip. I'm sorry I can't be any more help there; even when holding the clip in my hand, there doesn't seem to be any easy way to remove it.

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 black crud off the bearing surfaces.

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 1982-87 only)
  • Screws and washers for anti-flash shield (4 ea)
  • Ignition pickup mounting screws (2 ea - used on 1982-87 only)
  • Distributor cap gasket
  • U-pin for reluctor positioning (used on 1982-87 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 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 the rotor retaining clip, while not likely to survive disassembly, can be replaced with a small washer and tiny O-ring.

Distributor Shaft Seal

The Jaguar V-12 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 still are prone to advance mechanism seizing.

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.

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, thereby limiting how retarded the timing moves at idle. It's also a British non-metallic part, so it's cracked or broken.

The bad news: this part is apparently unobtainable. It's not included in the DZB105 kit.

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 nonservice 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 nonservice 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 seems to be a workable one -- is to install a generic flat washer in place of this thingy. Plastic or non-ferrous metal will work nicely. The loss of the inner stops for the centrifugal weights will evidently allow the timing to retard a little more at idle than it should (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.

Centrifugal Advance Reassembly

Should you grease the rotor carrier shaft before reassembly? Good question. If you can find a really high-temp grease (such as special distributor grease), it would probably be a good idea. If you can't find anything better than what was used at the factory -- and probably caused the seizure in the first place -- it may be workable or even preferable to lubricate this bearing only with synthetic motor oil.

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 such a clip. 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. If done properly, the carrier should have a very slight amount of up and down play, which won't harm anything.

Re-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 10° BTDC and the mark 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 the marks are 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, so 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 anticlockwise. 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.

Distributor Cap Replacement

Randy K. 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 1982-87 distributor cap has two fittings for a positive ventilation system. Air is drawn through a small filter, through the distributor, and into 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.

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 Ignition (Non-H.E. 1975 to 1982)

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.

Overview

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 600 kHz 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.

Ignition Amplifier

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 tachometer reading zero even when the engine is still turning -- are a sure sign the amp has failed.

Relocation

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 US$300.

(If you have a 1982 or later 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.)

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. However, at least one owner reports that the 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.

Ignition Amplifier Cooling

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 in Cooling System about cutting a hole in the A/C compressor mounting plate to improve air flow.

Replacement Amplifier

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.

Amplifier Repair

Referring to the early 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

Jan 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 intermittently 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 0.50 mm (both figures within specified range).

Tachometer Wiring

Jan 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.

Pre-H.E. Vacuum Advance Module

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 wanna 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.

Lucas Ignition (H.E. 1982 to 1989)

The Jaguar V-12 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 0.025" to make it easier for the electricity to jump the gap.

Twin Coils

One feature of the early H.E. is its use of 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. This is an old racing trick. 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 1989, XJ-S cars have gone to a Marelli ignition system that also uses two coils. However, these two coils are totally separate; each one is used to fire only six cylinders, thereby doubling the amount of time each one has to build up energy.

Ignition Amplifier

On the 1982-87 XJ-S, the 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 US$20.

One of the other components is a fairly standard condenser. While the remaining two components are more unique, 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.

Warning

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 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 on the 1982-87 XJ-S 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.

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.

Vacuum Retard

Ian Macfarlane, regarding his 1985 H.E. XJ-S:

In Australia the distributor has a retard connection on the vacuum module which is supposed to operate for about 15 minutes 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 degrees 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.

Marelli Ignition (1989-on)

In this age of electronic wizardry, many modern cars have done away with the mechanical centrifugal and vacuum advance mechanisms and do the whole job with microprocessors. In some cars, the distributor is done away with altogether, and separate ignition coils are used instead. By using coils with one primary and two secondary windings, each coil can operate two cylinders; the plugs fire at the top of every stroke, the spark at the top of the exhaust stroke being worthless, but the reduction in moving parts makes it worthwhile.

Since Jaguar incorporated the Marelli ignition system in 1989, this is essentially the type of system used. There is no centrifugal or vacuum advance mechanism; the timing is all done electronically. However, rather than use six separate coils, the distributor was kept, using two normal coils and directing the spark conventionally. This distributor is clearly lacking many of the internal parts of the earlier models, since it no longer handles the timing functions. The computer that handles the timing is located near the passenger's feet, and has a vacuum line to it.

Michael Neal adds:

There is also a nifty little jumper on the harness at the back side of the left intake manifold. Pull this sucker and your timing retards, perfect for those trips to Mexico. Usually the connector is red.

Intermittent Failures

Greg Madison suffered from electrical connections:

Occasionally when warm/hot the engine just stops. It will usually restart after a few tries or if left for a couple of minutes. It turned out to be the crankshaft sensor connector. I could jiggle the crank-sensor and car would start again. If you have the Marelli digital ignition system you will have a crankshaft sensor and a flywheel sensor; engine will not run if the signal is interrupted from either. Look for a two-wire connector on the left front top of the engine; wires should be in a hard plastic wire protector running down the front of the engine to the back side of the crankshaft pulley. I found the contacts in this connector to be green and nasty. Cleaning with spray-on relay and contact cleaner cured the problem. Run the engine and wiggle this connector and see if it stops. Also check the flywheel sensor connector, it's on the rear top left of the engine, looks like the crank sensor connector and hard to get to.

Cap and Rotor Durability

Vic Naumann says:

Marelli rotors are prone to burning and the caps can easily develop small cracks and admit moisture.

 

On to the Cooling System

 


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