Electronic Ignition

To all ignition experts,
I was going to ask an ignition question yesterday but was side tracked with
euphoria after my successful sortie. The question is what happens to the
inside of a distributer cap after it has had arcing? Does it have to be
replaced, cleaned with something or just left alone? With the Crane
electronic ignition system I installed, putting on a set of 8mm carbon
fiber core wires and closing up the plug gap to .025" really helped the
engine. However, there is still some poor ignition at the low end of the
acceleration curve in each gear.  To use the garden hose example again,
there is still some voltage leaking out of a small hole (less  resistance)
when the load is greater, like during acceleration. As the rpm's increase,
it smooths out and sounds great. Working backward from the plug end of the
system, the gap is right, the wires are very adequate, all the connections
are good so by the process of elimination, I'm left with the cap, the wire
from the coil and the coil itself. One possibility, and solution, is to
reduce the voltage, using a resister,  after the coil, and before it
reaches the cap/rotor assembly. The Crane ign. instructions even suggest
this possibility. It seems self defeating to have all the power(voltage)
available and then disable it with a resister. There must be some way to
get it all the way to the plug without loosing it along the way.  Someone
said to make sure the original condenser is out of the system; it is. You
guys that race must have some secrets tucked away that would help my
situation. From  the first day I was on this list, it was obvious that the
majority of the members are VERY "original condition" oriented. I repect
that. I realize that installing an electronic ignition is a long way from
that end. I do nothing to my car that is permanent and can't be undone when
the "original only" bug strikes. It's just with so much nice weather,
having it sit up on blocks for years isn't something I'm ready to do just
yet. As long as it's still running (is that laughter I hear) I'll be
driving it. The old VW bus and the Jag are both running at the same time so
I must be getting closer to the light at the end. Larry J. will be arriving
today and I'm looking forward to meeting one of you guys. The invitation is
always open  as long as you don't leave the islands, without first leaving
some advice at my house.  Give some thought to the ignition thing and I'll
report back with Larry's diagnosis.
Aloha, Rob XK-140 FHC

Rob I have a Crane ignition setup with optical trigger on my 140 and it
works a treat. I have converted many previous vehicles to pointless systems
including my MotoGuzzi LeMans  and swear by the reliability (and lack of
fiddling required). Fifteen years without adjusting anything (the Guzzi)
speaks for itself. The coil has a ballast resister but rest has no tricks
except a quality ignition lead system. Sorry I can't be off more help but
it does work!!
Best of luck.
- Bruce Lake XK140 FHC, MKII, Guzzi Lemans, Perth W. Aust

>To all ignition expertts,

I don't think I have qualified for the second "t" yet, but here is my
opinion anyway. My dad was an ignition expert who specialised in restoring
vintage magnetos and other unusual ignition systems. I spent several years
rebuilding obscure and obsolete motorcycle electronic ignitions systems.

>The question is what happens to the inside of a distributer cap after it
>has had arcing?

Typically, the arcing initially occurs across the surface of the
insulation, following the track of some moisture or other contaminant. The
heat from the arcing burns the plastic and and forms a carbon track which
facilitates more arcing, getting deeper and deeper into the plastic.

>Does it have to be replaced, cleaned with something or just left alone?

If you just leave it it will get worse, particularly if it gets a bit of
moisture in there as well.

My mother's Mk2 Jag (with electronic ignition) got a carbon track in the
distributor cap (probably when a plug lead fell off), and the occasional
misfire was ignored until the engine managed to crossfire, causing a
backfire while starting, breaking the starter drive main-spring and causing
no end of trouble because it was an auto and we were 20 miles out in the
country at the time.

If the problem is caught very early, the carbonised tracks can actually be
polished out, but I think your cap would be past that stage.

Where an item such as a magneto slip ring was badly carbonised and
unobtainable, my dad would somtimes grind or file away all of the plastic
(normally bakelite) 2mm all around the carbonised track and then build the
item back to original size with a suitable plastic filler. Epiglass low
density epoxy was his usual choice for this.

I don't think that this sort of repair is economically justified for an XK
distributor cap or rotor.

>With the Crane electronic ignition system I installed, putting on a set of
>8mm carbon fiber core wires and closing up the plug gap to .025" really
>helped the engine. However, there is still some poor ignition at the low
>end of the acceleration curve in each gear. To use the garden hose example
>again, there is still some voltage leaking out of a small hole (less
>resistance) when the load is greater, like during acceleration. As the
>rpm's increase, it smooths out and sounds great. Working backward from the
>plug end of the system, the gap is right, the wires are very adequate, all
>the connections are good so by the process of elimination, I'm left with
>the cap, the wire from the coil and the coil itself.

Or the rotor, or perhaps the electronic ignition unit.

>One possibility, and solution, is to reduce the voltage, using a resistor,
>after the coil, and before it reaches the cap/rotor assembly. The Crane
>ign. instructions even suggest this possibility.

Resistors in ignition high tension circuits (including carbon ignition
leads) are only there for one reason, and that is to reduce the high
frequency CURRENTs which cause radio interference. A resistor will not
reduce the peak VOLTAGE, which is entirely governed by the plug gaps and
the cylinder compression.

>It seems self defeating to have all the power(voltage) available and then
>disable it with a resister. There must be some way to get it all the way
>to the plug without loosing it along the way.

Yes, replace any components which have been damaged by tracking. It will
not happen again unless you open up the plug gaps again, or have a plug
lead fall off.

As an aside, multi cylinder magnetos protect against tracking by having a
"safety gap" which diverts the high tension if the votage gets excessive.
Lucas (and most other) coil systems do not have this feature.

The main effect of you electronic ignition as compared to properly
mainatined points is that the dwell angle at the coil is increased, meaning
that there is more energy in the spark, but as the voltage is fixed by the
plug gap etc., the energy goes into a higher spark current. Only when the
plug gap is increased does the extra energy convert to extra voltage.

The secondary voltage and crossfire/tracking are not changed in any
significant way when you fit an electronic ignition unit, as these are
determined mainly by the secondary circuit of the ignition system, not the
electronic ignition unit. (This would not be true if you fitted capacitor
discharge ignition, but CDI is generally not recommended for 4 stroke
engines anyway.)

>Someone said to make sure the original condenser is out of the system; it is.

Only remove this if the ignition system instructions say to. Most after
market ignition systems run OK with or without, but some need it in and
some need it out.

>You guys that race must have some secrets tucked away that would help my
>situation. From the first day I was on this list, it was obvious that the
>majority of the members are VERY "original condition" oriented. I repect
>that. I realize that installing an electronic ignition is a long way from
>that end.

I have no gripe with electronic ignition (I will probably put a "period"
system like a Judsen on my 150 when it gets to that stage).

>I do nothing to my car that is permanent and can't be undone when the
>"original only" bug strikes. It's just with so much nice weather, having
>it sit up on blocks for years isn't something I'm ready to do just yet. As
>long as it's still running (is that laughter I hear) I'll be driving it.
>The old VW bus and the Jag are both running at the same time so I must be
>getting closer to the light at the end. Larry J. will be arriving today
>and I'm looking forward to meeting one of you guys. The invitation is
>always open as long as you don't leave the islands, without first leaving
>some advice at my house. Give some thought to the ignition thing and I'll
>report back with Larry's diagnosis. Aloha, Rob XK-140 FHC

Another thought has occured to me...

If you are using the original 12V Lucas coil, I presume you have not fitted
a ballast resistor (to do so would be wrong), but the older Lucas coils
have a tendency to overheat with the increased dwell angle of electronic
ignition, typically causing a misfire after running for a while. The only
cure for this is to fit a more modern coil. If fitting a non-genuine coil,
I would recommend fitting a ballast coil and resistor, as giving the best
reliability with your electronic ignition system.

Sorry, I didn't intend to give a lecture, but the keyboard ran away with me...
- Mike Morrin

If you don't mind a few further questions... I was curious as to why a CDI
ignition isn't recommended for four stroke engines.  (CDI in my
understanding is where the coil is replaced by a high voltage transformer
and you dump a charged capacitor through it... as opposed to
"electronic points" where the energy is still stored in the coil and the
points are supplemented/replaced by electronics.)  All I know about
ignition systems is spark energy and risetime, I'm just curious what the
problem with CDI is.

I remember my Dad putting one in our station wagon in the mid-60s, to
little effect as I recall.  (But then, he put one in his Mini-Cooper too,
so there must have been something he liked about it...).

Is the Judson "electronic magneto" still available?
- Ed Mellinger

The effect is that CDI (unlike "transistor assisted") systems, changes the
basic waveform of the high tension circuit.  The voltage risetime is much
quicker, and the spark itself is shorter duration, but much higher current
(making it ideal for firing fouled plugs in a 2 stroke).
The problem is that with modern 4 stroke engines which generally run quite
lean, there is sometimes not enough fuel in the vicinity of the electrode

for the duration of the spark, and it just doesn't get ignited, causing a
subtle misfire.  Remember that the fuel is not evenly distributed in the
cylinder, but is swirling around in little clouds (which is used to
advantage in the Jaguar V12 HE design).

This effect was apparently identified in the mid 1970s, and subsequently
CDI has disappeared from almost everthing except lawnmowers, outboards and
some high performance motorcycles, all of which run fairly rich anyway.

Current high performance ignition systems tend to rely on inductive storage
to get long duration rather than high intensity sparks.

It is also significantly difficult to get a CDI system to comply with
current radio interference laws in some countries.

I don't think the Judson is still available.  I have a couple of them here,
one of which did service on 2 of my mother's Jaguars in the 60s and 70s
(but I think it is a bit sick) and another which I think is virtually new.

When transistor ignition first appeared in the early 60s, my dad did some
lectures to the local motor trade explaning the theory of transistor
assisted and capacitor discharge systems.  Later when he first got a Judson
Electronic Magneto (he mistakenly thought it was a CDI), he decided to give
a practical demonstration of the benefits.

So he organised a field trip of the local motor trade association to
Archibalds Garage, the local Jaguar agent, and he put my mother's 2.4 litre
Mk1 on the rolling road dynomometer, and checked the maximum power
developed with standard ignition.

He then (with the audience watching) connected up the Judson and tested
again, but was most embarrased to find that the available power dropped by
a couple of HP.  It just goes to show the value of a rehearsal.

I don't know why the power was down with the Judson, I suspect a small
timing difference.
- Mike Morrin

To all, I have installed a Crane electronic ignition system in my XK-140. I
can't tell if it has made the car more reliable because there has always
been something else causing a problem. The new system puts out a spark that
could light up Waikiki, and that illuminated another problem. The old
ignition wires couldn't handle the increased current. Like putting your
thumb over the end of a garden hose, when the engine accelerated, the
sparks came arcing out all over. Now it has a new set of 8mm wires that
deliver the spark all the way to the plug. With such a "healthy" jolt
available,what is a reasonable plug gap? They are set at .035" now but
something is wrong and it runs terrible. One guy said I could open the gap
up to .060" but would need a longer end on the plug to do it. Seems a
little excessive to me. It idles rough and misses terrible when I
accelerate through each gear. Comments will be appreciated. Keep in mind
that my engine is a 1957 MkI 3.5 liter with an 8:1 CR, not a stock 140.
According to the WEB site and Rob Reilly, the timing should be 2 degrees
BTDC and not the 10 on a regular 140 engine. I didn't know this until an
hour ago when I visited the site. What an incredible collection of
information. I wonder if this could make that big a difference? I still
have the positive ground intact. Hope to hear from anyone. Time is of the
essence. Aloha  - Rob XK-140 FHC

Rob, A gap of .060 is a little excessive, .040-.045 should do. Make sure
your plugs are new or blasted clean (I've had good luck with BP6ES plugs,
NGK) You mentioned rough running, be sure the new leads you put on are in
the right firing order. Its real easy to cross them coming up from the
distributor. As for timing, I would go back to 10 degrees BTDC. This should
make your idle a little smoother just to get things rolling. You can tell
if this is too advanced "The Old Way".  Find a reasonably straight stretch
of highway that has an incline about 4 to 6 % (i.e. not so steep that the
downhill lanes have "Runaway Truck Ramps", nor so flat that you can see
over the "hill") Drive up the hill at about 50-60 mph in third gear being
easy on the throttle, then push the throttle all the way to the floor. If
your timing is too advanced your engine will sound like it just swallowed
several pieces of "metal" and is rapidly grinding the metal and itself to
bits. This is engine "ping" or "knock". It is a function of your gasoline's
ability to deal with both engine load, compression, and advanced timing. If
your engine pings/knocks, pull over and retard your timing by a few degrees
and try it again. Conversely, if it isn't making noise you can try
advancing your timing until the engine starts to ping/knock. The whole idea
is to get your timing as advanced as you can with out bringing on engine
ping/knock.
A couple of notes; with your mechanical and vacume advance working right
this "test" should also give you a pretty good idle. If you have a high
compression head (9 to 1), or a head that's been shaved too much it will
ping/knock sooner even with the timing retarded. Try switching to the
highest octane gas you can find. I have even noticed a difference between
the major names "best gas". This is not an endorsement or a slam but I have
gotten the best results with Unocal High Octane and the worst results with
Chevron High Octane here in California. The gas in this state has some
strange additives but it's worth checking around if you are looking for
better performance from your Jag. -  "Fairplay"

If you changed the coil to a newer high voltage unit, then you are probable
crossfiring inside the distributor cap. The small caps will not tolerate
much higher than stock coil voltage!! Also, be sure to install a NEW rotor.
You may be shorting to the dist. drive shaft. I assume you have
disconnected the old capacitor? If you didn't install a new coil, then your
timing is probably the problem. Loosen the dist. and move it for the
smoothest idle, tighten it and test drive. If it pings, you will need to
retard. Since this is supposed to be the new improved way to go, WHAT
HAPPENED? Good Luck. I will be there next week. - Larry J

Hi all -- have been in our Cats since '63 (34 years) -- in ''63, '53 Mk
VII; in '65, '52 XK120 disc wheel OTS; in '66, '58 Mk VIII; in '67, '55
XK140MC OTS; in '76, '54 XK120SE OTS; in '89, '59 Mk IX. During the 34
years, I've stayed with Champions, going along as they modernized -- N12,
RN12, RN12Y, now RN12YC. Have always set gap at .025 because books on ALL
cars said that's it. To date, NO problems whatever with plugs!!! I hope
this is helpful -- Larry Martz

Thanks for the quick reply on my ignition problem. If anyone can explain
the theory and physics behind the "larger the spark- smaller the gap" idea,
I would sure like to hear it. - Rob XK-140

Rob - you got the reasoning right... the high voltage takes the easiest
path (actually the most readily ionized path) to ground... but I have to
differ with your conclusion: I would say that the hotter the spark, the
BETTER the rest of the ignition system has to be in order to make use of
it!  As Larry noted, one way to make use of a hotter spark is to widen the
plug gaps as you have done; this has the benefits he noted *if the spark
jumps the gap* and not the distributor cap, the plug wires, etc.  Narrowing
the gap merely makes life easier for the cap and wires, but doesn't have
any benefit for engine performance. I'll throw in my two cents and add that
an otherwise well-running passenger car engine (good mechanicals, good
carburetion, etc) won't benefit much (a few percent) from widening the gaps
from .025 to .040; you may get more consistent ignition at idle (where
cylinder turbulence is low and the mixture is spotty), and at high
speed/high load (where turbulence is extreme and you get the larger/faster
flame front benefit that Larry noted), but overall there are a lot of
engines that run darned well with plug gaps of .025-.028.  (Engines that
have to pass modern smog tests do use the wider gaps because of the idle
benefits, but that's not a concern of us XK folk ;-) ) I'd say to pop in a
new cap and rotor, and wires if you have 'em, and after that start thinking
about having someone look at your ignition using an ignition scope
(wonderful diagnostic tool in the right hands). At risk of pomposity, I'll
quote a bit from some mail I posted a few months ago in connection with the
"pull the coil lead whilst cranking" thread, with [comments] added relative
to the present discussion: "When the points open, the collapsing magnetic
field in the coil drives the coil secondary voltage up to the level needed
to cause a spark to jump the plug gap [or whatever other path is most
easily ionized].  The voltage attained varies with engine load, or more
accurately with the pressure in the cylinder at the moment the spark jumps
[and also with the plug gap].  At engine idle the voltage can be
suprisingly low, even just several hundred volts; at full throttle and with
the turbulence induced by high rpm, it can be many kilovolts... which is
why a weak ignition system shows up first on those full throttle runs up to
redline. The collapsing magnetic field energy has to go SOMEWHERE which is
why the open circuit voltage, without a spark gap present to bleed it off,
can rise to 20 kV even in a Lucas system, and easily 40-50 kV in a modern
high energy solid state system.  The available open circuit voltage is one
diagnostic of overall system health, and is one of the things tested with a
scope-type ignition analyzer."

If you have any questions or comments send e-mail to: ted@jag-lovers.org
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