Magneto K1F 42182
Contact Set 470608
Contact Set 54440887 (late style)
Contact Assembly 493836 (late style - requires non-taper retaining screw)
Contact Breaker Cover 458647
Contact Breaker End Plate 458633
Slip Ring 454496
Auto Advance Unit 47505
KVF and K1F Point gap = .012"-.014"
Spark Plug Gap = .020"
There is no need to remove any thing other
the points cover when using the timing device. It simply has one
to the centre points screw, the other to earth. The clever part is that
it measures the change in inductance through the armature as the points
open, giving the best indication obtainable when timing your ignition
Because of the audible and visual indicators provided, it leaves both
free to hold ATD when setting, thus allowing the operator to judge
backlash etc.I am sure you are very experienced in this procedure, but
I always tighten the ATD nut just a little then tap with a small brass
drift tighten gently again, check all is correctly timed (front and
if on a twin), if so tap and tighten progressively to obviate breakage
of the fibre ATD teeth. In my experience of magneto construction and
tapping on this nut this will not cause damage to the bearing if
out with care. Richard Duffin 6/4/09
Fitting a BTH Magneto to a Vincent: http://bt-h.biz/vincent_fitting.htm
1) Spark Plugs: For all Vincents applications
(as you know), magnetos are sometimes weak, and often need some help by
the spark plugs to get things going. I've found that the plug gap
never exceed .020" gap. Magnetos have a hard time firing past a gap
than .020". I've found that "Gold-Paladium" (or even "Iridium") plugs
much easier on a weak magneto, and offer better all around performance.
I like NGK B8EGV "Gold-Paladiums", but these might be a little too cold
for some Vincents. The best standard type plug for a Vincent that I've
found is the NGK B7ES set to .020" gap. The "Iridiums" only come in the
#8, and #9 heat ranges, and the better #7 heat range is not available.
I have a set of BR7EIX so not sure what this is about.)
2) Magneto Point Gap: The Magneto Point Gap should be an average of .012" measured between the opened point for the front cylinder, and the opening point of the rear cylinder. An example: If the opening measures .011" for the front cylinder, while it measures .013" for the rear cylinder, the average would be at .012". I do not like the idea of slightly changing this adjustment to make small changes in the timing. A weaker mag will benefit from slightly tighter point clearances rather than looser. The tighter point clearances allow the mag coils to recieve a slightly larger charge from the magnets (in simple terms).
3) Ignition Timing: Todays newer fuels seem to require setting the full ignition timing back a few degrees from the stock setting. I've found this to be true on all motors today. I've had good luck with no more than 34 degrees full advance. As you know, it is near torture to get a Vincent timed correctly. I found a handy way to mark your left flywheel with a TDC, as well as a 34 degree timing mark for the front cylinder. The next section will explain this.
4) Setting Up a Degree Wheel, and Marking the Flywheels: Since a Vincent has no marks for timing anywhere on it, timing is a very difficult job, and thus, many people just guess at it. This is very irresponsible. Timing is crucial for maximum power, milage, and the prevention of detonation. I've seen many ways of doing this, and my method works very well for me. First make sure your magneto point gap is set correctly. Then prepare a degree wheel. Get a degree wheel (a large one), and make a centrally mounted spindle out of copper tubing that mounts firmly to the center of the degree wheel that will be used to slip inside the right crankshaft end's hole after removing the "Quill". I don't want to get into the details of making up this assembly. The copper tube spindle should be able to rotate within the crankshaft end, but also to stay put without moving. Make up a pointer out of wire, and attach it to a magneto cover screw hole. To install the degree wheel, first the exhaust system needs to be removed, and the oil lines removed. This is a good time to do an oil change! The purpose of all of this is to get a reliable stamping onto the left flywheel that is visible through the left case oil drain hole. Once the flywheels are stamped, the degree wheel will never be needed again for ignition timing. The next step is difficult, and sometimes requires the aid of a helper. Bring the front cylinder to very near TDC "firing". This can be found by rotating the motor while feeling the air entering or leaving the cylinder through the spark plug hole. It is best to put the bike up on it's rear stand, and put the bike in top gear. Now use the rear wheel to rotate the motor forwards, and backwards. As the motor is rotated, and air is leaving the spark plug hole, you are approaching TDC! When you can rock the motor back and forth slightly, and feel the air push out, and pull in slightly. You are now very near TDC "firing". Now rotate the degree wheel to show TDC (0 degrees). Now you will need a dial indicator, and maybe a little extension on it to feed down the front spark plug hole in order to while contacting the piston top, and never contacting the sides of the threaded spark plug hole. Now, you have to try to "center" the degree wheel by taking readings in crankshaft degrees while approaching TDC from both directions of rotation. These readings are taken in both rotational directions, so as to take up any rod bearing slop. Since the degree wheel has been roughly set near TDC, find a comfortable position for the dial indicator to rest against that will guarantee that it will not again move during your degree wheel readings, or new readings will need to be taken. I hold my dial indicator up against the heads fins in a very stable manor with the probe centered down the spark plug hole. Now the crankshaft can be moved in small amounts forward or backwards a few degrees while watching how far down the dial indicator probe drops. I like to get the motor very near TDC by feeling the air at the spark plug hole, zeroing the dial indicator, and then rolling the motor no more than .050" drop on the dial indicator (this is about 12 degrees rotation). Then carefully roll the motor towards TDC, and at .030" from the zeroed TDC, take a degree wheel reading (this is usually around 8 degrees BTDC). While carefully holding the dial indicator, roll the motor past TDC to about .050" down on the dial indicator. Now roll the motor backwards to the .030" point before the zeroed TDC setting on the dial indicator. Now take a second degree wheel reading. Again, it will be near 8 degrees ATDC. You now have a range of total degrees between .030" before, and after TDC. Add both numbers for the total, and devide it by 2 (bisect the total). Finish rolling the motor backwards carefully this halved amount of degrees, and you are at true TDC. Now carefully move the degree wheel a small amount to show exactly zero degrees-TDC. Be very careful to never accidently bump the degree wheel untill you are completely finished. Now the left side flywheel can be seen if you remove the left case oil drain plug. Carefully place a stamped mark (centered in the hole) for front cylinder TDC. I like to use a small flat chisel to make a vertical hash mark. You can use the degree wheel to verify that you are, in deed, at TDC. Now roll the motor backwards to 34 degrees before TDC (BTDC), and put another stamp mark. I like to use a spring loaded punch for a dot for the full advance 34 degree timing mark. Now that this is done, the degree wheel will only be needed for cam timing in the future. The next time you want to set your timing, you take out the front spark plug, and find near TDC by feeling the air end it's out-rush, and back-up the motor to the stamped 34 degree timing mark. Now you go through the gyrations of loosening the ATD bolt (Auto Advance Device), and trying to find a point where a cigarette paper will just pull through the points with a little drag when the motor hits the 34 degree timing mark (assuming that you have the ATD locked to full advance, and taking out all of the cam gear slack). As you see here, this a job best left to the professionals! Rookies become professionals by mastering the task, so be very diligent, and you can do it yourself. James Mosher 11/29/07 (Jim sells Amal Concentric intake manifolds for Vincents at www.performanceindian.com seems like an OK guy who has done a Lot of research on Vincent tuning. He posted a complimentary article in the Vincent Carbs Tech Section)
is now used to check the timing. The light comes on as the points open.
I make small adjustments to the exact timing by adjusting the points
You rotate the mag by selecting top gear and nudging the rear wheel.
mag works quite happily with the points gap between 10 and 14 thou, and
one thou seems to equate to one degree on my mag. One flat on the gap
screw is equal to about 4 thou. Ernie Lowinger
B = Thread size 14 mm, P = projected nose, 7 = normal heat range, E =
reach, I = Iridium, V = precious metal ( may be thin platinum
X = series gap, S = copper core, R = resistor (neither resistor plugs
resistor plug wire are recommended with any magneto).
Higher the number = colder the plug.
Plugs that have been used with success on Vincents include B7EV, B7EVX, BP7EV and B7ES. Also BR7EIX, BR8EIX (Iridium, although resistor).
NGK: B7ES = normal Vincent engine in good condition or B6ES = oily engine (hotter plug).
R or Q = internal resistor (avoid), Y = extended nose (be careful not
hit piston), G = Gold Paladium, U = auxiliary spark gap (avoid)
Higher the number = hotter the plug.
Champion: N8Y = hotter plug for easier starting, but extended nose (check piston clearance) may be cooled by mixture. N4G or N5G also seem good spark plugs for a Vincent.
Some manufacturers numbering systems are opposite the other, for U.S. manufacturers (Champion, Autolite, Splitfire), the higher the number, the hotter the plug. For Japanese manufacturers (NGK, Denso), the higher the number, the colder the plug.
Bosch Spark Plugs:
W = (prefix)14mm diameter thread
M = (prefix) 18mm diameter thread
T1 = (suffix) Standard reach, thread 12.5mm long
T2 = (suffix) Long Reach, thread 18mm long
T11 = (suffix) 2 stroke plug
Heat range is from 95 to 370. Shown in the model numbers of the plugs. The lower numbers are hot plugs for low compression engines, the higher numbers are cold plugs for high compresion motors. For example, 260 heat rangeand above is intended for racing.
Denso equivalent for NGK B6ES is: W20ES-U ( noted in their lit as Non-resistor). The Platinum are W20EP-ZU. The Iridium are IW20.
KLG spark plugs:
F = standard reach (for iron heads)
FE = 3/4" reach and 14mm thread (for alloy heads)
M = 18mm thread
F = 14 mm thread
A = 7/16 reach
L = long reach
E = extra long reach (3/4")
S = short reach
The numbers that follow indicate the degree of resistance to heat. Thus a FE 80 plug is suitable for a hot motor, while an FE-50 is suitable for a cool running or older motor - as such a plug will resist the accumulation of soot and oil.. Higher number = colder plug. Lower number = hotter plug.
Jim Baltusnik 7/4/06, 11/2/07
Timing through the spark plug hole: 38 degrees = 15/32" BTDC or 11.9mm for Shadow, Comet, Meteor, Lightning. Then adjust to taste. Dowel down the plughole. (as verticle as possible) Paul Craven 3/28/07
I imagine that when they built and serviced KVF TT mags they would
1. The camring housing was concentric with the bearing bores in the mag, so the contact breaker gap was the same on both cam lobes when open. The special armatures would be as perfect as possible, the bearings set up precisely with a trace of end play and the right amount of grease, the slipring running concentric with the body
2. The camring opened the contact breaker exactly at the Vin firing intervals, and in the most favorable position(thereby hangs a tale) regarding the mag electrical flux, remembering the importance of a good spark when retarded for starting. Denis Minett recorded that the errors between the cylinder timings on most of them he fitted to Black Lightnings were in the zero to one degree range, about the best you can expect, and sufficient for all practical purposes
3. They would have had an apparatus to run the mag up to the maximum speed anybody would run the engine(minimum of 7000 crank rpm, I imagine) with an air gap of some figure and means to determine that the timing to both cylinders remained constant at all rpms, and the spark jumped the air gap reliably on both leads ditto. Their literature speaks of some small percentage of mis-firing allowed in mag testing, just how that could be measured at 7000 crank rpm I don't know, I guess it took some fancy instrumentation
4. Naturally the Lab Test depended on the integrity of the man (safe to say, especially in that day, not a woman) performing it, but these mags were going to get a real stressing with 13 to 1 compression and 6-7000 rpm engines on serious missions. There would be little point to sending them out just to get them back with a squawk that "It won't start!" or "It mis-fires!"
5. As Peter Gerrish has told us in his interesting story, in the Isle of Man the RMS would have a highly skilled rep, who knew everything from Aardvark to Zimbabwe about your Lucas mag, and would make durn sure that when he handed it back to you it would work, for a long time. Despite all the many defects with which the mag might be handed to him.
Bill Hoddinott 2/12/03
few years I'd been trying to acquire a genuine KVF TT
racing magneto for my Black Lightning Replica(depicted in the July 2001 MPH). These are scarce, and elusive. Recently, thanks to a want ad on Jim Baltusnik's thevincent.com website, and a response by Dutch VOC member Jan van Drenth, the one you see here came along.
Although the KVF TT was good enough to run the Burns and Wright Black Lightning to the F.I.M Official World's Motorcycle Speed Record in New Zealand in '55 at 185 mph, and despite millions and millions of successful road miles on all the standard B and C Vincents, it has long been the practice for some to deride and belittle the magneto. Since results count above all, I always thought most of that was unjustified.
This one is marked KVF TT 42201D 3-53 on the mounting flange. It has an un-painted diecast aluminum body which appears to be the same casting from which standard KVF mags were made.
The history Jan had on it was that a Series B Black Shadow was
to the U.S.A. in '49 by a Mr. Esch. The bike was Lightningized
raced in the '50s. Later it went back to England, and into the
of Chas Guy of Conway Motors, who sold it to a friend of Jan's, two
before his(Chas') passing in an accident. The bike, still
with this mag, and racing pipes, probably among other things, then came
to Jan; he put it back into original form, and later sold it on to a
German enthusiast. Jan said this magneto was rewound a year ago by Dutch magneto specialist Toon van Daal. On receipt it was found in good working condition and passed the 'Official Briggs and Stratton spark test'. I mean, hooking the HT leads up to the little B&S air gap device used for proving lawnmower ignitions, which involves a gap of about 7/32" (about 4mm), and turning the drive spindle with the fingers, when a spark jumps the gap. One lead at a time is tested, while the other one is grounded to the mag body.
The above means that this mag would have been sourced in the mid-'50s from the U.S. Lucas spare parts system, unless some U.S. Vincent dealer happened to have it on hand.
Like many of you, I imagine, I always thought the KVF TT was something very glamorous, as a special fitment on the production Black Lightnings.
(Photo - Lucas "Bumblebee" Racing Plug wire from 1950's-60's. Mag control lever and cable are reportedly original Vincent items.)
Since the KVF TT has its own legend, lore and mythology, acquiring this one prompted me to try to do a little detective work to pin down what facts are available, to which I will add some speculation, in hopes this will stimulate some readers to come forth if they have better information.
"Go to the Lucas records" you may say. Well, we can't,
rumor has it that since the Lucas establishment at Great Hampton
Birmingham 18, England, closed up some years ago, their irreplaceable
were thrown into a dump! Including, I fear, the records of the
Magneto Section from whence these KVF TTs issued. The equipment
craftsmen who made them, I assume, are scattered to the four winds. (Do
please note that word was received after this draft was composed that
records of Joseph Lucas Ltd. were not thrown into a dump, but moved to
the Heritage Motor Centre, Warwick, England after JLLtd closed up.
the HMC informed me that the records of the Racing Magneto Section were
not included, so we still don't know where they are. Bill. )
I possess a copy of "Lucas Quality Equipment and Spare Parts for Motor Cycles 1936-1957", the official period catalog. It should contain the KVF TT data, but unfortunately the 42201 unit is completely omitted there. This suggests that the number made is so small, that it didn't even warrant being included.
Readers may recall that in the Dec. '99 MPH, I had an article about Gunga Din, and included some info about the KVF TT that G.D.'s owner, Keith Hazelton, had sent to my pals Sid Biberman and Bill Jean for servicing. That unit was marked 42201A, had an Elektron casting with LUCAS imprinted in it, and was gold in color, with the LUCAS picked out in red.
A word about 'Elektron'. From what I've gathered down through
the years, Elektron is a magnesium-aluminum casting alloy that was
for aircraft castings possibly in the '20s or '30s. It was known
for being the best combination of strength and light weight
available as a casting alloy. Vincent used it for racing brake plates,
and I assume that the same material was used by the famous English
mc factories for the crankcases and camboxes of their KTTs, 7Rs, G50s,
and Manxes. It probably only cost a little more than good
casting alloys, but saved weight. Its biggest fault seems to
have been its inclination to severe corrosion if not carefully painted and sealed from the atmosphere. I recall standing before a display case in the Science Museum in London in '64, gazing at a three-valve Works 7R AJS engine on a stand, and observing the little pile of Elektron dust that was forming under one corner of the crankcase from the said corrosion.
So we have this factual evidence that up to January '52 at least,
Keith's KVF TT was made, the castings were made of Elektron. By
'53, Lucas had changed over to using the normal diecast aluminum body
a basis. I can further tell you that when I purchased a unit from
the U.S. Lucas parts system in about '61, it had a silver-painted
aluminum body. In those days we did such transactions by letter
that, not phone, fax or e-mail) and I well recall that the Lucas rep
stated that it was the last one they had, and to clear it out they offered it for a special dealer's price of $75. So I grabbed it, and fitted it, but soon found that it was not very practical for my road-going Black Shadow, since it didn't want to let the engine idle down quickly or slowly, which destroyed the road manners. I soon passed it on to another fella who wanted to race a Vincent, for the same price, so two young lads got a steal, one time long ago.
The very first Black Lightning, which has always been displayed in
Rider's Handbook, did not exhibit the screw-on cap characteristic of
other KVF TTs seen since, so I assume Lucas made up a special manual
for this one, and then got busy and planned to make it in small series
production. For several years with the special Elektron body,
reverting to the aluminum as noted above. Since it was a
unit, and needed a left-hand(they figured it looking at the drive
spindle end) manual retard control unit for a slack-wire advance, all the KVF TTs have always looked the same in general, apart from the body type. The aluminum- body model has no large LUCAS imprint, but it retains the arrow indicating rotation, that standard KVF mags don't have on the body.
As noted, the 42201 KVF TT doesn't appear in the Lucas
But, the 42324 K2FR DOES appear. This was a vertical twin racing
unit used on many serious racing Triumphs, BSAs, and a few Nortons, for
AMA Class C racing in America, and in England on, I understand, the G45
Matchless, and perhaps even the Porcupine AJS GP twin, as well as
many humbler racebikes for the Isle of Man, etc. The 42324
opposite to the Vincent mags, and would have its manual retard control
on the other side, but 42324 was also produced as 42206, a K2FR of
rotation with the left-hand control for the '51-'52 Douglas Plus 80 and
90 opposed twin racer. I speculate(never having seen one) that
42206 looked just the same as our KVFTT. I did own what I believe
was one of these 42324 K2FRs, thirty years ago, which was said to have
originated with a racing BSA twin, since blown-up, and yes, it had an Elektron casting, by then painted black.Now, it was about '48-'49 that demand started up for numbers of these twin racing mags, and I am going to speculate that our 42201 KVF TT was viewed by the Lucas Racing Magneto Section as merely one of the same family with these even-firing vertical twin jobs. We know that the armature for the Vincent is the same as that for the vertical twin Lucas mags, except the slip ring is different to suit the Vin firing order and rotation. We also know that these KVF TT and K2FR mags have a special
armature with the end cap and drive spindle formed in one piece of steel, unlike the standard equivalent which has a steel drive spindle cast(?) into a brass end cap. There is a bit of lore somewhere that Lucas went to this when the Porcupine AJS twin lost the Senior T.T. in the late '40s through the spindle coming loose in the end cap.
It appears that the KVF TT and K2FR were made for about ten years, from maybe '49, to '59, when the K2FR was still listed (in the next Lucas catalog to that cited above, also here) as a racing part for Triumph twins.
How did they look? I consulted a number of my Vincent friends to answer this one for you, by phone and e-mail. Bill Martz said flatly that the KVF TT that came with the '52 Black Lightning that he and Tom Auger raced for years in Southern California in that era, was painted gold, with the LUCAS imprint picked out in red. Keith Hazelton said the one he has for Gunga Din, which was made in January '52, and came from California, was also gold with the red letters, as it is today.
Somer Hooker said that of the few he has seen, some were painted silver, and some were left natural, like the one I have here now. Bob Kizer, who has a mag shop in Texas, said all those he's seen, were silver-painted. Vaughn Greene, well-known in the VOC as a monthly columnist for many years, said those he's seen were silver. So there you have it. Apparently up to sometime in '52-'53, they were gold, after that, either painted silver or left natural. And the gold ones were probably all with the Elektron casting.
How many were made? Since we know that probably all production Lightnings had them (about three dozen), and we know that the Lucas spare parts system stocked a few to sell to people who wanted to race other Vincent Twins, I would hazard a wild guess of 50-75 KVF TTs.
How good were these mags? Well, in my mind the World Record
it all. In his unpublished manuscript, "World Record-Breaking on
a Shoestring" Bob Burns tells us that the Lightning was geared for 6000
rpm at maximum speed, and was "a lovely great mill". And in K2FR
form they ran many a vertical twin for long periods at 7000 rpm, and
more. It's fair to say that the rotating armature mag is more prey to electrical troubles than the rotating magnet type which has predominated in the world's racing magnetos. All those windings, the condensor, etc. must be under a lot of stress at high rpm not only from the centrifugal force, and constant blipping up and down the rpm scale, but from the considerable engine vibration, and the pounding over the bumps when the bike jumps three feet in the air and crashes down in the Isle of Man,
Today, 50 years later, there is some disagreement about what condensors, etc. to use for repair work. My approach to a magneto that showed any signs of malfunction that I couldn't cure by attention to the contact breaker, pickups, etc., would be to entrust the job to a reputable mag repairer and let him handle it. The armature, I think, is nothing for an amateur to delve into.
That's about all the lore I have on the KVF TT, if you have something to add, or correct, don't hold back!! 2/5/03
The drive housing on pre-50 KVF magnetos was 15mm, and hardly enough meat (brass) to hold the steel tapered drive shaft. Like the Porcupine, there were many Vincents whose drive shafts became loose or came out after many many miles. In 1951 Lucas enlarged the drive to 18mm. The KVFTT used a non-magnetic stainless steel drive end housing to avoid the problem of the shaft coming loose. Lucas would not sell these armatures but only used them in production mags.
I've seen and or worked on about a half dozen KVFTT and it was
there were slight differences in all of them. This would
indicate they were made in small batches, which is why they weren't
by Lucas. The word LUCAS appeared to be engraved, maybe by
All had a LT###### number (Laboratory Test) so there must have been a
book on them. I personally know the chap who bought out the Lucas
magneto dept. and he has no records, only the tooling and
I was able to find the correct body as used on the KVFTT and was able
build a "replica" that was correct in every detail. The manual
end housing (containing cam ring) had to be made of billet, but it
The mag was correct enough that only an "expert" could tell the difference, if he took it apart, and if he knew what to look for. Good enough for a replica Lightning.
The Lucas catalog does not list every part on "racing" magnetos. They only list common replacement parts as they expect you to send the mag to them for major work.
Bill, thanks for your very informative article.
Also, some electronic ignition systems that
advance are not necessary properly set. So if you set it at full
advance you are not necessary correctly set at full retard and vice
if you set if at full retard ! Francois Grosset
End play is most important on a face cam model such as an NC_1 as the location of the armature influences the points opening (both time and distance). K models are not very sensitive to end play since they use a ring cam. The steel and brass thermal expansion coefficient is about . 000010 or ten parts per million. The thermal expansion of the aluminum case is about 20 parts in a million. Assuming a three inch armature and the expansion differential about 10 parts per million per degree centigrade. Therefore if the temperature rises from 70C to 190C, the case expands .0012" per degree faster than the armature. Therefore, the nip should be about .003" when assembled cold. Perry Gerhart 8/28/02
I was curious myself about increasing the magnetic field of old
After remagnetizing, you can definitely feel the "bump" is stronger
rotating the armature by hand. (when magnetic field of flux swaps
However, there is also a way you can mathematically prove the increase.
1. Either block the points open with piece of paper, or remove the cb assy.
2. Leave the cb retaining screw in place, and connect AC voltmeter to kill wire.
3. Rotate armature with fixed rpm such as hand drill. (maybe 800-1000 rpm)
5. Again measure spin the armature with the same fixed rpm source and measure the AC voltage at kill wire. You are measuring the AC voltage generated in the primary, which might be around 5 volts. If you now measure 6 volts, then you can assume you have an increase of 20% in the primary. You should get a proportionate increase in the secondary.
I only tested a few, but found increase of about 10-20%. For more information, visit the British Only web site and download the Lucas workshop chapter on remagnetizing. They give full specifications and data. Bob Kizer 8/28/02
For interpreting terminology see the Lucas KVF manual listed at http://www.britishonly.com/tech/manuals/sectionL5.asp.
A mag that gets harder to start when hot is probably in need of new windings and/or capacitor so you can stop here if that's your problem.
The assumptions are there is no spark using a new plug on either lead.If one side works swap the wires and plug and see if the problem moves.If you have a kill switch test without the contact breaker cover on.
Check that the lower High Tension lead goes to the front cylinder. Your wires are reversed if it doesn't.
1. Take off the breaker cover and remove the High Tension cable
to the mag from cylinder #2. Is it oily or worn down to the spring? If
so, fix it and check #1 . Now hold a rag with some solvent on the slip
ring track that has been exposed when you removed the HT cable. A stick
or pencil rubber helps here. Turn the engine over to clean the whole
This will make you into a contortionist if nothing else does. While
there unscrew the grounding (earthing) brush and check
for oil and put a Qtip in there and clean the contact surface while turning the engine. Now try for a spark again. If the mag has been failing gradually and this cures it you are in luck.
2. Under the contact breaker cover make sure the contact
breaker assembly turns when you kick the motor over. If it
look for a stripped or disconnected timing pinion under the timing
If it does turn, make sure the points are opening and closing. Run a
or emry paper across them and make sure they really are making
contact. Make sure the lock nut is tight and they have about .012" to
gap at their widest. Try to turn the carrier assembly by hand. It
should not turn clockwise but should move up to 40 degrees counterclockwise against the advance springs. If it does turn clockwise a limited amount and stops it may have been stuck on full advance. Check the advance mechanism on the cam pinion. If breaker assy turns freely without the armature turning (this happened to me once) the center bolt got too loose and the locating key stripped out of the groove under it. Now the timing is totally out. The temporary road fix says remove the
bolt and the breaker assy carefully. Look under the breaker assy and figure out where the key was and slide it back on with that part right over the groove that may still have the key remains in it. Tighten the bolt and drive away and get it fixed soon. It is possible to make a new key by brazing it on and filing it to shape.
3. Maybe the mag works and it just needs retiming. Turn the engine to top dead center on cylinder #1 on the firing stroke. The fiber cam follower on the points should be just hitting the ramp at about 6:30 'clock on the cam ring and starting to open. If it's nowhere near, go through the retiming procedure. Check that the Pinion bolt is tight, if it slipped that's why the timing is off. It's easy to strip the drive pinion while tightening the bolt too much (I know). Also if you hold the mag by the breaker assy while tightening you can strip the key underneath it (I've done that too). The road fix without degree wheels etc says to set the points just on the bottom camring ramp and tighten the pinion bolt well (with the engine still at TDC firing on #1). You can drive away and fix it right asap.
4. This check is for a mag that never did work or that stopped after you worked on (Restored?) the bike. Set cylinder #2 at top dead center on the firing stroke. The point cam follower should be just hitting the upper ramp of the cam ring. Now crawl down under with a light and look in the hole at the slip ring. You should see the copper contact patch right there where the brush would hit it. If it isn't (which happened on 2 different occasions to me) the bike won't run. Different things can cause this - the wrong slip ring, a slipped contact breaker assembly a slipped or stripped pinion , a reversed or wrong cam ring. Mine had a contact breaker assy from a parallel twin which will pop and sputter but won't run.
5. Has the cam ring moved? It should be tight and have one ramp at about 6:30 and the other at 11:00. If they're not there the contact breaker cover was reversed 180 degrees. If they are 180 degrees apart you have the wrong cam ring. Make sure the breaker return spring doesn't touch it at any time while rotating.
6. A low probability problem is that the mag is not grounded to the engine. To test lay a connected plug on the mag body and kick the engine over. If it sparks but doesn't spark laying on the engine then find a way to ground the body. It should be sufficiently connected via the mounting bolts. Mike Hebb 7/6/02
My original mag was very tired and I did not like the idea to spend money on it so I made up an electronic ignition of various components laying around in my workshop. As a Boyer for Norton Commando gives an max advance of about 32 degr, I thought this should be enough for a breathed on twin. I made a housing and installed the unit. One pick up coil is cut out of the circuit. The magnetos on the rotor have to be set according to the V twin´s layout (50 degr) and Bingo you have an ignition for Vincents! I use an old dual coil from a Kawasaki but it really does not matter much - any old jap dual coil will do. Check for low resistance in the primary winding - the lower the better.
I fixed the ignition to 36 degr advance only to find that the engine pinked badly. Carbs were reset and ignition reset accordingly on the roadside by turning the housing in the clamp. Now the bike has very nice tickover and revs freely up to 6000 without pinking - after checking ignition again with a strobe I found I run now on 32 degrees! Even with 36 degr it did not kick back when starting so the Norton unit has enough advance/retard for an old Vin. I choosed the Norton unit because of the stroke length (89/90mm) and similar rev characteristics (at least the std 850).
The Rowbotham unit is slightly different to
because the stator is set eccentric to give more accessibility but I
it unneccessary - in fact a Commando ignition cover was turned 2mm
in outer dia and now covers my unit without space problems. You can use
the Atlas layout as well on a Vin because the housing can be machined
slot into the Vins limited space. Best on my system is the setting of
ignition on the roadside: open the clamp with an Allen key and turn the
whole unit - like the car distributors. You can always adjust your
in a minute to cover different running conditions (bad fuel/high
If you make a scratch on the outer body you can return back to the old
setting without need to strobe!
Parts are cheap: Boyer is about 75 Euro,coil is free from the local bike breakers .Be sure it is from an old jap bike with points ignition - these have lower resistance than CDI coils. Hartmut 7/6/02
Lucas Magneto Manual: http://www.britishonly.com/pdf/lucas/sectionL5partA.pdf Requires Acrobat reader. Ken Smith 6/19/02
After sleeping on this all night, the
finally occurred to me.
1. Autos and single cylinder have ignition polarized so that the spark plug receives a negative polarized voltage. This is because electrons are more easily emitted from a hot electrode, i.e., your spark plug center electrode. This is the principle how vacuum tubes work.
2. Twin cylinder magnetos deliver a positive voltage to one spark plug, and negative to the other. Vincent magnetos are polarized so that the front cylinder receives the negative voltage as this is the one that receives lesser quality spark from the "retarded" side of the mag.
3. If you will remove the armature from a twin with high mileage, you will notice one side of the brass grounding surface of the armature will have a depression in it, and the other side will not. This is because of direction of electron flow. A tiny amount of brass is vaporised with each spark, hence the spark erosion principal.
4. Due to age of rubber seal at drive side, oil vapor is allowed to enter the mag body. One effect is that it tends to gum up the grounding brush at the flange (drive side) of the mag. This brush is spring loaded and will normally follow the contour of the brass grounding surface. But when gummed it might only touch the high side, and not follow the depression. Also
remember, this brush is the return for the HT spark voltage in addition to grounding the contact breakers.
5. Remove this brush, clean the gum and allow the spring to move freely, and I will bet your kill switch will kill both cylinders.
6. After such high mileage, if in fact your armature has the depression, it's time you had the mag expertly overhauled. Trueing this surface in the lathe is one of the necessary steps in restoration.
7. Remember, the kill switch is mounted on the handlebar. The handlebar is "grounded" to chassis.
8. The only electrical route from the armature primary common internal ground to earth ground is through the grounding brush which rubs the brass grounding ring. This brass grounding ring now has a "dimple" due to very high mileage which is typical with Vincent mags. Because the grounding brush is frozen in it's holder, it can no loger follow the contour of the brass grounding surface of the armature.
9. The grounding brush located at the flange end of the body serves two purposes.
a. To serve as a return path for the HV output to earth.
b. To serve as a path to ground the common connections of the primary winding, points and capacitor.
10. The magneto *will* work with this grounding brush missing. Without the alternate low resistance path (grounding brush)
HV will seek it's return path through the bearings via jumping the gaps in the bearing paper insulator cups.
11. If the kill switch totally fails to function, it's because the grounding brush is gummed up and no longer touching the brass grounding surface on the armature.
When points open, voltage is induced in
Although it seems to be instant, in fact there is rise time too quick
for us to recognize. When voltage rises to the point it's able to ionize the spark plug gap, the spark occurs. Any "extra" voltage
is exactly that. The only way to utilize this extra voltage is to open spark plug gap more, but then you;re really running risk of insulsation breakdown failure. Keep spark plug gap at .018-.020" However, it's a good idea to "rotate" spark plugs every 5K miles to even out the wear. Remember, one gets positive and the other gets negative voltage, so spark erosion is different on each. Bob Kizer 2/21/02
Using or making the end cover of the magneto so that the brush holder is .010 to .020 from the points holder retaining bolt when the latter is fully home.
That the bolt head is highly polished,
That the wire to the kill switch is of marine quality (heavy insulation and each strand of the wire is tinned all the way). Number 18 stranded wire will be sufficient.
And that the kill switch be of the highest quality whether it's a push button, momentary toggle switch, or an on-off spst toggle switch. An on-off spst toggle switch has the advantage that, if it is somewhat hidden, it also prevents the bike from starting unless the purveyor knows magnetos. Further, in the case of an emergency cutoff, using an on-off toggle switch, you do not have to hold a momentary toggle switch till the engine stops. A simple flick of the toggle lever will definitely stop the engine. Then you can get away from the fire or the coming explosion. The disadvantage of the spst switch is that, if you forget to turn it off, kicking will be totally useless.
Keep in mind that the points cover, wire, and switch are in parallel with the points so any leakage degrades the quality of the spark. Perry Gerhart 2/20/02
By damping out oscillations, the resistance also decreases the overall amplitude of the voltage swings in the ignition circuits, which can get pretty wild (as you'll know if you've ever watched an ignition scope). This can make life a bit easier for the electronic bits in an electronic ignition system. I suspect that either or both of these effects -- interference reduction and/or lower circuit stress -- are in mind when resistor wire/caps/plugs are specified with electronic ignition systems.
Finally, I'm not aware of any way that HT
resistance could increase any of the useful properties of the spark
intensity, or duration). On the contrary, being a purely
element, resistance tends to decrease all of these by a small, but
measurable amount (I don't have my reference books handy, but I'll be
to guess something like a couple of percent). For most bikes in
situations, this is not a critical couple of percent... to a large
any spark that delivers the minimum ignition energy (a few
to the cylinder will run the engine quite well, and a "better" spark
hotter, or longer) will not make any more power (sorry, Dr.
But in difficult situations it could be otherwise. A magneto
at kick-start speeds is certainly challenged for enough voltage to fire
the plug, especially a partially fouled (electrically leaky) plug...
extra HT resistance certainly wouldn't help matters. Similarly,
mixtures take more spark energy to fire -- for example a big carbureted
V8 with poor mixture distribution and a bad case of "lean stumble" --
the popularity of
multiple-spark systems like MSD among the hot-rod crowd. Here again the few percent of spark energy lost to the resistor might be the difference between a miss and a fire. Most of the time, the difference between resistor and non-resistor HT circuits is not noticeable.
Likely this is more than you or anybody wanted
to know about HT resistance but I just wanted to mention the basic
at work. On my Shadow I run the original mag, copper wire and caps, and
NGK plugs gapped .020-.022 ... but I must confess to not remembering if
the plugs are resistor or not! So you can see it is not an issue
that I have lost a lot of sleep over; the bike is a second-kick starter
in nearly every situation, which I attribute largely to having had Dave
Lindsley rewind the mag and replace the condenser a few years
Ed Mellinger 6/16/00
Remember to state whether bike is positive or negative earth. Chris Tilley