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Vincent Magneto - May the Spark be with you !

Electrical parts numbers
Black Shadow/Rapide
 Magneto KVF42134  (KVF GM1)
 Contact set  470877
 Contact set  54440890 (late style)
 Contact assembly 54440863 (late style - requires non-taper retaining screw)
 Contact Breaker 470542
 Contact Breaker Cover 458647
 Contact Breaker End Plate 458633
 Armature 458679, 458359 (1948-50),  (459142 from 1951 on)
 Cam Ring 458661
 Contact Breaker Springs 470688 (stronger springs 407206, sidecar 416001)
 Spring and Pin  458613
 Slip Ring 454497
 Auto Advance Unit  47505
 Rotation - Clockwise
 Pick-up 458367 (right)
 Pick-up 458368 (left)
 Brush and Spring 451260
 Nut moulded 410600
 Cam 459155
 Plate, contact breaker end 459105
 Cup, insulating 451379
 Cup, insulating for body bearing 459005
  Nut, shaft 170104
  Bearing, contact breaker end 189291
  Bearing, drive end 189244
  Sundry parts set 458675

 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
 Armature 458361
 Cam 456622
 Slip Ring 454496
 Auto Advance Unit 47505

KVF and K1F Point gap = .012"-.014"
Spark Plug Gap =  .020"

Fitting a BT-H Magneto:
If you do not have a fixed pinion kit to replace the mechanical advance / retard unit then you need to get that first.
If you do not have a timing disk you may time it by measuring through the plug hole.  (I prefer to use a timing disc for consistency as it is easier to find TDC.  Many people just measure through the plug hole. Whatever works for you is OK.)
Read through the instructions and acquaint yourself with the parts.  Read them again. (You can also view them online at and there is a good example fitting at : )
Find your before TDC firing position on the compression stroke of the REAR cylinder.
Fit the magneto as shown in the instructions.  Align the magneto so that the fixings are approximately central in the slots in the magneto body.  This will allow you too make small adjustments to the timing later by taking off a minimum of parts.
Before you fit the fixed pinion, double check that you have the arrow on the end of the shaft pointed up.
When you connect up the coils double check that you have the rear cylinder high tension lead going to the coil that has a yellow tag fitted to the blue lead.
Don't forget to take the timing rod out before you turn the engine over.
Eddy 9/1/10

Degree travel down bore in inches :
0 -------- 0.000 
1 -------- 0.000 
2 -------- 0.001 
3 -------- 0.003 
4 -------- 0.005 
5 -------- 0.008 
6 -------- 0.012 
7 -------- 0.016 
8 -------- 0.021 
9 -------- 0.027 
10 -------- 0.033 
11 -------- 0.040 
12 -------- 0.048 
13 -------- 0.056 
14 -------- 0.065 
15 -------- 0.075 
16 -------- 0.085 
17 -------- 0.096 
18 -------- 0.107 
19 -------- 0.120 
20 -------- 0.132 
21 -------- 0.146 
22 -------- 0.159 
23 -------- 0.174 
24 -------- 0.189 
25 -------- 0.205 
26 -------- 0.221 
27 -------- 0.238 
28 -------- 0.255 
29 -------- 0.273 
30 -------- 0.292 
31 -------- 0.311 
32 -------- 0.330 
33 -------- 0.350 
34 -------- 0.371 
35 -------- 0.392 
36 -------- 0.414 
37 -------- 0.436 
38 -------- 0.458 
39 -------- 0.481 
40 -------- 0.504
Tom Gross  9/1/10

Rod-Timing your Vincent:   Best to  place the motor in High gear and bump the rear wheel around quite lightly as you near the upper piston positions.  With plugs out and coming up on the compression at TDC,  first find true TDC  a timing disc is the best method for accuracy }  as there is some crank rock to either side  while the piston remains still.   The disc allows this to be split evenly for absolute racing grade timing results,  but with some practice one can come quite close to this by "feel "  and observing piston movement. 
Mark your rod  rather deeply here - held vertically sighting the eye across and level at the far upper plug thread - the mark should coinside with that top thread -  full up ie TDC.    Then  remove the rod and with a steel rule proceed to scribe upon the rod - later deepened with a thin sharp edged file as follows -  in steps  below that initial mark  -  distanced as noted:
                       3/8 inch =   34 degrees 
                       13/32 inch =  36 degrees
                       15/ 32 inch =  38 degrees 
                       31/64 inch =  39 degrees 
                       1/2 inch    =  40 degrees  
  At each mark the piston will be further down the bore.   This rod becomes a valuable spoke and poke tool when away from home and your degree wheel,  this of course still the best in-shop method.  Many do cling to the timing rod though and practice makes perfect.  Should the running be a bit sluggish just  open up on your magneto points by 2 thou to 14 thou {standard setting at 12 }  which will bump up the advance,  or  if she pinks and feels rough close down to 10 thou to retard her a  bit.   With a Series  D  distributor just rotate the ignition head  Towards the front wheel  a wee bit to  retard - or back towards  the front cylinder to advance.  Doesn't take much as the breaker device spins at half  the crank speed { so its movement is doubled if shifted }.    The point gap trick also works.   1/2 inch  or 40 degrees  is the inlet valve opening point,  and the exhaust valve closing point is at 1/4 inch measured on the stroke.  Sid Biberman  8/9/10

If you suspect a problem with your ATD,  it's pretty easy to uncover it and watch it while you start up, rev it a little and see it the weights go out and then come back in and check that they are all the way in after you shut down. You'll get a little oil mist but it shouldn't take long.  Mike Hebb  10/17/09

BTH Magnetos:   ( Comet)  (Twin)

Weak Mag: The magneto gives the best spark to the rear pot, the one it is timed on. So if the Mag was starting to fail, the front cylinder would go first.  Sunbeam  10/12/09
ATD Nut Torque:   Very low - if the tapers are lapped together. It is a self-locking taper (these are defined by the included angle, and - notoriously unreliable - memory says less than 10 degrees) so tapping it on provides the grip, and the nut (in theory) needn't be much more than finger tight. That's why the nut needs to double as an extractor.  Sunbeam  10/4/09
With the
ATD  fully retarded - the stop ears  touching,  the end loops of both springs around the pegs must be actually pulling on the pegs - not just floating around  them.   If they don't, the springs are tired/too long.  Very common.   If this is the case replace or shorten by one loop and reform the ear so as to produce this  condition. The idle speed needs being set with the motor warmed up, oil thinned out to acheve a stable slow hot  idle.   Sid   6/17/09
Some may not know that one can access the
ATD springs for changing, shortening,  etc.  without  need for complete ATD removal and  need to retime the ignition.  If all is well with the center withdrawel bolt one has only  to back it off  a bit - just enough allowing removal of the horseshoe clip and the dished thin washer.  No  need to pop off the entire gear assembly.  Replace the bits and retighten,  careful not to overload the fibergear teeth.  Note that  there will be drag felt in the  movement whenever the point heel  is rubbing over the cam ring  lobes,  so best to find that free position between the lobes  for checking  for return action.   A good  spritz over the mechanism  with  WD 40 or  light oil  helps keep the action  clean and free.   Be very careful  handling  the springs - easy to drop one into the  timing chest !   Sid   6/16/09

To avoid dropping springs or other small parts into the timing chest, pack the area around the ATD with cloth before attempting repairs.  Prosper Keating  6/16/09

Magneto Timing Light: I have sold the last of my home produced inductor timing lights, but during my time on this project and in my quest to improve on my first efforts I came across a fantastic device from the USA supplied by Aircraft Spruce and speciality Co.     Part # 12-16903 these units are superb, but can be much improved by fitting slightly larger croc’ clips (the originals just fly off the points screw causing some frustration!)

There is no need to remove any thing other than the points cover when using the timing device. It simply has one connection 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 statically. Because of the audible and visual indicators provided, it leaves both hands free to hold ATD when setting, thus allowing the operator to judge against 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 rear, 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 repair, tapping on this nut this will not cause damage to the bearing if carried out with care.  Richard Duffin  6/4/09

Fitting a BTH Magneto to a Vincent:

Timing Light: Yes, you can wrap the upper portion of the magneto point sec. plate center bolt  to isolate it  from touching the plate and then continuity will  be  made across the closed points.  A layerof Scotch tape usually works.   Don't jar the plate loose when removing  the bolt, and be sure the brass plate is correctly  keyed in the shaft at all times.  Sid  5/2/09

I use Evox Rifa PME271E capacitors.  These are the same ones used by Chris Gould who has rebuilt several thousand magnetos over the last 15 or so years.  Chris has not had a single capacitor failure.  John Mead   10/5/08

Spoke timing: I use an old spoke and nipple with notches filed at TDC and 1/2" BTDC to be even with the top of the spark plug hole. Bruce Metcalf  8/3/08
Strobe timing:  The ESA (the part that stays in phase with the crank) and inside of my primary cover are marked and I time my Shadow through the primary filler hole.  For the stationary pointer,  I use a piece of aluminum bent into an L and epoxied to the inside of cover. Paul Zell  8/3/08
Strobe timing: This is easy on a Series "D" or any Vincent running the Lucas distributor ignition.  Marks on the gear and nearby forwards on the alloy are simple  to do.  I made an ATD cover out of clear lucite to help retain the oil from being  flung out.  One then simply  moves the distributor head to bring  the marks in line.  Sid Biberman  8/3/08
Piston travel as it  relates to ignition timing  in degrees.  All  important  for  those using  the spoke and poke method of  ignition timing.  This can be quite effective if   one is careful to "split the rock " carefully on ether side of  TDC.   3/8 in. =  34 deg.,  13/32 in.= 36 deg., 15/32 in. = 38 deg., 31/64 in.= 39 deg,  and 1/2 inch =  40 degrees.     (Paul  Richardson) 
Ignition Timing Specs:

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 should never exceed .020" gap. Magnetos have a hard time firing past a gap greater than .020". I've found that "Gold-Paladium" (or even "Iridium") plugs fire 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  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)

A plug that you may want to try is the NGK Iridium IX. They may offer one of those that will suit the specs in a hot Meteor.  Former Vincent
dragster of note Jim Gattis recommended these to me, as he uses them on his Special and I use them on my Rapide (I use BR8EIX - 5044).   Someone mentioned that these plugs might be of the dreaded resistor  type, but both Jim and I have found them to offer Immediate improvement  in response and idle. I don't know about the resistor thing, but I run a  stock magneto, lovingly restored by Doug "Mr. jtan" Wood and so far, so great with these plugs.  Bev Bowen  10/19/07

Fast Idle: If the carb slides are fully returning and in sync,  it is most likely due to tired ATD return springs.  These have relaxed their pull on the pegs in the fully retarded position.  The end coil eyes must still be able to exert a return pull  - fairly soft but consistant - not just floating around doing nothing at idle or the flyweights  knock about allowing erratic advance to occur. This once started picks up the revs causing even more advance. Replace or shorten by a coil or two to restore the  original length.   Note,  the springs can be gotten at by backing off  just a bit on the central bolt  - not enough to loosen the taper fit,  and removing the horseshoe  washer and disc.  Careful not to drop bits into the timing chest.  Sid Biberman  4/18/07
Fitting the ATD is straightforward. First set the contact gap to 12 thou. Now set the engine up with the rear piston in the right location, say 36 degrees before TDC on the firing stroke with the mag in place. Thanks to the magnetisation, the heel of the contact breaker will 'lock' on the edge of the cam, lower one for rear cylinder. The locking effect is stronger on the rear pot as you know. You will have already set the ATD  at full advance with a clothes peg. So you just push it smartly onto the taper, and holding it there, tighten the nut by hand and then tighten further with the spanner. The taper will have held the ATD in the right location. So far so good.

The timing light 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 gap. You rotate the mag by selecting top gear and nudging the rear wheel. The 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 adjuster screw is equal to about 4 thou.    Ernie Lowinger  4/02/07

Spark Plugs:

NGK codes: B = Thread size 14 mm, P = projected nose, 7 = normal heat range, E = 19mm reach,  I = Iridium, V = precious metal ( may be thin platinum tipped), X = series gap, S = copper core, R = resistor (neither resistor plugs nor 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).

Champion Codes: R or Q = internal resistor (avoid), Y = extended nose (be careful not to 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

Timing a Vincent Comet:  9:1 compression ratio.
 35° is right with the fuel we use now.  If you set 35° full advance with a untouched std ATD  the 'initial' (full retard) igniting setting will be near TDC , may be after so difficult to start the engine.  To be perfect , you have to bend a bit the 'tongues' stop of your atd to reduce its travel to about 15 or 16°   then time your ignition Full advance 35/36° , check that the ATD returns freely to its retard stop and check it;  the best is to get and initial advance (full retard) of 4° but it will easily start  set at 2 to 7° BTDC.   From 8 ° BTDC  you should sometimes feel some backfire in your foot ....; it also depends of the carb settings but it is another story.   Francois Grosset  3/4/07
Comet Ignition Timing:  For a 9:1 CR... speaking from personal experience,  I would go with 33-34 Deg for running on modern unleaded. but I would investigigate the advance properties of your ATD.  When I was running the mag I tried 3 different ATD's and got 3 different results, with the best being an old unit with only 26 deg of swing, but with heavier springs which stopped the ATD coming before 200 rpm, which seems to be the norm with current refurb units.  Neil  3/4/07
Fitting a BTH Magneto to a Vincent Twin:     12/28/06

Identification of Non-Vincent Magneto: All K2FCs have the HT pickups that are retained by 3BA slotted hex head screws.  Additionally the end plate (can ring housing) is retained by three hex head (usualy also slotted) screws, 1/4-20.  I am not certain what standard that and at the moment I am not in a position to check my references.  A red competition would be correct.  The points  cover will be a screw on but could be a wader or not depending on its application.  If the screws that retain the end plate are cheese head but still 1/4-20 and the label is a black non-competition type it is a K2F used on some models of Triumphs possibly else where but not that I have witnessed.  This type of magneto will have a screw on points cover with a black bakelite/plastic baffle and an earthing stud for shorting the points to stop the engine.  Doug  12/06

Setting Points: After finding with a degree wheel the exact desired position when the points break  (w/  full advance wound on) one can adjust the piston stops  center bolt to contact  the crown at exactly that piston position - and lock it down.  Now one can  always find that crank position by bringing the piston up to bump the stop ---  at which moment the points will break ,  releasing a bit of  cellophane  in the time honored English manner.   You can use a buzzer  if you insulate the  point plates center bolt.  When the buzzing stops the plug will have fired - which will occur as the piston bumps the stop.    It should  cease buzzing  as the advance unit is  wound round to the  limit .  This is handy on the road  so that a degree wheel is not needed.   If a bit off you can alter the point gap  to sync the breaking .  It's good to know that one can advance the timing  by widening  the gap, and  retard it by closing down on the gap.   This works on a "D"  distributor as well .   Sid Biberman (7/14/06)

Very good article on magneto`s. Very duff info on "any old jap dual coil will do" on boyer ignition. More duff and dangerous info the lower the primary winding resistance the better. On 12 volts..nothing less than 3 ohms. On 6 volts nothing less than 2 ohms. Take heed lower resistance will damage the boyer amplifier box. This info relates to analogue systems not digital.. Kirby.  11/18/05
Leads: When holding a KVF in your hand, drive end toward you and label on the top so the pickups also point upwards, number 1 is on the left, number 2 on the
right. This would mean that whan the magneto is installed the top goes to the rear cylinder and the bottom to the front.  Doug Wood  8/26/05
Spark Plugs: If you're after 'exotica' in the NGK line use whatever heatgrade your bike needs and swap the last letter 'S' with a 'V' , you get a higher performance plug - v grooved. It will without any doubt whatsoever  last longer and outperform the standard 'S' plug and is about 6 times the price.  Check the NGK website and it'll give you the V-Rated equivalent (if available) of any of their plugs.    Marc  4/28/05

Spark Plugs:  For the Vincent I use N9YC or N7YC depending on the compression ratio.  N9YC for 7-8:1 and N7YC for 9:1.   John Mead  3/22/09

Spark Plugs:  I think you may still be able to get NGK platinum plugs in non-resistor, at least my local VW bug shop has them.  They carry a VX suffix, BP7EVX for example.  Paul Zell

Spark Plugs: NGK B 6 ES for oily engines, 7 for good ones, 8 or 9 for fast road/race.  John Langdon  5/27/05
Remagnetizing Magnetos:     3/27/05
Condensor on Cut-out: On Rolls Royce Merlins they used the SIMMS Magneto as well - I have one here. Anyway - if a magneto is serviced well it should work for a long time.All my customers complaining about magneto problems were satisfied once the instrument was completely overhauled. If you have mag problems try the following: Somewhere in the cap of mag there is the contact (usually a coal block) for cut out. Fit a condensator between the coal and earth. Most mags benefit from that and at least get you home. Avoid all supertrick plugs and caps or leads. Use only copper leads and rubberplug caps without any resistor in it. Check that your favourite plugs are without a resistor ! Most common plugs nowadays have a built in resistor that makes life difficult for an old mag.  Hartmut  2/13/03
Condensor on Cut-out: Years ago a friend of mine was touring Europe on his Velo Thruxton.His mag. began cutting out.  He did this same trick and ran it for 7 years more this way.  He then vintage raced it for several years.  Afterwards he sold it at an auction.I went over and looked and it still had the external condensor keeping it going!  Somer  2/13/03
Lucas Magneto Lab Test:   I don't know exactly what they did either, but I am willing to believe they were serious about it at the Racing Magneto Section.  I have recently been informed that this was a hallowed place at the Lucas plant.  A nice lady, one Mrs. Edwards, ran the front office, no-one was allowed inside the RMS, and everything in there was a deep, dark secret.

I imagine that when they built and serviced KVF TT mags they would ensure that:
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

The following article is "KVF TT TALES"  By Bill Hoddinott  2/5/03

For the last 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 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 imported to the U.S.A. in '49 by a Mr. Esch.  The bike was Lightningized and raced in the '50s.  Later it went back to England, and into the hands of Chas Guy of Conway Motors, who sold it to a friend of Jan's, two weeks before his(Chas') passing in an accident.  The bike, still Lightningized 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, since rumor has it that since the Lucas establishment at Great Hampton Street, Birmingham 18, England, closed up some years ago, their irreplaceable records were thrown into a dump!  Including, I fear, the records of the Racing Magneto Section from whence these KVF TTs issued.  The equipment and 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 the records of Joseph Lucas Ltd. were not thrown into a dump, but moved to the Heritage Motor Centre, Warwick, England after JLLtd closed up. Unfortunately, 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 developed for aircraft castings possibly in the '20s or '30s.  It was known for being the best combination of strength and light weight commercially 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 racing mc factories for the crankcases and camboxes of their KTTs, 7Rs, G50s, and Manxes.  It probably only cost a little more than good aluminum 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, when Keith's KVF TT was made, the castings were made of Elektron.  By March '53, Lucas had changed over to using the normal diecast aluminum body as 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 diecast aluminum body.  In those days we did such transactions by letter (imagine 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 the Rider's Handbook, did not exhibit the screw-on cap characteristic of all other KVF TTs seen since, so I assume Lucas made up a special manual mag for this one, and then got busy and planned to make it in small series production.  For several years with the special Elektron body, then reverting to the aluminum as noted above.  Since it was a clockwise 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 catalog.  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 probably many humbler racebikes for the Isle of Man, etc.  The 42324 rotates 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 clockwise 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 this 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 says 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 probably
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,
for example.

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

Great article. Here's a little more. Lucas made 2 styles of KVF-TT as you said. The early (electron) has Lucas cast into the body. The later was diecast. The main problem with the electron mag was that the electron would decay and the bearings would work loose. Now you had an armature moving around. They then changed the bodies to diecast. Lucas was no
longer cast into it. It was stamped. You'll also notice that close to the base they stamp the serial number. I have a 52 Shadow Special. A diecast mag was fitted to it at the works. The build sheet even has the serial number of the magneto on it. This was Ed Labelle's old bike which still holds a record at Daytona from the 60's. The armatures were also slightly different. They allegedly had silver in them. Pictured is a NOS KVF-TT armature. It has a serial number that is stamped in it as opposed to engraved as was the practice then on convential armatures. Also pictured is a Scintilla magneto as used on Picadors (drone planes). They had ties to both America and Switzerland. I don't know of any of them being fitted at the works to race bikes. They were actually supposed to be the most reliable of them all. The one pictured here is NOS. I have also had some gold racing mags over the years. They were typically K2FTT's. These were for parallel twins. I had a G45 motor once and it had one. The bodies were as big as the KVF-TT's. The TT series bodies were larger than a regular KVF/K2F magneto.
Somer  2/5/03

From Bill's great essay on the KVFTT-
""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.""

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 obvious there were slight differences in all of them.  This would certainly indicate they were made in small batches, which is why they weren't cataloged by Lucas. The word LUCAS appeared to be engraved, maybe by pantograph.  All had a LT###### number (Laboratory Test) so there must have been a log book on them.  I personally know the chap who bought out the Lucas magneto dept. and he has no records, only the tooling and parts.   I was able to find the correct body as used on the KVFTT and was able to build a "replica" that was correct in every detail.  The manual advance end housing (containing cam ring) had to be made of billet, but it looked correct.
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.    Bob Kizer 2/9/03

It is sometimes needeed to reduce the ATD travel by bending the stops or by welding a bit of material to it. With modern fuels the recommended ignition timing for full advance (38 or 39°) is too far, especially with higher compression pistons.  I used to time the engines 35 -36°  full advance to avoid any pinking. To start correctly and to get a correct idle speed,  2 to 6° ignition advance is fine  (say 4°). 36° less  4°  gives 32 °  advance travel needed at crankshaft. As this is a four stroke engine, one spark is needeed every Two crankshaft turns so the ATD travel needeed is 16°.  The standard ATD  travel is larger than that and sometimes a bit worn out which can give 20 °  which means 40° crankshaft ! To compensate for this, the only way to avoid any pinking is to 'retard'  the full advance setting but, of course it also retards the initial advance (or full retard) and the result is difficulties to start and/or get correct idle speed.  Too short ATD travel (say 12°) forces you to advance a lot to the full advance set up to get the right power (ex:35°) but at the same time you advance too much your initial timing set up (35°-24  = 11° full retard )and there gives some backfires.

Also, some electronic ignition systems that include 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 versa if you set if at full retard !    Francois Grosset  9/15/02

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

Magnetizing Magnetos: Altthough "modern" Lucas magnetos were made with higher quality (alnico) magnets, the can still loose a small amount of residual.  The three enemies of a magnet are (1) heat, (2) vibration, and (3) time.  The magneto generates it's own heat during operation, and we know Brit bikes have some vibration.  You also know your magneto is probably 50 years old by now.  Magnet manufacturers say that storing a magnet without a "keeper" in place will cause the
residual to slowly decay.  In the case of magnetos, the armature acts like a "keeper".

I was curious myself about increasing the magnetic field of old magnetos. After remagnetizing, you can definitely feel the "bump" is stronger whilst rotating the armature by hand. (when magnetic field of flux swaps poles)    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)
4. Regmagnetize
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

I built my own version of a magneto magnetizer.  It is powered by 110 volts, uses three 2000, 400 volt electrolytic capacitors, a voltage doubler, and some switches (and an isolation transformer). The charged capacitors are discharged thru a rewound armature coil of 300 turns and 275 peak amperes giving 85,000 ampere/turns, more than enough to saturate the magnets.  Doug Wood uses two coils of many turns.  We have compared the level of saturation and found the two methods identical. Perry Gerhart  8/28/02

Here are some easy mechanical do it yourself magneto checks to diagnose a failed magnito on a Vincent twin without going through the manual from step 1 or sending it to a specialist. They are best done without removal.

For interpreting terminology see the Lucas KVF manual listed at

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 connection 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 ring. This will make you into a contortionist if nothing else does. While your 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 doesn't, look for a stripped or disconnected timing pinion under the timing cover. If it does turn, make sure the points are opening and closing. Run a file or emry paper across them and make sure they really are making electrical contact. Make sure the lock nut is tight and they have about .012" to .015" 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

I´m surprised at the difficulties people have with their ignitions. If a magneto is properly maintained it should be very reliable.Usually the only thing the owner checks is a spark at the plug - wrong! Many mags seem to give good sparks but inside the combustion chamber under pressure they fail. Only solution is to have it remagnetized and everything else checked as well.IOf you have the mag out you should be able to produce a spark by turning it with your hand. This spark should at least jump an airgap of min 5 mm.A good mag will do 8mm. Check your plugcaps for resistance and of course your plugs as well! All resistance over a couple of Ohms should be rectified.

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 mine because the stator is set eccentric to give more accessibility but I found it unneccessary - in fact a Commando ignition cover was turned 2mm smaller 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 to slot into the Vins limited space. Best on my system is the setting of the 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 ignition in a minute to cover different running conditions (bad fuel/high altitude) 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:    Requires Acrobat reader.  Ken Smith  6/19/02

Q.  The twin magneto is fitted with centre carbon cap and has a kill switch attached.  For the life of me I can't fathom why it only cuts out one cylinder?

  After sleeping on this all night, the explaination 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 secondary. 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

Lucas Magneto Info:  (Bob Kizer's site)

The use of a Magneto Kill Switch is a fine idea.  The main problems are:

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

Regarding magneto slip-ring removal. Difficult without a special tool but heating to about 150F will soften sealer/glue often found behind slipring. Try pulling off with gloved hands. 150F is just too hot to touch. A simple tool can be made. Find or make a washer 1/4 to 3/8" thick. ID just larger than that of brush contact surface. OD 1/2" larger than OD of slipring. Cut in half and install into slipring groove. The armature can now be supported by this split ring resting on a can or sleeve into which the armature can be pushed.With gentle steady pressure, armature will separate.   Steve Hamel  10/4/00

Spark Plug:  NGK B6EV

Spark Plug:  Specs are:  Denso W22EP-U  That is a long reach, extended tip 3/4 inch/14mm ND plug. With a solid functioning magneto, the plugs are gapped at 20 thou.  With a D type coil ignition, 28-30 thou.  Mathew Biberman  7/18/00
Spark Plug: I find the platinum NGK B7EVS work fine on my twin.  (Champions apparently have more internal resistance.)  David Topless 7/18/00
I know from having read a friend's post on the GuzziList that Champions are not soldered internally, but use a push fit to connect the electrode end of the
sparkplug to the HT lead end of the sparkplug.  Anytime there can be a loose fitting, internal resistance has to go up.   BTW, this information was confirmed by breaking the porcelain on a Champion plug.  I personally have had no problems with NGKs, and seek them in preference to Champions.    Glenn Bewley

A useful way to think of resistance in the HT circuit is that it is similar to a damper in the suspension: it helps damp out oscillations a bit more quickly, especially high frequency ones.  The high frequencies are the ones most prone to radiate, thus, the principal use for resistance in the HT circuit is to reduce radio interference... and also interference with other electronic things e.g. electronic ignitions,voltage regulators, Nintendo Gameboys, etc. etc.

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 circuit resistance could increase any of the useful properties of the spark (risetime, intensity, or duration).  On the contrary, being a purely dissipative element, resistance tends to decrease all of these by a small, but probably measurable amount (I don't have my reference books handy, but I'll be willing to guess something like a couple of percent).  For most bikes in most situations, this is not a critical couple of percent... to a large extent, any spark that delivers the minimum ignition energy (a few milli-joules) to the cylinder will run the engine quite well, and a "better" spark (faster, hotter, or longer) will not make any more power (sorry, Dr. Jacobs).   But in difficult situations it could be otherwise.  A magneto ignition at kick-start speeds is certainly challenged for enough voltage to fire the plug, especially a partially fouled (electrically leaky) plug... and extra HT resistance certainly wouldn't help matters.  Similarly, lean mixtures take more spark energy to fire -- for example a big carbureted V8 with poor mixture distribution and a bad case of "lean stumble" -- thus 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 principles 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 ago.   Ed Mellinger  6/16/00

Spark Plugs: Does anyone have comments or experience on the relative virtues of projected vs. regular plugs?  I currently have NGK B7EVX platinums, and thought I'd try the BP7EVX projected equivalents.  I gather the idea is that they're effectively hotter at low engine speeds, and cooler at high speeds, both of these being desirable.  Dave Hartner  6/16/00

The magneto pinion is made (should be made, sometimes whale is used)  from Tufnol Carp brand material. This is a linen weave material impregnated with resin.  Its acronym is SRBF. Synthetic resin bonded fibre.  Its been around for many moons maybe back as far as the 1900`s  Another version is SRBP Synthetic resin bonded paper. Similar but with better electrical properties. But has not got the physical strength of SRBF.   Both come in various brands covering a range of different properties.  I have a list of 19 different grades including some fibre glass weave ones. So when someone mentions Tufnol,  ask them which one they are referring to.   Trevor  6/15/00
A tip from the Big Sid camp is to get a later Magneto, as employable for a kill-switch, with a take-off on the end-cap, and run a regular car-type condensor in-line from that to earth... this overcomes the Mag's internal condensor breaking down.  Tigger  6/06/00

I have just updated the Boyer Bransden electronic ignition system with the new Bransden Digital system. Bransden make the black box (electronic digital amp) and the trigger plate.  I believe Kirby Rowbottom makes the distributor and drive housing for them and can also supply the total system  including coil.  I have used the Bransden pre micro Digital for the last 2 years with no problems the only drawback was the 3 to 4 amp it drew and the difficulty of fitting the 2 coils behind the mag cowl.
The digital system draws 4 to 5 amps for start up to give a fat spark but then only draws less than 1 amp also it uses a single dual output coil that fits very neatly along with the amp behind the cowl.  I was able to retain the Rowbottom distributor and I even was able to mark the rotor in the distributor so that I can use a strobe to set the timing.
Kirby's Phone No is Int=44 1889 584758 (England)
PS If you fit this system mount the coil as far away from the distributor as you can 3 to 4 inches seems OK with me.  Henry Martini  5/04/00

Boyer Brandsden Electronics
Frindsbury House
Cox Lane, Detling
Maidstone, Kent
ME14 3HE
Ph:   01622 730939
Fax: 01622 730930

Remember to state whether bike is positive or negative earth. Chris Tilley

If you are thinking about stoning the cam ring, not to worry about it, because depending what grit of stone you use , and only use a very fine one say 200 or greater. It is doubtful if you will remove any more than a couple of thou.

The cam ring is not in need of stoning!! In all cases of this nature I have found the fault is in the machining of the end housing of the magneto. The cam recess in the housing is found to be not concentric with the bearing recess on the other side of the housing. A simple check for this is to carefully measure the points gap on both cam lobes, if there is a difference the answer is to have the cam recess machined then sleeved and re-machined to be concentric with the bearing recess,this type of machining is a little tricky and requires the making of mandrels to ensure concentricity Should the gaps be the same say 12 thou on both lobes then go ahead and stone the cam but I have found cams to be accurate when measured on a dividing head outside of the magneto.  Andrew Rackstraw
Cam rings: Bringing both camring breaker lobes into equal opening condition can only be acheved satisfactorily with the magneto mounted on its motor and all set-up with a degree wheel as if to set ones ignition timing. A true reading is best observed with a continuity tester across the points although a strip of cellophane twix the points can do a resonable job w/ luck.    Or one can do it at his bench if set-up with an adaptor to carry the degree wheel mounted on the magneto drive shaft it self.   Carefully acertain which lobe does lead the other of the two in striking the fiber heel.  This is the one to trim back, the other is your master - and to be copied.  After checking that the master is consistant at breaking the gap -- this event is precisely located to occur at the desired piston position /  - degree wheel /pointer reading, say  38 -39 degrees BTDC on the compression stroke, then  the second firing event is dead off . All of this while the magneto is locked at full advance of course .  now read and note on the wheel exactly how many degrees earlier and  where that second lobe bumps the heel .  With a strong light peer in and locate the  actual contact area , then using a little sharp carbide scribe or a spot of white-out  mark the side adjacent to that contact area .  Now the cam ring can be  slid out of the end housing to be worked on , noting exactly its position so you can  refit later  A composition rubber / abrasive wheel will acheve the slickest , most controllable cuts on hard steel . Period .  Study the lobe slope and take a few  strokes up towards its peak, blending in sweetly .  Clean and replace the ring exactly as it emerged   Back-up the fly-wheels and bump slowly again towards  39 degrees coming from 48 -50 . Note where it bumps , write it down / note it on your wheel . Repeat slowly and in lite  steps until the reading nears and then occurs where desired , 38 -to 39 degrees now  on both  lobes . You can deal similarly with the actual    gaps each indicate with your feeler gauges.  A certain aid to sweet running  and maximum power production .  We find only rarely does any given  magneto give equal breaker readings and  much is gained when they do as they were designed, and Irving desired .   S.M. Biberman 

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