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Setting up and Timing a K2F Magneto

Discussion in 'Other Norton Motorcycles' started by texasSlick, Aug 9, 2015.

  1. texasSlick

    texasSlick VIP MEMBER

    Jan 2, 2013
    It seems like this topic keeps coming up, and I have to write it over and over. Hopefully, one comprehensive discourse will settle it. If anyone finds anything confusing, please let me know so I can revise.

    The following procedure assumes the magneto armature is properly centered and aligned. This part of magneto set up is not a DIY project, and is best left to competent magneto rebuilders.

    1) The first step in setting up a Lucas K2F magneto is to check the point gap on each ramp. The proper gap is 0.012 inch, but it is far more important the gap be the same on both ramps, than hitting 0.012 exactly. I have measured the timing difference for unequal gaps, and I find the timing difference between cylinders varies 2 degrees for each 0.001 inch difference in gaps.

    Checking the gaps is best done with the magneto off the bike, but it can be done on the bike. Remove both spark plugs so you can rotate the engine without fighting the compression. Rotate the engine (forward direction) until the rubbing block shoe is fully on the ramp, just past the leading edge of the ramp (the mid point of the ramp is irrelevant to timing, so do not use it as your gap reference point). Carefully insert a thickness gauge being careful that you are not wedging the gap open with the gauge, either because the gauge is too thick, or because it is cocked going in.

    Repeat on the other ramp. There should be no measurable difference in the gaps, or at most 0.001 inch. If this is the case, proceed to Step 6.

    2) There are two reasons why the gaps are different; most probable is the cam ring is not centered in the magneto housing, the other is a poorly machined cam ring having a greater thickness on one ramp vs the other. Cam rings manufactured in the 50's to 60's suffered from being made on machinery worn out by the demands of WWII. Newly made cam rings are made on CNC machines and are spot on.

    Either way, the cam ring has to come out. Before removing the cam ring, make a note of which ramp has the greater gap. Remove the contact block. The cam ring has a small hole on each ramp (for oil wicks), and a small Allen key can be inserted into each hole and the ring pulled out. If the ring is stuck, try wedging a small tool with an "L" shaped tip behind the ring - there is a groove at the rear of the ring into which the tool tip can be placed. Wedge evenly around the ring as the fit is close and it will jam if cocked.

    When the ring is out, measure each ramp thickness with a micrometer to be certain poor machining is not the cause of gap difference. A ramp thickness difference less than 0.005 can be corrected by the centering of the cam ring. Consider a new cam ring if the thickness difference is greater than 0.005.

    Visually inspect the leading edge of each ramp. A normal ramp has a rather abrupt rise, a worn ramp has a gentle slope. The trailing edge of the ramp is less likely to wear, thus you can use the trailing edge as a guide to evaluate the profile of the leading edge. A new cam ring is necessary if the ramp profile shows wear.

    Equalizing the gap requires the cam ring be shifted on the diameter joining the two ramps. In theory, the shift needs to be 1/2 the gap difference, and the ramp with the larger gap must be shifted away from the ring center.

    3) Sand a small amount off the back side of the cam ring behind the ramp with the larger gap. Start out by sanding an arc of no more than 45 degrees. On the opposite backside, place a strip of cellophane tape behind the ramp with the smaller gap. Start out with a strip covering an arc no more than 30 degrees.

    4) Replace the cam ring, and contact block. Check the point gaps. A small difference can be corrected by increasing the arc covered by the tape, rather than doubling the tape thickness. Work carefully, you do not want to screw up a $100 cam ring.

    5) When the gaps are equal or within 0.001 inch, check that the gaps are the specified 0.012 inch, if not, set to 0.012. Remove the cam ring again, oil the felt wick in the groove inside the cam ring housing. If the wick is missing, make one from felt weatherstrip. Cut felt plugs using a leather punch and plug the holes in the ramps so the plugs contact the felt strip in the groove, and the rubbing shoe.

    6) Install the cam ring, and contact block. Do not install the long screw that secures the contact block. Using small alligator clips, connect one lead of a VOM, set up on Ohm scale, to either lug A1 or A2, and the other lead to lug B, as shown in the photo below. Check your connections: when the points are closed, the VOM should indicate zero Ohms (or an audible sound), and when the points open, the VOM should read infinity (or no audible sound).


    7) Set up a timing wheel on the engine's alternator rotor and install a pointer on one of the stator studs.

    8.) Rotate the engine by hand, and while looking in the left cylinder spark plug hole, watch for the intake valve to come into view. Continue rotating until the valve disappears from view. At this point, the engine is approximately at bottom dead center (BDC) and is about to begin the compression stroke. Rotate the engine about 180 degrees, and with a rod or slim screwdriver in the left plug hole, feel for the piston to come to top dead center (TDC). Rock the engine back and forth and split the difference where the piston can be felt to pass through TDC, and set the pointer and degree wheel to zero at that spot. You might want to mark the rotor for future reference.

    9) If the magneto or automatic advance unit has not been disturbed from a previously running machine, the rubbing block should be on the cam near the 5 o'clock position. If it is at the 11 o'clock position, re-do step 8. If you are setting up a magneto that has been off the machine, loosen the AAU from the shaft taper.

    10) Cut a small piece of 1/4 or 5/16 vacuum tubing (about 1/4 inch long) and wedge this into the tabs of the AAU, holding the yoke open (advanced position) against the return springs. Check that the tubing fully advances the yoke.

    11) It is best to rotate the engine with a socket on the camshaft nut, clutch center nut, or oil pump drive worm nut, and using a long handled bar rotate the engine backwards about 35 degrees.

    12) If setting up a magneto that has been off the machine, rotate the contact block until it is barely in contact with the cam leading edge at the 5 o'clock position. Press the AAU onto the magneto shaft and tighten the center bolt with the fingers only.

    13) Check that the VOM leads are still as set in Step 6; the VOM should be indicating points closed at this point. Slowly rotate the engine forward until the VOM indicates points open. Note the reading on the degree wheel. Rotate the engine backwards again until points are again closed. Slowly rotate engine forward until points open, noting the reading on the degree wheel. Do this several times until you are confident your technique is producing consistent results. I have been able to obtain consistent results within 1/2 degree.

    14) If the value on the degree wheel in Step 13 is not your target timing point, break the AAU on the taper and shift the contact block relative to the AAU as necessary to bring the points opening toward the target. Repeat Steps 13 and 14 until the points open at your target timing point.

    15) Now rotate the engine 360 degrees and repeat Step 13. The value on the degree wheel (at this point, the right cylinder is firing) should be within 1-2 degrees of that for the left cylinder.

    16) If the point gaps were equal in Step 1, and if the cam ring machining is up to CNC standards, the specification of 1-2 degrees given in Step 3 is assured. If you cannot achieve this tolerance, consider a new cam ring (review Step 2).

    17) Install the center bolt in the contact block, tighten the center bolt in the AAU, and REMOVE THE WEDGE in the AAU.


    1) The magneto drive chain should have 3/16 to 1/4 inch up/down play in mid-run. Adjust by sliding the magneto on the three mounting studs. Caution: It is known that an overly tight chain will cause the AAU to "stick" in advanced position.

    2) The lower high tension pickup goes to the left cylinder.

    3) At the high tension pickups, the high tension wires should be passed thru a brass washer, then the wire strands splayed open. Do not solder.


    PS ... Comments are welcome. PM me so I can revise as necessary to make this a useful "tool" for setting up a K2F.
    Last edited: Jun 20, 2018
  2. 1down5up


    Oct 17, 2014
    Thanks for the informative post, (considering it was probably my other thread that prompted you to this post).

    A few general questions, if he magneto has just been serviced, and a new cam ring etc etc installed would you still expect to be within 1-2 deg on the other cylinder or should it be spot on? Or is it just inherent with these older bikes that there is some discrepancy between cylinders.

    Also, any pointers on the bottom but on the magneto? Took me forever to get it off, figure there must be a better way than 1/16th of a turn at a time

    I have just pulled out my magneto and sent away for a service as there was quite a bit of play in the shaft, I also had issues with the self extracting bolt not pulling off the taper, nothing that a sharp walk with a hammer. Opulent fix but was wondering if this was normal. My coil was covered in oil etc from a bad seal but nothin had come through to the points housing.

    Finaly, is 32deg sill an appropriate advance with modern fuels? Or with higher octane should that drop to 30deg or so? (How much difference does 1deg make and how noticable is it?)

    Feel free to move or delete if you wanted to keep his post more informational
  3. Nortoniggy


    Nov 17, 2010
    The most important thing is that the position at which the spark plugs fire are 180 degrees apart on the magneto, 360 degrees on the engine. This is reliant on the ramps of the cam ring being exactly 180 degrees apart as you use the opening of the points to set the timing. I could envisage a situation where there was a difference in the fully open points gap on each cam but the ramps were in the correct place, or alternatively the points gap was the same but the ramps were slightly out. I would have thought it was better to pay more attention to the points opening position on each cam and make sure those are 180 degrees apart.

  4. Bernhard


    Apr 20, 2011

    I will second that :!:
    it goes without saying that I have had K2F magnetos as much as 7 degrees out, and a brand new Lucas boxed cam ring brought in the 1970s that was 41/2 degrees out between the 2 cam lobes
  5. texasSlick

    texasSlick VIP MEMBER

    Jan 2, 2013
    A magneto rebuilt by a competent and trustworthy technician, should come back with a properly centered cam ring, but likely not a NEW cam ring, as they are rather expensive (about $100) and a rebuilder is likely to let anything passable thru. IF the ring IS centered, then both point gaps will be equal (the rebuilder should do this much), then IF the ramps on the ring have been machined 180 degrees apart, the magneto will fire the cylinders 360 degrees apart.

    If the cam ring is machined spot on, that is, the ramps are exactly 180 deg apart AND the ramp thickness is exactly equal on each, but the ring is off center, then the point gaps WILL be unequal and the engine will fire early on the side with the larger gap. Thus it becomes imperative to check the point gaps at the very start.

    With a new CNC machined cam ring, and point gaps within 0.001 inch, the timing on each cylinder to within 2 deg should be easily achieved. There is nothing inherent in sloppy timing except that old stock cam rings were sloppy, having been machined on war worn equipment. As Bernhard says, NOS cam rings often had ramps off 180 degree apart. The only remedy to fix these was to stone down the early ramp leading edge .... better to fit a new CNC ring.

    Regarding getting off the lower nut: It is the most bitch of anything I have ever encountered in shade tree mechanics! Tips .... remove the outer gear box cover and the oil junction block, if only to see better. I ground some of the meat off a Whitworth spanner to get just a little more turn. Be sure the threads on the stud and nut are perfectly clean before replacing the nut so you can spin it on with your fingers, and do not use LockTite. NOTE: Later (1965+ ?) replaced the lower stud with a bolt, and the nut was accessible from inside the timing case. For those with such machines, these tips do not apply.

    Regarding self extracting nut: They work great when they work. When they don't, it is usually because they strip the internal left hand thread. Your method of a sharp rap with a hammer is first option if you can get some tension with the internal thread. If completely stripped, as mine is, then next option is a small gear puller.... back off the center bolt 1-2 turns, then pull on sprocket while pushing on center bolt.

    Regarding timing set point.

    When the 32 deg specification was written, 100 Octane fuel could be found at any pump. Moreover, the factory stock Atlas had only 7.5:1 compression ratio. With modern fuels, especially if the machine has been fitted with 9:1 or higher pistons, then the 28 degree setting that the Cdo guys target for is more appropriate. Mine is set to 30 degrees.

    Finally, how much difference does 1 deg make? Not much, just like cutting one slice off a baloney ... one slice is hardly noticeable, but sooner or later you don't have any baloney. :D Seriously, one has to try and see how the machine runs ... CR and the fuel octane make a greater difference, as well as how you operate the machine.

  6. johnm

    johnm VIP MEMBER

    Feb 26, 2008
    I have posted this link before but some may have missed. This is by the far the best analysis of rebuilding rotating armature type magnetos on the web.

    http://www.britbike.com/forums/ubbthrea ... Post446733

    Magnetos can be a real pain to get on and off. The following can help. Perhaps not suitable for concours machines but excellent for people who ride the bike. I have done all the following on my race bike.

    The bottom nut is the hardest to access. BSA made a very long wasted blind threaded "bolt" to replace the lowest nut. This makes it perfectly accessible.

    Also if you are not too fussy about perfect looks it is worth:

    - dremmeling the mag casing around the two top nuts to give more clearance.
    - machining the faces on the nuts down to the next spanner size. (leaving a step at one end of the nut so it covers the washer properly)
    - slimming down a ring spanner to fit.

    If you do all this you can remove the mag in 2 minutes.
  7. texasSlick

    texasSlick VIP MEMBER

    Jan 2, 2013
    Good tips on dealing with the bottom nut. The BSA "long bolt" is an option if you are not fussy as JohnM states.

    The link JohnM provides is certainly a comprehensive treatise on rebuilding a mag DIY, but it does require tools and expertise above the common level, particularly with respect to re- magnetizing. For this reason, I would not attempt the job myself, and recommend to most to send it out to a pro. While the cost may seem high, remember that it is not all labor .... parts are included, and a rewind of the coil or armature is included. By the time you incur these costs, you will not have gained much, and could possibly do the mag some damage not knowing the intricate details.

  8. worntorn


    Dec 22, 2006
    Any of you Magneto Men ever use the Brightspark Easy Caps to fix sickly condensors in an old K2f?
    I ordered one of these today. The Mag works great cold right now, but the bike will not restart when hot.

  9. texasSlick

    texasSlick VIP MEMBER

    Jan 2, 2013
    That description of runs cold, quits hot is classic Lucas aluminum/paper electrolytic capacitor old age failure.

    I have no personal experience with the Brightspark. It seems to be a reasonable alternative to a complete rebuild. From my limited knowledge and experience about electrolytic caps, the only commercially available capacitor that was a PERFECT replacement to the Lucas, was a Panasonic polystyrene cap that is no longer available. Most professional K2F rebuilders use a polystyrene cap similar to the Panasonic, or have a back stock of the Panasonic caps.There is more than just matching capacitance, such as dV/dT (change in voltage per unit time) and temperature stability that determines what type of capacitor best matches the Lucas. Polystyrene, or ceramic (Brightspark) have an indefinitely long life expectancy ..... unlike the Lucas aluminum-paper caps which can be expected to fail in 30 -40 years due to old age deterioration of the paper.

  10. johnm

    johnm VIP MEMBER

    Feb 26, 2008
    There is a sometimes acrimonious discussion in the thread I posted on the suitability of the Brightspark conversion. Much of which is more than most of us wish to know. Certainly the author of the article is not keen.

    From my reading the conversion will work for a time.

    The question is how much time. 5 hours 50, 500, 5000 ? There is no hard data presented.

    I agree few of us will rebuild a mag as demonstrated in the article. But it gives a lot of information on how to evaluate the quality of a rebuild. My own experience is that many rebuilders do not properly address the mechanical aspects of the rebuild. Which is precisely what can lead to the large errors in opening times of the points and timing discrepencies between cylinders described above. I destroyed two sets of pistons because of this issue so these days I verge on paranoia when it comes to ignition timing :roll: .

    While the author of the linked post is not given he is actually a PhD physics professor at an American university with a demonstrated track record of extremely high quality rebuilds of mags and complete machines. I would rate his work at absolutely first class. Unfortunately not in the business of rebuilding mags except for his own machines.

    I can add a third reason why the points gap can be different. The shaft of the rotating armature is out of parallel or off centre with respect to the body of the magneto. The problem with my own mag was the shaft was out of parallel. This could be seen as a variant of Slick's first reason. But in this case its not the cam ring which is not central but the shaft.

    I also agree and support Slick in his posting above.
  11. texasSlick

    texasSlick VIP MEMBER

    Jan 2, 2013
    JohnM wrote:

    . " I can add a third reason why the points gap can be different. The shaft of the rotating armature is out of parallel or off centre with respect to the body of the magneto. The problem with my own mag was the shaft was out of parallel. This could be seen as a variant of Slick's first reason. But in this case its not the cam ring which is not central but the shaft."

    This point is EXACTLY why the cam ring housing should not be moved or tilted (an often posted remedy for tweaking timing) to center the cam ring. This is another reason why I do not recommend DIY rebuilds, or installing the Brightspark, which requires disturbance of the cam ring housing and most assuredly means the housing will go back with shaft out of parallel.

  12. Rohan


    Aug 26, 2010
    There are a mightly lot of those brightsparks installed though, with minimal reported problems.
    That seems a pretty good record. ?

    I was saddened to see that Ken is with us no more, RIP.
    Maybe I missed this news ?
  13. Bernhard


    Apr 20, 2011
    You are not the only person on this website who has chewed up pistons because of an inaccurate magneto that didn’t spark at 0 and 180 degrees on full advance.
    The main problem is now that most K2F magnetos are now at least 50 odd years old and may have suffered abuse in the hands of other people, and armatures fitted from elsewhere-who knows what kind of life it has had :?:
  14. Triton Thrasher

    Triton Thrasher

    Feb 10, 2009
    I don't think we have a "mean time to failure." Many of the installations are on minimal miles.

  15. Rohan


    Aug 26, 2010
    Even just sitting there and not failing, that is a better record than the original condensors ?,
    which could be faulty off the shelf. And didn't improve with age...

    In the computer business, that mtbf was considered an absolute joke.
    Some marketing folks must have dreamed that one up.
  16. Possum


    Jan 4, 2012
    Texas Slick

    In your 'General Notes, #3' you recommend, '...do not solder...'.

    I have always soldered & am interested to know your reasoning for not soldering.

  17. texasSlick

    texasSlick VIP MEMBER

    Jan 2, 2013
    My factory supplied Owners Manual says to do it the way the note is written. Perhaps (perhaps means maybe ... I do not know for sure) soldering may score pickup track.


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