The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Lucas, Ignition, Charging, Electrical => Topic started by: Swarfcut on 17.05. 2020 09:32
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Having a look at a surplus bare magneto armature, which passes the first test.....does the points taper still fit, is the earth track smooth? So, on to the next basic test....continuity on the LT side of the coil, OK so far.
Now we come to the HT side, there is nothing between the HT spike and either LT lead. The armature bobbin section is already split from the ends, shagged condenser removed so easy access to the wiring into the coil.
Now HT is funny stuff, so the question is "Can I wire up a low voltage supply, external condenser and spark gap to test this coil, or should the HT winding show some continuity when tested with a cheap multi meter? It may appear to have infinite resistance, when in fact it would work under different simulated working conditions. Windings are good, no sign of mechanical or chemical degradation, looks too good to condemn without a fair test.
Swarfy
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Mornin' Swarfy,
Really, you should see several thousand ohms from spike to either LT lead on a bare coil. About 0.6 across the low tension tails. Most often, the HT will be around 5000. Some may be a tad less, others up to 6500 on some original factory ones, probably C versions. Most rewinds are done to about 5K, although over here in France I have seen fairly wild variations depending on the recipe used by previous repairers for the turns ratio primary:secondary and the wire gauges.
A cheap meter - or an expensive one for that matter! - ought to show the continuity clearly. Assuming the ends of the leads and the spike are clean, if it's Open Line / Infinity then there is a break in the HT winding somewhere, pretty well for sure.
That said, it may actually spark quite well on test, as the spark will hop across a small internal break and come out looking surprisingly healthy and - quite often - without consuming too much current to do it. If you had an ammeter on your test set-up, you could see what it took . . . A good one should deliver a decent spark across the Lucas spec 5.5mm three point gap at no more than 2 amps of applied current up the low tension side, using a make-and-break. If you were able to spin the mag and determine the speed, it should work from about 130rpm using those test gaps (cold & fully advanced, if manual). And it should also work as a bare coil with no more than, say, a 10%ish increase in required current when hot (around 50°C for test purposes) - when it will also need a few more rpm (150-160 ish) if testing it dynamically.
But even if it does all of that, if there is a break in continuity, it's a one way street sadly as the gap inside gets bigger with erosion, so even if on test it seems OK, it would be a brave man who'd cross a desert with it!
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Thanks Mr G. Just as I suspected, but hey ho, ready for a bit of experiment. LT resistance is close to your quoted figure, so worth a go. Take your point about long term reliability, and what goes on deep inside but it will be interesting to see if it can be coaxed back to life.
Off piste maybe, but was recently challenged to fix a reluctant Briggs and Stratton mower engine fitted with the infamous Magnetron Coil. This is a one piece ignition unit, laminates, coil, integral plug lead and cap. No ignition points, it's triggered by magnets on the flywheel. Dead as a door nail electrically, but with the plug cap off, measured quoted resistance from plug lead to mounting plate, and when refitted, it sparked. Turns out that plug cap contains a hidden suppressor, obviously this was open circuit.
So if you've no sparks, try it with the plug cap removed to expose the central conductor before you punt a new ignition unit. Takes a bit of devious manipulation to get the boot off and remove the inner cap, it's crimped in place, but as it doesn't work anyway, have a go.
Swarfy.
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Those B&S ignition systems are rubbish. Need a magnifying glass and a dark night to see the spark from one of those (if it even has one). In similar vein, last weekend my son came around to start the project bike for me (right hip's not great at present). No sign of life whatsoever, so checked the sparks - not great. Discovered the new plug caps had resistance, when they weren't supposed to. I avoid suppressed caps on magneto ignition as they make starting more difficult. Also, they can damage a magneto - I quoted an article on this not so long ago. Anyway, the project non-start turned out to be stale petrol - had turned a browny yellow colour. It was no more than a month since buying that lot, so the quality must be getting worse. In looking for alternatives I found one can buy petrol from garden machinery people that will last a couple of years or more. Aspen or something, but at £4.7 a litre think I'll give it a miss.
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Oh the joys of mowers Swarfy! Close to my heart, or should I say a pain at the other end!
But, having managed to bust my big mower the other day at exactly the wrong time of year in a place where grass literally grows in front of your eyes, where there's a lot of it and I haven't got a sheep (and with normal parts & services not being available during strict lockdown) in desperation I pressed into service an ancient 3.75 bhp Briggs&S engine which had sat in a wet corner of a wet shed for a good 10 years . . . and to its huge credit, having bolted it onto an engineless base lurking in another corner of shed and found a suitable-length blade in yet another, blessed it with a drop of fresh oil etc, it went after a few pulls (and a few syringes of neat fuel through the carb) A mate here said 'that suppressor, it'll be dead as the proverbial parrot' or the French equivalent - but in fact it seems to be still living and I haven't even taken the plug out to look at it.
A minor miracle given that me and mowers, we're just not good mates at all.
Maybe your armature will play ball too!
Right, time for another blast on a bike - the joy of being able to go out at will again. Been doing nothing much bar riding around with an insane grin this past week since our rules were relaxed! But I'm rather sad about all the cancelled events, same as most of us I guess. Not enough active riding years left (even with a good covid-free tail wind) for these lost pleasures not to matter, with my 50th anniversary of obtaining a licence coming up next year. Where havethose years gone?
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"Not enough active riding years left (even with a good covid-free tail wind) for these lost pleasures not to matter, with my 50th anniversary of obtaining a licence coming up next year. Where havethose years gone?"
Agree - 56yrs for me - took my test in a 5t truck to get 'all groups' in one go. Can't get HGV at 17 these days, it's a right palava. Gave up the HGV part when I hit 70 as it was costing me over £60 a year just to keep it on licence.
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Mornin' Swarfy,
Really, you should see several thousand ohms from spike to either LT lead on a bare coil. About 0.6 across the low tension tails. Most often, the HT will be around 5000. Some may be a tad less, others up to 6500 on some original factory ones, probably C versions. Most rewinds are done to about 5K, although over here in France I have seen fairly wild variations depending on the recipe used by previous repairers for the turns ratio primary:secondary and the wire gauges.
A cheap meter - or an expensive one for that matter! - ought to show the continuity clearly. Assuming the ends of the leads and the spike are clean, if it's Open Line / Infinity then there is a break in the HT winding somewhere, pretty well for sure.
That said, it may actually spark quite well on test, as the spark will hop across a small internal break and come out looking surprisingly healthy and - quite often - without consuming too much current to do it. If you had an ammeter on your test set-up, you could see what it took . . . A good one should deliver a decent spark across the Lucas spec 5.5mm three point gap at no more than 2 amps of applied current up the low tension side, using a make-and-break. If you were able to spin the mag and determine the speed, it should work from about 130rpm using those test gaps (cold & fully advanced, if manual). And it should also work as a bare coil with no more than, say, a 10%ish increase in required current when hot (around 50°C for test purposes) - when it will also need a few more rpm (150-160 ish) if testing it dynamically.
But even if it does all of that, if there is a break in continuity, it's a one way street sadly as the gap inside gets bigger with erosion, so even if on test it seems OK, it would be a brave man who'd cross a desert with it!
Hello all, I have just joined this forum. But have owned a A10 for over 40 years, but not been able to ride it for most of that time. The first thing that I have noticed is the amount of spare parts and accessories that you can buy now for the A10 that was not around 40 years ago.
I can remember reading somewhere about using a 3 volt battery and a ammeter to test these coils, but cannot remember the wiring diagram for doing this. I think it was In a lucas service sheet for the K2F. If anyone can put together the wiring diagram with the ohms resistance for the coils that would be a great help,for us all.
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Speedy, My two recommended sources for any information and parts for Lucas Ignition are Priory Magnetos and Brightspark Magnetos. The latter has online information freely available to enable you to test your magneto. Just look in the library section, Lucas workshop manuals are all there.
40 years in the shed? A mere ripple on the millpond of life!! Head over to the intro section and tell us how you fell into this sad affliction.
Welcome to the Forum.
Swarfy.
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I can remember reading somewhere about using a 3 volt battery and a ammeter to test these coils, but cannot remember the wiring diagram for doing this. I think it was In a lucas service sheet for the K2F. If anyone can put together the wiring diagram with the ohms resistance for the coils that would be a great help,for us all.
Try search, lots of stuff to be found, this may be useful:
> https://www.a7a10.net/forum/index.php?topic=8138.0
> https://www.a7a10.net/forum/index.php?topic=1375.msg9797#msg9797
& btw, am still a little proud of my spark pictures > https://www.a7a10.net/forum/index.php?topic=1412
Now, waiting for some words\pictures in "Introductions, Stories & Pictures" :O)
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Thank you for your help in finding the K2F magneto diagram for testing the coils with an ammeter and 2 volt battery. This diagram is in the Lucas service sheet.
Now the armature of the K2Fmagneto is insulated by the paper bearing packing washers, And if these washers have deteriorated the bearings become pitted and burnt by carbon particles from the carbon brushes, as the armature shorts out through the bearings.
So if you fit a aluminium magneto drive gear, doesn't this also short out the armature, and in turn reduces the magnetos output. And can burn out the secondary coil ?.
Has anybody got any ideas on this.
Ps
The Lucas service sheet for the k2f magneto can be found on this forum. And as far as I can make out the primary coil should be 5 ohms WITH 20SWG wire and 200 turns. And the secondary coil should read 5K ohms with 40 SWG wire and 11,000 turns. The condenser should have a value of 0.2 uf 400volts. The magnetos built in magnet dose not have a specific magnitization value, meaning it can be remagnitized with either N or S direction. But the K1F needs to be magnetized in the correct polarity.
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Now the armature of the K2Fmagneto is insulated by the paper bearing packing washers, And if these washers have deteriorated the bearings become pitted and burnt by carbon particles from the carbon brushes, as the armature shorts out through the bearings.
The reason for the insulator washers is to ensure that the return HT current passes by the earth brush, or brushes in cases where there is an auxiliary one on the cb unit, rather than partly or wholly via the bearings. Not really a carbon particle thing - just a case of avoiding using the bearings as a return path. You'll see on many a mag that the return current has worn a dimple, or 2 dimples, on the brass endpiece against which the earth brush bears . . . Having said that, there are many mags without insulated bearings, including some Bosch units. I have always regarded them as the Gold Standard among early magnetos at least - so I guess they thought a decent earth brush was 'good enough' back then.
So if you fit a aluminium magneto drive gear, doesn't this also short out the armature, and in turn reduces the magnetos output. And can burn out the secondary coil ?.
Nope. The armature's HT side is quite unaffected, so makes no odds to the most important bit - the HT coil. No short there, no reduction in performance of the coil. Many machines use steel or alloy drive arrangements anyway - AMC, Norton, some Beesas and Triumphs etc etc. If there were no earth brush, then the return current might work its way through the drive train as well as the bearings to get back to base, but as there always is or should be a brush, not a problem.
The Lucas service sheet for the k2f magneto can be found on this forum. And as far as I can make out the primary coil should be 5 ohms WITH 20SWG wire and 200 turns. And the secondary coil should read 5K ohms with 40 SWG wire and 11,000 turns. The condenser should have a value of 0.2 uf 400volts. The magnetos built in magnet dose not have a specific magnitization value, meaning it can be remagnitized with either N or S direction. But the K1F needs to be magnetized in the correct polarity.
Sort of. The wire gauges in different mags vary, and I think rather in thousandths than SWG. Primary resistance on K2Fs will be about 0.55 ohms; secondaries on K2Fs typically about 5000, but some were higher back in the day, and depending on the relative number of turns and the wire used you'll get some variations between winders.
Typical condensers will be between about 130 and 200nF. Good ones will be leakproof tested with 500v insulation testers to at least a Gigaohm. There are also important considerations with ref to their ability to handle current without fusing. Spikes in primary voltage can be surprisingly high 'at the break' and rolled paper capacitors rated in the 200-300v range would be at risk of damaging their self-healing properties. Bear in mind that voltage ratings are usually given in DC volts, but mag primary circuits are AC generators so you need to reduce the stated rating by about 0.7 (the inverse of I.41, the square root of 2) to get the equivalent AC rating.
On any multi cyl mag with a two-lobe cam, polarity isn't important, true. You get one neg and one pos spark whether you like it or not. Some people said in the old days you should swap your plugs over now and again to even the wear between them, as erosion patterns are different if the spark jumps from centre to earth electrode or vice-versa; I don't know anyone who does that! On singles, it's best to set things with a negative spark, either by magnetising in the sense that provides that, or by arranging the camring and contact breaker to get there.
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Thankyou Bill for explaining these points for me. It has been a it confusing as to why paper insulation washers have been used to insulate the armature. So in reality you could run the magneto without the paper washers and secure the bearings with metal shims. Or would this mean the armature would be to ridged so it would vibrate, as the paper washers would cushion the armature.
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Whilst on armature issues, we're told a cam ring should be set up so the points are opening near maximum flux. When rotating mine there is a definite pull as the armature approaches the magnet and another pull as it leaves. The second pull occurs a couple of degrees or so before the points open. Presumably this timing is correct, or do I need to move the cam ring? I ask because even on the rear cylinder of a vee twin I need all the spark I can get. Am currently modifying a distributor to 60* but completion will be some weeks away, especially as my pal's cylindrical grinder is playing up and I need it to grind the old cam off.
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Points opening should occur just after maximum flux when the poles are changing (in theory). If you replace the paper shims with metal, you've provided a electrical path via the race and ball which could cause erosion if the earth brush fails.
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beat me to it, don't know a lot but my thought would be an effect like trying to weld the balls to the bearing rings
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A mate of mine wondered why his headstock bearings kept failing on his BMW R45. It was because there was no earth wire from the headlamp to the frame so the earth tracked through the headstock bearings. Same applies to magneto armatures. If there is no other earth route the bearings will be shot in no time. Regarding flux and points opening... ideally the points should open just as the polarity switches in the armature. The moment of switching sets up an electrical flux which conducts (I should say inducts actually) into the coil and ramps up through the thousands of turns - that's the only way I can explain it - electrophysicists please don't get picky! If the points open too early there is no flux so no spark. The strongest flux is at the moment of switching, from that point onwards the flux is steadily collapsing but, for a while, still doing enough to conduct into the coil, so if the points open late you still get a spark, but a weaker one. So, timing the points to the internal structure of the magneto is a good thing to do, which is why Lucas provided an eccentric stud under the press fit button on the cam ring housing. By turning the stud with a screwdriver you can rotate the cam ring relative to the points. If you're very brave or a bit cavalier you can play about with this. From the earlier explanation you will deduce that the earlier the points open the better, so you can twiddle with the eccentric screw to make the points open as early as possible and if this hasn't killed the mag it will have made it better! You should only do this on a manual magneto in the full advance position and you will have to reset your engine/magneto timing afterwards as well. The problem with the internal timing is that the flux collapses very quickly so you need to catch it whilst it's falling but before it has fallen very far. How good your mag is in terms of its consistency i.e. the points open at exactly the same time every revolution, will affect how close to the point of maximum flux you dare set your eccentric screw. If your mag is absolutely top notch you can set the eccentric screw very finely adjusted to point of max flux but if your mag has some wobbly bits like a loose cam ring or worn heel to the points or dirty points etc. your points will open, electrically, at a slightly different time each revolution. In this situation you should not gamble with the eccentric screw because there will be some occasions when the points open earlier than usual and the mag won't spark - hello misfire! I thought I'd throw my two penn'orth in as Groily needs time off for good behaviour! As a p.s. I note somebody mentioned V twins. An interesting case. Normally, one cylinder fires at optimum flux, let's say 0 / 360 degrees on the cam ring, the other cylinder fires 60 degrees later (or 420 degrees later depending on how you look at it but the maths and geometry are the same), but only 30 degrees late on the cam ring because the mag rotates at half engine speed. Typically a V twin will fire at kickstart speed on the cylinder which fires on max flux then generates sufficient engine speed to fire on the cylinder relying on the low flux side of the mag. More mag speed equals more flux (sort of - electrophysicists back off!). This illustrates that having the eccentric screw on a conventional mag set to not quite maximum flux isn't a deal breaker because there's no way you are going to be 30 degrees out! Furthermore it explains why a manual mag, whilst stopping the bike kick back, will be difficult to start if retard the lever/cam ring too much. The closer to max flux on points opening, the easier the bike starts. Of course the strength of flux is directly proportional to magnet strength but don't get me started on that one! Good night!
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I would not be tempted to adjust that cam ring, which means that when building a mag from the best bits I have it looks as if I will be either very lucky or definitely on a losing streak depending on the points housing I select from my scraps.
Is this likely to be of any real consequence? Without electrical workshop test gear, my only test is whether it actually works!
Thanks to those two Forum Members who have posted the theoretical and practical finer points and aspects of this electrickery.
Swarfy.
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I would not be tempted to adjust that cam ring, which means that when building a mag from the best bits I have it looks as if I will be either very lucky or definitely on a losing streak depending on the points housing I select from my scraps.
Is this likely to be of any real consequence? Without electrical workshop test gear, my only test is whether it actually works!
Thanks to those two Forum Members who have posted the theoretical and practical finer points and aspects of this electrickery.
Swarfy.
If you don't adjust it the mag will probably work but the cam/points/flux may not be in the optimum position relative to each other. You can test the internal timing if you can rig up a way of turning the mag smoothly and slowly, ideally on a motor with a variable speed. A piece of string wrapped round the armature threads will do, like starting a lawnmower! Start with the eccentric screw in the fully retarded position and advance it until you lose the spark, then give a nudge back into the retarded zone and all should be well. Obviously, if you've built your mag from bits and pieces and some aren't very good you'll need to be a bit more cautious and retard the eccentric screw a bit more to compensate for any inconsistencies in points opening .
To be honest I shouldn't be encouraging people to build mags out of bits and pieces because there are dozens of things which might be contributory factors in the mag not working properly, not all of which the less experienced will spot - sorry if this sounds rude! If lots of people start building mags out of bits and pieces we end up with lots of unreliable mags on the road and the mags then get a bad reputation, undeservedly. Then we get back into that old argument about electronic ignition versus magnetos. A properly built mag should last for many thousands of miles assuming usual routine checking and adjusting.
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The Lucas magnetos are from the SIMMS company that Lucas brought out. The armature is from a design made by Siemens comonly refured to as a shuttle armature. Invented in the 1870s. So the complete magneto design is over 100 years old. Interestingly on light air craft a battery powered ignition system is not allowed, instead they have two magnetos per engine . These magnetos are now made by Champion, with being for aviation use they have to go through stringent testing every so many of hour's of flight. You can also see that magnetos are used in drag racing, so realy it is the way that the magneto are set up that count,and how well they are being g serviced, for happy motoring.
Has anybody got the Eddy Dow servicing sheets for the A10. Thank you all for helping in this topic.
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Probably didn't explain my query clearly - not the first time and unlikely to be the last!
I explained that when turning the armature slowly, there's a distinct pull as it passes the magnet, with a 2nd pull slightly later. On the mag in question, the points open a few degrees after that 2nd pull. But my question is - at what point is max flux - after the 2nd 'pull' or between the first and second?
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G'day Speedy.
All I could find.
https://www.a7a10.net/forum/index.php?topic=11599.0
http://www.britishmotorcyclemanuals.com/acatalog/Eddie-Dow-Gold-Star-catalogue-Book_0442.html
Cheers
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Probably didn't explain my query clearly - not the first time and unlikely to be the last!
I explained that when turning the armature slowly, there's a distinct pull as it passes the magnet, with a 2nd pull slightly later. On the mag in question, the points open a few degrees after that 2nd pull. But my question is - at what point is max flux - after the 2nd 'pull' or between the first and second?
Could your “second pull” be the fibre heel on the moving point touching the cam ring ramp?
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Probably didn't explain my query clearly - not the first time and unlikely to be the last!
I explained that when turning the armature slowly, there's a distinct pull as it passes the magnet, with a 2nd pull slightly later. On the mag in question, the points open a few degrees after that 2nd pull. But my question is - at what point is max flux - after the 2nd 'pull' or between the first and second?
When I'm building a magneto I try to achieve good mechanical 'feel' before fitting the points. Magnetos are invariably old, have been fiddled with, and have had incompatible parts swapped in and out. Before fitting the points there should be no feeling of friction nor any significant resistance in the bearings due to preload nor any endfloat. When the magneto is in this state it should be possible to feel the resistance of the magnetism very distinctly. It feels almost like air pressure resistance which can be burst through. This should happen twice every rotation at 180 degrees apart. The armature and magnet alignment is symmetrical so, unless something really horrible has happened, there will only be two 'bumps' per revolution. Any other 'bumps' must be due to friction, either the earth brush, pickup brushes or the points heel. I suggest you remove all external components including the points to identify what your 'bumps' are!
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Maybe ‘pull’ is the wrong description. One can feel as the armature approaches the magnet, and again when it’s passed it (around 20* of armature movement). Same 180* later. It’s this window of approx 20* I’m referring to. Whereabouts in that does max flux occur? In the middle? At the end? As currently set up the points for the rear cylinder open very soon after that second ‘pull’ / episode or whatever one wants to call it.
I looked at experimenting with advancing the cam ring, but there’s no adjusting screw – just a rivet (looks rather like those used to fasten engine number plates to cylinder blocks) limiting cam movement, so I’ll leave it alone and concentrate on modifying the distributor I plan to replace the mag with. Machined up a new 60* cam yesterday – just need to get the cylindrical grinder working so I can accurately remove the existing cam lobes ready for the new one to drop on.
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The eccentric peg screw is under a cover that looks like a rivet head. You can ease it up and off with a knife.
Points open at the end of the magnetic pull that you can feel.
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Thanks TT. When I looked inside after removing the cam ring, the thread of said screw looked more like a spiral, leading me to believe it was a drive-in rivet.
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It’s not intuitive, is it!
As the mag wasn’t supposed to be home-serviceable (or even very BSA agent-serviceable), apart from the points, manuals and service sheets don’t tell you much about them.
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Have you looked at the contact breaker plate, the moving contact can wear a groove in the plate from it rubbing it. Also the leaf spring can sit proud of the cam plate and rub the cam ring if the tuffnel block is worn. No adjustment on the leaf spring, only the play in the fixing holes. These leaf springs are not sold with a new set of points, and not sold on their own either. So be carefull as to what you do with them.
Could you please post the drawing for making a new cam points ring. To see how much lift you are giving the contact breaker arm.Also the material that you made it from. I would think EN8.
Thank you.
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Speedy - I'm not making a cam points 'ring' - I'm making a 60* cam for a distributor to replace the magneto. Material silver steel so it's easily hardenable once fettled.
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Thanks for clearing that up. Best of luck with the mods to the mag.