Magneto only sparks on one side...

[sckemp]

Hello, I've had my '51 plunger A10 for two weeks. It had been laid up for 10 years and today I got it running. It seemed to go well on both cylinders but it was also sparking through one of the HT lead pick ups onto the retaining tab. Then that side completely stopped sparking... The other side still sparks as usual. Points open fine both sides, leads and pick ups all have continuity through them, a multimeter test shows ca. 4000 ohms resistance between plug cap and centre screw on both leads indicating HT winding is good. I can't see why one side would work and the other wouldn't. Surely any issue would show up on both sides.

Some more info. The bike was taken off the road 10 years ago due to magneto issues. Mag was refurbed at the time and the owner at the time never got it back together again. When I got the bike, no sparks but I went through checking all connections, replaced condenser with easycap and shimmed to get the right end float and to get points gap equal on both sides. The result was fat blue sparks that jumped a 4mm gap from bare ends of both HT leads on turning by hand. So far so good. I installed the mag on the bike and set timing to 5/16 BTDC with ATD at full advance. Happy to say it was at 5/16 BTDC on both sides. Again so far, so good. Flood carb, couple of kicks, we have a runner! Then I noticed the sparks exiting the plastic housing of the pick up onto the retaining tab and after that, no more sparks on that side. As I say above, the connection through that HT lead is intact right through the HT circuit to the armature (I.e. points centre screw) so what could be the problem?

Any ideas? Thanks in advance (sorry - bad pun).

[groily]

Think you answered your own question. The HT pick-up from which the sparks were hopping out is leaking badly. If the spark is exiting there, very little or nothing will be getting to the plug. They do that when they're past it (some of the cheap pattern ones are known to do it from near-new) - and this problem would only affect the one side. Quick solution - all other things being equal and in good order - is to get another pick-up, or preferably a pair. Decent ones are handed, so if going for just one, you need to specify whether it's the rear or front pick-up (engine or gearbox side), and whether you want/need a 45° angle on the thing.
You could try wrapping the outside of the pick-up in a bit of rubber, or shoving a bit of inner tube between it and the clip to see if the arcing stops and the spark comes back on that side. Might not be successful if the inside of the pick-up is allowing leakage from the brush/spring to the mag body, but it sometimes/often is enough to prove the point. You may find the pick-up's surface has a slightly 'pumice-like' aspect to it in one area or another, where little sparks have been eating away at the material.
Cheers, Bill

[sckemp]

Thanks Bill. Makes sense - but is it normal for it to leak with visible sparks then for it to leak so directly that it doesn't need to arc anymore so you don't see it disappearing? Do you see what I mean? Anyway I will try with a piece of inner tube. Thanks again.

[sckemp]

Yep, that's sorted it! Will order some quality replacements. Sounds so obvious now but it's all part of my Brit bike education.

[Bellanca A10]

Hello fellow A7A10 enthusiasts, this is my first time posting here. I own a’62 A10 w/factory alternator (model number escapes me right now) that has exhibited the following:
It ran great for the first year since I purchased it. Then started only running on one cylinder. I managed to limp home on the #2 (right) operating cylinder. I pulled into the shade of my garage and saw that the number #1, or left, magneto pick up (or contactor?) was arcing to the mag body. Problem solved?! I ordered two new pickups, installed them and now the same #1 cylinder is firing intermittently (without the arcing). I’ve swapped out the spark plugs and HT wires to no avail. The bike has always started nicely when cold, even with this issue. I started the engine yesterday for the first time in about a year and the engine fired on the first kick. Then, before engine warmed up, #1 started misfiring again.
I removed the mag and I’ve looked at the points. They are opening and closing 180 degrees apart. It doesn’t seem like this problem could be caused by the condenser because the right side seems to be running perfectly. Plus, the problem only started after the arcing issue.
Any ideas? Thank you.

[Swarfcut]

Hi.  Getting some sparks means the magneto is working, condenser is fine and the fault lies between the HT spike on the internal coil, and the spark plug, assuming there is no spark at all from that lead.

   Start with the slip ring on the magneto armature. It should be smooth, clean, no sign of carbon deposit and have an undamaged brass segment.  The pickups need to be clean, with spring loaded brushes in place and free moving. These carbon brushes need to be hard, hard enough to just mark paper. If they write like a pencil, they're too soft and will deposit carbon dust on the slip ring track.
    There are D shaped fibre washers under the pickups. As well as being further insulation from the magneto body, they position the pickups the correct distance from the slip ring. Test the plug lead and cap by swapping to the good side.  Even if  the pick ups have been changed, do a continuity test between the brush and the plug lead connection.  There is also another carbon brush at the drive end, under a brass slotted screw cap, here again it should be clean and free moving. This is the earth connection to the armature.

    Although all may appear in order at low voltages, HT does strange things, always searching out the path of least resistance, and yes, running it in the dark can often indicate the source of wayward sparks.

     If the magneto is still off the bike, it is a good time to strip it to its major parts, in order to check the slip ring more closely for signs of tracking. You won't upset the bearings if all is simply replaced in the same way it came apart. The bearings will benefit from a dab of grease. Plenty on the forum about magneto servicing, and the strip down procedure  to avoid damage. Both Priory Magnetos and Brightspark Magnetos have excellent informative websites, well worth a look.


  The forum has an introductions section, let us know a little more of your experiences.

 Swarfy.


 Additional. The later type steel backed (rather than brass) points carrier will produce misfiring and erratic running if the points spring touches the cam ring. This is because the electrical path to earth is different from the earlier brass points carrier. Make sure the  points carrier is replaced correctly on the keyed taper and that the points rotate without any wobble.

[Bellanca A10]

Thanks Swarfcut,
My backing plate is brass. I’ll check to make sure the spring is not contacting the lobe ring when I reinstall the points plate. Actually, the internals of my mag look pretty good. Points gap was .012”. There is no evidence of arcing inside-no carbon traces, etc. The steel disc of the slip ring that the pick up brushes run on is smooth and shiny. The armature and windings look good and do not look to be the same age as the bike. The points are not burned at all although they could use a slight dressing which I’ll start now. I never did have very good luck with dressing points years ago on automotive ignitions. I always just gave up and installed new points.
I think I found the issue though. The pick ups are not the same length from their mounting flange to the springloaded brushes. I did not notice that the original and replacement pickups were not identical to their mate. I can’t remember if the replacements came in one box as one part number; however, if they did, I can see my mistake of thinking they were symmetrical. By my measurements, even though I think they were installed in the wrong positions, the pickups should still both be contacting the slip ring. The brushes both have worn a concave shape where they have been rubbing on the convex slip ring surface. Although, the problem pickup/missing cylinder pick up does not have as pronounced of a concave shape as the side that was firing normally.
I think I’ll just order new pick ups again since I need to order new gaskets for the mag, and both inner and outer right engine side cases.
I’ll also lube the appropriate parts on the points since those parts seemed dry. And of course, I’ll grease the ball bearings.
It will take a week or so to get the parts. I’ll post hopefully with a successful outcome.

[Swarfcut]

   The brass type points plate will not  cause a misfire if the spring touches the cam ring, even so it's a tight fit in there. You look to have a good handle on where the fault lies and on the face of it the magneto is working well and the problem is the usual mediocre quality of pattern parts.
   
    Twin cylinder magnetos have a relatively small brass segment. Hope the maggy has not been fitted with a slip ring from a single, unlikely but possible, which has a brass segment extending all the way round the slip ring. Thinking about it this would theoretically fire both plugs at the same time but with less intensity than normal to each plug, also there would be a bias if the electrical paths were not identical.  You described the segment  as a steel disc, which does not sound right.

     Here is a link to a further source of information.       https://www.themagnetoguys.co.uk/     The technical link brings up all you need to know. There is a good description of the differences of the various slip rings.

 

 Swarfy.

[beezermacc]

The most common cause of sparking on one side, then not at all, then banging in the exhaust, is POOR QUALITY BRUSHES! I know that putting stuff in capital letters is like shouting! …. and the quality of brushes has been mentioned in previous posts so apologies for any repetition. Most of the pattern pickups on the market come from Wassells. They sell some in Lucas boxes which are fine. They also sell some in white boxes. I have found, in my experience and it may be only me and Wassells do also sell a lot of good stuff and maybe I have been unlucky but..... the brushes in the pickups in the white boxes have a glossy appearance and very flat ends and you can draw with them, just like a pencil, all day. Maybe they're not all like this except the ones I've come across. It is probably possible to buy poor quality brushes from other suppliers too so I'm not saying Wassell are the only suppliers of brushes that are sometimes not very good and maybe nobody has bothered to tell Wassell about it? I think I did once but maybe I dreamt it. The brushes in the Lucas boxes are good (Thank you Wassell for supplying these perfectly good pickups and brushes which I recommend, as well as the other ones made in the UK), but I always clean the tips before I use them as they are capable of leaving marks initially, but they are good brushes. If you are unlucky enough to have brushes of the 'sabotage my bike' type in your magneto your bike could fail after a few miles or it might be unaffected, but in my experience it will fail. It will fail because the slip ring has a carbon track around it which extends the brass strip all around the slip ring so, basically your slip ring is converted from a twin to a single. When the slip ring delivers the spark from the HT end of the magneto coil / armature to the plug lead it will normally send it through the brass strip to the cylinder under compression because it has no alternative. If, as a consequence of using the 'sabotage my bike' brushes your slip ring has a 360 degree track the slip ring has a choice of which HT lead to send the spark down so it sends the spark down the lead with no compression because, like us all, the slip ring wants an easy life and it's much easier sparking in an open cylinder than one under compression. Of course, if you take your plugs out and check for sparks everything seems normal because the brass part of the slip ring conducts electrickery marginally better than carbon dust and with both plugs out the slip ring will default to the easiest route home which is via the brass strip. If there's a big black line all round your slip ring you can clean it with a bit of emery paper threaded through the pick up windows and kicking the bike over. Don't give yourself a shock whilst doing this. Maybe tape the kill button down. Written specially for those who enjoy my rants!

[Bellanca A10]

Swarfcut,
Thanks for the link to the magneto guys. It was a wealth of information. My reference to the steel disc was a poor choice of words. I meant the cylindrical outer surface of the slip ring. I cleaned that surface and it is a slip ring for a twin with about 1/3 of the circumference being brass and the rest being the non-conductive material.
Beezermacc,
You were right on about the quality, or lack thereof, of the pick ups. Or maybe I received one correct and one incorrect part.
I have attached a couple pics. The calipers are set to the dimension from the inside of the mag housing to the surface of the slip ring. Notice how one pic shows that the brush would have about 1/8 protruding from the pick up (plastic) housing. This was the the side that was firing normally. Notice the other pic. The pick up housing is longer. It’s so long that the brush would be flush with the plastic. This would of course prevent the brush from continuously riding on the slip ring. This is the side that was firing intermittently. I swapped the pick ups with each other and the result is the same. The one pick up housing is too long. Now I’ve got to order another correct one. The problem is I don’t know which is considered the “right” and which is the “left.”
I ordered the gaskets to complete this repair. I hope to be starting on the first kick again soon!
Bellanca A10.

[Bellanca A10]

Darn, I attached two of the same pic. But you can see that the brush would be flush with the pick up housing.
I’ll attach the other pic here:

[beezermacc]

No offence but I think you may be barking up the wrong tree regarding the length of the noses on the pickups. The noses need to project so that they are close to the slip ring so that the brushes aren't twisting. provided the slip ring isn't out of round (and some are) the springs will keep the brushes in contact with the slip ring. Even if the brushes don't make good contact the HT current is powerful enough to arc onto them. I come across pickups where the brushes are stuck in and the magneto has been working quite happily arcing 2 or 3 mm onto the brushes. Your photos aren't particularly hi res so I can't be sure which brushes you've got fitted but they look suspect to me.

[groily]

Not just you Beezermacc! The Lucas green box ones do seem ok nearly 100%. The ones in white boxes supplied with pick-ups seem almost always to be too soft.
Where possible. I avoid those pick-ups too, in favour of UK made ones. The exception is for screw-on pick-ups as per late K2F etc, for which the better UK product has been unavailable for a while. The other difficult choice is where a cranked front pick-up is needed on a manual mag - the better quality cranked ones don't clear the cb end casting, so it's the cheapo jobbie, or squeeze a vertical pick-up on.
All the cheaper plastic pick-ups provide poorer--than-they-should performance when hot. One can watch the revs needed to make good sparks drop off significantly with heat. Beyond about 40°C it is very obvious. When you get to about 60° there is often a very big difference. Lucas test temp was 50°.  But at least with decent brushes fitted, the mag should work on both sides, and will start a hot engine with a vigorous prod. Usually!

And just seen latest post from B'macc. I agree on all points.

[beezermacc]

Ref. Groily's remarks. Another issue with the white box universal pickups is the quality of the casting. I find that they nearly always need cleaning out where the brush slides (doesn't slide!) in and out. There is so much rough plastic 'flash' in there that the springs catch on the residue and the brushes jam. I've bought some 5.25mm drills which I now use for cleaning the brush slots out.

[Swarfcut]

   Some modern pickups have a brass sleeve visible  to support the brush and make a better contact with the spring. My old original Lucas ones just look like a black hole. Do they all have a brass sleeve leading to the internal conductor?

 Swarfy.