Is this possible? (mag missing brush)

[Minto]

After some recent running issues I had the pick ups and brushes out today to check and clean the slip ring etc. As I pulled the RH pick up out the mag it was missing the brush part, the spring was still stuck in the pick up tunnel but no sign of the carbon brush part. The LH one was fine and in very good condition with just a small round ridge worn in the end. I had a quick careful poke around with a piece of bent wire inside the mag casing and the carbon brush part fell out, it looked virtually untouched, markedly less worn than the other.
Is it possible that the motor would even run with the carbon brush missing? Or is it more likely that it fell out as I removed it, though I’m not sure how it could’ve really as the spring end was tightly inside the pick up tunnel.
Anyway I put the brush back in the spring and it
Seems to run better now and no longer misses like it was, just a wee stutter just after changing up into 2nd a couple of times but that’s probably down to me dropping the throttle needle a notch in a previous attempt to sort the poor running.
If anyone has any thoughts I’d appreciate them.

[RDfella]

Could be when you removed it, but if you've been having misfires, likely the brush was dislodged last time the holder was fitted. A good spark should jump half an inch, so a missing brush would probably not be noticed in the short term. How long has it run since the brush holder was last off?

[edboy]

a10 s were always known to keep running no matter how little was spent on them. brushes were only replaced as a final solution to no starting back in the 70s. i have to admit my first a10 was a dog which had been run into the ground. at age 19 i had no idea.

[Bsareg]

I doubt the spark would jump 1/2" within the mag. There are safety gaps screws with limit the length of spark to protect the windings. These are the screws that the unwary omit to remove which then breaks the slipring when the armature is removed !

[Minto]

Thanks for the thoughts on this
RDFella, it’s difficult to know how long since they were last out, this is the first time I’ve had a look at them, I’ve owned the bike since Feb this year and done around 500 miles, sometimes running ok sometimes not so well. I would say that this is the best it’s run so far, but it was only a fifteen minute ride before work.
The one brush was definitely worn less than the other, so my guess is it’s been rolling around in the mag body for a while.
I might remove the brush again and see how it works, just as an experiment to see if that misfire reappears.
Cheers all

[Minto]

So, I took her for a ride a couple of weeks ago and she ran really well for about 40 miles, then started missing again. I assumed that the carbon brush must’ve dislodged itself again, but on checking both were still in place. So I just took the points cover off and noticed that the carbon brush on the kill switch circuit had disappeared and found bits of it in the points housing and thought the bits must be shorting between the housing and some other part, so cleaned it all out. Took it out for a ride round the block, still misfiring. Got it home and had another check in the points cover and found yet another large piece of carbon brush lurking in there. I cleaned up the points and reset the gap. Haven’t had chance to try it properly yet but it started easily but was spitting back through the carb when I blipped the throttle. Of course this could be the carb adjustment I made a while ago needs undoing.
Any thoughts??

[berger]

i have not been to the pub, I know nothing but- it could be tired set of points or maggy condenser failing

[Bsareg]

Sounds like it could be soft brushes leaving a ring of carbon on the slip ring. Try writing on paper with one, if you can read it easily, they're c##p.

[Slymo]

A good mag will easily chuck a 1/2" spark although there should be a safety gap it the mag so that it doesn't not spark when it needs to. As mentioned give the slip ring a clean with a soft cloth whilst your in there. make sure to stick a bit of paper between the points as you turn it over as otherwise it will let you know what it does with a jolt.

[Triton Thrasher]

If the distance from the end of the spring to the slip ring, was much less  than the safety gap, the spark would jump to the spring and the engine would run normally.

I don’t know how much less it would have to be, because the plug gap under compression complicates things.

[Minto]

The pick up brushes seem decent quality, no good for writing with. I’ve give the slip ring a wipe with a rag dampened in petrol through one of the pick up holes.
I’ve renewed the leads and caps.
I was wondering whether the condenser was getting tired. Is there an easy way of determining this without dismantling the mag? I know the condenser is buried in the armature so I’m hoping I don’t have to mess with it.
Cheers all

[Slymo]

Its a mare of a job pulling the condensor out. You can be reasonably confident that if the mag works and is chucking a nice fat spark then there is nothing wrong with the condensor. If the spark is weak then it might be time for an armiture out but it is a job that requires some tooling and some skill. The endfloat needs to be set with shims and unless you have access to a re magnetizer then its best to leave it to an expert. My guess is that your problems were caused by the rouge brush. Install it carefully and all should be jake!

[groily]

You can be reasonably confident that if the mag works and is chucking a nice fat spark then there is nothing wrong with the condensor.

The key thing here is 'Does the mag work hot?' You'll often get perfectly decent sparks on the  bench and from cold. And then find performance deteriorates as it gets hot. Six times out of 10 maybe that's the condenser breaking down, the other 4 times it's the coil packing up, or the slipring being leaky when hot, or any combination. If the condenser is an original it is 90%+ sure it's weak. If the HT coil is an original it's more than evens against it sadly owing to the deterioration of the insulation materials of the day.

Just to add, there is actually very little risk of losing significant magnetism on a K2F, owing to the design of the pole pieces. On many others, yes, but the K2F is good in this area. You can leave a body empty for years and the thing will still be quite strong enough to function just fine. So you can take the armature out, no problem, if you want.

[duTch]

 

.......So you can take the armature out, no problem, if you want.

    But if you do, take note of ;

 

.....There are safety gaps screws with limit the length of spark to protect the windings. These are the screws that the unwary omit to remove which then breaks the slipring when the armature is removed !   

[Swarfcut]

Minto. All is not lost, just a few other things to check.

 Undo the points retaining bolt, gently remove the points plate. Give the housing a good clean making sure all carbon particles are removed. If the points carrier is a brass one, there should be an additional earthing brush which bears on the magneto points housing. This is often overlooked. There is another earthing brush beneath the brass screw adjacent to the magneto name plate. Once more, often overlooked. Good chance to dismantle, clean the points, and lubricate the pivot. If you have a later steel backed points carrier, make sure the points spring does not touch the camring. The design of the electrical pathway is different, so the steel plate type does not have the carbon brush, but the spring touching the cam ring earths the points and gives erratic running.

 Before replacing the points plate check the keyway in the armature and the locating tab on the points plate. There should be no rock between the parts.
  Groily knows more than a thing or two about magnetos, and by all accounts replacing the original condenser with a more modern variant is a relatively easy cost effective cure, providing the armature is reasonable. 

 Otherwise its a case of a swap to a cheaper version of electronic ignition, retaining the faulty maggy as a carrier, as RoyC did recently.
 This saves the cost of a new dedicated housing and keeps the bike looking unmodified.

 DIY magneto servicing is relatively easy, plenty of information available as regards basic dismantling and electrical testing. An exchange armature is another possibility. Reading earlier posts on this Saga, there is the possibility of carbon brush particles within,  between the armature and body, so a strip down  and a good clean out (not forgetting those spark gap screws) may be next. Providing everything goes back as was, the armature endfloat will be the same. Cleanliness is the key.  Good chance to give those bearing a little bit of HMP Grease, and to inspect the slip ring properly for traces of tracking.

 Brightspark Magnetos and Priory Magnetos are highly recommended as sources for parts and information.

 Swarfy.