My big Magneto repair project

[a10 gf]

You can check that now with a degree disc.

Got my special setup, see timing, running it off a drill, checking at all speeds.

[a10 gf]

Am thinking about how much strength may be left in the mag body magnets, and possible need for remagnetization.

How much 'resistance' should I expect to feel when turning the armature past the point of max flux, turning the armature shaft with two fingers pinching the threads at drive side ?

Yes, maybe difficult to evaluate this with words (ideally I should have a known good mag for comparison, but those mags I know about that are in seemingly good working condition are on some friend's bikes, and can't expect anybody to remove one so I can play with it!)

Thanks
e

[a10 gf]

Parts are in place, slipring & brushes, shimming, 0.22uf 600v cap supposedly of the 'good' type, initial test gives strong sparks turning by hand and very good at various speeds, l\r looks close to 100%

Regarding magnetism, I suppose if one gets a good spark at slow rotation by hand, it must be ok.

Playing with the advance\retard with mag running, get approx. -16 degr. difference between full retard and full advance. What was quite interesting is it was impossible to detect any visible difference of the spark strength at the plugs, just as strong in full retard, rotating by hand or with the drill at any speed. The saying goes that the spark should be weaker at retard due less magnetic flux at that point, could really not spot any difference at all. Could maybe differ under compression though.

As an anecdote, if it is the original label, type nr shows this mag (or at least the body) started it's working life on an Ariel 500, with autoadvance\fixed camring. If anybody wants to check their mag, Lucas lists 42248E for auto and 42263B for manual (1951 parts catalog).

Pictures of the not-so-scientifical but very useful test setup, l\r timing check with strobe + the 180 deg marks on the drive pinion. Using plugs, caps and cables that will go on the bike later on so they get tested as well.

Will post some pictures and details of the inner work + tweaking later.

[a10 gf]

And just for fun, was it possible to get a photo of one of today's sparks...

Some really closeup sparks : topic=1412

[a10 gf]

...update & results:

-New capacitor stopped the heavy sparking at the points.

-Offsetting slipring-side bearing cup + finetuning the armature shimming equalized and stabilized l\r points opening gap, and got l\r timing spot on.

-Occasional misfiring fixed, main probable remedy the new slipring and brushes, in combination with the above fixes.

-Fixed tendency of timing to jump totally off now and then (up to 15 deg.) This was (I think) due to the points opening with the very uneven l\r gap, hitting the lobes of the cam very unevenly (one very hard, one very soft), and influencing how the points spring would control the points.

Parts presumed in advance to be defective or worn (armature, points+plate, weak magnets, worn or asymetrcal camring) were actually fine.

Test run with the drill setup for some 15 hours in total, looks stable as hell at any speed. Next week I guess I'll have time for real life test, getting it back on the engine, with good hope the sparks will be as strong under compression.

[a10 gf]

Some info on the armature work. Shimming done between the grease-ring and bearing, got the thickness right there, not needing any external shims between maghousing and pointshousing.

The capacitor \ condenser was fitted without dismantling the armature (had previously cleaned up the old contents, also without dismantling, but the safest way to work is maybe? to take the armature apart first). Seeing no real need (the future will tell) to fill up with epoxy, epoxy was used just to secure the capacitor + giving some extra support\strength to the wiring. Then, it will be easy work if ever the capacitor needs changing again. Definitely not the cleanest work I've ever done (a little too much enthusiasm in getting it finished), but results  are durable and solid enough.

Let me add that the Haynes manual wrongly states "If the condenser is at fault .\. the armature will have to be stripped and rewound".

Have not found any more info about the winding resistance, but the readings of around 0,5 ohm primary \ 5k secondary are believed to be within spec, as the mag gives a good spark.

Bearing removal\fitting by heating it with a small butane flame (not melting the slipring!) then quickly cooling the brass with cooling spray can for electronics, the bearing then went off and on quite easily, no risk of damage.


After final reassembly all is well, and it's back on the test drill setup, sparking like never before  

[a10 gf]

Now, just one last part needs to be added: a complete A10  
(& I love the doorbell kill button)

Will continue with my experiences refitting the mag + adjusting timing.

[a10 gf]

Preparing for the timing job...

Moment of points separation: added 2 connection points for easy use of a lamp. These are properly secured and will stay on the points plate.

Having tested the different known approaches, using a lamp seems to be absolute king, no doubt whatsoever when points opening. Now, using measuring grips (or whatever they are called), no more fiddling with loss of contact, wires falling off or shorts as the points plate is turned.

[beezalex]

Nice work, there.  One more thing of interest, though would be a spark test.  Spark testers can be purchased
relatively cheap
and they allow you to test the energy of the spark.  I believe 3000 volts is considered the bare minimum which corresponds to a gap of 1.5 mm.  It's about 2000 V/mm of air gap, so with the tester you can find out just how much you're getting at any given rpm.

[a10 gf]

beezalex , = this one ?
(Didn't need it on this project, but it's a handy device to have available)

The v\mm info is interesting. So 10mm would be 20.000v. Safety gap screws removed, I get a spark at well over 1 cm, rotated by hand. Another test, also hand rotated, taking off a pickup, getting a strong spark between slipring and the safety screw (approx 7,5 mm gap), I'd think all this are signs of a healthy mag.

& thanks for the comment.

[a10 gf]

And....  

After the A had a long, long stay at the bottom of the garage, now mag finally got back on where it belongs, timing lamp over points + TDC\advance device worked perfect, checked & looked over whatever I could remember, tickled the carb, waited a while looking for leaks, fire extinguisher ready, 3 or 4 kicks and... GF came back to life. So did I !

e

[rocket man]

good topic it got me looking for my spare mag which i found in the loft
i put my hand on the ht lead and i turned the shaft and got a bloody
big shock up my arm i think about 3000 volts at least i know it still works
the one on my bike is electronic  i dont think i will be holding the lead  again

[LJ.]

Well done Erling and thanks for a really good read, I can fully imagine the satisfaction you got from re fitting the magneto to the bike again. I expect you'll be out riding all weekend now. Well done!

[groily]

Congrats! Nice job.
Re the Q raised earlier in the thread - 'how magnetic should the box be?' - I don't know exactly, nor how to measure it. But with a decent mag it can be quite difficult to steer the armature up to the drive end without it being pulled one way or the other.
Dave Lindsley (posts passim) will remagnetise a box for 'between 10 and 15 UK pounds' he told me this past week. No need for keepers and all that, just send the case. He tells me he's got empty boxes, never used, which go back decades and will still pull tractors up steep hills.
Couldn't have been more helpful.

The latest one he's getting from here, off a machine that's not mine, the armature literally fell out when the cb end housing was taken off . . . So I guess the answer is the magnetism should at least defy gravity. This one had been used as the simple rotor shaft to carry an electronic trigger for years. So it didn't matter till now, when the originality mantra kicked in, plus owner's fears for the 6v dynamo as the summer months come to an end.
 
But nothing goes to waste in la France profonde, and the electronic gizmo is going into . . . another guy's A7. At least the tool boxes are big enough for all the gubbins.

[a10 gf]

Thanks for the comments, So, how did it turn out ?

1st trip
...out of the garden for god knows how long since last time. Rain and health had me postponing my test flight for a while. Engine now starting 1st kick, let it warm up, all is well. First a cautious ride on some small streets near home, runs very well. Ok, let's try it on some larger roads, with traffic around. Brakes are there, lights are good, tires fine, runs very well, feels good! Ahh, I thought: success! On to the highway. Blasted past a black BMW, close to 80 mph no problem (if the speedo is roughly correct...), life is great, I am 16 again! Let's head home to celebrate.

Then, 500 m from home:
...nightmare on Elm Street   engine died net... made me feel cold and dizzy. Sure sign of ignition failure, both personal and the engine... disaster. Refusing to start. Not possible! all the work I did was a complete failure? I am a complete failure!! Quickly pushed it to a small side street to avoid the deplorable feeling of being looked upon in such a state. My back condition excludes any pushing home. Felt lost in the jungle, no tools, apart from a small Leatherman-like toy, no matches to light a fire, no weapons, nothing to eat, it starts raining, getting darker, no hope !

After the shock
...a little composure. Off with a plug cap, yep, no spark. Can't be the mag internals, quite meticulous work, and had run it for dozen's of hours on test, why should it fail after 30 min on the road, the world can't be that malevolent and evil ! Let's take a deep breath... maybe points locking nut loose, no points gap? Off with cover, points were at open position, then poked a little in there and realized the pointsplate rotated free! I had not secured the drive pinion nut properly   . Combination of disgust and joy!

So be it then
...how to get it home, running. The toy-tool pliers\screwdriver saved the day. Removed the tacho gear to gain access to the nut, which thankfully had not fallen off. Off with the rocker covers, TDC located, armature turned to just before points opening, securing the nut passably with the leatherman pliers... yes! back alive 1st kick . Quick ride home to safety and tools!

A lesson learned, and a success, the engine has never behaved that good, especially at idle and acceleration.
Worth a small smile.

e