The BSA A7-A10 Forum

Technical => Lucas, Electrical, Ignition => Topic started by: a10gf on 30.07. 2009 10:03

Title: My big Magneto repair project
Post by: a10gf on 30.07. 2009 10:03
So, finally got the magneto beast dissected (once more), after postponing it way too long, A10 stuck in the garage. This time needs a slipring, capacitor and shimming (and very unsecure about the state of everything else...). Any good tips welcome.

Will tell how it went (either success or to have to send it away).

Before I proceed, some questions (have searched the net a lot, but not 100% sure of the values found):
What's the best value and type for a capacitor.

Primary winding gives approx 0,5 ohm, secondary approx 5,1 kohm, readings probably as they should be ?


Edit: I really like the old lucas equipment (when it works, which it does when maintained). Have evaluated, (and of course see advantages in) going 12v + electronic ignition and everything else available, but always revert to keeping the 6v, lucas regulator, dyn & mag, feeling it's part of some 'soul' this bike maybe has  ;) and getting things to work is part of my soul
Title: Re: Mag repair project
Post by: Triton Thrasher on 30.07. 2009 11:37
Check the state of the bearing tracks.

Radial play between the cam ring and its housing and wear on the points pivot do strange things to high speed timing.
Title: Re: Mag repair project
Post by: beezalex on 30.07. 2009 17:01
What's the best value and type for a capacitor.

Not sure what the value is, the ones I've gotten aren't labeled, but they have to be high-voltage and heat-resisant, so generic caps won't do.  Bob Kizer of podtronics fame sells them here in the US at a reasonable price.

http://www.podtronics.net/magnetos.htm
Title: Re: Mag repair project
Post by: a10gf on 30.07. 2009 18:55
Excellent link, beezalex, lots of info! There I read 'A resistance of around 5K ohms indicates a good winding.' + important capacitor info.

Triton wrote:
Quote
Radial play between the cam ring and its housing
Yes, another possible source of timing errors. ok here, just moves freely.

And remembered I've got Bacon's 'Restoring Motorcycle Electrics' with it's very good k2f general restoration procedure with pictures,  incl info about capacitor\condensator value, 0,2 uF 400v.
Title: Re: Mag repair project
Post by: a10gf on 30.07. 2009 23:37
Continuing the investigations and reading Bacon's book mentioned above, I came across this, which explained a (for me) longstanding big mystery: why are magneto bearings isolated...

 "to insulate the bearings and stop current passing trough them, as this would damage the balls and tracks"  *ex*
Title: Re: Mag repair project
Post by: beezalex on 31.07. 2009 16:13
Yup, particularly with grease, it would weld little carbon pits in there.  BTW, I used mylar shim stock which comes in many thicknesses to make shims that would fit perfectly.
Title: Re: Mag repair project
Post by: Triton Thrasher on 31.07. 2009 17:47
I used paper cups, then dripped Loctite into them.
Title: Re: Mag repair project
Post by: a10gf on 01.08. 2009 15:51
Nest step, getting a spark from the armature while out of the mag body. Connecting a sparkplug between armature body and slipring output of the secondary winding, then shortly 'flashing' the primary winding with the + of a 6v battery. And yes, got sparks !

Question, has anybody done this test, and how strong a spark is to be expected?

Then in an attempt to spot any heat related failure, the armature was slowly heated to approx 75 deg.c. then redid tests when hot, cooling down and cold, still sparking.
Title: Re: Mag repair project
Post by: fido on 01.08. 2009 18:24
I used a metalised polyester capacitor and potted it into place using epoxy resin.
Title: Re: Mag repair project
Post by: a10gf on 03.08. 2009 16:25
Ok... next ! All this may be common knowledge, but new to me, and others may find it useful:

Difference in points opening gap size between top and bottom cam lobe. First eliminating armature endplay, then could it be:

- eccentric points plate
- bent armature shaft
- nonalignement of cam housing at mag body side
- eccentric cam housing at cam side
- bearing cup eccentricity
- camring outer clearing to camring housing > movement
- difference in cam lobe thickness

...and maybe even more possibilities.

The problem has irritated me for a long time, and wondered what the heck could be done to get the points gap decently equal, without destroying otherwise good parts in the process. Took the time these days to take a good look, and some good measurements, eliminating as much as possible.

The fix was easy, slight difference in insulation paper thickness top\bottom of bearing cup, in relation to the points gap difference between top\bottom cam lobe, took a few attempts with different paper thickness to get the right bearing offset, and eureka !

Browsing The Haynes manual, about the gap it says "if there is a variation the cam ring has worn unevenly and has to be replaced", no other possible causes mentioned. Well, I'm glad I didn't buy the cam first and realizing afterwards it was not at fault at all.

Important detail for manual timing control magnetos: The timing control plunger needs a strong spring, or else the cam could move when the points hits the lobes, thus pushing timing way off randomly.

Edit:

Contacts, plate and cam:

The original contacts plate, with nos lucas points from ebay, pricey but very good, points both lining up quite perfectly (pattern points I've tried were a catastrophy). Also tried a new pattern cam, but the old one was actually fine and went back into action.

Measured cam gap to housing, around .002, could be better, but much timing testing showed it had little or no impact in practice., as the cam is firmly locked downwards by a strong retard\advance spring. Points spring is well clear of camring.

Upon reassembly, got the oiling wick at the bottom of the camring inserted, a 2 parts wick, one filling the cavity in the housing, and one small length inserted afterwards trough the cam hole. Apart from some normal signs of use and maintenance after like 50 years, the plate and cam is still in very good condition.

-------------------

Edit:
added text to arrows on the housing, the 'thick' resulting in moving the points plate slightly down relative to the upper camring lobe, equalizing the points gap difference on this particular mag.

Title: Re: Mag repair project
Post by: RichardL on 03.08. 2009 17:24
Erling,

Does this mean that, from your list, "bearing cup eccentricity" is the chosen diagnosis, with the eccentricity caused by the paper insulator or cured by modifying the paper insulator?  

Also, I can't figure out what the arrows in the photo are pointing at, perhaps because I don't have a manual advance magneto. *conf*

Richard L.
Title: Re: Mag repair project
Post by: beezalex on 03.08. 2009 17:28
Good stuff.  I've often wondered about doing this, but it just seemed way too fiddly.  Glad someone decided to nut up and try it.
Title: Re: Mag repair project
Post by: Triton Thrasher on 03.08. 2009 17:32

Difference in points opening gap size between top and bottom cam lobe. First eliminating armature endplay, then could it be:

- eccentric points plate
- bent armature shaft
- nonalignement of cam housing at mag body side
- eccentric cam housing at cam side
- bearing cup eccentricity
- camring outer clearing to camring housing > movement
- difference in cam lobe thickness

Not the first two. They can't cause timing or gap discrepancies.
Title: Re: Mag repair project
Post by: a10gf on 03.08. 2009 19:19
Triton, yes it was an elimination job, looking trough every part of the magneto that could have anything to do with it.

Richard, nothing to do with manual or not, picture just giving some rough idea of
Quote
slight different insulation paper thickness top\bottom of bearing cup
Fixed (on this particular combination of parts making up this mag) by inserting a 'shim' by the bearing cup top (resulting in moving the top lobe of the cam downwards vs the armature\points plate).

Beezalex, glad to be of help.

--------------

I guess the whole 180 deg point gap issue comes from many magnetos currently in use being assembled from parts from here and there or are worn. I see now how even any tiny tolerance deviation somewhere, in some part of any mag, will affect the points behavior at the 2 cam lobes, f.ex., with cam just 0.01'' off-center relative to points, setting the points for correct 0.012'' gap on one side could then result in 0.022'' at the other side.

Continuing the matter, I see one can really finetune the 180 deg. points gap this way (alternative would, I think, be grinding down one side of the camring *conf* ). Am not yet down to 0.00 diff. (guess it's impossible!), but will try to get close, still have a little to go on on one side of the bearing cup before there is no place for some suitable thin isolation (cigarette paper won't do....) and of course, there is another limit to moving the bearing, the armature may touch the magnet.

Anyway, armature shimming sorted, points gap close to equal, capacitor and slipring is in the post, soon the moment of truth:

1. Jez, no spark at all *rant*
2. if sparking, will it be consistent at high rpm + heat
3. will it have acceptable L\R timing
Title: Re: Mag repair project
Post by: Triton Thrasher on 03.08. 2009 22:19

3. will it have acceptable L\R timing


You can check that now with a degree disc.
Title: Re: Mag repair project
Post by: a10gf on 03.08. 2009 22:44
Quote
You can check that now with a degree disc.
Got my special setup, see timing (http://www.a7a10.net/BSA/techpics/k2ftiming.jpg), running it off a drill, checking at all speeds.
Title: Re: Mag repair project
Post by: a10gf on 05.08. 2009 20:39
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
Title: Re: Mag repair project ...got spark!
Post by: a10gf on 06.08. 2009 19:14
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% *smile*

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.
Title: Re: Mag repair project
Post by: a10gf on 06.08. 2009 21:26
And just for fun, was it possible to get a photo of one of today's sparks...

Some really closeup sparks : topic=1412 (http://www.a7a10.net/forum/index.php?topic=1412)
Title: Re: Mag repair project
Post by: a10gf on 08.08. 2009 10:42
...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.
Title: Re: Mag repair project
Post by: a10gf on 09.08. 2009 12:45
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  *smile*
Title: Re: My big Magneto repair project
Post by: a10gf on 13.08. 2009 22:06
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.
Title: Re: My big Magneto repair project
Post by: a10gf on 20.08. 2009 16:35
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.

Title: Re: My big Magneto repair project
Post by: beezalex on 20.08. 2009 22:21
Nice work, there.  One more thing of interest, though would be a spark test.  Spark testers can be purchased
relatively cheap (http://www.jcwhitney.com/webapp/wcs/stores/servlet/Product?storeId=10101&Pr=p_Product.CATENTRY_ID%3A2004216&productId=2004216&CustomerMemberID=ChMI3OekhJaznAIVlEzlCh0uDfX4EAIYAg&CustomerMemberID=ChMI3OekhJaznAIVlEzlCh0uDfX4EAIYAg&catalogId=10101&redir=k216837&redir=k216837)
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.
Title: Re: My big Magneto repair project
Post by: a10gf on 20.08. 2009 23:03
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.
Title: Re: My big Magneto repair project
Post by: a10gf on 28.08. 2009 20:11
And....  *smile*

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 (http://www.a7a10.net/forum/index.php/topic,368.msg10533.html#msg10533) 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

Title: Re: My big Magneto repair project
Post by: rocket man on 28.08. 2009 23:28
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
*smile*
Title: Re: My big Magneto repair project
Post by: LJ. on 29.08. 2009 10:46
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!
Title: Re: My big Magneto repair project
Post by: groily on 31.08. 2009 19:51
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.
Title: Re: My big Magneto repair project
Post by: a10gf on 09.09. 2009 21:03
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  *sad2* 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  *eek* . 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 *smile*. 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
Title: Re: My big Magneto repair project
Post by: LJ. on 09.09. 2009 22:05
 *lol* *lol* and they *always* get you home! But I bet you enjoyed every minuet of it. Well done nice story.
Title: Re: My big Magneto repair project
Post by: beezalex on 15.09. 2009 16:14
Glad to hear the issue was minor.  I'm in a similar situation with my back, having had surgery 9 months ago.  Necessity is the mother of invention and a couple of months ago I had the same thing happen.  And yes, with minimal tooling, they can still get you home.  Thanks for the inspiration, I'll be starting my first mag rebuild soon.
Title: Re: My big Magneto repair project
Post by: a10gf on 15.09. 2009 16:34
Quote
and a couple of months ago I had the same thing happen
Gives some peace of mind to read I'm not the only one forgetting things, and the back, it's an exhausting pain when it sets in, one had to learn the hard way to start being more careful.

Have had the opportunity to use the bike for a few longer tours in between the continuous period of rainy days, and the mag seems stable and good, and engine running fine. Next, on to some of the other things soon needing attention!

& Thanks, LJ.


Title: Re: My big Magneto repair project
Post by: duTch on 12.11. 2013 22:54
I understand eccentricity(only too well *eek*), but can't understand how a bearing can be eccentric, but can only assume the races are good, but the ID or OD are manufactured out of whack...???..... or do you mean the bearing is round, but is not centred in the casing ?

 Slightly related, just curious- but anyone know what thread pitch is the C/B centre bolt? seems to measure 5/32", but can't pick the tpi? seems about 30 with my not-so-good gauge, closest I can find to that is BSW/BSC both @32tpi -Thought maybe 3BA, but not so fine and doesn't measure big enough?
 Cheers

 Thanks E, just spotted your post in A/B Gasket after I posted- I think I have it now cheers
Title: Re: My big Magneto repair project
Post by: a10gf on 12.11. 2013 23:04
Hi there, the bearing itself is round and fine, it's the bearing's placement in the mag housing that needed a nudge, see this picture > http://www.a7a10.net/forum/index.php?action=dlattach;topic=1375.0;attach=3083;image showing the placement of thinner vs thicker material, to slightly move the bearing (cup) off center vs the housing.
Title: Re: My big Magneto repair project
Post by: KenF on 13.11. 2013 05:58
... but anyone know what thread pitch is the C/B centre bolt? ...

duTch, it should be 3BA (0.161" x 34.8 tpi), and the head should be 4BA (0.248" AF).

Ken.
Title: Re: My big Magneto repair project
Post by: duTch on 13.11. 2013 20:04

 Thanks Ken, good to know- didn't think bsc or ww would work.

 a10gf,
Quote
it's the bearing's placement in the mag housing that needed a nudge,
,

 I guess it's what I had in mind, but either misread it or am dyslexic....I may have a similar issue, and the cam ring could be affected similar...?
  I'll continue with this back in 'Cam ring capers'
 cheers
Title: Re: My big Magneto repair project
Post by: a10gf on 14.11. 2013 08:15
^^^
Quote
and the cam ring could be affected similar


To try come up with some more explanation ref. my particular mag: the camring measured fine (no thickness\position difference between upper & lower cam), but still the point gap + timing  varied quite much between L\R. Slightly adjusting the bearing cup (using different isolation material thickness) so the points plate centered properly vs the camring cured that problem.
Title: Re: My big Magneto repair project
Post by: pjm01 on 14.11. 2013 10:49
duTch .....  had a similar issue of needing to determine the 'number of TPI' when doing my A7 clutch and I don't have thread gauges. Cut a thin strip of paper and pressed it firmly onto the bolt thread leaving a clear impression of the helix, then by careful measurement and simple counting the TPI's can be found. Also made an impression from the newly supplied nut and compared it directly to the shaft impression ...... they were different, hence nut did not 'pick up on the shaft'. Peter M
Title: Re: My big Magneto repair project
Post by: duTch on 14.11. 2013 12:32

 
Quote
the camring measured fine (no thickness\position difference between upper & lower cam), but still the point gap + timing  varied quite much between L\R.

 Yup a10gf same, only have digital 'Clayton-vernier' calipers to measure but couldn't find a discernible difference in cam profile/thickness, except the ring was 2 thou out of round, so gave it a squeeze with the multi-grips but in retrospect, may not've been a good move as the short measurement was across the 'cam lift diameter' (if you know what I mean), so squeezing it to make it equal(longer), also reduced/eliminated the ability to utilise the sloppy fit (in the housing), with packing to completely rectify the problem (just realised that this arvy when playing).
 Have come to a mental block, will add later if able.....

 Pete, thanks- until I bought the (nasty)gauges, I think I used my fingernail, and stopped counting lumps when the measrurey thing got to an inch or fraction of.....