Author Topic: And now for the magneto  (Read 1670 times)

Online groily

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Re: And now for the magneto
« Reply #15 on: 26.04. 2023 07:46 »
For the plug, I'd say NGK B6HS, short reach no resistor, for iron head engines. Others may have more specific advice for early A7s and there are equivalents from other makers. My iron A10 ran NGKs mostly but I also had some Bosch W7AC at one point. Champion do the L86C, and there be a good few others.

Those tubular fibre insulators are essential, or the cb centre screw and / or the second small retaining screw will almost for sure short the live point to earth on their way through. The little screw also needs a fibre washer under its head to complete the job. The mag will very probably be a spark-free zone if they're not there. Fiddly to make and not that easy to find, so if you've got a complete assembly coming, well done.
The less wobble of the opening point on its pivot post, the better, so with any luck the new one will be better than what you have and won't need a ball bearing!.
Bill

Offline Devlin

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Re: And now for the magneto
« Reply #16 on: 26.04. 2023 13:21 »
After a visit to Priory Mags website and a hour or so reading I have decided that to go the easy cap route I first need to sus out what blob of solder is what, I have three so one will be the earth and the others will be the winding ends and I assume one blob will have 2 wires and one will have one I also assume that the blob at the slip ring end should be ignored as the original capacitor is at the other, so I have 2 options desolder the bigger blob hoping it has both ends of the windings or wait till I get a small bearing puller and had the bearings off, does anyone agree with my assumptions
Devlin   
Isle of Arran 49 A7 LS

Online groily

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Re: And now for the magneto
« Reply #17 on: 26.04. 2023 17:01 »
With the armature out, as original there are two visible wires at the condenser end, one visible wire at the cb end (where the low tension live connects to the cb centre screw), and then there's the HT end that disappears into the slipring. The wires at the condenser end may not be visible if they have been buried in resin if a replacement capacitor has been fitted in the past.

The earth low tension and capacitor earth, and HT earth, are all done in one; the other side of the condenser has a live wire with 2 internal strands in it. One strand is straight off the coil, the other goes from the condenser to the cb end via a channel that goes back along the length of the bobbin. If you've got an original, then there will be blobs of solder covering the heads of the 5BA screws that attach the condenser to the armature.

To identify which wire is which off the coil at the condenser end, it's easier to have a look at some pix. Whatever way you want to go on sorting it, the orientation of these things is always the same on the inside. So here's a description and pix of what's what. Different mags are covered but there's plenty on K2Fs:
http://www.brightsparkmagnetos.com/condensectomy/index.htm

While self-interest says I naturally wouldn't want to dissuade you from using an easycap, I think you really need to know whether the coil is any good as the number one priority. It's the expensive bit and it's a PITA to have to do things twice. I'd be pleased if you bought a condenser, but I wouldn't feel good if it didn't help.
Whether it's worth a go depends how much you like playing with these things! But I would certainly want to see it running on the bench - hot - somewhere close to the Lucas spec before putting it back on the bike, otherwise you'll get more practice than you might want at extracting pinions and retiming the thing!
Bill

Offline Devlin

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Re: And now for the magneto
« Reply #18 on: 27.04. 2023 17:50 »
I finally got the capacitor end off the armature and have two nice clean copper wires poking up, however when I put my meter across them I get various readings from open circuit to .60Mohms to 17.61 Mohm then back to open circuit IR is good at 200ohms @100 volts, unsure if the coil is is holding the small applied current and no idea what I should be looking for and should I get any readings at the HT spike
Devlin
Isle of Arran 49 A7 LS

Offline Devlin

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Re: And now for the magneto
« Reply #19 on: 27.04. 2023 17:53 »
I finally got the capacitor end off the armature and have two nice clean copper wires poking up, however when I put my meter across them I get various readings from open circuit to .60 ohms to 17.61 ohm then back to open circuit IR is good at 200ohms @100 volts, unsure if the coil is is holding the small applied current and no idea what I should be looking for and should I get any readings at the HT spike just tried diferant clips and getting consistant .63 ohms
Devlin
Isle of Arran 49 A7 LS

Online groily

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Re: And now for the magneto
« Reply #20 on: 27.04. 2023 18:56 »
Blimey! Assuming you're getting the meter onto the strand of the 'double strand live side' that is from the coil, you should see half an ohm odd between it and the 'other' low tension wire, which is the earth. That's the primary winding, same as measured across the open points when all is assembled.
If you're not getting onto the strand that comes off the coil - but are just touching the strand that goes to the cb end, now detached from the other strand - then you'd see Open Line or loads of mega ohms. (Edit - I read your 'Mohms' comment, not the repeat where the 'M' had gone.)
Suggest you ensure that the two strands on the double strand side are properly soldered together after the disinterment and check again, or if they are separated, try from each strand to the earth side.
No need to be applying any volts or current to measure the coils, just use the Ohms scale.
If you were putting the meter across the condenser by any chance, on the resistance scale, you'd see a rapidly rising number that stopped at Infinity - as the meter's battery tried to charge the condenser up. But I don't think you're doing that if you're 'on the wires' and they're not connected to the condenser?

For the HT, you should see the several thousand ohms mentioned from either the earth low tension tail to the HT spike / slipring brass or from the live strand from the coil to the HT spike / slipring brass. Again, simple resistance, no applied voltages or anything.
Bill

Offline Devlin

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Re: And now for the magneto
« Reply #21 on: 27.04. 2023 19:18 »
Thanks, Yes its across the "twin" wires and the single at .63 ohms so not far out I will zero the meter once more before I recheck  I will solder the ends of the live together as I cut the blob off and I will recheck the HT spike to either or both  tomorrow 
Isle of Arran 49 A7 LS

Offline a10 gf

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Re: And now for the magneto
« Reply #22 on: 27.04. 2023 19:38 »
Myabe somme ideas to be picked up in this topic. f.ex checking left-right timing.

https://www.a7a10.net/forum/index.php?topic=1375.15


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Offline Devlin

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Re: And now for the magneto
« Reply #23 on: 30.04. 2023 12:20 »
Another quick question, can I put the A/R unit in the sonic cleaner as I am unsure how the fibre gear will react to carb cleaner solution
Dev
Isle of Arran 49 A7 LS

Offline muskrat

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Re: And now for the magneto
« Reply #24 on: 30.04. 2023 20:27 »
G'day Devlin.
Although the ultra sonic won't hurt it the "carb cleaner" might. What medium are you using?
Give it a go with just hot water and dish washing soap. I know it won't hurt rubber/plastic.
Cheers
'51 A7 plunger, '57 A7SS racer now a A10CR, '78 XT500, '83 CB1100F, 88 HD FXST, 2000 CBR929RR ex Honda Australia Superbike .
Australia
Muskys Plunger A7

Offline Devlin

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Re: And now for the magneto
« Reply #25 on: 30.04. 2023 20:54 »
Thanks, reason I asked is it started to soften the gear lever rubber, although that is probably starting to break down anyway given the age
Isle of Arran 49 A7 LS

Offline Devlin

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Re: And now for the magneto
« Reply #26 on: 12.05. 2023 17:33 »
The magneto is sparking once again a big thanks to all the members on here and a huge thanks to Bill Brown at Brightsparks also Paul Wolf who rewound the bobbin to suit the easy cap, learning curve for sure but the satisfaction of achiveing a positive outcome is priceless
thanks again ]
Devlin
Isle of Arran 49 A7 LS