The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Lucas, Ignition, Charging, Electrical => Topic started by: Adz on 21.08. 2025 12:00
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Hello BSA Gods.
So pretty sure this has somthing to do with my my bike isnt charging.
I opened the dynamo and it rained crud and metal parts.
I have no idea what I'm looking at. What it's supposed to look like. Why it's happened and if it's repairable....
Any education would be really helpful.
Thanks.
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I would say from an non expert side of things but having owned and ridden an A7 for 40 years that needs a serious rebuild. Plenty of people on here will be able to recommend some very good people to carry out the work. It looks very much like its melted the solders joints and taken the commutator apart.
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Right. Thanks.
Also I noticed the sprung contact breaker point on the regulator was all gummed up and stuck on. Maybe this could have caused the issue?
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Draining the battery through the comm when the engine is stationary?
Very possibly.
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The bad news is that the armature has failed big time. The good news is that it is fixable, can be upgraded and the only stumbling block is the money.
Once the dynamo is off the bike, the type can be identified by the model number stamped on the body. Early A's used a so called short body, E3H version, later bikes have a higher output E3L, with the longer body, both rated at 6V output. Reckon it will be an E3L, same basic version used over all A series Plunger and S/A Bikes. Yours looks to have had some abuse already...look at that screw in the centre of the ball race. Once off the bike, two long through bolts hold the whole thing together. The armature complete with its bearings, drive cog and bearing carrier will then slide/tap out out of the body when these bolts are removed. Alternatively remove that slot head screw and remove the armature from the brush end bearing. Extracting the drive cog then presents no problem as the armature can be held still. Cog can be very tight on the shaft taper.
You could just replace the dynamo, like for like, or swap the armature, used or new repro. As the control box is suspect, this must be checked, as it is probably the cause of the failure, again it may not be fixable. But if you can put practicality above originality, an opportunity to upgrade to a new full 12 volt system and solve the problem. The existing dynamo housing can be rebuilt with 12Volt innards.
Plenty on the Forum about the merits of electronic control boxes and the benefits of moving to a 12 Volt System. Plenty of options, all is not lost.
Swarfy
Additional. Worth posting the pictures of the damage here...
https://www.a7a10.net/forum/index.php?topic=15504.msg136896#msg136896
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Thanks all for taking the time to get back to me. All the info is really helpful.
I'll have a think about the 12v upgrade but my initial thoughts are keep it original.
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I can fix yours or supply a second hand one with a warranty, or a new one with a warranty. Give me a ring if you're interested. Other dynamo fixers are available!
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The old exploding commutator. I have lost count of the number of these that I have encountered plus the many that I have found before they self destructed.
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I have had a couple of commutators explode when running a 6v E3L with a 12V regulator. If you are going for 12V, make sure it's done properly with a new armature and field coil.
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plus the many that I have found before they self destructed.
Yep, I guess we've all seen armatures before they self-destructed.
I've seen engines etc too.. ;)
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Thanks all for taking the time to get back to me. All the info is really helpful.
I'll have a think about the 12v upgrade but my initial thoughts are keep it original.
I get your wanting to keep it stock but the 12v upgrades wouldnt be noticeable , and the advantages of 12 volts are better lighting you can fit LED bulbs far less current draw and brighter lights and if at some point you wanted to fit signals there are lots of options that dont look out of place . If you want to go the 12 volt route check out dynamo regulators site for 12v pos or neg earth [ you will want neg earth if your thinking of LEDs ]
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The other advantage of a 12v conversion is the option of fitting heated grips.
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You can have positive earth leds now I have Paul Goffs website sells them, bloody bight as well
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You can have positive earth leds now I have Paul Goffs website sells them, bloody bight as well
I looked at his lights but with postage etc too expensive I went with some from Amazon ....auxito h4 .....needed some mods to hook up but at $41.00 CDN a lot cheaper than Goffs offerings and seem to work well , not that I do a lot of night riding anymore .
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Yeah I see you're not UK based, shame Paul sells some great kit but you're crippled by the p&p
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I looked at his lights but with postage etc too expensive I went with some from Amazon ....auxito h4 .....needed some mods to hook up but at $41.00 CDN a lot cheaper than Goffs offerings and seem to work well , not that I do a lot of night riding anymore .
Possibly a lucky escape there. He's not known for his customer care skills.. ;)