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BSA_WM20, gavin eisler, George Kaplan, Gordon Gray, Hillbilly bike, Howard Inough, MikeG, NickL, NYBSAGUY
Total Likes: 18
Original Post (Thread Starter)
#858873 09/19/2021 10:37 PM
by MikeG
MikeG
Pretty sure I know the answer, but I'll ask just the same. My A10 has always been a reliable and easy to start bike since I had the mag redone. Before that cold starts were OK but once hot it was a no go till things cooled a bit. Now it's started doing it again and I suspect it's the condenser ( or so I was told) like the last time. It's definately a no/weak spark situation. Once started it runs fine and pulls strong so I don't think its a fuel issue. I guess the easy way out is to replace the condenser with one of the Brightspark external ones. Any thought/ideas or experience with these? I had a hard time convincing myself that thats the issue, but when I look back it's been almost 25 years since that mag was rewound and the condenser replaced so I guess it could be?
Liked Replies
#859122 Sep 22nd a 06:17 PM
by Magnetoman
Magnetoman
Originally Posted by MikeG
I sent you the cracked broken mag housing as you wanted to do try repairing it?
I'd forgotten who had sent that, so thank you very much again. I wanted to determine if I could demagnetize a magneto sufficiently to allow me to TIG weld the housing, and then remagnetize it. Your cracked case allowed me to determine that was possible. Again, thanks very much.

Originally Posted by MikeG
I understand that removing it causes a loss of magnetism, is that effect compounded every time it is removed, so that if it's removed, reinstalled and then removed again is there a loss each time?
Most of the loss occurs on the first removal, with less on subsequent removals. Although a B-H curve is typically represented as a single loop, in fact it is an infinite number of nested loops. How a system moves on and between those loops when something changes depends on the previous history of the system. Although the operation of an electromagnetic device like a magneto is considerably more complicated than can be explained here, the following simplified explanation might help.

Removing the armature changes the load line of the system, bringing it to a lower equilibrium point on the B-H loop. Replacing the armature moves the system back in the general direction of the original point, but along a different hysteresis loop so it ends up with a different, lower magnetization than it originally had. The next removal also brings it to a lower point, but since it is starting from a lower point, the amount of movement is smaller than it was on the original removal, so when the armature is replaced the system returns closer to where it had started prior to the second removal. I crudely drew this in the next figure.

[Linked Image]

When the movements are small enough the system moves back and forth between load lines without further loss. In operation, a magneto changes its load line as the armature revolves, but the changes are small enough that the system sweeps up and down what is effectively the same hysteresis loop without loss on each rotation.

The above applies to all magnetos, including ones made before the 1930s when Alnico first appeared. However, the hysteresis curves of pre-Alnico magnets are such that removing the armature just once drops the magnetization by too much for it to recover sufficiently when the armature is replaced. The magneto still would work, but it would have to spin quite a bit faster than kickstarting speed to generate enough voltage to fire a spark plug.

Lucas states that normal kickstarting speeds are 300-500 rpm. A remagnetized Alnico magneto will provide a nice spark even a bit lower than 300 rpm. However, one that has been freshly magnetized, then the armature removed and replaced, will be at the upper range. Depending on how strong your leg is, that may be acceptable, but a bike that sparks at 300 rpm and is properly carburetted is a joy to ride.

As a general comment, many of the statements made by two people in this thread about magnetos and condensers are inapplicable or simply incorrect. Although I've debunked them before, the time I spent doing that clearly was wasted. Instead, I spent a lot of effort to produce the most comprehensive thread about magnetos likely to be found anywhere so people can find accurate information there on condensers and magnetizers. However, there is a trend in some areas of society to denigrate experts and expertise, and maintain that all opinions are equally valid. So, rather than accepting advice based on actual experiments from someone known to be a trained expert, instead someone reading this thread can give equal weight to anecdotes, opinions, and random technical words found with google.

[Linked Image]
Attached Images
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#859500 Sep 27th a 05:54 PM
by Magnetoman
Magnetoman
Originally Posted by MikeG
Still not sure why it would only act up when hot but since CHECKING THE BASICS it seems to have pulled out of it. Lesson learned-even on a bike that sits in heated storage and gets run only a few hundred miles a year you gotta do more than change the oil.
This is why diagnosing electrical problems from a distance is more of a guessing game than it is a science. The simple-minded idea that misfiring when hot indicates the condenser was a reasonable guess as recently as a decade ago, but there aren't many original Lucas condensers still working in magnetos. The increased electrical conductivity between the plates that aging Lucas condensers exhibited when hot was specific to the chemical breakdown of the wax in them, and is not a common trait of most condensers.

Some years ago I bought a NOS Lucas RB108 voltage regulator. Even though the regulator points were closed, the measured resistance across them was >20 MΩ. After I burnished the points several times I got it to drop to 5 Ω. Finally, after using #320 emery paper, it dropped to 0.007 Ω. The point being, even though the points in a magneto might have been in contact with each other over the winter they still can oxidize enough to cause trouble. If the increase in resistance were linear in time (which it isn't), and assuming that RB108 had been manufactured 50 years earlier, on average it would have increased in resistance by 200 kΩ during six months of storage. That much resistance certainly would have been enough to cause problems with a magneto.
3 members like this
#858958 Sep 20th a 08:28 PM
by Magnetoman
Magnetoman
Anyone can, and does, post "answers" to questions. So, no different than elsewhere on the internet, you can get technical words strung together as if they make sense, debunked nonsense repeated often enough some people believe it must be fact, baseless opinions stated with conviction, anecdotes offered as fact, or snarky drivel. But, if you're lucky, sometimes you can get useful facts that are relevant to addressing the question you asked. It then falls to the person who asked the question to decide whose advice is likely to be correct, who is just repeating somet information or misinformation they read, and who should be ignored.

I try to post accurate information, and I try to offer additional explanation and clarification when I think it would be productive. But, sometimes it's pointless to respond to certain posts. If MikeG has additional questions I'll try to answer them, but he'll have to decide whose answers might be correct, and whose should be ignored.
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#859153 Sep 23rd a 01:35 AM
by NYBSAGUY
NYBSAGUY
What's hilarious about this discussion is that, on the one hand, we have some people who have read their first aid manuals cover to cover. At least, they remember that a friend of theirs did, and it was great, and told them how to dress wounds of all sorts, from legs hanging off, to bleeding fingers, to eyes hanging out of their sockets. And all of these blokes lived - real world!

And on the other hand, we have a couple of guys who have been practicing neurosurgeons for several decades, and not only read the books, they actually wrote them.

But the first crowd thinks the second crowd are all a bunch of toffee-nosed know-it-alls, who like to talk down, whose word can't be trusted... Because, after all, what works in the field for keeping a bloke's leg attached, is way different from what goes on in a sterile surgical theatre or medical lab.

And never the twain shall meet.

Quite funny, really, this internet thing.
2 members like this
#859699 Sep 30th a 02:06 PM
by Hillbilly bike
Hillbilly bike
There you go, if your old lump has an electronic ignition and or regulator your bike is Yamaha.... That should eliminate about half the guys on this site.... grin
And include LED bulbs and sealed batteries...and any modern tread design tires...And god forbid anyone using synthetic oil....And don't dare use air in tires that isn't from the 1960's.. wink
2 members like this
#859741 Sep 30th a 11:44 PM
by Magnetoman
Magnetoman
Originally Posted by Hillbilly bike
There you go, if your old lump has an electronic ignition and or regulator your bike is Yamaha.
Originally Posted by NickL
I like some of the originality but like to keep things practical.
I have modern bikes with EI, electronic voltage regulator, fuel injection, etc., so I prefer to keep my old bikes old. However, I don't judge those who do to their bikes whatever makes them happy since very few motorcycles are one-of-a-kind examples that should be preserved in original condition for future generations. If someone wants a Mikuni, electronic regulator, or fuzzy dice hanging from a sissy bar on their A10, that does not make them a failure as a human being. Nor does it if someone else wants an Amal, mechanical regular, and magneto on theirs. At least, as far as I'm concerned, although other opinions may differ. Of course, preferring Triumphs over BSAs is an entirely different matter...

I got a fair amount of crap early on with my as-original rebuild on the Vincent Owners Club Forum from a few people with quite strident views that one must modify. Although not everyone seems to realize it, decisions on what to do with a bike are completely personal and totally arbitrary. Explaining what choices someone made and why can be quite useful (e.g. magneto vs. EI, Amal vs. Mikuni, etc.), but what essentially amounts to using insulting names for personal decisions is unhelpful.

The personal, arbitrary choice I made for my Gold Stars has them with modern tires and brake linings, LED bulbs, and total-loss NiMH batteries. One of them has a Magdyno, and if I decided it needed to have a full-time charging system I'd install the Podtronics regulator I bought for the purpose from Coventry Spares shortly after getting the bike seven years ago. However, I have no intention ever to swap the magnetos for EI.

The above gives me the riding experience on all three of them that is "essentially" the same as it was when they were new, which is what I want. However, someone else might well make completely different personal, arbitrary choices.
2 members like this
#859095 Sep 22nd a 11:37 AM
by MikeG
MikeG
Originally Posted by Magnetoman
Originally Posted by MikeG
I guess now I won't know what I really have till I get the time to dive into it.
Ah, the joys of trying to remotely diagnose an electrical problem based on the information provided ("say, did I happen to mention before that it isn't Lucas, but BTH, and my cousin said he fixed it for me with pickups from a Honda rototiller and lampcord for the HT leads?" ...
Originally Posted by Magnetoman
Originally Posted by MikeG
I guess now I won't know what I really have till I get the time to dive into it.
Ah, the joys of trying to remotely diagnose an electrical problem based on the information provided ("say, did I happen to mention before that it isn't Lucas, but BTH, and my cousin said he fixed it for me with pickups from a Honda rototiller and lampcord for the HT leads?" ...

True that, and as I recall I sent you the cracked broken mag housing as you wanted to do try repairing it? I had a spare engine that I pulled the mag off of and had to change the points housing from my old one to retain manual spark advance. It had been rebuilt, just not sure who did it and which armature I used. Anyway, I have a further question on the effect of removing the armature! I understand that removing it causes a loss of magnetism, is that effect compounded every time it is removed, so that if it's removed, reinstalled and then removed again is there a loss each time?
1 member likes this
#859144 Sep 22nd a 11:40 PM
by Magnetoman
Magnetoman
Sorry, but I've already spent too much time here addressing issues that are amply covered in my extensive magneto rebuild thread. Read that thread and if you have questions sent me a PM. If I find them of sufficient interest I'll add answers to that thread so everything can be found in one location rather than spread out all across Britbike.
1 member likes this
#859495 Sep 27th a 02:52 PM
by MikeG
MikeG
A follow up then. I finally had a chance to dig into things Friday. Turns out that poor connections and corrosion in the left plug wire were causing very high resistance. The slip ring was also dirty, but not exceptionally so. Not a problem when the mag is spinning fast enough to generate a good spark but enough to matter when kicking it over it seems. Still not sure why it would only act up when hot but since CHECKING THE BASICS it seems to have pulled out of it. Lesson learned-even on a bike that sits in heated storage and gets run only a few hundred miles a year you gotta do more than change the oil. blush
1 member likes this
#859636 Sep 29th a 06:09 PM
by Hillbilly bike
Hillbilly bike
No magneto on my A10 BSA....It also has an electronic voltage regulator and 12 volt Dynamo with new parts inside...Who will be the first to tell me the generators aren't reliable grin. And a Mikuni TM carb instead of a finger wetting Amal...
Attached Images
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