Author Topic: Is electronic ignition the way to go?  (Read 12582 times)

Online KiwiGF

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Re: Is electronic ignition the way to go?
« Reply #30 on: 12.12. 2012 00:42 »
Here's my 2 cents worth. I'm in the electronic ignition camp! Mainly because I have bad memories of constantly messing about with points and trying to get the ignition timing right. So I bought a new style BTH mag, which is self powered and does not need a battery to work.

The new BTM mag is great in principle and looks the part as well, but I have some doubts about the quality of manufacture. I had issues with the "locking pin" BTH timing method being very

inaccurate (I posted this elsewhere on this forum) that I think had resulted from not keeping to manufacturing tolerances, coupled I guess with poor quality control as the issue was not picked up by

the manufacturer. I suppose you could say this of a lot of the aftermarket products for the A10! (but the mag is not cheap so having to "fettle" it is a bit annoying).

The cap on mine also showed signs of being filed by hand to make the rubber grommet fit where the wires enter the mag, but its' still a faff getting that grommet in place after removing the cap, and it's never going to stop water or petrol getting into the electronics so I fitted the mag so the grommet is facing downwards.

Inside the cap of the mag there is a fair bit of sealant used to keep wires from moving about, this does not seem the best way of doing the job but it is better than nothing (see pic). It did make it difficult to remove the cap for the first time, as the sealant used had (accidentally) stuck the cap on. Of course there should never be any NEED to remove the cap.

To be fair BTH offered to replace the mag due to the fault with the locking pin but due to the cost of shipping to/from NZ I decided to keep the mag and time the engine using a "home made" method on

the basis I would not have to do the timing again, unless I had to remove the mag or drive gear for any reason.

The mag is a direct replacement for the std KTF but I found the BTH mag casing hits the A10 crankcase so you end up not having much timing adjustment available from the mags 3 slotted stud holes.

The 2 coils the BTH comes with I wondered where to  fit for quite a while, as I did not want to drill holes in the frame and I did not want to rigidly bolt the coils to the frame and possibly have them fail due to vibes, in the end I simply wrapped the coils in a bits of rubber inner tube and (comprehensively) cable tied them to the frame, HT lead pointing forwards, and directly underneath the front seat mounting lug, and almost out of sight.

The special extra long bolt for the bottom stud holding the mag on cannot be used with the BTH as the casing gets in the way, so a std nut is needed instead for that stud, which is a PITA to tighten!

The spark looks very "weak" from the BTH compared to a std mag (BTH claim that is "by design" and not an indication of a problem) to the point it can only be seen in the semi dark but the bike starts

fine with a "normal" kick. I've found the plugs are a bit prone to needing a dry if the carb floods the engine, but I've hardly ridden the bike so time will reveal all.

Lastly, there is very litle info available on how to fix or service the new style BTH mag, this may or may not be a problem depending on whether they need fixing, or wear out!
New Zealand

1956 A10 Golden Flash  (1st finished project)
1949 B31 rigid “400cc”  (2nd finished project)
1968 B44 Victor Special (3rd finished project)
2001 GL1800 Goldwing, well, the wife likes it
2007 KTM 950 Adventure, cos it’s 100% nuts

Offline chaterlea25

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Re: Is electronic ignition the way to go?
« Reply #31 on: 13.12. 2012 16:03 »
Hi All,
Yea they look messy inside  *sad2*
On the single cylinder one I worked on, theres an electronic pack (CDI??) fitted into the end of the end cap
so the wires going to it are very near the rotor end flying around  *sad2*
it took a lot of fiddling to get them restuck in place  *problem*

1961 Super Rocket
1963 RGS (ongoing)

Offline KenF

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Re: Is electronic ignition the way to go?
« Reply #32 on: 16.12. 2012 08:19 »
A few posts on this thread seem to have drifted away from the original question about electronic ignition, but just to complete the picture ...

One of the main things I learned from the article is that probably 30% of the magnetism is lost once the armature is removed

That sort of figure is true enough for some magnetos, John.

I recently measured a BT-H KC2. From its fully magnetised state with armature aligned with the pole shoes, its magnet lost 6% of its strength the first time the armature was rotated half a turn, and it then lost an additional 21% of its initial strength when the armature was first removed from the magneto body. Those losses are permanent until the magneto is remagnetised. However, the loss of magnet strength upon removal of the armature can be avoided by placing the magneto body in an external keeper before the armature is removed and leaving it there until the armature is replaced. A heavyweight cast-iron vice with 6" jaws is ideal for the job. Any work on the mag body, such as replacing the drive-end bearing, then needs to be carried out while the mag body is in the external keeper.

I think that's true of early mags but understand that later ones like our K2Fs with alnico magnets are OK.

You're quite right that the K2F doesn't suffer anywhere near as badly as the KC2 from removal of the armature, Ian. I did a similar test to the above on a K1F (which has an identical magnetic circuit to the K2F). There was a 3% drop in magnet strength when the armature was initially rotated, and a further drop of only 2% when the armature was first removed and replaced. However, it's more to do with the design of the pole laminations cast into the magneto body, that the mere fact that the K2F has an alnico magnet. Most, if not all, of the post WW2 Lucas rotating-coil magnetos and magdynos have what I call a 'self-keepering' feature. It's explained in some detail in Self keeper explanation on my company's web site.

There is no such thing as "an internal keeper" this would in effect "short out" the magnetic field

True enough that if an internal keeper completely shorted out the magnet, the magneto wouldn't be much good. But, sure enough, the Lucas K2F magneto and most, if not all, of their post WW2 rotating-coil magnetos and magdynos do have an 'internal keeper' or 'self keeper', which is clearly visible in the armature cavity of the magneto body opposite the magnet. It partially shorts out the magnetic circuit. The earliest reference I've found to this is in Bosch's British patent 171087 dating back to 1920. There, Bosch start by saying:
  • In magneto electric machines the currents induced in the armature coil produce a magnetic field, the so-called armature re-action which is directed oppositely to the field of the permanent magnets. The magnets are weakened by armature re-action and the electric effect of the magneto is consequently reduced.
To combat this they describe that a
  • magnetic side shunt for the lines of force of the armature field is obtained in the case of a rotating armature by means of a special formation of the magnet pole shoes ... towards one another until the magnetic resistance of the side shunt is greater than that of the principal path (which consists of the armature core plus the double air gap between armature and pole shoes) but is not greater than that of the magnet itself.
They conclude by saying:
  • By bringing the pole shoes nearer together the further advantage is obtained that the magnetic circuit is practically closed even when the armature is removed from the machine, for example, during repairs. This prevents demagnetisation of the magnets which would otherwise occur.

Adopting this feature is what enabled Lucas to be able to say in their Workshop Instructions for the N1, KN1, K1F, K2F and KVF magnetos and also for the MO1L and MN2L magdynos:
  • The high-energy magnet ... does not need a keeper across it; although a very small amount of energy is lost at the first removal of the armature, subsequent removals do not affect it.

All the best,


Online muskrat

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Re: Is electronic ignition the way to go?
« Reply #33 on: 16.12. 2012 09:44 »
 Great explanation Ken, even I sort of got it. Mags have always been magic to me.
I'm in the electric ignition camp, probably for that reason. Being a young bloke of 51 mags had just about disappeared by the time I started riding.
I just remember fiddling with the A7's mag and even got it serviced by Peter Scott. It went OK but when I retired the racer and put it's Boyer on the '51 performance increased by at least 25%. All 3 of my BSA's have it and 2 start 1st kick hot or cold every time the other (A65) takes 2 kicks. Yes a good charging system and battery are a must. If the dynamo wants a rest (stops working due to broken belt/chain) a 4 amp battery will run them for about 80 miles (1 hour at my speeds LOL).
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
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Re: Is electronic ignition the way to go?
« Reply #34 on: 18.12. 2012 09:02 »
I also bought a BT-H unit for my race bike, but was underwealmed by the short duration pale spark. Came to the conclusion that a magneto should throw a far longer duration spark and burn more methanol, so reduce bore wash. So the BT-H will go on a road engine.
I then invested in a Joe Hunt, flange was too thin carried the taper too far out, had to mill my crank cases to get it to fit and it still failed within two seasons, faulty coil  *sad2* Have had that coil replaced and will persevere but nothings ever easy.
I do like the fact that a magneto powered race engine only has a kill wire, whereas with coils and electronics... wiring faults are very common in the pits.
My single has a mag and has been a reliable beastie if not parked in the rain.
A good rider periodically checks all nuts and bolts with a spanner to see that they are tight - Instruction Manual for BSA B series, p46, para 2.
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Offline Russ

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Re: Is electronic ignition the way to go?
« Reply #35 on: 09.01. 2013 01:09 »
Hi Brian

I have a magneto and generator which are complete, but I have no idea what condition they are in as I haven't started my project yet, but as I read this post I thought I might as well start somewhere.
I'm with you, I like the idea of having the original equipment fitted.
Can you suggest where in Aus is a reliable place to get these refurbished or perhaps this is something you do yourself.
I'm in Traralgon.  Victoria.

thanks Russ
1951 A10 Plunger.

Offline Butch (cb)

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Re: Is electronic ignition the way to go?
« Reply #36 on: 09.01. 2013 10:22 »
Yeah - I had both the mag and dynamo refurbed when I was doing the rest of the bike. I left it all 6 volt, and I'd have to say I'm more than happy with the lighting for night time riding too. I'm OK with being left with a very occasional fiddle with the points. Electronic ignition, 12V conversions, belt drive dynamos all just look to move the problems elsewhere.
Warning - observations made by this member have a 93% unreliability rating.

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Offline Topdad

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Re: Is electronic ignition the way to go?
« Reply #37 on: 09.01. 2013 11:19 »
Well Steve ,bet you didn't expect all this feed back when you first posted , just shows the breadth of experience from all the proceeding guys with as you'd expect a different view depending I'd think from  personal experience gained over time all very pertinent but in the end down to you mate whichever route you go down don't skimp ,if mag ;get it refurbed ( I used the guy mentioned a couple of posts back and absolutely not probs with my mag and wouldn't part with it after 9 yrs ) if eleccy ingnition go for the best you can afford ,as you may guess I'm firmly in the maggy camp simply due to having memories of having to sort out so many Trumpet mates bikes when the battery failed or coil or condenser etc but that was over 35 yrs ago plus and I know things must have improved but  honestly can't remember ever suffering loss of sparks when I was a kid  on my A10 , I even submerged the bike totally in a flood once simply pulled it out with the fire brigades help and  dried it  and me out  with wd 40 ( the bike that is ) and a cloth and we were on our way to kent within 1/2 an hour running completely on song. interesting post best wishes BobH
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Online bsa-bill

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Re: Is electronic ignition the way to go?
« Reply #38 on: 09.01. 2013 17:19 »
whichever you choose to supply the spark at the end of the line lies a plug and I suspect that these days an L86 or N5 or their ilk are just not made to the same standard they used to be, the quality products now are the more modern plugs that can demand a higher price (return) for the manufacturer.
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Offline a10gf

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Re: Is electronic ignition the way to go?
« Reply #39 on: 09.01. 2013 17:31 »
Is it true some bikes won't start/run when the mag gets a bit too warm?
Quoting the original 1st post, happened to my mag when I got the bike, one of the tiny winding wires from the armature lost contact when things expanded due to heat. Cannot call it an electric fault, more of a mechanical one, and due to the way the mag was refurbished once upon a time.

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Offline ian davies

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Re: Is electronic ignition the way to go?
« Reply #40 on: 09.01. 2013 17:44 »
Let me put it this way, all electronic ignition conversions for classic bikes should be sold with free RAC recovery.
ian davies

Offline Viking

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Re: Is electronic ignition the way to go?
« Reply #41 on: 10.12. 2015 10:16 »
Let put it the other way: All mags and mag rebuilds for classic bikes should be issued with free AA recovery.  ;)

Offline morris

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Re: Is electronic ignition the way to go?
« Reply #42 on: 10.12. 2015 11:40 »
Let put it the other way: All mags and mag rebuilds for classic bikes should be issued with free AA recovery.  ;)
Let me put it this way, all electronic ignition conversions for classic bikes should be sold with free RAC recovery.

Since I have one on electronic and another one on a mag, does that entitles me to a double coverage?  *dunno*
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Offline warmshed

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Re: Is electronic ignition the way to go?
« Reply #43 on: 10.12. 2015 19:34 »
Electronic ignition is very reliable these days, unless you buy a really cheap chinese set-up.  How many cars or modern bikes do you see with reliability issues?  In all the years using electronic ignition on classic bikes only once was there a failure, ( not mine, a friends) a coil fault, this was sourced locally on our German trip and on our way.  Every time I went to Germany on a rally there was someone that had Mag problems. luckily I carried my old mag with me and was able to help one failure.
mags were good in their day and in tip top condition still great.  If you have a problem your stuffed, its a recovery job.

If you are using your bike locally then not really a problem, just pop home barrow a trailer.  If you do use the bike as they are meant to be used then electronic ignition is great to have.

Go to any show and you will see people trying to start their bike but the mag says no, especially when hot.

Each to their own but because " my mags been good for 50 years" does not make it more reliable.

Online Triton Thrasher

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Re: Is electronic ignition the way to go?
« Reply #44 on: 10.12. 2015 20:49 »
Neither is perfect.  The magneto is far removed from the robust magnetos used on planes.

The available electronic conversions do not appear to be made to OEM automotive standard and require a power supply that could tax a 6V dynamo.

My experience with a Tony Cooper rebuilt magneto has been very good. Nothing could start more easily, hot or cold, wet or dry.  Except maybe a bike with an electric start.