The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Lucas, Ignition, Charging, Electrical => Topic started by: Gasket4450 on 08.09. 2013 18:48
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An old problem, I know, but this one is a bit odd.....( that's the problem, not the writer...!!!). I have built a 1959 A7 from scratch, and have been trying unsuccessfully to get it to fire up. It is a mag model with auto A/R, and I have checked, double checked, and re-checked the timing, so I believe that is OK. B6HS plugs, brand new, and a rebuilt 376 monobloc. Spent weeks trying to get it to go, with some odd results: it will fire up on the left cylinder with the right plug out. It fires on the right cylinder with the left plug out. Each plug gives a healthy spark when earthed on the engine ONE AT A TIME........put them both against earth, and the spark is reduced to a feeble, yellowy-looking thing. I rebuilt the K2F mag, but the only thing I wasn't able to check was the dreaded condenser - does anybody think this might be the cause of my problem ? Has anybody ever come across these symptoms in the past ?
I built my A10 about three or four years ago, and I use it every week with no problems, so this really has got me foxed ( ..or sounds like that, anyway.....). Any help would be most welcome.
I am thinking of buying one of those Brightspark gadgets, which would at least give me peace of mind, depending on replies and advice here, and will of course report back.
Norman
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Sounds like a problem with the slip ring. I did have one fail on one of my bikes but it was a long time ago so I don't remember details. It only needs a hair line crack which will fill up with carbon and give strange running like you describe.
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hi, could you swap the mag with your a10 ?
just a thought
rob
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Hi Norman,
Definitely the slip ring is tracking
I have had this problem and have seen the same with others
I posted about this some time ago
HTH
John
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So, if the mag must come out to check or replace the slip ring, I say, go ahead and install the BrightSpark EasyCap at the same time. I know, not good science, since you will be changing two elements and not knowing which to thank, but riding is more fun than science.
Richard L.
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You may only have to clean the slip ring and make sure you have good pickup brushes. Some are too soft.
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Hi, and thanks to all the useful suggestions. I never even thought about the slip ring being duff ( bought on Ebay as "....in good useable condition...." ), so will concentrate my efforts there first. Today seems like a good day, as it's raining in Kent ! The price of a recon armature is a bit frightening, so let's hope it works.
Thanks TT for the carbon brush tip - I have come across lots of other snippets in this Forum regarding those. I guess it's just pot luck unless you pay for genuine Lucas parts. Thanks also to 'manosound', my thoughts exactly re the EasyCap.
And finally, to Derby Rob: yep, I did consider swapping over the mags, but then thought to myself: " Err, what happens if I never get the A10 running properly again ? Aaarrrgh !!!!! *sad2*", so that may be the very last resort.
Once again, this cracking Forum may have saved the day. My thanks to all for a bit of lateral thinking
Norman
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Norman
I had mag problems recently and sent mine to a place called Priory Dynamos, he is also an A10 freak.
The armature was rewound, new condenser, points gap levelled up, new cracked brush pick up unit and a couple of other bits and I thought the price was fantastic at £144. The new mag is on now and it does not miss a beat. Even better it was only away just over a week.
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Hi, and thanks to all the useful suggestions. I never even thought about the slip ring being duff
Norman
Yes, it looks such a simple part you can't imagine it going wrong. The same with a rotor arm for a car. Some years back my MGBGT died and I called the AA / RAC (I forget which it was now). The guy had a poke around for a couple of minutes and announced he had traced the problem to the rotor arm. The car was already about 25 years old so he didn't hold out much hope of getting a new arm locally so he towed me home (about 2 miles). I thought to myself, this chap is clueless, what can go wrong with a lump of bakelite and brass? I did get a new rotor arm locally as it happens, mainly just to satisfy myself that he was indeed wrong in his diagnosis. I put the new rotor arm in and it ran perfectly. *ex*
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Well, the saga continues, but we are getting closer. I took the armature out of the mag today, and guess what.......?
A big, black, greasy carbon skidmark all the way round the centre of the slip ring. Five minutes with some cotton buds dipped in petrol soon had it looking like new. I'll try some replacement brushes from two different suppliers, and see what happens. Unfortunately, however, once it was clean, I noticed around the centre was what looked like a very thin jagged black line, about an inch and a half long, which I could feel with my finger nail. Aha ! *idea* For those of you who have already guessed what I am about to say, yes, it was a hairline crack. Top marks to all of you who saw that one coming.
Fortunately, I had a spare, almost new, slip ring, so that has gone on, together with new bearings and seal, and we'll see where we go from here. Once I have also fitted the EasyCap, I am hoping it will make all the difference. If all else fails, I shall give your man at Priory Dynamos a try Bikerboy ( Thanks for that ).
I have to be honest and say I would probably never even have noticed the crack if it hadn't been mentioned in this Forum....Doh!!! Watch this space.
Norman
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while you are waiting try the other bikes mag my then get a good nights sleep in the mean time john
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Yes, it looks such a simple part you can't imagine it going wrong. The same with a rotor arm for a car. Some years back my MGBGT died and I called the AA / RAC (I forget which it was now). The guy had a poke around for a couple of minutes and announced he had traced the problem to the rotor arm. The car was already about 25 years old so he didn't hold out much hope of getting a new arm locally so he towed me home (about 2 miles). I thought to myself, this chap is clueless, what can go wrong with a lump of bakelite and brass? I did get a new rotor arm locally as it happens, mainly just to satisfy myself that he was indeed wrong in his diagnosis. I put the new rotor arm in and it ran perfectly. *ex*
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I had exactly the same problem with my 1938 Wolseley tin top. I came home twice on a recovery truck due to duff rotor arms. Also had an issue with a reproduction Lucas coil (seems they also reproduced the unreliability *smile*) The problem with the rotor arms seems to be the wrong type of plastic (too much carbon) and a rivet too long.
The problem seems to be poor quality electrical parts coming from China which should be labelled "for display purposes only."
I now only buy ignition parts from a reputable supplier and had no problems since. I think this is a lesson to be learned for BSA parts as well judging by the amount of posts regarding the wrong type of material in carbon brushes.
Jim
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Norman.
Just a quick thought, Have you checked whether you plug caps are suppressed? If they are this could also give you grief.
Regards John
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Well, the saga continues, but we are getting closer. I took the armature out of the mag today, and guess what.......?
A big, black, greasy carbon skidmark all the way round the centre of the slip ring. Five minutes with some cotton buds dipped in petrol soon had it looking like new. I'll try some replacement brushes from two different suppliers, and see what happens. Unfortunately, however, once it was clean, I noticed around the centre was what looked like a very thin jagged black line, about an inch and a half long, which I could feel with my finger nail. Aha ! *idea* For those of you who have already guessed what I am about to say, yes, it was a hairline crack. Top marks to all of you who saw that one coming.
Fortunately, I had a spare, almost new, slip ring, so that has gone on, together with new bearings and seal, and we'll see where we go from here. Once I have also fitted the EasyCap, I am hoping it will make all the difference. If all else fails, I shall give your man at Priory Dynamos a try Bikerboy ( Thanks for that ).
I have to be honest and say I would probably never even have noticed the crack if it hadn't been mentioned in this Forum....Doh!!! Watch this space.
Norman
There have been problems with 'soft' brushes which can cause problems the dust of which can then coat the inside causing internal tracking. A friend had this problem with his pre-unit Triumph and would appear to be a well know problem when he discussed it with the local Mag guy. He cleaned out the mag and fitted the hard brushes and since had had no further problems.
The correct 'hard' type, I believe, have a 'V' groove? Hopefully somebody may be able to better advise how to identify the various types, but something to be aware of if replacing the cracked ring does not do the trick?
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Bikerboy made some very kind remarks about my magneto services but I'm Priory Magnetos Ltd actually! (but I fix dynamos as well!) If you look for Priory Dynamos on Google you may not find me. I would strongly advise using pickup brushes of known quality which can be guaranteed by the seller. The springs are equally important as they should not be so strong that they dig big grooves in your slip ring. Also the modern slip rings, made from a plastic material are excellent and don't crack on assembly.
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My thanks to all the useful advice so far - it seems a lot of people out there have had similar problems in the past. For those of you who are interested in this saga, I have copied part of an e-mail below, which I received from Ken Targett at Brightspark Magnetos, ( ' KenF ' of this goodly Forum ), who gave my mag a good going over. Those of you of a nervous disposition should look away now......... !!!
" Hello Norman,
Your magneto parts arrived safely, and I have now checked them out. The points of note are:
• The magneto body was fairly well magnetised. I have managed to increase the magnet strength by 11%.
• The pick-up brushes are indeed too soft for a twin-cylinder magneto. We can supply a pair of the appropriate grade if
you wish.
• The armature appears to have its original windings and condenser.
• The condenser should ideally have a leakage resistance in excess of 2000 megohms when tested at 500 V. Your condenser's leakage resistance registered 0.1 megohms when cold, and 0.0 megohms at 50 deg. C. Because it is so leaky, it failed to give a sensible reading of its capacitance on our capacitance meter.
• There is a lack of continuity through the high-tension winding, i.e. there is a break in the very fine wire of the winding. Despite that, a broken winding can still work, with a spark jumping the break in the winding as well as at the sparking plug. Not at all satisfactory, because the extra spark burns away the insulation, and also erodes the copper wire and makes the break bigger. I have tested the windings on our coil tester (click here for details) using a 5.5 mm 3-point standard test gap. The low-tension break current required for consistent sparks was 1.7 amps when cold, and 1.9 amps when heated to 50 deg. C. Those figures aren't terrible. So, if you only need this magneto for very occasional use and it doesn't matter that its performance will fall off over time, then you could use the original windings. I can't give any guarantees at all about how long the thing would last. It will be far preferable, of course, to have armature bobbin rewound. We don't do rewinds ourselves, but send them out to a time-served rewinder who guarantees his work for one year. The turn round time is about three weeks.
• I have also checked the slip ring and pick-up mouldings on our tester for that purpose (click here for details). The slip ring, which looks like the original, tested good, cold and hot.
• The pick-up mouldings are of Taiwanese manufacture. Both tested good when cold. However, after heating to 50 deg. C, connecting one of them to the test circuit required 35% extra LT current in order to maintain the circuit's spark, and the other pick-up required 40% extra current. They are therefore very leaky when hot and need replacing. "
The slip ring referred to is not the cracked one I found originally, but a NOS replacement I found hidden away in the workshop. *smile* The main problem, of course, appears to be the condenser, as suggested by several of you at the start of this thread, but I would never have been able to check the plug caps, and they obviously are not helping the problem. My fault for buying cheap imported rubbish, I suppose. Anyway, good to read such an in-depth analysis of the faulty mag, something I would not have been able to accomplish in my limited workshop at home.
So, good news then. All I have to do now is wait for the bill to hit the doormat.......... Oh well, beans on toast, and bread and jam for the next month, I 'spose !!!
Still haven't plucked up the courage to remove the A10 mag yet, John, as a group of us are still riding out regularly before the summer disappears, but thanks anyway. My thanks to everybody who replied to this post - nearly everything you all suggested seems to have been covered in Ken's e-mail. It pays to talk to the experts. *conf* ( Should have done that in the first place - Doh! )
More to follow, probably
Norman
while you are waiting try the other bikes mag my then get a good nights sleep in the mean time john
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The best money I spent on my bike was a mag rewind & condenser job. After years of kicking and oathing at it, it's now a first (second at worst) kick starter.
It cost me around 180 bucks, but I love it!
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Yep, you're dead right. My fault for trying to build a mag from all the spare parts I had........what I should have done, of course, is what I'm having to do now, and that is to bite the bullet and pay out big money to get a decent job done *smiley4*.
I am expecting a ' first or second kick start ' every time when the mag comes back. I will report on progress as we go !
Adm edit: solution given in http://www.a7a10.net/forum/index.php?topic=7813.msg
All now fixed, thanks to Ken Targett at Brightspark