Author Topic: Removing A7 magneto...  (Read 2976 times)

Offline Felters

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Removing A7 magneto...
« on: 13.09. 2011 04:15 »
Went to the Ace Cafe Brighton Burnup at the weekend... on the last couple of miles into Brighton a persistent misfire crept in *roll*

Bizarrely when we were all congregating at the Ace at the start of the ride out I parked up with a bunch of guys from Manchester - and one of them asked me if I had checked the contents of the magneto?

Anyway I parked the bike up, mooched around, sat on the beach with my fish and chips and called the fourth emergency service. The AA came and did what they could but really only told me what I had already guessed and called for a relay truck.

So I've got the Haynes manual and the service sheets on here - but is there anything else I should be looking for when I take it out later today?

Cheers
Mike
'59 BSA A7 and '02 BMW 1150RT

Offline MG

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Re: Removing A7 magneto...
« Reply #1 on: 13.09. 2011 09:43 »
Before you take it out, have you tried cleaning the slip ring?

I had it happen on the freshly rebuilt CSR recently, the brushes in the (repro  *problem*) pickups were so soft that it would only take about 5 miles until she started to misfire, then finally stopped after another 2 or 3 miles. I took out one pickup, cleaned the slip ring by inserting a piece of cloth soaked in petrol, turning the engine over (cut-out button pressed!!!), and off we went again, for another 8-10 miles until the whole thing started all over again.
I replaced the brushes with a set from SRM and presto, no more problems ever since. If you ever happen to find pickup brushes that will draw thick black lines like a soft artist's pencil, throw them away! The good ones will leave almost no perceptible line at all when rubbed over a piece of paper.

It is just a small chance, more likely the mag is faulty indeed, but who knows, worth a try at least. I reckon you have checked everything else (cut-out contact, earthing brush, plugs, HT leads, etc, etc)?

Cheers, Markus
1955 A7 Shooting Star
1956 A10 Golden Flash
1961 Matchless G12 CSR

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Offline Beezageezauk

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Re: Removing A7 magneto...
« Reply #2 on: 13.09. 2011 11:06 »
Mike,

The usual symptoms that would need you to remove the magneto would be a mis-fire when the engine is hot.

Have you tried to fire the bike up since you got home?  If you have and the mis-fire is there from cold then the problem could be one of those mentioned by Markus and could be resolved with the magneto in situ.

If it's ok from cold and only mis-fires (and won't start) when hot then that is normally the sign that it needs a new condensor and an armature re-wind.

Good luck with it and keep us posted.

Beezageezauk.

Offline Felters

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Re: Removing A7 magneto...
« Reply #3 on: 13.09. 2011 11:19 »
Yes it fires up cold but rapidly starts to fail.

I'm struggling to get the large dynamo sprocket off the crank. Undone the nut but it isn't shifting. Do I need a puller of some sort?

Mike
'59 BSA A7 and '02 BMW 1150RT

Offline bsa-bill

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Re: Removing A7 magneto...
« Reply #4 on: 13.09. 2011 19:22 »
A puller would be good, in fact best
however if you put the nut back on and screw it ALMOST fully on (leave a thread), put a pry bar or large screwdriver behind the sprocket and apply a moderate pressure then hit the nut with a soft hammer (brass or polyplonker) once (with feeling) it should spring off.
If it doesn't come off first time this is not a method to persist with unless you have a spare idler pinion shaft handy, works every time for me though
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 Beezageezauk

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Re: Removing A7 magneto...
« Reply #5 on: 13.09. 2011 20:10 »
Mike,

Am I reading you right here and you're taking your dynamo off?

I'm pretty sure you don't have to remove the dynamo to take the magneto off!!  Even if you have an automatic advance/retard the unit will come off through the hole in the inner timing cover.

Beezageezauk. 

Offline Felters

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Re: Removing A7 magneto...
« Reply #6 on: 13.09. 2011 21:32 »
The advance/retard unit doesn't want to come off so I though that I might have to remove the inner timing cover...

I unbolted the adv/retard and it slackened off and then started to tighten again as stated in the Haynes manual. But the bolt just keeps rotating - the unit never seems to come off the shaft!!!

Mike

'59 BSA A7 and '02 BMW 1150RT

Online RichardL

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Re: Removing A7 magneto...
« Reply #7 on: 13.09. 2011 22:27 »
You definately do not need to take off the inner timing cover, otherwise you would be doing that every time you had to time the engine. Once the bolt starts turning freely, gently push it in or tug it out (wish I could remember which it is) while continuing to turn anti-clockwise. The disengaging thread should then catch and the auto-advance unit should disengage from the taper.

Richard L.
Plan on signing up for the world-wide 2020 DISTINGUISHED GENTLEMAN'S RIDEon September 27, 2020. This year it's a solo or pillion ride in dapper attire. Watch website at https://www.gentlemansride.com for details.


Offline MG

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Re: Removing A7 magneto...
« Reply #8 on: 14.09. 2011 10:09 »
Quote
gently push it in or tug it out (wish I could remember which it is) while continuing to turn anti-clockwise

"tug it out" it is!

1955 A7 Shooting Star
1956 A10 Golden Flash
1961 Matchless G12 CSR

www.histo-tech.at - Restoration, Repairs, Racing

Austria

Online Brian

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Re: Removing A7 magneto...
« Reply #9 on: 14.09. 2011 11:45 »
Just as an aside to the topic this is what I did to get the dynamo sprocket off mine.

Online Sav

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Re: Removing A7 magneto...
« Reply #10 on: 14.09. 2011 15:03 »
Bit late to comment on this but in my experience mag problems are usually indicated by a failure to start when hot. It sounds much more like a peripheral problem, brushes / points / lead / plug.

What are the symtoms of the missfire? popping and banging or losing a cylinder?


Sav
1961 A10SR, spent a fortune at SRM
1961 A7SS, finally the right green
2011 New addition 1937 Empire Star, twin port, high pipes. Turned out to be the most unreliable bike I have handled.
2017 finally found the liner/barrel were flexing and causing all the overheating/nipping up. Early B33 barrel fitted and it's reliable at last!

Offline Felters

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Re: Removing A7 magneto...
« Reply #11 on: 14.09. 2011 20:02 »
Sav - it won't start when hot, only cold...

I've now taken it out of the bike. The self-extraction system needed a bit of help from a large hammer!  *eek*
'59 BSA A7 and '02 BMW 1150RT

Online RichardL

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Re: Removing A7 magneto...
« Reply #12 on: 14.09. 2011 20:37 »
Ouch *ex* *work* *grins*
Plan on signing up for the world-wide 2020 DISTINGUISHED GENTLEMAN'S RIDEon September 27, 2020. This year it's a solo or pillion ride in dapper attire. Watch website at https://www.gentlemansride.com for details.


Offline Felters

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Re: Removing A7 magneto...
« Reply #13 on: 14.09. 2011 21:46 »
and this is what the armature looked like... whether that's good or bad I don't know. But it doesn't seem to work!
'59 BSA A7 and '02 BMW 1150RT

Offline bsa-bill

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Re: Removing A7 magneto...
« Reply #14 on: 14.09. 2011 22:00 »
slip ring looks like it's carbon tracked and the other end looks dirty from either the earth brush or could be grease from bearing.

I'm no expert with magnetos despite a fair bit of experience  gained of late.
If you have a meter I suggest you read the thread "resistance should there be some" in Lucas, electrical, ignition - I got a lot of help from forum members including how to test the magneto with a meter
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