The BSA A7-A10 Forum

Technical => Lucas, Electrical, Ignition => Topic started by: bsa-bill on 21.09. 2010 19:02

Title: Mystical Magneto
Post by: bsa-bill on 21.09. 2010 19:02
As reported elsewhere I swapped the reconditioned magneto from the non starting rocket Gold Flash onto my Golf flash and it started so thought it must be OK.
Then while trying out a colour tune I found it was not always sparking on one side.
Today I decided to give it a run to Wooler a round trip of about fourteen miles, not to far from home should I get trouble, well it started second kick but was fuffing and spitting on one side, however once it got a handfull of throttle it went fine and smooth and rather well.
Junctions proved a problem as the misfire would start as soon as revs got down and on two or three occasions it would continue to run on one even after it was opened up.
investigations after I got home proved plugs, leads, pickups and points were fine and it started once and once only, after that there was absolutely no spark at all.
the one thing I though might not be right is that the cam ring appears to be not in the same place as the one on my other Flash's magneto, seems a bit further round (clockwasi), not sure this would stop it sparking , the points will still have to open and close?

The warranty is out but only by a month or so. I phone FTW who said to send it to them for checking

I understand the non starting when warm thing but why no spark at low revs??
Title: Re: Mystical Magneto
Post by: trevinoz on 21.09. 2010 22:12
      I had a similar problem a while back with a mate's bike.
It caused a lot of head scratching as the magneto was newly reconditioned including a rewind.
The problem turned out to be the slip ring which was, I think, a BTH one fitted by mistake.
The spark had to track over the insulated section of the slip ring to reach the pick up.
At low revs the spark is weaker so does not want to track but as the revs rise so does the voltage and consequently it will track.
The reconditioner rectified the problem by replacing the slip ring but he also had to rewind the armature again.
Have a look at your slip ring and see if the conducting strip is under the pick up when the points open.
Title: Re: Mystical Magneto
Post by: bsa-bill on 21.09. 2010 22:20
Cheers Trev, I'll check that soon as I get it off (it will have to come off whatever is up with it)
Title: Re: Mystical Magneto
Post by: lawnmowerman on 22.09. 2010 10:51
Bill. I have exactly the same problem on my SR. Seems to be worse when retarded on starting. Sometimes it happens on the road and it seems to clear if I retard the mag then advance it again. Even when warm on idle, if I retard the mag it misfires on one side.
I will be interested in the outcome.

Title: Re: Mystical Magneto
Post by: chaterlea25 on 22.09. 2010 12:13
Hi Bill and All,
I had similar problems recently with a K2F,
Unusual in that it went onto one cylinder on full advance??????????
It had the steel type points plate fitted, I swopped this over to a brass points setup and it ran better but still not right
I went looking closely and the peg that limits the movement on the camring was way to the other side than that of my spare mag, this caused the spark to occur when the brush had left the brass part of the slipring *ex* *ex*

The peg has a rivit driven into it to stop interference *eek*
It can be carefully drilled out and the slotted end of the peg is revealed, It has an eccentric so turning it moves the range on the camring. some epoxy will fix it in place then.

I also found that the steel points plate type are more advanced in relation to the keyway compared to the brass pointsplates ???? ????
I filed away some of the leading edge of the fibre heel to bring the timing back to where the brass points were opening
Result  *smile* *smile* *smile*

John O R

Title: Re: Mystical Magneto
Post by: bsa-bill on 23.09. 2010 13:04
had a comparative look at the magneto this morning against the one that was on the 61 Flash ( now on the Rocket Gold Flash ).
Two things - the the cam ring for the points is about 90 degrees out compared to the one off the Flash, also the slip-ring appears to be connecting to the wrong pickup, on reflection of course this could be down to the camring being 90 degrees out as the points would be open somewhere in the middle of where they should be.

I tried the old test of swapping the leads over but the result was the same - nowt produce other than sweat.
It is a wonder that the thing ran at all, leaving Wooller on Tuesday was like something out of a cartoon, bike was popping and banging with an occasional mega backfire, people started, dogs barked, cats ran, I had in my helmet.

Anyway it will come off today to be posted back to FTW tomorrow
Title: Re: Mystical Magneto
Post by: chaterlea25 on 23.09. 2010 13:21
Hi Bill
Is it as simple as the end cover is fitted a quarter turn from where it should be ???? ???? ???? ????

John O R
Title: Re: Mystical Magneto
Post by: bsa-bill on 23.09. 2010 14:59
John - that rather obvious point did not register with me when looking at it, I'll check that out, wonder if it can be done in situ - probably not, time to try out that flexi screwdriver thingy

A little later

No John not possible , the end is not square, two flat side and two curved plus the bit at the top for the clip.
Can't see the bottom so it's possible it could be 180 degrees out but that would hardly matter

thanks anyway
Title: Re: Mystical Magneto
Post by: bsa-bill on 29.09. 2010 16:24
FTW phoned while I was out on Tuesday re the Magneto.
I had put in a note to say I had noticed how far the cam ring was out compared to my other Magneto, turns out that was all that was wrong with it  *red* *doh* *doh*.
The cam ring had come off its peg and rotated, this can happen apparently if the bike is run with the end cap off the Maggie, can't recall ever doing this but maybe it can happen whilst setting the timing ??.
Anyway he has moved the peg out a bit and put the cam back where it belongs, should get it back early next week or maybe before.
I am bit reluctant to delve into stuff that just been reconditioned, particularly Magnetos because I know not a lot about how they produce all that energy, I'm familiar with what the whirl y  bits look like but that about it.
Title: Re: Mystical Magneto
Post by: ian davies on 03.10. 2010 17:53
Hi. several weeks ago i completed a 140 mile round trip on my A7 she didnt miss a beat, two weeks later i got her out of the shed gave a kick, and she was running on the left cyl only. After doing all the checks you do when this happens, i got nothing, she wouldnt fire at all, although a good spark at both plugs. When kicking over there was a sort of slight backfire. To cut the story short, i removed the mag and stripped it, i had allready got a new condenser to fit, but on stripping the mag i found the problem, a pin hole in the coil insulation arcing to the condenser case, covered the hole with a dolup of araldite, left to set over night, reassemble, refit, and she started first kick and has been going extremely well ever since. Saved a couple of hundred quid i reckon. But i suppose it will give up one day.
Title: Re: Mystical Magneto
Post by: bsa-bill on 03.10. 2010 18:17
Hi Ian, interesting
As writ elsewhere my spare Magneto off my Gold Flash has now decided to play up (since putting it on the Rocket Gold Flash), it has never given any trouble on the Gold Flash in the last ten years since reconditioning, but the other day it point blank refused to produce any spark at all when warm, tried it yesterday cold  and it started the bike with one kick.
I think I'll have a look inside it once I get the other one back from FTW, if it needs reconditioned I'd be tempted to go digital ( cheaper than a recon )
Is there much to be afraid of in there? and how would I test a condenser ( I have meters both analogue and digy)
Is it possible the winding insulation has broken down in ten years considering it has not covered many miles, although due to necessity it ended up spending the winter before last in a damp garage?
Title: Re: Mystical Magneto
Post by: chaterlea25 on 03.10. 2010 22:10
Hi Bill,
Test the HT winding by checking from the slipring to the centre screw with an ohm meter,
As a rule of thumb, 4k ohms is good, much less means internal shorts in the windings
open circuit readings with a digital meter can be decieving as the connection to the slipring can be iffy, remove the bearing and slipring and check to the wire sticking out
Have a visual on the condenser, if they fail you can sometimes see the "blow"
unsolder the condenser connections and check with a meter 0.2 or so microfarads
If you have a megger tester you can charge them up on the 250v setting, connect one lead,  keep the button pressed and touch the other probe to the second leg, remove after a few seconds
wait a minute or so and CAREFULLY  short out the condenser connections with a well insulated piece of wire or something ???? ????
There should be a good flash and a bang when you do this *ex* *ex* *ex*
BE VERY CAREFUL *ex* *ex* *ex*
This is the surefire (LOL) way to test the condenser *eek* *eek*

There have been some very poor and unsuitable condensers fitted by mag recon guys in recent times!!

John O R