The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Lucas, Ignition, Charging, Electrical => Topic started by: patcross on 29.02. 2016 02:59
-
hello, I have a 62 a10 I'm attempting to rebuild the mag on. the bike hasn't run in 30 years, so a rebuild is a must. I purchased the co4 brightspark condenser, did the condensectomy with ease, no problems there, magnets seem strong, so didn't mess with them. I installed new points, put the fibre washers and plastic washer under points as described in instructions. Make a long story short, if I spin the mag with a drill, it has very weak sporatic spark on one side, but not the other. I switched the plug wire pick up from one side to the other and same result, no spark at all on the same side. Could the slipper ring be the problem or corroded wire going into slipper ring? All my other pre unit bsa's and triumphs I've restored I've changed over to electronic ign, but wanted to keep this one original. Thanks for the help, I'm in Indiana enjoy restoring any bsa's and triumphs.
-
Sounds as if you did the condenser job OK , but just check that the spring blade on the moving point isn't touching the camring on the way round, also that the screw that secures the blade isn't too long and touching the capacitor board on one of the metal surfaces. Either could short out the low tension side, the former is the more likely if there are some sparks, as the blade might be kissing on one side of the camring only.
After that amount of time it's possible the coil is a bit tired shall we say! Did you check for basic HT continuity (from the brass bit on the slipring to the mag body)? Should be about 5000 ohms there. If it isn't continuous, then maybe the slipring to coil connection is bad, or there's a break in the HT winding. Also worth ensuring the slipring is clean with no carbon traces going round it due to soft brushes leaving deposits.
Hard to say without having the bits to hand, but it's always going to be high risk to reuse a mag that hasn't run in 30 years without thoroughly testing the windings. The mag ought to spark gaps of 7/32nds of an inch, at about "2 sparks per second" when being turned anti-clockwise (advanced, if it's a manual mag).
-
Ideally you should not spin the mag without both pickups and plug leads connected, with a reasonable gap to earth on the magneto casing.
Are you turning it in the right direction?
If it's a manual magneto, is the cam ring in the fully advanced position? Any other position weakens the spark.
Do the points open just after the strongest pull from the magnets can be felt?
Is the earth brush in good order? Do you know what the earth brush is? It's not the kill switch brush.
Erratic sparking is not completely unlike a bad condenser. New parts can be faulty, or not properly in circuit.
-
Hi Patcross,
give a try and change the pick up at the side with no spark.
If the pick up is wrong, the spark is inside the mag.
cheers Klaus
-
thanks for the replies, I checked the brass area on the slipper ring with the body and there is no continuity. I removed the armature and checked the continuity of the brass slipper to the armature and there's no continuity there either. May try to remove the slipper ring tomorrow and see what the wires look like. I'm guessing corrosion there.
-
Either that or a break in the coil, yup. With the slipring off, you'll know when you measure from the spike on the coil to either of the low tension leads. The connection from coil to slipring is only a push fit of the spike into a very small hole in the slipring, and it can become corroded as you say. Care needed when extracting bearing race, and also slipring as the flanges are rather brittle.
Low tension resistance should be just over half an ohm and probably will be, HT anywhere from 4500 to 6000 in round numbers, depending on the winding 'recipe'.
I remain of the opinion you probably need to get the coil rewound after all this time, and at the same time I'd replace the slipring because they can become surprisingly porous, especially when hot. The condenser will be shot if it's an original, 99.9% certain.