The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Lucas, Ignition, Charging, Electrical => Topic started by: victortrry on 17.05. 2014 11:05
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Just had the magneto overhauled, beautiful day for a ride, went out with some mates travelled 106 miles, stopped no spark. Took the spark plugs out to see if faulty but OK, took pickups out of magneto brushes look good, no spark at the points.
Any ideas?
Victor
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Possibly it's Earthed somewhere?
check that the points spring is not touching the body of the Mag
or that the cut off switch / wiring is not earthing out?
Hope this helps..
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As WozzA has said, also cam can move out and come off pin then turn, new points can bed in and loose the gap, I once had a weennie blob of grease short the spring to the maggie body
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A mate recently stopped for fuel and when he went to start "nothing".
Spark plug lead was touching the head and shorting out.
Russ
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If it's the mag, the overhauler will fix it for free.
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New steel replacement points can break at the base plate. happened to a friends bike on a ride. i'll send in a picture if i can find them.
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Hey Vic, you say the pickup brushes are ok, but am surprised no-one has asked the obvious if you cleaned the slip-ring...?
I had a similar thing a couple of months ago...played around checking all the obvious for a afternoon and morning, found a broken points retainer spring but otherwise did fairly much nothing and then it started.. *dunno*
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I cleaned the slip ring with a white rag there was barely any colour on it. anyway I am taking it off and give it back to the repairer.
Victor
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Here is what can happen with steel based replacement points.
http://s244.photobucket.com/user/takka22/media/001_zpsa069537d.jpg.html
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I took it back to the repairer today, he checked it and found the points plate was earthed, what had happened was the ring that sets the spark at 180 degrees and is held in place with a rivet had turned until the metal spring that
operates the points was touching. Now fixed but tomorrow the hard stuff doing the timing.
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This is a perennial difficulty with the steel points assembly if insufficient clearance is given to the blade spring on the opening point. Because on the steel assembly the opening point is the low tension live one, it is critical the spring can't kiss the camring. Whereas with the brass sets of older design, the sprung point was the earth one so if it rubbed, no problem (until rubbed through and broken, which also happens).
If the camring was able to turn, that is troubling. The register pin should locate it, and the cb end cover should hold the camring firmly in the contact breaker end housing of the magneto. If the end cover allows some axial movement, and if the camring is a loose fit, it is possible it could disengage from the locating peg. If that happens, and the camring turns, the internal timing of the magneto wiill be lost, ie the points won't open at the right place in relation to the magnet. A bit of error will not always be noticeable, but more than a few degrees and things will come to a stop. A double whammy if the spring is also touching earth.
The spring blades are equipped with slotted ajustement at the 'tail end' and the blades should be so fitted that they don't kiss anything. If the 6BA screw at the tail is fubarred, then a repair is needed. Nor must they prevent the opening of the moving point. And the camring needs to fit nicely in the housing, and be secured by whatever end cover + gasket or other spacer is necessary to make it so. Often, the gaskets in the recess on screw-on end covers don't actually contact the cam ring . . . so slop is in-built if the camring is a loose fit. Similar issues arise with the other types of end covers.
If it IS a loose fit, the chances are that the spark interval won't be your 180:180 anyway, as K2Fs are notoriously awkward to get spot-on (compared say to BTH magnetos).
Lucas said the steel assemblies, fitted on most later mags, were 'low-inertia'. I'd say they were 'low cost'. I'd also say the spring tension on the moving point is often higher than necessaey, promoting wear on the heel, and noise.
That's my tuppence worth!
Good luck!
Bill
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Thanks Bill
The end cap on the magneto is the bakelite one and there is no gasket to hold the camring in. I will make a gasket for it to stop the axial movement.
Victor
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Victor,
There should be a rubber ring in the recess in the perimeter of the end cap.
Originally square section but I use O rings.
Trev.
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Trev, Don't wish to hi-jack here, but just an aside re square section 'O' rings- I've had various need for these, but usually just get a funny look, even at bearing shops which are about the only places that have a supply of even round section ones. Are square ones normally available...??
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Trev, Don't wish to hi-jack here, but just an aside re square section 'O' rings- I've had various need for these, but usually just get a funny look, even at bearing shops which are about the only places that have a supply of even round section ones. Are square ones normally available...??
I have found ones of suitable section on spin-on oil filters and cut them to length.
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Dutch, have you tried plumber's suppliers?
Plumbers use a lot of square "o-rings". I get my fibre washers there.
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There are square section rings, "quad rings" I think they are.
I used one on my Norton kick start shaft for a while but eventually fitted a garter seal.
Trev.
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Thanks guys, just a general query for future reference, no particular application for now.
I used to know where to find various things,...(I know what some are thinkin' here.>!) but have forgotten through no need, and places of old have shut down or moved- had to do the Gas shop for copper bends last week, when replacing the coils on my Gutzzi- (don't ask, I'd have to tell 10 other stories to tell the story)
*eek*