The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Lucas, Ignition, Charging, Electrical => Topic started by: victortrry on 19.10. 2014 04:40
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I went for a ride today but the bike stopped. It appears that the AAunit has turned on the magneto shaft. Can anyone suggest a fix for this.
Victor
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Hi Victor
I think some of our maggie experts will have come across this and likely give a more definitive answer than I can, but the first thing I thought was "why".
so maybe you need to look at the maggie, it's not a huge drag so either something jammed it or the AA unit was not tightened up fully.
For a fix I'd employ my years as a farm bodger par excellence and as it's on a taper that is perhaps not as taper mated as it should be I'd take the maggie of the bike and use some fine grinding paste to mate the two tapers up, also look at the nut and internal threads of the AA unit.
(now bodgers asbestos suit on)
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I would try Bill's bodge AFTER you wiped both tapers with carby clean and check the threads, then try again.
Cheers
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Hi Victor,
Have you removed the timing cover?
Is the fibre gear on the auto advance stripped?
Richard
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I am going to pull it apart on Tuesday. The fibre gear can't be stripped because it still has a spark but in the wrong place.
Victor
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The fibre gear can't be stripped
That's a new one on me!
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I pulled the timing cover off and found that the nut that tightens the AAunit was loose. Only last week I had done the timing and installed the unit. I had it in gear and the footbrake on to tighten it. The fibre gear is not stripped. Why did it come loose?
Victor
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as you probably know that nut is also the device that pulls the gear off the taper, on my (new) AA/unit the nut does occasionally seem to not not want to go on properly, the unit needs to be onto the taper firmly before you tighten it up, some even advise giving the unit a tap onto the taper before tightening the nut.
Quite possible that's all that has occurred.
One further thought - did you have the horseshoe washer under the nut - little devil can escape sometimes.
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The correct procedure for tightening the ATD is a) make sure the tapers are clean and undamaged. b) with the ATD removed completely, fit the wedges to hold the mechanism open, make sure the nut is pushed all the way into the ATD trapping the dished washer and horseshoe washer c) Offer the ATD to the mag spindle gently, left hand on the mechanism, right hand keeping the nut pushed against the horseshoe washer until you feel the nut touch the mag spindle threads d) gently turn the nut clockwise onto the threads whilst pulling the ATD away from the engine to maintain pressure between the nut and horseshoe washer e) run the nut up finger tight then back it off about 1/2 a turn and pull the mechanism off the taper to enable free rotation whilst timing the engine. If you push the ATD onto the taper with the nut very loose you run the risk of the left hand extractor threads biting (as mentioned before) before the right hand threads of the nut engage on the mag shaft. The only other explanation I can think of is the nut bottoming on the mag shaft before the taper is tight. The mag shaft thread is 3/8 BSF so if you get a 3/8 bolt or bottoming tap you can run it into the ATD and compare with the length of the mag shaft, or even try the ATD on a spare magneto I you have one. Having repaired lots of mags and ATD's it is very unusual to come across an ATD that doesn't stay on if it's tightened up properly.
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*????* I got a question about the horseshoe washer...
I noticed on mine that the washer is DISH shaped
(possibly from being pulled inward by the ATD bolt)
is this correct? or should it be flat?
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When they are made they are flat but they get dish shaped because the back of the head of the nut gets bowed because of the gap in the washer. It will probably be OK.
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*smile* Thanx..
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I followed the instructions and installed the AA unit so this is hopefully the last time this happens and I can ride with confidence.
Victor