Author Topic: Auto Advance mechanism  (Read 1244 times)

Offline huddie

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Auto Advance mechanism
« on: 27.05. 2010 12:41 »
Hi All, Got the mag out at the moment as I have a "will not start when hot" problem.  Couple of questions, First did I see a topic detailing a mag stripdown and test?. If there is ( I can't find it) I would be very interested in reading it. Second question looking at the AAR mechanism, how does one seperate the drive cog from the rest of it?. Mine is not a fibre one and I was just thinking I might change it for a fiber one. I can remove the "C" shaped washer from behind the nut and the flat washer(looks like it sits on two pins) then comes off over the nut, but I can't see how to seperate the rest.
Regards for now Huddie

Online groily

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Re: Auto Advance mechanism
« Reply #1 on: 27.05. 2010 14:32 »
Huddie, if the ATD's a good one except it's on a pinion made of steel or alloy, why take it apart if it looks OK? If the springs pull it back firmly, if the thing's all in one bit and moves nicely, why wouldn't it be usable?

If you do want to get it apart, then you have to get the steel press-on collar off the opposite side from where the weights etc are, withdraw the working bits, then - unless it's been bolted or screwed up (which it could be if it's into metal), unrivet the pinion from the backplate. A fibre one would have to be riveted in.

On the mag strip, there are quite a few places on the web which will show you an exploded K2F mag. They are not hard to strip down until you get to the bearings, as long as you take out the 2 safety gap screws - one each side just below the HT pick-ups. (You have to do that to allow the armature to come out of the body without damaging the slip ring).  The bearings can be a b*****d unless you have a tool to get the inner races off the armature. Hammers are bad here, chisels a no-no. You can use a piece of stout copper wire in the inner race's groove on the drive end, squeeze it in the vice and tap the armature out - sometimes. You can also crack the race in 2 that way. The contact breaker end is particularly delicate as the female taper for the cb backplate doesn't want messing up and IMHO only a proper puller will do. Which is a swine, as that race has to come off to complete the mag strip whereas the drive end one doesn't. And the alloy housings needs treating very gently too when getting the outer races out if they have to be extracted. If you do all that, then you'll need a selection of shims for end-float and some new insulator washers for refitting the bearings to set them firmly. The bearings are angular contact ones and need to be set right. Plus other bits and bobs, like new brushes probably.

If you're not sparking hot and the basics are OK - points gap, slip ring, pick-ups, HT leads etc - it'll almost certainly either be the HT windings breaking down or the condenser has failed. In either case, the best bet is an exchange unit usually, unless you've got bearing pullers and other odds and sods to strip the armature. Condensers can be got, and so can rewound bobbins for self-assembly, but if the thing is old anyway, it's worth going for an exchange or getting your original redone. Looking at around 110 GBP at the moment for that. If you need bearings, shims and other odds and ends, the bill mounts quite fast. I have yet to sort one for much under 200 GBP by the time  I've replaced all the 'I might as well' bits.

As to your Q about testing a mag - now you're really asking. This is hard. The easy test is to turn the darn thing and see if there are sparks! But that doesn't help you, as there aren't . . .
Searching 'Lucas Service Sheets' will get you a long way - but the testing process outlined in them is way beyond most of us. Because a mag is an ac generator using induction to get the HT voltage (and is not a dc device), normal Ohm's Law stuff doesn't apply as we're talking impedance rather than simple resistance. There are no clear static resistance tests for HT windings, although if it's any use a good armature on my bench shows 7500 Ohms from end to end of the HT coil (or from brass strip on slip ring to mag body). LT coil resistance should be very very low - they're made of quite fat wire. I don't know what's right or wrong for HT coils, except that millions of ohms is bad, and so's nil!  Lucas did not give a resistance reading for the HT winding that I can find - if anyone has a fast and good number, I'd love to know what it is. But they do say that the LT current shouldn't exceed 1.2 Amps running on a test rig far too complex for me to have attempted to make one. In a nutshell, and for what it' worth,

    *Resistors impede current. The higher the resistance, the higher the impedance.
    *Inductors impede a change in current. The higher the inductance, the higher the impedance.
    *Capacitors impede a change in voltage. The higher the capacitance, the higher the impedance.

Put another way:
      *For a resistor, voltage (Volts) is proportional to current (Amps) ? and therefore current (Amps) is proportional  to voltage (Volts)
       *For an inductor, voltage (Volts) is proportional to the rate of change of current with respect to time (Amps per second).
        *For a capacitor, current (Amps) is proportional to the rate of change of voltage with respect to time (Volts per second).

It's a bad case of calculus, all this stuff, and it's not my thing really, but anyway:

Resistor: Voltage and current proportional.

Inductor: Voltage proportional to time-differential of current, or current proportional to time-integral of voltage.

Capacitor: Current proportional to time-differential of voltage, or voltage proportional to time-integral of current.

I doubt the last bit has helped (didn't help me much either) - except to say that the reasons people like SRM and others have the equipment they do, like Magmasters, are good ones!

On a simpler note, the body of the mag should be good and magnetic. I can't measure magnetism and no-one's ever given me a 'Gauss-ometer' or whatever would be needed. But there should be loads of pull as you try to pass a ferrous object though the body from end to end. Weak magnetism could be a cause or partial cause of your problem, obviously - but that again can be taken care of by a rebuilder. Dave Lindlsey remagnetises for a few pounds, and I imagine others do too. Or you can go to the web again and look at the options for making home-made remagnetising systems - and stand well back when you apply gawd knows how much electrickery through a pile of mighty capacitors!

Whatever, good luck!

Offline LJ.

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Re: Auto Advance mechanism
« Reply #2 on: 27.05. 2010 15:13 »
... and I hereby nominate Groily for this years Golden Spanner award!   *respect*
Ride Safely Lads! LJ.
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Offline huddie

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Re: Auto Advance mechanism
« Reply #3 on: 28.05. 2010 21:11 »
Hi groily, many thanks for taking the time to go into such detail.As for the aar device it was just being nosey really. I didn't know how to do it having looked at it so I thought I'd ask. I guess the bottom line on the mag rebuild is "know your limits" and I guess I will have to seek professionsl advice.
kind regards for now Huddie.

Offline MikeN

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Re: Auto Advance mechanism
« Reply #4 on: 28.05. 2010 21:29 »
When a friend of a friend re-magnetised my bare mag body he asked me to supply it to him with a "G" clamp. It was returned with the clamp clamped across the body to act as a keeper . So preserving the magnetism .The clamp allows you to work on the body, assemble and set up the bearing end float and not loose any magnetism.Which I thought was agood idea.