Magneto dead?

[JimF]

My 250 "AC" bike was notorious for having what I would call a "hot" spark. One kick starting or a helluva backfire everytime.

Yesterday it rained on the bike in the parking lot all day. When I went to leave it took a 6 or 8 kicks to get started, but it started and ran fine in the rain all the way home.

This morning I went to start the bike and it was dead. Pulled the plug, smelled gas, grounded the plug, closed the garage door to make it dark and no spark was present.

Tonight I went to diagnose the problem.

1) Points are working; measured them with an ohmmeter opening and closing (switching from 0 ohms to infinite ohms when the engine rotates.)
2) Coil is working; I tapped a 6VDC battery charger onto the primary winding terminal and the spark plug snaps with every touch of the charger.
3) Spark plug is working as evidenced above, as well as the integrity of the HV lead is confirmed.

This seems to tell me that I am getting no AC voltage from the magneto windings when I kick it over, right?

I measured the winding I am using for the ignition and it has low resistance which is what I would expect.

I put a DVM on AC volts and kicked it over and the meter registers something - not a lot, but then I am only getting a quck single rotation.

What can I do to test the magneto windings?

I can't imagine how the magneto went from working to non-working overnight.

Jim

[DewCatTea-Bob]

" My 250 "AC" bike was notorious for having what I would call a "hot" spark. One kick starting or a helluva backfire everytime. "
I measured the winding I am using for the ignition and it has low resistance which is what I would expect.
What can I do to test the magneto windings? "

____ The alt.power-coil for the ignition has a slightly greater resistance-reading than that of the power-coil meant for the lighting-system - (about .7 vs. .4 [+/-.1-ohm] ), so you ought to check the EXACT resistance (below 1-ohm) of your two stator-windings.
__ A ""hot" spark" could possibly be from powering the ignition with the alt.power-coil that's intended for the lighting-system... I've seen a number of such lighting-coils which had become burnt-up (from a nice copper-color to a very dark-brown!). _ No-doubt those coil-windings had gotten that way due to the fact that the (higher) produced current was mostly SHORTED through the ign.points, after the owners had used the wrong alt.power-coil wire-lead for running the ignition (which I happen to know is not an uncommon mistake !).
Of all such burnt power-coils I've seen, about 1/3rd had remained installed on running engines, so it takes a lot of punishment before the light insulation-coating on the stator-winding fails and then begins allowing the winding-turns to short/leak between one-another, which of-course thus begins weakening that stator-coil.


" I can't imagine how the magneto went from working to non-working overnight. "

____ Perhaps the heated winding-turns cooled-down enough to allow their insulation-coating to fail more critically.

____ Anyhow, our story leads one to suspect that rain may have something to do with your problem, perhaps allowing some alt.current to bleed-off at one of your wiring-connections.
However otherwise (without the rain story), it could just be coincidental that your alt.rotor might've broke-loose from the crankshaft, (which is still a possibility that's in-line with all the outcomes of the trouble-shooting you've done thus far.
__ I'll later list any other possibility I may think of for this circumstance.


Hopeful-Cheers,
-Bob

[JimF]

The bike is nice and dry now Bob. I guess the 'alt.rotor' could have come loose... Although the prospect is dissapoiinting. That's kind of why I wanted to be absolutely sure the problem is in the 'alt.rotor' before I undertake the task of going in again.

Thanks for pondering this...

Let me know if you think of more for me to try.

[graeme]

If the rotor was loose wouldn't it be heard or felt?
I have heard a loose rotor/flywheel on a 450 and it sounds like big end failure.
Are 250's not the same?
Graeme

[wcorey]

condenser?


Bill

[DewCatTea-Bob]

By: graeme...
" If the rotor was loose wouldn't it be heard or felt? "

____ Well, before a alt.flywheel/rotor becomes loose enough to freely spin and thus be audible, (which is possible on a engine-model that's sparked by a battery), the rotor will very likely first begin slipping just a bit, and that slip (or a number of slips) could be enough to cause the alt.power-coil to produce it's output at a time when the points can't make any use of it, (and so then the rotor can never get a chance to become loose enough to notice on it's own), with an AC-powered type engine.


Dukaddy-DUKEs,
-Bob

PS. Note that I've now edited & added to my previous-post.

[DewCatTea-Bob]

By: wcorey...
"condenser? "

____ Of-course a shorted-out condenser could cause the ign.spark to not become produced, but aside from such rare occurrence, Jim had measured some amount of produced power, which couldn't be measured in his VM.read-out if still connected with an internally-shorted condenser.


Dukaddy-DUKEs,
-Bob

[JimF]

More tests reveal - the condensor is not shorted (ohmic measurement) and I tried kicking it over with the condensor out of the circuit and there was no change in the syptoms which redundantly excuses the condensor from fault. The condensor was a valid guess, worth a try and worthy of elimination.

My three coil wires read as follows:

Wire "A" reads 0.2 ohms to ground. It shows no connection to wires "B" and "C."

Wires "B" and "C" read as 1 ohm between them, and no connection to ground.

I am using the B to C coil for the ignition as I have to use one side of the coil to 'power' the igntion coil and the other winding grounds either through the closed brake switch or through the brake light filament if the brake switch is open.

I believe I must be using the correct winding for the ignition as I cannot use the winding which is grounded internally as that would preclude me from implementing the brake light circuit using the coil's current to power the bulb.

That I still read a resistance value through the ignition coil windings bodes well that the coil has not opened up internally.

That I am seemingly getting no voltage out of the coil would indicate that the alterantor flywheel has indeed slipped or is loose. Correct?

Jim

[DewCatTea-Bob]

" Wire "A" reads 0.2 ohms to ground. It shows no connection to wires "B" and "C." "

____ Your alt.wire-lead "A" must be the (original-red) one intended for the lights ! _ However your reading of only .2 seems to be (at least .05-ohms) rather low.


" Wires "B" and "C" read as 1 ohm between them, and no connection to ground. "

____ These two must be the (original white & yellow) wire-leads meant for the brake-light & ignition. _ However your reading seems (at least .1-ohm) rather high.


" I am using the B to C coil for the ignition as I have to use one side of the coil to 'power' the igntion coil and the other winding grounds either through the closed brake switch or through the brake light filament if the brake switch is open. "

____ This is (of course) how it was originally meant to be.
And-so I've assumed that you're already well aware that a broken brake-light circuit could cause similar issues, and therefore must've already checked & eliminated that possibility. _ Right ?
Of course besides the (originally expected) busted light-filament, any related loose wiring circuit-connection (associated with the brake-light circuit) could possibly lead to cutting-off of the ign.spark.


" I believe I must be using the correct winding for the ignition as I cannot use the winding which is grounded internally as that would preclude me from implementing the brake light circuit using the coil's current to power the bulb. "

____ Right, you're certainly employing the correct alt.power-coil for the ignition (& brake-light) circuit.
However when you stated: "the brake light circuit using the coil's current to power the bulb",, it's unclear as to what you actually mean by "the coil's current" ... If you had meant the current which is run-through the 'ign.coil' , THEN your statement is not-quite ultimately-true,, cuz the current which actually fully powers-up the brake-light bulb-filament, is the (MAIN)- current which the ign.points shorts to ground, (and THAT current of-course never passes-through the ign.coil !) .
__ And BTW, I had been wondering how you finally decided to accept your brake-light system to be...
Have you since found your (stock type) brake-light setup to be acceptable ? _ And did you also retain the emergency toggle-switch setup ?


" That I still read a resistance value through the ignition coil windings bodes well that the coil has not opened up internally. "

____ Your chosen wording leaves it possibly unclear as to whether you're referring to the ign.coil or the alt.power-coil meant for powering the ignition. ...
I'll assume you're in reference to the later.
__ Correct, your 1-ohm reading indicates that circuit is good,, and otherwise, an open/broken circuit would've given you an 'infinite' reading instead.


" That I am seemingly getting no voltage out of the coil would indicate that the alterantor flywheel has indeed slipped or is loose. Correct? "

____ Well not exactly, (unless the flywheel-rotor is COMPLETEY loose!), cuz no matter how the alt.flywheel-rotor becomes re-'timed', it will still produce the very same amount of power ! _ But if it has really slipped, then it very likely will not offer the needed power WHEN required (for producing the ign.spark, at the TIME when the points open).
Besides, I thought you had claimed that it is still putting-out SOME measurable power !?
__ You could help confirm a slipped-rotor by trying substituting (for a short time) the other alt.wire-lead ("A") circuit (meant to power the lights), by connecting it to the ign.coil in place of the original alt.power-coil wire-lead circuit which you've BEEN using. _ And if you THEN get ign.spark, then your alt.rotor must still be properly timed and thus not the source of your no-ign.spark issue, (in which case we may then concentrate on other possible sources).


Hopeful-Cheers,
DCT-Bob

[JimF]

Well, I carefully checked everything again and it comes down to no AC power being generated by either coil.

I spin the motor with the kicker and the best AC voltmeter I have reads zero volts on both coils.

Next step is take the left side engine cover off and take a look.