My monitor is showing the stator potting as black? If so, that's a pattern stator.Any theories
Bear in mind, assuming standard stator, output is only a maximum of 11-12 Amps even if the engine's being revved like a small 2-stroke.What is charging system? Stock rectifier & Zener or something else? Has wiring harness been obviously modified.
Can you see where wires shorted to ground or is it just inside stator. The chassis wiring needs to be checked for shorts to ground if cause is not obvious. The charging system is not fused.
'70 Daytona according to Jerry's Forum Profile?What year is bike & motor?
Which coil terminal (as in "-" or "+")?clutch cable
rubbed through the plastic coating and shorted on the coil terminal.
Very unlikely; the rectifier separates AC (alternator) and DC (including ignition); that'd have to be faulty as well for there to any chance of a DC component affecting an AC one.would the dead short be a reason for the demise of the stator?
Risking telling you something you know already, @oldgoldie means check the outer part of the rotor hasn't come loose from the centre - the central hex. can be tight on the crankshaft but the metal around it - that holds the magnets in place - can come loose from the central hex. The way to check is, with the centre secured to the crankshaft, grab the outside of the rotor with both hands or a strap wrench and attempt to turn it, If you detect any movement between rotor outer and centre, 'fraid it's toast.rotor is tight
Uh-uh, 'fraid that wasn't the fault (unless the bike's electrics are 'negative ground' and/or your bike is otherwise peculiarly-wired?) ...The cable shorted to the positive making a solid ground at times as the ammeter would go to a full negative,
Mmmm ... I've got Ammeters on my T100 and my T150 ... T150 'cos I was aiming for 'conkers', T100 because it's '69 and originally standard ... as diagnostic tools, both are about as much use as a chocolate fireguard ...the ammeter would go to a full negative, otherwise during its demise it would swing wildly. and intermittently show a charge as it shorted or not .
'Fraid there is simply and absolutely no possibility whatsoever that Brian's explanation is correct.A likely cause of the fried stator winding is the intermittent short circuiting that Jerry describes. Even though the maximum current is only 10 or 12 amps, that's into a load at a nominal 12V, but the alternator is trying to drive current through the rectifier into a near short circuit and so the current may therefore be well in excess of 10 amps.
As there cannot be a "higher current", similarly this cannot be the explanation for any higher temperature.The higher current could raise the temperature of the windings beyond their designed range to the point where the enamel insulation fails (normally 150-170 degrees C, unless Lucas used really high spec wire!) Once the insulation fails in a small area of a coil you can get a "shorted turn" which will then self-heat the insulation of more and more turns until destruction of the whole coil occurs.
The only vaguely-useful thing in Brian's post ...check the rectifier
Stuart, I made no mention of wires breaking. Look at your picture. What do you think is the brown colour on all the wire turns of each coil that you can see? It is enamel INSULATION, and that stops one layer of wires shorting out to the next. Failure of this enamel due to excess temperature causes shorted turns, and this can cause devices with windings like transformers, motors, alternators to "burn out".Nor is there any such thing as a ""shorted turn", Brian has invented this term from his basically-flawed explanation.
This is an older Lucas stator:-
... however, it's exactly what your bike's looks like inside the potting and is basically what any stator looks like inside. Do you see any insulation on the coil wires? So how can there be any sort of "short" if a coil wire breaks?
This is wrong again:-stator it connected to the frame/ground, instead of "floating", this will cause large currents to flow through part of the bridge rectifier to ground/battery positive on each positive half cycle, which does not go through the fuse.