Testing Stator Coils

[DewCatTea-Bob]

[quote= tobydmv ...
" The light coil seems extremely weak in output.
I put a small CEV test lamp on the light coil output wire and it barely made the element glow at idle speed. "

____ That issue is somewhat common at idle,, but above 2500-RPM, a std.25w.bulb should then become adequately lit-up !
Perhaps you may have the two circuits of the lighting-coil improperly connected.



" Appears that the scrambler is equipped with the 28w unit. "

____ Indeed it ought-to be, as that's std.issue for a 1966-Scrambler !
__ And do you still have the three alt.stator wire-leads connected-up as if your electrical-system had the '40-watt' mag.version ? _ Cuz if-so, then you have the white wire-lead circuit of the lighting-coil short-circuited, which of-course would thus-then tend to significantly cut power to the headlight !
So if you haven't done so already, be sure to get that white-wire circuit ungrounded ! _ And try your test again, to confirm that the light then lights-up sooner & brighter.



" The bike idled perfectly for about 5 - 10 minutes and then died and wont restart.
So I had a look at the valve clearance/lash and the intake had no clearance between rocker and valve shim at TDC. The exhaust was around .0016". "

____ With the v.clearance set so extra-tight,, then once the cyl.head heated-up, those clearances had to have gone negative and-thus too much compression must've then leaked-out to allow the engine to continue running.



" The valves were really tight in the guides and when removed had some bronze dust on them. "

____ Did the head innards look like they've been kept well oiled ? _ Cuz I've seen such evidence in cyl.heads that were on engines of which had had broken oil-pumps.



" Looks like i'm headed for a head rebuild. "

____ Perhaps even more than just that, if the oil-pump has been out of commission for too long.
However I wouldn't be too concerned of that unlikely possibility,, cuz in such case, the valve-clearances would've then been rather LOOSE instead of tight !
__ Do you not have a spare complete cyl.head to substitute for the time being ?


Dukaddy-DUKEs,
-Bob

[tobydmv]

Perhaps you may have the two circuits of the lighting-coil improperly connected. " Appears that the scrambler is equipped with the 28w unit. "
____ Indeed it ought-to be, as that's std.issue for a 1966-Scrambler !
__ And do you still have the three alt.stator wire-leads connected-up as if your electrical-system had the '40-watt' mag.version ? _ Cuz if-so, then you have the white wire-lead circuit of the lighting-coil short-circuited, which of-course would thus-then tend to significantly cut power to the headlight !
So if you haven't done so already, be sure to get that white-wire circuit ungrounded ! _ And try your test again, to confirm that the light then lights-up sooner & brighter.

Bob, I will try that. But I remember when soldering the coil leads I noticed that the ignition stator coil had two leads coming from it. Yellow and white I believe. If I unground the white lead wont that break the ignition stator coils field? Well maybe I have that reversed in your favor. I will try it once the head is back together.

[DewCatTea-Bob]

[quote= tobydmv ...
" But I remember when soldering the coil leads I noticed that the ignition stator coil had two leads coming from it. Yellow and white I believe. "

____ That's only consistent with just the '40-watt' alt/mag.stator (which was replaced with the '28-watt' version for the '66/67-Scrambler-models) !
So unless someone has replaced the stock '28-watt' alt.mag with the older 40w.model, then your motor-number should still have the 28w.version !



" If I unground the white lead wont that break the ignition stator coils field? "

____ Your thinking in that regard would be quite correct IF your engine somehow happened to have the older 40w.version. _ But in the 28w.version, the power-coil intended for the ign.system is rather directly internally grounded (and-thus doesn't so-depend on any extra wire-lead [as is intended for the concocted brake-light circuit of the older 40w.system]) !
__ I've already previously covered this difference,, so since it seems you didn't understand, you should try reading my earlier post, and ask any questions about anything that's not completely clear to you.
____ It needs to be understood (hopefully by all) that even-though Ducati (stupidly !) gave both their 40w and their 28w 4-pole alt.mags the very-same three wire-colors, the two versions have fairly significant differences ! ...
While both models have two independent power-coils, (one for ignition & one for lighting), their three wire-leads are-not identically connected-up to those differing power-coils exactly the same way !
While the functions of the Yellow -(ignition) and the Red -(lighting) wire-leads remain the same on both model-versions, the main confusing difference is that the White wire-lead of each stator-model provides a completely DIFFERENT function ! _ As on the 40w.version, it's used to keep the ign.power-coil floating internally, so that it can then be rather grounded externally,, while on the 28w.version, it's white-wire is rather connected to the lighting-coil instead ! _ As that power-coil was (somewhat un-thoughtfully) chosen by Ducati to be tapped-into for a wee-bit of charging-power to keep the (near functionless) battery merely trickle-charged.
__ This matter has been an issue of consternating-confusion amongst many during the past decades, as there's been few knowledgeable sources who care (like myself) to help keep the differences all straight ! _ And since most other sources just entail only details concerning the older & more populous 40w.model, it's thusly no-wonder that most try wiring-up 28w.models as if same as the 40w.version.
__ It's too-bad that Ducati didn't have someone in charge of such things, who would've seen-to-it that more logical-sense was dispensed when designing the construction of such variations ! _ (If it had been up-to myself, I would've had the 28w.model's white-wire designated for the lighting-coil circuit, and the red-wire for the bat.charging-circuit,, and most distinctly, have rather had a green-wire for the ign.power-coil circuit [so as to help clearly distinguish the 28w.model from the 40w.version]!)
__ And while I'm currently spouting-off about such illogical Ducati-born inconsistencies,, I'll also point-out that the varied claimed wattage-ratings (of the two alt/mag.models), are comparatively misleading since the so-called '28-watt' version was evidently rated only by the power-consumption that it's intended load-system draws from just it's lighting-coil only, with no consideration of the additional power certainly drawn from the other power-coil (which of-course definitely powers the ign.system) !
Quite certainly, both alt/mag.models are each capable of over 56-watts total !


Dukaddy-DUKEs,
-Bob