Motoscrubs.com

Good afternoon again-

The 1966 Scrambler does not start. Last fall, it started "every once in a while" but was not dependable.

I did order points and condenser, and installed them, but... it made no difference. Then, it got cold. The primary coil wire was "loose" in the coil, as I did not have that knurled nut holding it in. I had been relying on friction. Over the winter, I located a 6 volt ducati coil with coil wire on ebay, and I bought it.

As spring has arrived, I have started in working on the bikes. The scrambler seems to have "no spark" at the sparkplug. I took the tank off, to replace the knurled nut on this coil... and it is a different size. Rats. I measured the resistance on the coils.

The "original coil" with green label, has 4 ohms resistance between 1 and 15. Between 1 and the primary, I have 9-ish K ohms. Seems right.

https://lh3.googleusercontent.com/-bOeJ ... G_5003.JPG

The ebay coil has 2 ohms resistance between 1 and 25. 4K ohms between 1 and primary.


I reinspected the points and condenser. Seems correct.


I inspected the 3 wires coming from the alternator. There appeared to be greenish-ness at the connector on the frame, so I thought I would remove and clean that, and ... the wire insulation is brittle, crumbly, bleahh... I have definitely made matters worse there. I sort of wish I had left that alone... then again, maybe that was why it wasn't starting...

I MIGHT be able to cut back, and solder and extend new short wires with shrinktube over the solder, but... the insulation further back, within the black outer casing must be crumbly as well. I suppose I might have to pull the side cover, and re-wire the entire alternator.

yellow appears to be connected to 2 black wires, 1 going to stoplight switch, other going to stop light? I think?

Red appears to be connected to a dark blue wire that disappears into the harness, going forward.. .to headlight assembly?

white appears to be connected to a green wire, which I believe goes to the ignition coil. terminal 15.

https://lh3.googleusercontent.com/-H0OJ ... G_5012.JPG

And so, I tested what I could.

With all three alternator wires disconnected...

- between white and ground , is infinite resistance

- between red and ground, appears to be zero resistance (well... perhaps .5 ohms?)

- between yellow and ground, is infinite resistance



- between white and red is infinite

- between red and yellow is infinite

- between white and yellow is 1.1 ohms



And my question... are these numbers okay? Does anything here indicate why I don't have any spark at the sparkplug?

Sincerely,

Bob Woolner
Hillsboro, New Hampshire USA

The insulation on some Euro stuff seems sometimes to just perish in time.
I recently replaced a nice looking Swiss induction motor for a friend, as the plastic covering the wires was just crumbling away. Some colours seem worse than others.
I recently replaced the alternator cable on my '74 single with 3 phase industrial cable. Some might frown at that on the grounds of inappropriate application. But, it would have to be pretty bad to be worse than the original cable I think.
To replace the cable, you have to remove the stator, which is not a horrendous job, but does entail removing left engine cover, clutch, flywheel.
You might not have a choice, if it needs to be done. Simple soldering job.

The original Ducati coil is not a good choice. They have a poor reputation. An alternative is a coil from a Norton Commando, which is a much better Lucas (!) 6 volt type, and is the same size as the Ducati coil, so wlll fit your bracket clamp perfectly. I tried a VW 6V coil for more oomph when I had points, and it worked great - but is bigger.

Is this your wiring? http://www.culayer.com/images/magneto.pdf

I can't really speak to your wiring colors, but when you get two wires that connect to opposite ends of the same coil there will be a very low resistance if the coil is good.

The colors may be original, maybe not, and I would think it depends on if you have the '40-watt' or '60-watt' coils. It's been so long for me that I don't recall. Dew-Cat-Tea Bob left us a mountain of information before his passing on the electrical system, you could try searching for answers through his old posts.

The thing I would recommend is to change out those crumbly wires. I had the same thing on one of my bikes. No matter how far back I split the sheath the wire insulation underneath was dried out and would crumble to dust the second I pulled the sheath away. I could not find anywhere to splice in new wires to old ones.

It takes a flywheel puller to get the wire replacement job done as you will likely be replacing the wires all the way back to the coils. But the good thing is that you will see what kind of alternator you have and you can measure the coil's resistance easily while they are staring you in the face. Presuming they are all good which is highly likely, you can then route new wires back out keeping track of your new wire colors.

Jim

Hi Bob,

as being a narrow frame Scrambler model, and according to the workshop manual http://motoscrubs.com/Ducati_Manuals/4-5-speed-shop.pdf p. 35 ff, your bike ought to have a magneto ignition, and a 40W flywheel alternator, but a wire loom with 2 different electrical schematics (dependant on the engine no., till/from 92171). Anyway, a HT coil for a battery ignition (DUCATI red labeled, LUCAS/Norton etc.) will not do the job reliably !
Other models like the Mach1 or wide case bikes were equipped with a 60 or 90W W alternator, and battery ignition.
Best advice is, to replace the alternator cable with a common 3phase household type in oil resistant quality, as descibed by Jim. Avoid the PVC insulated grade, but use the soft, black rubber insulated version.
To identify the alternator type hidden inside, you should disconnect all 3 wires and then measure if any of these has a connection to ground, or the engine casing, respectively. In case of a 40W alternator, 2 wires must not have a ground connection, only that one used for the ignition power, in particular. The 60W alternator shows continuity to ground for all wires.


rgds Hans

From your measurements it sounds like you have the 'flywheel magneto' ignition. Under the flywheel there are two coils. The lighting coil has one end going to the red wire. The other end goes to ground. The ignition coil has ends going to the yellow and white wires. The yellow wire goes to the ignition coil and points. The white wire goes to the stop light. There is a switch on top of the bike tail light to be used if the stop light burns out. The white can just be grounded if you don't want to bother with the stop light. It looks like you will be pulling the flywheel to replace the wire harness anyway!
Dave

ducwiz wrote: Anyway, a HT coil for a battery ignition (DUCATI red labeled, LUCAS/Norton etc.) will not do the job reliably !
Other models like the Mach1 or wide case bikes were equipped with a 60 or 90W W alternator, and battery ignition.

Hans is correct about the required HT coil being different from a battery-ignition type.
I don't know what I was thinking.

Good morning all-

Thanks for the suggestions, and advice. I have looked over the pdf wiring diagram suggested by duc_whiz, and yes, that appears to be what I have. And Dave also have answered another question I had about the red wire (to lighting), and the yellow and white wires. Do I read the diagram correctly? The red wire is from a single coil, the other end grounding inside the alternator. The yellow and white are opposite ends of the other coil's winding. If so... does it really matter which goes to ignition coil, and which to brake light? I have also found a previous thread on this forum, with great information from DewCatTea-Bob... that implies it DOES matter which goes to ignition coil.

Another question, also brought about by my reading of DewCatTea-Bob's post - I have 2 ignition coils - either of which could be used. The "original" or so I think, measures 4 ohms across 1 and 15. That original has a green label, which according to that DewCatTea-Bob posting, is the correct one, BUT the resistance is too high across 1 and 15, at 4 ohms. I have another coil, purchased from ebay, without a label, BUT the resistance is only 2-ish ohms, which according to that forum posting, would be a better choice.

Does the white or yellow matter?

Which Coil to use?

As to the wiring itself... I think I am going to try soldering on some short extensions, and shrink-tubing the rotten insulation, to at least TRY this, before pulling the side casing, flywheel etc. to replace the wiring.

Thanks,

Bob W
Hillsboro, NH

Bob,

The 'flywheel magneto' models use the green marked coil and the battery models use the coil marked red. I'm not sure of the resistances. I think it would matter if you reverse the yellow and white connections. Sometimes they appear the same color because of fading. If you strip back the black sheathing on the cable you should be able to tell the difference. I would just ground the white wire, then see if you can achieve spark. I have found that a Honda C100 AC coil works better. My Mark 3 flooded easily when kick starting it. When I switched to the Honda coil, this eliminated that problem. If you do pull the flywheel, make sure you use the correct cone shaped tool, and orient it properly when replaced. The flywheel phase has to be correct in order to maximize the coil energy.
Dave