250 Mk3 project - NC wiring harness

[Dave_the_Rave]

Firstly, hello I'm Dave and the project I am embarking upon is my own 250 mk3 bike.

Here's some pics

So thats my brass flywheel and what I am guessing is a spanish electric start.I would like to convert to kick start, so I believe I require a 6v wiring harness. I have 6 magnets in my flywheel, I have only encountered 4 magnet flywheels before.

I'll need a stator plate and coil and then the beginning of the wiring harness. Having looked around on the market for a wiring harness I have only found WC options, I have been advised that I might have to make my own, so here I am throwing myself at your mercy, I'm prepared to do the legwork and do the learning. What should my first move be please.

Thanks DtR.

[Jon Pegler]

Your stator plate is from a widecase machine, probably a 350 Road or Mark 3.
The visible coil that is not encapsulated in resin is the designated coil for a Motoplat electronic ignition system, not for an electric start.
The Mototrans Forzas with electric starters used a slightly different Motoplat stator and rotor..
You could use the stator you have to convert to 12 volts, but only on a widecase bike.
If you have a narrowcase machine you need a stator plate with three mounting screws rather than the four that you have presently.

Jon

[Bevel bob]

The Mark3 was made in Narrowcase and widecase not much is interchangeable so you need to be clear what you have. Some suppliers dont seem to be aware of this and send out widecase stuff if you say Mark3. As the mark3NC was so close in spec to a Mach1 I say thats what I have!!.

[Dave_the_Rave]

Ok, thanks, lesson learned.

I'm in the UK, and I am pursuing this project with the intent of completing the bike to mach1 standard (narrow case).
Following the thread so far, let me double check, I can use the 6 magnet flywheel I have if I get a 3-pole stator plate to run my bike at 6v ?

If this is the case, am I scratching around for an old spare parts version or am I best off acquiring new? (wheres best to start looking in either case?)

Thanks DtR.

[Bevel bob]

I think you will need the complete alternator ,i think you will find that they were common to other Singles, the 60 watt would be best,(some are 40 watt). You could spend lots on a new system of course. I have gone for a simple upgrade to 12v by un-earthing the coils and linking them (dead easy) and fitting a new rec/reg under the seat. I have retained the points and adv unit but fitted a Pazon/Boyer (cheap) ignition assist unit under the front of the tank this allows easy timing ,gives points an easy life and is simple. My bike was pictured in the middle of the pack at the Jurby meeting in the recent "the bike show" programme which covered the classicTT. Don't blink !!.I have a red crash hat.

[Dave_the_Rave]

Please pardon my ignorance, did you make a thread re your 12v conversion? I agree it sounds quite easy but elecs are not a strongpoint so sadly I am shamedly asking to be babied through the process.

Thanks DtR.

[Bevel bob]

If I remember correctly, the wiring on the bike was pretty standard ,the rectifier was already fitted I just changed the bulbs ,coil and hooter for 12v items and linked the alt earth wires in the stator . the electronic points box came with its own simple instructions.If it was complicated I would have been F--------ked!.

[Jordan]

If you are game to experiment, here's a low cost possible conversion to 12V for Ducati singles:

Ebay item 262620667563 buys you a combined rectifier/regulator for 2 wire alternator. Stated rating of 20 amps, looks like it can handle the Ducati electrical power.

Ducatis with battery ignition have 3 wires, 2 yellow and a red, coming from the alternator. That's 3 wires, but by just not using the red one (insulate the end), you alternator will function as a 2 wire. Connect these to the 2 terminals marked AC on the rec/reg. The B+ terminal goes to the battery. The earth is by bolting the unit to the bike's frame. Battery is also earthed, of course, and all loads can be connected to the battery's (+) terminal, via fuse(s).

Ducatis with CDI have more wires, but the same can be done with the 2 yellows and insulating the red.

This is not suitable for batteryless "magneto" style ignitions.

No guarantees, but I'm doing something similar with my widecase - OK so far, touch wood.

[ducwiz]

Ducatis with battery ignition have 3 wires, 2 yellow and a red, coming from the alternator. That's 3 wires, but by just not using the red one (insulate the end), you alternator will function as a 2 wire. Connect these to the 2 terminals marked AC on the rec/reg. The B+ terminal goes to the battery. The earth is by bolting the unit to the bike's frame. Battery is also earthed, of course, and all loads can be connected to the battery's (+) terminal, via fuse(s).

That's correct, Jordan,

but for the wide case alternators only, either Motoplat or Ducati. The 60W Mach1 stator has only 2 wires, because the center connection (which is the red wire on the w/c models) is permanently grounded by soldering at a terminal on the stator plate, near the inner bore. So, this one cannot be easily converted into 12 Volt system. You have to desolder an insulate this connection. Read an excerpt from the workshop manual for reference: http://renato2.bplaced.net/DUCATI/electrical_system-NC.pdf

Dave,

From my point of view, you must not mix Motoplat and Ducati alternator parts, as the permanent magnets in the rotor have to match the iron yokes in the stator with respect to their dimensions, as well as the radial air gap between rotor and stator.

The stator on your fotos shows badly damadged wires. As the windings are potted, a repair work seems to be expensive, or even impossible, as access to the electrical connections inside was not foreseen. Hence, you better go in search for an original 60W 4 pole alternator, or purchase a new 12 V alternator set, like this http://www.electrexworld.co.uk/acatalog/STK-160.html or this http://www.powerdynamo.biz/eng/systems/7247/72474main.htm.

cheers Hans

[Jordan]

Good point Hans, about my 12V conversion description only being for widecase singles.
I tend to forget about narrowcases, because I've never owned one, silly me.
To convert the n/c, it's a little more work to remove the rotor and disconnect and insulate the wires from the ground point, whilst keeping the wires connected to each other.

I don't agree there is any harm in mixing a Motoplat and Ducati rotor and stator. I had a hybrid like that for years, and although the M'plat CDI charging coil within the stator did eventually fail, I don't blame the Ducati rotor for it. Indeed, I just checked a rotor of each make, and they are dimensionally virtually identical, with both providing half a millimeter radial clearance, with 94mm ID. Also, the stator pole pieces' OD is 93mm in both cases. The pole pieces in the rotor have the same length and gap between them, and an insignificant difference in width.
Even if there were substantial differences, as long as the number of poles is the same, and radial clearance close to the same, and magnet strength similar, the result might be a different shape of voltage waveform (as viewed on an oscilloscope), but I cannot see that would necessarily matter anyway? It only has to make electricity to charge a battery. Even a "dirty" waveform would satisfy that demand. Of course, if the dimensions were grossly different so that not enough current were generated...

The practice of potting or encapsulating stators and other circuits may improve reliability (or maybe not), but they certainly make it much more difficult and sometimes impractical to repair. I've abandoned Motoplat stators for this reason. I do however prefer their pickup sensors as they look more solidly made than Ducati's - they are both potted anyway.