Recharging 250 MK1/MK3 Magneto

[vintbikeparts]

I don't KNOW anything for sure. The bike has been built from several donor basket cases but is very much as original. I would like for the electrical to stay stock as possible but I'm ok with any non-visible budget minded upgrades. It has the correct headlight, handlebar switch, brake light and switch, doesn't have horn or battery.
The stator which had one lead shorted to ground ( assuming this due to bad solder/ empty hole in insulated bar that the other wires go through) reads approx 1 ohm on upper coil wires and no continuity to ground. 0.5 ohm on lower coil wire to ground. I have no idea why this was done, I didn't start with anything remotely resembling a complete bike , the engine was apart and virtually no wiring was present. The insulation had rotted off stator wires. The carrier plate is marked 120608.
The other stator, which I believe came from a 200cc engine doesn't look modified and measures about 1 to .5 ohms between wires on upper coil, depending on how long meter held in place. lower coli output wire about .5 ohm to either of other wires.
Neither coil goes to ground. carrier plate marked 600114.
Also I have one brass and one alloy bodied rotor, both with 4 magnets. the timing mark is in line with the leading edge of a magnet on one and the trailing edge on the other rotor.
I hope this helps with your diagnosis/ suggestions.
Jerry

[DewCatTea-Bob]

____ Well Jerry, this post of yours needs more coverage than I'm going to give it right now, as I now believe that other parts are of more important concern at this time. _ I hope to cover everything else later!


" The stator which had one lead shorted to ground ( assuming this due to bad solder/ empty hole in insulated bar that the other wires go through) reads approx 1 ohm on upper coil wires and no continuity to ground. 0.5 ohm on lower coil wire to ground. I have no idea why this was done, "

____ With your new/added info, I'm now thinking that your ASSUMED Mark-3 stator is possibly not actually the common 3 wire-lead Mark-3/SCR type of stator, with 1 of it's 2 ign.circuit wire-leads (assumed) removed - (thus leading to the conclusion that it has been modified!). ...
__ Is your 'Mark-3' actually a (rare!) 4-speed model? _ Because, (while I never owned one of those), I understand that THOSE models did not employ a brake-light, and thus BOTH alt.power-coils have just one wire-lead each, (with their [opposite pole] lead-ends both grounded to their stator [coil-cores] ).
So I'm thinking that that's what you may really have. _ (Since you don't really "KNOW" that it's a modified 3-wire stator.)
Unfortunately, I've never had a 4-speed Mark-3 stator in-hand to examine.


" The other stator, which I believe came from a 200cc engine doesn't look modified "

____ It seems that you have TWO stators that I've never held in-hand, (that's rare!)...
I know that the 200-models first had a 3 wire-lead stator (which I've never had the opportunity to examine),, (and later came with the common twin wire-lead stators, which I know to be the same as used on 4-speed Monza models).
Without being able to examine one of those old 200-stators, I can't well advise how BEST to make use of one of them.
If you're INTENT on restoring your Mark-3 to stock, then it's of no use for your project anyhow.


" Also I have one brass and one alloy bodied rotor, both with 4 magnets. the timing mark is in line with the leading edge of a magnet on one and the trailing edge on the other rotor. "

____ I've also had rotors with their marks in those positions!
You could use either but, I'm sure the alloy-rotor was from the Mark-3.
__ So do you have fairly-good reason to be sure that either one or the other of your two complete alternators, actually came along with your Mark-3 motor? ...
It could be helpful to know your source for all your various parts - (whether they're from the same source or not).


____ I'll soon post the added-info (as I had mentioned I'd do previously), to my first reply-posting to you here. _ So watch for that later this eve.


Tillater,
-Bob

[bettyann]

Vintbikeparts:

Give me the part# stamped on your brass roter, it's next to the word ducati, and I'll tel you what Duke/motor type it fits.Capt Paul

[vintbikeparts]

Brass rotor part # 31.20.34, Alloy rotor part# eg4421.4002. Thanks for the help.
Jerry

[DewCatTea-Bob]

By: 'vintbikeparts' ...
" Looking forward to more info. "

____ Jerry, did you ever notice that I had finally posted the additional info which I had promised to add to my post on page 4, (added to my first reply to your very-first post) ?
I just recently REedited it, so it's about as good as it could get on the subject !
Hope it all makes good sense for you, and if not, please ask for clarification of anything stated within.
__ Also hope you can answer some of the questions I had.


____ I don't recall ever seeing a Mark-3 which came stock with a brass-rotor, but I think some of the earlier ones did. _ However, I am aware that some dealer-mechanics suggested that owners with the later models (with the 29mm SSI), replace their alloy-rotor with a brass unit, to help keep them from stalling near idle.
The brass-rotors were used mainly for the Motocross/Scrambler models.


DUKE-Cheers,
-Bob

[vintbikeparts]

Bob,
Many thanks, I'll be working on it later this week.
Jerry

[bettyann]

Your brass flywheel # 31 20 34 is not a 5 speed part,could be 4 speed scr flywheel.
The alloy # 4421 4002 also isn't a mk1,sebring,nor monza 5 speed, Could be wide case but I don't have a wide case parts book.
The 40w brass flywheel(mk3 & scr) part # 31 20 94.5 speed. 28 w later scr only brass part # 31 20 95 5 speed.
I'm having a printer make copies of the factory 1964 thru 1968 narrow case parts book, and when I know the price, for reprinting,I'll let any one buy a copy. This book,578 pages, is the book all ducati dealers used to look up spare parts.
Models covered, monza GT sebring, mach1 mark 3 early scrambler & late scr, All narrow case motors 5 speed.
Capt Paul

[DewCatTea-Bob]

By: 'vintbikeparts' ...
" I'll be working on it later this week. "

____ How about telling us some details about your Mark-3 project?
Do you know which model of Mark-3 you have? _ What are the first 3 digits of it's motor-number? _ What carb do you have for it?
____ There were four versions/generations of the (non-DESMO) 250 Mark III / Mark-3 ...
__ The original Mk3 was the 'Diana Mark III' which was a sport/racer-version -(marketed towards road-racer want-to-be types), of the 1961-62 4-speed 'Diana 250' -(which was a sporty-version of the ' 250 Monza').
That Mk3's main differences from the Diana, was 27mmSSI DelLorto (in place of the 24mmUBF), with 28.5mm intake-port (in place of a 26.5mm port), plus a wilder cam with lighter rocker-arms (in place of the screw-adjuster type), and 10:1CR 3-ring piston (in place of 8:1 4-ring type), and a simple electrical-system (copied-over from the off-road 'Motocross' model), which had no battery or horn, nor even a brake-light set-up ! _ As it's standard (for the time) 4-pole alternator had just 2 wire-leads - one for the lights and one for the Green-label ign.coil AC-(actually PDC!)-type ignition-system. _ It also had considerably higher gearing with 43/18t sprockets (in place of 45/17t).
I myself never owned one of those original 4-speed Mark-III models, however I believe it was only for special-order from the importer, (as not every DUKE-dealer got one), starting in 1962,, and no longer available by late 1963. _ (Hopefully, somebody like Tom B. could tell us roughly how many were imported.)
__ Then there was the more familiar 5-speed version which became available in late 1963, and came with a brake-light & switch, along with a 3rd alt.wire-lead to run that new set-up (as also on the 250-Motocross as well, then).
I have owned two of this 2nd-generation 'Mark III' model -(still called the 'Diana'), one was an early 1964 model and the other was titled as 1965 but no-doubt actually made in late '64,, and as I recall, it's stock gearing was still the same 43/18t sprockets as the 1st-gen model had.
__ Then there was the 3rd-gen/king of Mark-3s, which came-to-be in 1965... It's main changes were a 29mm SSI, with 1mm larger intake-port, a still wilder cam -(the Mach-I cam), and 3mm larger valves matched with larger valve-seats and a 9.8:1CR 3-ring piston, and 40/18t gearing,, to then achieve it's claimed 110-MPH. _ Basically, at this point in time in 1965, Mk3s were much the same as the then new Mach-I model, except for retaining their established & lighter electrical-system.
And by this time they started coming stock with aluminum flywheel-rotors, and had 'M3' stampings added to their motor-case numbers.
This 3rd-gen version came with the small tool-boxes that everyone thinks are so cool to have on their DUKEs. _ Also rear-sets & larger/curved kick-starter lever.
I've only ever owned just one of this model of Mark-3, which was the model that carried-onward the DIANA-name and was responsible for the 'DUCATI' name-brand to stand-out, as not just another 'cycle' -(or "bike" as a lot of you younger-types say these days) !
It would be nice if Tom B. would confirm it but, I think that it was with the introduction of this last -(3rd-gen) narrow-case version of the Mk3-line, that the official-name was (quietly) altered from '250 Diana Mark III', to merely '250 Mark 3' . _ People always liked to say "Diana", so it was difficult to ever get that name completely dropped, before the wide-case Mk3 version took-over the name.
__ Then in 1968 there was the wide-case 4th-gen '250 Mark 3' (non 'D') model, (and was no match for the previous 3rd-gen version), with a 10mm longer con.rod and slightly milder cam -(I assume to better work with the more restrictive muffler which came on Mk3s & other DUKE-models starting then). _ It came with the same new electrical-system as all the other (non-early w-c Scrambler) wide-case models did, (using battery, 70-watt 6-pole/6-coil alternator & the small solid-state box). _ So this Mk3 version was the first to include a horn and an ignition-switch & key ! _ Thus by most all rights, it should've actually been called a 'Mach-1', instead.
That's another DUKE-model which I've never owned, but once noticed that a stock one had (lower) 40/15t gearing.
By this time the DIANA-name was completely out, and this 4th-gen version was the second-rarest of all the 250-Mk3 models.
Unfortunately I've never gotten a chance to race a wide-case 250 Mark-3 against a 2nd-gen DianaMarkIII, but I'd bet on the Diana-version to have the advantage, (mainly due to weight difference).
____ I no longer have any of the 250 Mk3 models I once owned, (as my last one was sold-off before 1980). _ (But I still have all their cyl.heads! _ And may be willing to sell them some day.)

____ I ask that all of us who do own any version of a 250Mk3, let us know which one of these 4-gens of Mk3 model-versions ya have, so we can all get an idea of just how rare each version is, these days.


Mk3-Cheers,
DCT-Bob

[vintbikeparts]

As you ask, the bike started as a chissis which still had rear wheel, fender, one toolbox, centerstand , shocks etc still attached. It was all painted powder blue but original mk3 decal was found under paint on toolbox.The rest was a mixed in with an assortment of parts from many models and a few things were sourced from ebay etc. Engine # is DM250M3 972**. The bike has a 29mm SS1and is set up with flat bars and rear sets.
Back to the original topic, will the 3 wire stator ,with lower coil grounded on one side, work for me based on previously disclosed info?
Jerry

[DewCatTea-Bob]

" Engine # is DM250M3 972**. "

____ You have a 1966 model, the most desirable version!!


" will the 3 wire stator, with lower coil grounded on one side, work for me based on previously disclosed info? "

____ Yes, so long as that stator actually is what it seems to be...
__ The top power-coil should have two wire-leads - 1 yellow & 1 white, and neither should read any continuity to the stator-plate/ground, but should read .5 to .9 ohms with an ohm-meter connected to both wire-leads.
__ The lower power-coil should have only a single red wire-lead, and read .4 to .7, to ground/stator, on your ohm-meter.
__ It's much advisable to replace all 3 original wire-leads with fresh 16Ga wire of the same colors !

____ Thanks for telling us a little about your project !


DUKE-Cheers,
DCT-Bob