Advance mechanism

[DewCatTea-Bob]

By: JimF...
" I have no clue as to its state of tune. "

____ If the story behind this Duke of yours is pretty-much true, then I've (previously) correctly clued-in those details.


" I've been told it was a Diana, but here in the States the label "Diana' label is tossed around about every 250 Ducati to the point that it is almost a generic term for any and every narrow case Ducati 250. "

____ In my-own experience, that's fairly true (if somewhat exaggerated) for most road-bike Duke-models, (but I don't recall of anyone ever referring-to a Scrambler-model as a "Diana").


" Here is what I do know: narrow case, street bike frame, 250 engine with no special suffix stamped into the motor, 5-speed gearbox, AC voltage electrical system, no advance mechanism "

____ All that tends to confirm that your Duke is a (1963-64*) 'Diana Mark III' !
(* Too-bad you didn't include the motor-number.)


" I asked the second owner if he ever set the timing. He replied that he did not which makes me sure that he did not pull the advance mechanism out. "

____ For the story on your Duke to be consistently-true, it's motor-number must then be older than 88297, (as beginning with that m.number, an 18-degree AAU became employed).
__ Did you ever take a picture of whatever it is that you have in place of an AAU ?


" At this point in time I could:
1) Add an advance unit and re-time the bike "

____ I suggest delaying that useful improvement, until "November".


" 2) Re-time the bike from its current 21 degrees to 40 degrees so as to better suit the timing to the ignition system. "

____ While I really don't think the "bike" itself needs to be re-timed, the 'engine' could stand to have it's ign.timing reset,, providing that you're of the opinion that it would be worth your trouble (to pick-up a couple more ponies).
__ I'd aim to reset the ign.timing to 38 or 39 degrees BTDC. _ But doing that means setting-up your degree-wheel and moving the points-plate, etc.,, so perhaps you ought to settle for merely-just opening-up the points-gap a bit, instead (for now). ...
The standard gap-setting is .012 to .018", so you could open your points-gap out to (as far as) .020", and know that you've advanced your ign.timing outward towards the intended direction, (and learn LATER exactly where the timing ended-up at).
__ After you've told us the current gap-size of your points-gap, 'Bevel bob' could give you a better idea of about how many thousandths you'd have to increase your gap out-to, in order to obtain the full additional 18-degrees. _ I-myself used to know exactly how many degrees would result for each 1-thousandth of points-gap but, I've since forgotten for sure what the actual relationship is - (I'm now guessing it's [about] 2.75-degrees [+/- .5] per .001"),, however B.bob has had some more recent experience with whatever the relationship is, and hopefully he will confirm how many degrees you can get per-thousandth of increased points-gap.


" If I am risking the chance of incurring engine damage from running 21-degree timing when I should be at 40 degrees, I would not hesitate to change the timing. "

____ Well the retarded ign.timing will not hurt anything (except perhaps fuel-mileage), (and in-fact, your engine has no-doubt been running a few degrees cooler that way).
But still, if your current points-gap is under 16-thousandths, then at-least you ought to open-up the gap to at least .018".


Duke-Cheers,
DCT-Bob

[JimF]

Sorry Bob, but I took no photos primarily because there was nothing to take a photo of! It was just a cavern behind the points plate.

The engine number is 88103.

engine_serial_number.jpg

I have honestly seen a scrambler on eBay being touted as a 250 Diana. I have also seen scrambler-specific parts, Monza tanks and the like on eBay being touted as "Diana" parts.

I know you've stated what you think the bike is, but the story I got and relayed here is just a story and I don't want to try and create a fictitious heritage for the bike.

[DewCatTea-Bob]

" I took no photos primarily because there was nothing to take a photo of! "

____ Well whatever there was in place of the AAU/points-cam, would've been interesting to see !


" The engine number is 88103. "

____ That makes it a 1964-model !


" I have honestly seen a scrambler on eBay being touted as a 250 Diana. I have also seen scrambler-specific parts, Monza tanks and the like on eBay being touted as "Diana" parts. "

____ Well, on 'eBay',, I believe that's done simply so as to draw more attention to the listing.


" I know you've stated what you think the bike is, but the story I got and relayed here is just a story and I don't want to try and create a fictitious heritage for the bike. "

____ Well Jim, unless the 'story' was made-up so as to 'cover' a fictitious assemblage of various parts from different Duke-models,, then there really isn't any other Duke-model (besides a 'Diana Mark III') that it could possibly instead be !
The piston & camshaft will no-doubt review the fact that at least the engine is a real Mark-III motor.
Does the motor still retain the stock 18t.sprocket ?
Also, the rear-wheel should have an original 43t.sprocket.
Have you ever checked it's (road type)- frame for the specific details which distinguish it -(a Mk.III) from a Monza/GT ? _ (For instance, it should have no brackets for a regulator-unit or side-covers.)


Duke-Cheers,
-Bob

[DewCatTea-Bob]

By: Bevel bob...
" you can always put it back if the kickback is too much. "

____ As I've meant to indicate, (with the battery-less ign.system),, kickback is not really an issue, unless a random-type kick-starting procedure is (mal)- practiced.


" I'm not sure that the mag ignition would work well with the AAU. "

____ Well it should go without saying that it would certainly work (as intended) with a 18-degree AAU, of-course. _ So however, it's only the possible use of the (more common) 28-degree AAU which should be in-question.
And yes, it too COULD be employed, as well. _ BUT simply installed same as the 18-degree unit normally is, would cause the ign.coil to get well overheated (by all the extra AC.juice which the 28-degree AAU's points-cam would divert through the coil [instead of the points] ) !
So a diode would then need to be included within the power-feed to the ign.coil/points-circuit, (so as to cut-down the current-juice in half).
And furthermore, if a diode bridge-block were employed for the job, then a (normally wasted) source of DC-juice could be tapped-into for some-other possible use, such as for charging a battery (for powering a horn & brake-light).
This new source of DC is power-juice that's normally entirely shorted to ground through the ign.points (and WASTED !). _ Therefore THIS source of power-juice is entirely FREE ! _ And it will easily keep a battery charged-up too, (without need for a regulator if the chosen battery is not too small) !
Unfortunately without a battery however, the amount of it's available power near idle, is insufficient to fully power-up a standard brake-light,, and it also will not fully power-up a (high current drawing) horn, (at any RPM). _ Which is why a storage-battery (of any size) would be required for normal-running of those particular loads.
However for powering merely a brake-light only, a (fair sized) capacitor may be substituted (for a battery).
__ So,, a good fall-time project would be to install a 28-degree AAU, and a pair of power-diodes (which are more convenient within a bridge-block),
so as to then have your Duke fully street-legal and obtain an improved AAU-range.


Dukaddy-DUKEs,
DCT-Bob

[JimF]

The frame has been buggered-up a bit in the back to accomdate the custom rear seat. The tail of the frame was cut off and the loop was welded over the back tire. It's a home-brew weld job, not a scrambler loop.

A couple of home-made side covers hide the empty battery tray. (I actually put an empty battery box in there and I filled it with a few tools, a spare spark plug, spare light bulbs etc.)

A pair of home brew side covers are attached to a couple small rectangular bars on the frame that may have been added as I've not seen this type of thing on a Ducati frame before. The rear-most bar on each side is just ahead of the shock mounts, the front bars extend (if I recall) from somewhere around the battery tray outward and then upward.

frame_details.jpg

The bike has a 43-tooth rear sprocket - can't count the front at this time.

There are no brackets for a regulator or tool boxes, but with the frame being chopped in the back and the unusual frame bars I don't know that other things weren't changed too.

It does have a white-faced Veglia tach and an early 150-mph speedometer with the grooved rim.

It also has a scrambler air filter attached.

[DewCatTea-Bob]

" The bike has a 43-tooth rear sprocket - "

____ No other Duke-model besides the 'Diana 250 Mark III', came stock with that size rear-sprocket !
__ Taking into account most available clues, I've now become even more certain that your Duke is a real 1964 'Diana Mark III' . _ And I find the story on it to be acceptably believable, as well.


DUKE-Cheers,
-Bob

PS. - Note that I've now added wording to my previous-posts above/(with 'DCT-Bob') .

[JimF]

Just to tie up loose ends with regards to this post, I am, unless otherwise convinced by any subsequent posts, going to leave everything as is.

The bike starts easy and runs well. Seemingly my 21 degree timing on an no AAU engine is not harmful and so I will leave it alone at least until this riding season ends.

Thank you all for your help and advice.

[Bevel bob]

There can't be many Ducati singles being used as a daily driver, my 250 is often the only Ducati at meetings in the Uk, and i have never met another on the road. Keep it running JIm.

[DewCatTea-Bob]

By: JimF...
" I am,
going to leave everything as is.
so I will leave it alone at least until this riding season ends.

____ Well that's somewhat disappointing. _ Seems you'd be more interested in learning how much improved your engine-performance would be with the ign.timing set nearer to factory-spec.
__ I think that you should at least check your points-gap and if it's found currently set with less than 16-thousandths gap, then open it up at least two more thousandths (which should then advance your RETARDED ign.timing at-least about another 5-degrees).
Your ign.timing really ought to be set at at-least 32-degrees BTDC,, and if your points-gap happens to be currently set with the minimum-gap of .012", then you could gain between 10 to 18 degrees of advance by increasing your points-gap out-to the maximum-gap setting of .018" .
Certainly you could get that -(reduced task) done sometime BEFORE the end of this riding-season.
____ I'm also somewhat disappointed that 'Bevel bob' didn't bother to confirm (within his last post), his past research of how many degrees of change results for each thousandth (of an inch) of points-gap change.
__ If anyone-else soon intends to check their Duke-engine's ign.timing (with use of an attached degree-wheel), then how about letting us know exactly how many degrees of change you can possibly obtain by merely altering just the points-gap setting between the .012 & .018" extremes,
okay please ?


Hopeful-Cheers,
-Bob