Recharging 250 MK1/MK3 Magneto

[DewCatTea-Bob]

By: amartina75...
" Your original argument that Ducati did not mark all of their rotors the same is true.
So all together that is 6 rotors checked, 5 were the same as mine pictured and one was different, "

____ Back in the early-70s when I was building a motor from several basket-case collections, I decided to use a different alt.rotor than had been original with the crankshaft, and picked-out a nice rotor without any concern for the location of it's factory-mark. _ Then-later when I went to install the chosen rotor, I then realized that it's timing-mark seemed off-placed,, so I compared it with the original-rotor and noticed the obvious difference. _ That then led me to check-out the rest of the 4-pole alt.rotors which I had accumulated, (over a half-dozen, from 200/250 & 160 n-c.motors [no newer than 1966]),, and I then discovered that the bunch-of-em displayed four DIFFERENT timing-mark locations relative to their magnet-arrangement orientation, (which at the time was quite perplexing, as to exactly WHY !).
So I then had to sort-out what's-what with all those alt.rotors, so that they could then be properly 'timed' for whatever motor-model they'd be chosen to work on.



" It doesn't make sence to change the location of the mark on the rotor, when they could have just changed the angle they specified to install the rotors at. "

____ INDEED ! - That's what makes my point about it seeming to be as if Ducati wanted to make this issue as complex as possible (when it could otherwise be quite straight-forward & simple !).



" In fact if they were going to mark the rotors differently for every application, why not just place a mark where they actually wanted them installed at. "

____ EXACTLY ! _ And indeed they did do it that particular way on SOME models.
__ It seems that you now have a firm-grasp on this screwed-up issue. _ I'm glad that at-least YOU for one, now fully realize the relatively complex details of this perplexing matter.



" So if anyone didn't know where their particular rotor came from they should check the location of the mark before they install it. "

____ Right ! _ Once an alt.rotor's original-origin is lost track of, it's then a matter of pure-chance that it gets installed properly-timed with crankshaft & ign.timing, (even with the instruction of the workshop-manual).



" (considering all the rotors I see on ebay selling without the matching stator) If they follow your instructions they could install the rotor correctly without any factory mark at all. "

____ That's right... Since the factory-placed timing-mark locations (on 4-pole rotors) were not ALWAYS place-located at some particularly LOGICAL-location,, their existence is not only of NO-use, those factory-marks are even apt to be MISLEADING !
So-therefore I've had to point-out that issue, and also indicate how to come-up with timing-marks which actually have some-sort of useful-LOGIC for the existence of their particular location-point.



" However there is one thing that you are overlooking, or haven't made clear so that someone reading this post in the future would have trouble.
As I mentioned before, the rotor is placed over the stator so that you gain 10deg. of advance (if you follow the instructions in the book) "

____ If I properly gather/grasp what you actually mean, then I agree that you are correct in that I hadn't yet addressed any instruction-issue that's been directed from ANY workshop-manual, (as I hadn't-YET been asked to specifically-address any particular book's related instruction-method).



" the stator is alligned with the offset in the cylinder. (see pictures below)
If you mark your rotor by "geometry" and you do not account for this difference (like the factory did) you will have two different marks when in fact the marks should be the same. "

____ I can't be sure I'm correctly following exactly whatever particular point which you actually mean to convey here-above, so this is one of those times when it would be quite helpful to have your point presented in other-words.
__ However because your chosen-wording has also mentioned: "(like the factory did)" , and also: "(see pictures below)",, I thus think I've realized what seems to be leading you astray (concerning the 10-degree [non-issue] issue). ...
__ The upper-picture which depicts the required angle between the mag.rotor's timing-mark and TDC, just-happens to be drawn with TDC located at the 12-o'clock position, and is-not really meant to intentionally indicate it's TDC.point as being actually vertical (as opposed to tilted 10-degrees),, so that diagram-figure should-not be considered as being actually real-life orientated.
__ The picture showing a degree-wheel which happens to be 'set-up' with it's 0/TDC-point set at '12-o'clock', can possibly be misleading...
A degree-wheel can be set-up at ANY orientation, and need-not necessarily be set with it's '0' orientated particularly at the 12-o'clock position,, just so long as the 'pointer' is set to point-at '0' whenever the crankshaft happens to be at TDC, (is all that's actually required) !
To ASSUME that the workshop-manual had actually meant to indicate that the 10-degrees difference actually needs to be taken-into-account when discussing anything to do with engine-timing related matters, would certainly be quite-MISLEADING (and-thus lead to the kind of confusion that's now arisen here) !
__ IF the stator was mounted to the motor-case in an exactly VERTICAL-position (rather than tilted 10-degrees along-with the cylinder),, THEN, then the 10-degrees difference would indeed become an additional-concern needing to be dealt-with & figured-in (with alt.rotor-position & ign.timing timing-concerns).
But since EVERYTHING is directly-related strictly to 'TDC' alone, it then-therefore matters-NOT whatever particular amount of degrees of inclination the cylinder happens to be inclined at, (so long as the stator is likewise inclined) !



" figure 33 from Ducati Workshop Manual, note the position of the keyway in the crank is at 0deg. at TDC and mark is alligned with 0deg. "

____ It seems you've possibly misread/misunderstood that diagram-figure's intended indication-matter...
While that diagram does indeed purposely mean to depict the crankshaft being at 0-degrees & TDC,, that uncommon 'oC' figure indicating some angle-of-degrees, is actually not intended to represent a 'zer0', but rather some 'X-number' amount of degrees, (depending on the particular model [in the associated listing] ).
(Obviously, the chosen angle shown depicted, is too large to compound-upon the 10-degree discrepancy-issue [and possibly even-further complicate probable additional misinterpretation of the manual's actual intended-meaning].)


____ Now if all of the above point-making fails to address whatever particular point you think was left unaddressed before, then I'd still be at a loss to realize whatever you had actually meant to convey,, and I'd thus-then be left quite curious as to exactly what you specifically mean concerning the 10-degree discrepancy issue.
However if it's now all cleared-up, then we will have straightened-out another uncertainty left in the murkiness of the rather poorly executed workshop-manual.


Hopeful-Cheers,
-Bob

[tonyduc]

Reviving this old post since i have related questions. I have a 67 250 MK3 vin 97022 which I am restoring, it has a magneto and no battery system. I have a couple of questions:
First, regarding static timing, from reading the factory manual and other information online I don't see information on static timing for magneto systems with no battery. Not being an expert on ignition timing I am assuming that's because adjusting the advance timing is done on this system via degrees from TDC of advance on the rotor as described in above posts, rather than via the points?

Second, from posts above the advance unit on my MK3 should be 18 degrees type (not 28 degrees), from the attached pic #2 can someone tell me if I have that type of advance unit 18 degrees (part no. AA369)?

Little more information on the pics, I bought a 250 timing cover + parts on eBay since mine was kinda ruff which is why I have two pictured side by side. This leads my to my third question unrelated to timing, the eBay cover looks and fits identical except the oil pump looks different, the part number on that cover is 175 KA 3001, the original from my bike is 250 KA 3001. Is the pump with the 175... number correct for the 250 MK3 ?
Thanks
Tony

[Jordan]

If I understand your question, no it is not that ignition spark timing is achieved by setting the position of the alternator rotor relative to the crankshaft.
However, if you have the no battery type ignition, timing the rotor is important, because it ensures that the spark occurs (points open) when the continuously varying voltage output (sinusoidal waveform) is near a peak.

For spark timing, there is information in a workshop manual covering models including 1966, which may be relevant to your bike.
Static timing is 21 to 23 degrees advance.

[double diamond]

The timing cover marked 175 is not correct for a 250 but it will work. The oil pressure relief valve is in the oil pump housing on the 175. On the 250 the valve is in the timing cover.

The AAU pictured with the 175 cover appears to be the battery/coil ignition type point cam. The AAU pictured with the 250 cover appears to be the magneto type point cam. Notice the difference in degrees the the points are open on the two cams. Ducati only gave full advance ignition timing figures. You can determine a static timing figure by subtracting the degrees of advance from the full advance specification. Or, lock the AAU at full advance and time statically at the full advance specification.

Matt