2 ques, shifter box and modern carb

[Nick]

Another way to ease starting is to put the bike in gear, then roll it backwards until the piston comes up against compression. Then put transmission into neutral and kick. This gives one and one-half revolutions for the crank to build up inertia to overcome compression. Or, back it up against compression and push start.

Whatever you do, don't make a habit of simply kicking at the kickstarter without knowing where the piston is. You may damage both the kickstart mechanism and your leg.

[LaceyDucati]

Bob

Regarding the 200's, to my knowledge there appears to be three different Italian 200's.

Which has caused me some confusion over the years as in the UK 200's are refered to as A or B series, suggesting only 2 types. Basically as you know the early 200's are the same as the 175's as far as head bolt pitch, base gasket shape, centre joint etc.

The later "B series" engines had similar bottom ends to 4 speed 250's, with cases machined to suit the smaller cylinder and "square" head bolt pitch as per the earlier 200's. The barrel casting was similar to the 250 but machined to suit the 200 liner and "square" head bolt pitch. Therefore the base gasket has the same outside shape as a 250 but with a 73mm hole instead of 80mm and the "square pitch" instead of the "rectangular pitch". The dowel hole is as the earlier 200 but oil hole as per 250. The head as you said was as per the earlier 200's.

Then the problems start! I have seen 200 heads with the "retangular" bolt pitch. They are definatly 200's as they have 67mm hemi chambers with no squish. I also have original factory base gaskets as per 250's ("retangular" pitch) but with a 73mm hole. As I anoyingly no longer have the heads, I can't produce the evidence! I think these were possibly the last batch of 200's and were esentially produced from the 250 casting, head as well. It is posssible they were only produced in limited numbers and for a limited market. As I've only seen parts I'm only guessing, I've asked around and others in the UK have also come across the same. If anyone else knows more detail or has one, I would also like to know as well! As the "B" series designation is probably a UK invention maybe there should be a "C" series as well! It makes Gasket kits for 200's a potential minefield!

Off subject, so feel free to move this discussion to a new subject!

Regards Nigel

[DewCatTea-Bob]

____ Thanks for your response Nigel !


[quote= LaceyDucati ...
" Regarding the 200's, to my knowledge there appears to be three different Italian 200's. "

____ I-myself have never heard-of a third-type of 200-motor, and-also there's no parts-listings for any third-type included in my old* parts-book covering the first two types of 200-models, (however my particular 175/200 parts-book is the first-one to cover any of the 200-models).



" The later "B series" engines had
The barrel casting was similar to the 250
Therefore the base gasket has the same outside shape as a 250 "

____ I don't happen to recall these cyl.base differences between the A & B series, but that particular difference* in cyl.base-shape (* as only seen just on the right-side, where the cyl.base partially-engulfs the tower-shaft housing, [as the cyl.fins do]), indicates that the 250-motor was already in the works for production, by then, (since that-difference was only required for altering the square-pattern's right-side head-bolt locations outwardly to accommodate the 250's larger bore).
So apparently then, Ducati had planned for both the 200 & 250 models to be produced for overlapping model-years, (which I had previously assumed wasn't really done with pre-intent).
This clue confirms that the B-type 200 was based-upon the 250, (rather than the 250 being based-upon the B-type 200).



" I have seen 200 heads with the "retangular" bolt pitch. They are definatly 200's as they have 67mm hemi chambers with no squish. "

____ As you've figured, I've never encountered any of such (here in the U.S.),, but that doesn't mean too much, as I've had relatively little experience with many 200-models.
__ Anyhow,, while the MC.piston-crown's dome may've possibly fit into a 200 hemi-chamber, the 350 piston-crown's squish-band ought-to have run-into rather major clearance issues,, which Tim didn't make clear as being so very obvious, (as I assume he would've, if such extremeness was the actual case).



" I also have original factory base gaskets as per 250's ("retangular" pitch) but with a 73mm hole. As I anoyingly no longer have the heads, I can't produce the evidence! "

____ Well a picture of one of those cyl.base-gaskets (seen next-to a 250-version), would back-you-up quite well-enough (to prove that such a 200 bolt-pattern exits).
And if also seen next-to a A-type 200 cyl.base-gasket, would then show us the difference in their "outside shape".



" I think these were possibly the last batch of 200's and were esentially produced from the 250 casting, head as well. "

____ Certainly fair reasoning,, as the latest Italian-250/350 head-castings were likewise produced similarly, from a bare 450 head-casting.



" feel free to move this discussion to a new subject! "

____ Probably not worth creating a new dedicated thread for, unless others chime-in with more good related info concerning such rare 200-stuff.


Dukaddy-DUKEs,
-Bob

[Timmy250]

Bob, I did get the idea from you, thanks. And indeed replaced the original bolt with one a bit longer. The fork spring, as I found it, was bent a bit at the pivot point near the bolt, straightened that and added the backing piece - which looks for all practical purposes like a thick, rectangular washer, with the hole offset to the left, as viewed. If the gear were to be thrown back far enough, it would just miss the tip of the rectangular washer. I suppose it could, in theory, nearly shear the spring at that point, if the gear pushed out that far. This definitely pushes the starter gear with more force than before. Possibly too much, the coiled kick arm return spring has difficulty overcoming the fork spring to return the gear to its raised resting point. If problems do arise, I will return to the drawing board.

On your squish question, it's 30 thousands, or a tad under, but not as small as the 24 thou minimum I saw listed somewhere.

Racking my brain to figure out what an AAU is. All-around-underachiever...?

Tim

[Eldert]

Hi Tim

AAU stands for automatic advance unit

Eldert

[LaceyDucati]

Bob

Just back from a short break, so up to my eyes in catching up, but will lay out the gaskets and post the photos as soon as I get time.

Nigel

[DewCatTea-Bob]

[quote= Timmy250 ...
" Bob, I did get the idea from you, "

____ Okay then,, even-though my fix-idea didn't occur to yourself independently, I presume you did at-least conceive how the inclusion of the added backing-plate would be fairly helpful for preventing the leaf-spring from once-again becoming bent in the same usual*un-sprung area (of the base of it's 'Y' shape, [* whenever clobber-wacked by the ks.gear]).



" The fork spring, as I found it, was bent a bit at the pivot point near the bolt, "

____ Right, as that's definitely the "usual" area where the leaf-spring gets "un-sprung" at, (with just the stock-sized washer under it's mounting-bolt) !



" straightened that and added the backing piece - which looks for all practical purposes like a thick, rectangular washer, with the hole offset to the left, as viewed. "

____ Seems you've indeed conceived the intended fix-concept pretty-much correctly.



" If the gear were to be thrown back far enough, it would just miss the tip of the rectangular washer. I suppose it could, in theory, nearly shear the spring at that point, if the gear pushed out that far. "

___ I grasp & understand what you're meaning to say,, but of-course we rather realize that before the leaf-sheet could get sheared, the pressure transferred through your rather thick & stiff backing-plate would more-likely rather lead to cracking the motor-case mounting-post, (thus the need for replacing the original relatively short mounting-bolt, with a longer/deeper-fitting version !).



" This definitely pushes the starter gear with more force than before. "

____ Yes indeed but, only significantly more-so while the ks.gear is in it's normal disengaged retracted-position, (as once that gear is moved into it's engaged-position,, the spring-pressure is then not so greatly increased, [compared to that of the stock pressure] ).



" Possibly too much, the coiled kick arm return spring has difficulty overcoming the fork spring to return the gear to its raised resting point. "

____ Of-course I get what you mean, but ya gotta take the-bad with the-good it seems. _ However the kick-lever return-spring really shouldn't have any significant difficulty overpowering the increased resistance (caused by the extra compressing of the leaf-spring). _ So if your kick-lever is-not easily & fully returning-back as it should, then I'd suspect another collaborating-factor restraining full-return. _ Cuz I-myself have never experienced any noticeable resistance-change in kick-lever return-action due-to the backing-plate mod, on it's own.



" If problems do arise, I will return to the drawing board. "

____ Have you not also seen another old related post of mine, in which I've suggested my other-idea of rather adding a coil-spring underneath an up-side-down installed leaf-spring (or a fabrication of the like) ?




" On your squish question, it's 30 thousands, or a tad under, "

____ Then your comp.ratio is likely only about 7.4:1, (if you trust calculated-CRs).
__ Since you haven't followed-up on whether your cyl.head-chamber actually has a squish-band, or is rather a pure hemi-chamber,, the rest of us are left to assume that your cyl.head is indeed not a later-late/(type "C") 200 item.



" Racking my brain to figure out what an AAU is. "

____ The Automatic Advance Unit is the mechanism which advances the ign.spark from it's preset static-timing towards it's set max.advance-point... And with the 250-Monza/Diana's rather extended 28-degree range, kick-backs ought be rather mild (in comparison to the Motocross/Mark-III type ign.timing-arrangements).


Duke-Cheers,
-Bob

[Timmy250]

Bob, not sure if I know what you mean about pure hemi vs squish band, but the head's flat machined outer circumference part, the one that contacts and seals with the top of the liner, extends into the combustion chamber a bit less than the flat edge on the piston circumference. In other words, the domed parts of the head and piston match with a bit of clearance after the two flat parts meet. That's where I found the 30 thousandths squish, where the flat surface of the piston's outer edge approaches the flat edge of the outer perimeter of the head at TDC.

Ummm, come to think though, since my liner is nominally bored to 76.5 mm, compared with the stock 74 mm, then about 1.25 mm more of the flat perimater edge of the head extends into the combustion chamber over the case with stock bore. I dunno...

If hemi part of the head had a diameter of at least 74 mm, would that make it a pure hemi head, at least at stock bore? I mated the piston to the head before installing to make sure there was no obvious mismatch, could see the flat parts of both piston and head overlapped to form squish at the perimeter, but didn't think about how they would have matched up if the piston were 74 mm instead of 76.5.

Tim

[DewCatTea-Bob]

[quote= Timmy250 ...
" not sure if I know what you mean about pure hemi vs squish band, "

____ I guess rather than having stated "pure hemi", I preferably could've wrote 'totally hemispherical' instead, (as 'pure' could only be the case if the more flattish valve-faces also rather matched the same spherical-contour of the hemi-chamber as well). _ But in any case, once the included squish-band machine-work has altered an otherwise perfect hemispherical combustion-chamber, it's certainly-THEN no-longer totally-pure as such.
__ Previously, I was sure that you were already aware of exactly what is meant by the term "squish band",, but your post tends to lead me to suspect that you may have developed doubts of what's exactly what concerning such. _ So thus I'm not very sure how deep to go into this.
____ It seems that the developed reason for why we've gotten to this particular point, has to do with the (rather SLIM !) possibility that you may have possibly somehow fitted a 200-cyl.head (which is a true-hemi, and-thus has no squish-band), together-with your 350-piston. _ And-that then perhaps that mismatched combo was the actual main underlying reason for why you discovered the need to shim-up your cyl.jug, so as to avoid any possible contact between your 350-piston's crown and the outer-edge of the 200-head's (non squish-band equipped) hemi-chamber.
__ But even if that's not-really the case, (just as I believe),, we still may have something to get further straightened-out...



" the head's flat machined outer circumference part, the one that contacts and seals with the top of the liner, extends into the combustion chamber a bit less than the flat edge on the piston circumference. "

____ Concerning the cyl.head,, I rather clearly understand that you're worded-explanation means to indicate that the "flat" 'horizontal' surface now extends further into the cyl.bore, since IT was-not also bored-out to equally match the new/increased bore-size of your over-bored cyl.liner.
And, concerning your oversized piston,, I understand that you're meaning to indicate that it's 'horizontal' ("flat edge") upper-surface (at the top of it's outermost max.bore-size), has an extended-radius which suitably matches the width of the protruding horizontal counter-surface of the cyl.head.
__ That's all well & good, (as expected by the manufacturer of your over-sized piston) !



" In other words, the domed parts of the head and piston match with a bit of clearance after the two flat parts meet. "

____ This wording seems to imply that after those two 'horizontal' "flat parts" meet together, that then the dome of the piston and the dome of the head-chamber, fit together with (only) a "bit" of clearance.
That would seem to depict a resulting comp.ratio far,far beyond any expectable c.r., ( [as interpreted by me], since I'm thusly led to envision the resulting TDC.chamber then being quite tiny) ! _ So I really don't think you actually meant that.
__ So rather, I deduce that you must've meant that when the outermost/top-edge of your 350-piston is placed into flush contact with the cyl.head's bottom-edge -(exposed ledge) of the combustion-chamber,, that then there's still a "bit" of clearance between the squish-band of the head-chamber and the squish-band of the piston-crown.



" That's where I found the 30 thousandths squish, where the flat surface of the piston's outer edge approaches the flat edge of the outer perimeter of the head at TDC. "

____ THIS wording is rather fairly clear, and makes better sense.
So I understand that you're meaning to indicate that the two corresponding horizontal "flat" overlapping surface-areas (of head & piston), have been set to have near .030" of clearance, (as you've figured to be properly-set accordingly, as has been recommended rather for the squish-band clearance).
__ Well, neither of THOSE overlapping horizontal-ledge surface-areas are any part of the 'squish-band' (for which a minimal-clearance is expected) !
The particular clearance-area which you're referring-to, is-NOT what's meant as being the 'squish-BAND' ! _ And THAT particular clearance-space (of 30-thou) which you've referred-to, could possibly be set as low as merely-just .005 to .010".



" come to think though, since my liner is nominally bored to 76.5 mm, compared with the stock 74 mm, then about 1.25 mm more of the flat perimater edge of the head extends into the combustion chamber over the case with stock bore. I dunno... "

____ That's indeed correct, and I had assumed that your previous wording had already been meaning to take that into account. _ As that 1.25mm of extra-added surface-area, is the "flat" (on both head & piston) which you've set your 30-thousandths of clearance for.
Although this area may be somewhat confusing,, cuz with a standard-bore setup, those two horizontal ledges don't exist to be concerned with setting any clearance between.



" If hemi part of the head had a diameter of at least 74 mm, would that make it a pure hemi head, at least at stock bore? "

____ First-off,, the 200-cyl.head, (like it's matching cyl.bore), has a 67mm 100%-hemi combustion-chamber (which I consider as being "pure"), because 200-heads don't include any 'squish-band'.
Now if a 250-head's hemispherical combustion-chamber remained fully hemispherical all the way outward to it's 74mm bore-size, THEN that would indeed make it "pure" hemispherical, (or 'full-hemi' as others may say).
But since 250-heads include a 'squish-band' (located at the outer-edge of their combustion-chamber),, that 'band' interrupts the otherwise pure hemi-shape, and therefore the hemi-chamber is only partial (of the full chamber-capacity, since the squish-band area/volume is also part of the resulted non-pure hemi.combustion-chamber).
__ So reading your question again, the short-answer is 'yes' !



" I mated the piston to the head before installing
could see the flat parts of both piston and head overlapped to form squish at the perimeter, "

____ While it's certainly obvious why it may be fair to refer to THAT area/space as being a sort of "squish", that further-outward space is-not what's normally referred-to as the "squish band" ! _ As the real 'squish-band' is actually the neighboring 8mm-wide surface-area/band that's obviously seen between that overlap-ledge/flat-area and the (resulted reduced-volume) hemi-chamber,, (and also, along-with an obviously matching 'squish-band' on the outer-edge of the piston-crown, as well).
__ So it's rather between THOSE two 'bands', where your squish-clearance should actually be set at !
Which means that your current actual squish-band clearance is likely larger than intended, (by an amount that depends on the piston-manufacturer's designed space-clearance relationships, [regarding the overlapping "flat"/horizontal 1.25mm-ledges compared-to that of the actual 'squish-band'] ). _ In other-words, if the manufacturer had intended for both of those space-clearances to be the same, THEN you're already set,, but if the 1.25mm-ledges were intended to-be separated by less (than that of the squish-band area), then your resulted squish-band clearance is correspondingly larger, (than your .030"),, (and also accordingly, your comp.ratio is lowered).
__ How much did you have-to shim-up your cyl.jug, in order to attain the particular squish-clearance which you ended-up with (between piston & head) ?



" but didn't think about how they would have matched up if the piston were 74 mm instead of 76.5. "

____ In that rather regular case,, neither of the 1.25mm-steps, (of either the revealed-ledge* on the head's horizontal mating-surface, or the corresponding "flat" ledge outboard of the piston-crown), would be in existence,, (* as the expected cyl.bore-size would only be 74mm as well [as the piston] ).
__ So by-now it ought-to be fairly clear that with a stock-bore, there would then be no such overlapping horizontal "flat" ledge-surfaces to set any kind of squish-clearance for. _ Thus leaving only the ACTUAL 'squish-band' to set a squish-clearance between !


Hopeful-Cheers,
DCT-Bob

[Timmy250]

Hi, took the head off after measuring squish, pic shows where the solder laid, and yeah, lots tighter at the flat perimeter edge, so that's not the correct place to measure.

Also, valves are 37 and 33. But pic shows biggest reading I could get on intake port. Diameter of hemi part of head is 74 mm. So, maybe that's just a mystery.