Vento 350

[Jon Pegler]

The 'back to front' points is because they are Motoplat points.
Strangely, they are shown in the 'back to front' position in the Forza and Strada handbooks, but not in the Vento one.
Mind you, the Vento handbook had a number of revisions throughout it's production.

Jon

[graeme]

Unknown cam shaft measures,
21.807 - 29.96
21.809 - 30.0 (bevel end)

The cam shaft in the supposedly 1975 450 Scrambler looks the same.
Viewed from the removed cam bearing support.

Graeme

[DewCatTea-Bob]

" Unknown cam shaft measures,
21.807 - 29.96
21.809 - 30.0 (bevel end) "

____ That means that your cam's intake-lobe is ONLY .04mm taller than it's exhaust-lobe.
__ I'm sorry I had doubted your successfully measured figures the first-time, as your unusual figures had led me to assume that perhaps you had measured the shaft-core's diameter to get your (then) identical base-circle figures. _ But now that you've got differing base-circle figures, and no-doubt got them after reading my last detailed post for correctly obtaining the desired figures, I'm now more confident that your measured-figures are indeed actual for YOUR camshaft.
__ The reason for my doubt of your obtained figures is because all the camshafts I've ever measured from w-c.250 & 450-Scramblers, (6 or 7 units), were ALL pretty-much identical with the very-same resulted lift-figures. _ Of-which, my memory has been '8.0mm' for the in.lobe and '7.8mm' for the ex.lobe.
However YOUR resulted lift-figure (for BOTH lobes) of 8.2mm tends to make me suspect that my memory is incorrect and perhaps that this cam.model's lift-figures were actually 8.2-intake & 8.0-exhaust, (although I'm doubting that).
It has been exactly 20.5-years since I last miked this particular cam.model, so I should try to find my old camshaft-data notes to make-sure that my memory has not failed me.
But one-thing is indeed certain... there's no other cam.model that your presented camshaft could possibly be, as no other stock-camshaft even comes close to matching all the details of yours !
__ While I never KNEW of the actual lift-figures of the REAL '450Scr cam.model', I've been led to believe that they were (at least) 9.0mm-intake and 8.5mm-exhaust, and your intake-lobe would have to be at least 8.5mm for me to even suspect that it could possibly be a real "450 Scrambler cam" !


" The cam shaft in the supposedly 1975 450 Scrambler looks the same. "

____ I'm sure that both are the same stock cam.model, as it seems that you have motor-parts from both a pre-1974 & a post-1974 450-versions, which originally employed the very-same cam.model (which is actually the ['White' color-coded] camshaft first employed in the 1968 w-c.250-Scrambler).
__ This w-c.camshaft's part-# has (unfortunately!) been assigned the very-same number -(0601.29.010) as the original ('White' color-coded) n-c.250-Motocross cam.model, which is a VERY different camshaft (which likely may-not easily swap-exchange into a used w-c cyl.head, due to it's fairly larger base-circle [compared to that of a w-c.camshaft] ) !
__ This w-c.Scr-camshaft's valve-timing is supposed to be: 27BT/75AB-intake & 60BB/32AT-exhaust, thus providing a MILD* valve-overlap of just 59-degrees,
(* extra mild for a 450 !).
THIS 'White'/Scr.cam-model has no business being in a 450 ! _ And had to have been installed in 450-models by the factory due to a cost-cutting compromise !
I have fair reason to believe that this particular 'White'-cam.model was ORIGINALLY designed for the w-c.350-Scrambler due in part to the fact that this cam.model has .2mm higher lobe-lift (than the other 250Scr.cam-models), and the w-c.250-Scr.models already have 2 other DIFFERENT Scrambler-type camshafts designed for THEM, while the 350-Scr.model NEVER got any other camshaft specifically designed just for IT alone ! - (As it, [at least for the U.S.market], was always fitted with a [too wild] Green&White-cam.) _ And also, I've heard tale from good sources that 350-Scr.models made for some markets other than the U.S.market, were stock-equipped with a "white" color-coded camshaft, (which no-doubt was THIS same particular Scr.cam-model !).
__ While this w-c.Scr cam.model starves a 450, it does work very well in a muffler-equipped 350 ! _ In fact, with no other changes in otherwise identical 350-Dukes, the 350 with THIS cam.model will actually trot-away from the other w-c.350 with a stock G&W-cam ! - (That is, unless they both have no muffler,, in which case, the two w-c.350s will stay neck&neck until the revs exceed 6000RPM, at which point the G&W.equipped 350 will then begin (merely) inching-away from the 350 equipped with this 'White'-cam.)
__ Whenever given the chance, I've always swapped the stock-camshafts between 450-Scramblers & 350-Scramblers, as that cam-swap is very BENEFICIAL for the performance of BOTH Duke-Scr.models, (cuz the G&W.cam is too WILD for a muffled-350, and the White-cam is too MILD for a 450) !
So I highly-recommend that those who are stuck with the stock-cams of their w-c.350 & 450-springer Duke-models, make that cam-swap ! _ (Unless of-course, ya can instead source the MOST-preferred cam.model for your particular Duke-model.)


DUKE-Cheers,
DCT-Bob

[graeme]

Bob, I would imagine these cams could have been slightly altered over the years to repair any damage?
Also what left the factory back in the '70's may not have been always the same ?
From your experience how does the Desmo cam compare in the 3 different engine sizes?

Graeme

[DewCatTea-Bob]

" I would imagine these cams could have been slightly altered over the years to repair any damage? "

____ I'm not sure what you mean exactly,
I tend to doubt many get repaired (without losing their original specs).


" Also what left the factory back in the '70's may not have been always the same ? "

____ It's my guess that each camshaft-model would get done a bit differently from one production-run to the next, (even-though intended to be the very same cam.model), but even-though the base-circle's diameter would likey vary somewhat between production-runs, the cam-grind's final lobe-lift height would be fairly well within the cam.model's spec.range.
__ Of your particular cam.model, (which may be referred-to as the '1968 w-c.250Scr-cam.model'), I've had one unit from a late'68 250Scr, another from a late'69-250Scr, another from a 1970-250Scr, another from a 1969-450Scr, two from 1970-450Scr.s, and one from a 1974-450Scr,, and all of them had pretty-much the same measure-results for the lobe-lift of each of their cam-lobes, (which I still believe I recall as being 8mm & 7.8mm), although I'm sure that there was a tolerance of up to .005" between them. - (In other words, 8.0mm +/-.0025" [.06mm], on the intake-lobe.)
__ Your 8.2mm lobe-lift results is about .006" higher than any other I-myself have ever measured before (of that cam.model),, and while that extra lift-height doesn't seem like much difference, it stands-out (to me).
I'm fairly confident though, that your presented camshaft is the same cam.model as is the unit still installed within your 450-springer cyl.head. _ Which BTW, you ought to remove and ALSO measure-out ! _ Cuz it would be fairly interesting to discover if your next measuring-job results with your same figures AGAIN, or comes-out more-like that which I'd expect.
__ I highly recommend that you replace that mild-cam with some other cam.model anyhow, as doing so will make your 450 MORE fun to ride !
In 450-engines, I've installed the following cam.models,, the Gray/w-c.250M3-cam; the G&W.350M3-cam, and the G&W.250F1-cam...
The 'F1-cam' makes a 450-springer run at least as fast as a 450-DESMO ! _ While the 'Gray-cam' is the best-choice for running with a muffler and makes the 450-motor funnest to ride,, but I'd have to say that, (of those three cam.models), the '350M3-cam' provides the strongest power over-all (in a 450).
HOWEVER, I never got to try-out either of the REAL 450-cam.models - (450Scr.cam, 450M3.cam) in a 450-Duke, yet I'm quite sure that the '450M3.cam-model' would make a 450-engine perform BEST, of all.



" how does the Desmo cam compare in the 3 different engine sizes? "

____ The (standard) DESMO-cam.model is the same 'Blue&White' cam-grind for ALL standard-production DESMO-models ! _ And it was based on the 250F1-cam and originally designed for the '1968-250Mark-3D' Duke-model.
And while the factory also specifically designed unique DESMO-cams for the 350 -(the 'Red&White-D.cam'), and the 450 -(the 'Gray&White-D.cam'),, Ducati cut production-costs by employing the same (mildest) DESMO-cam in all three engine sizes.
It's (rather wild !) valve-timing is: 70BT/82AB-intake & 80BB/65AT-exhaust.
It's cam-lobe lift-height is 9mm-intake & 8.5mm-exhaust.
The DESMO-cam's lift-ramps, (compared to nonDESMO-cams), appear to provide a slightly steeper lift-rate, which makes for a slightly greater 'average-lift', (meaning that the valves are held-open somewhat longer at the higher lift-heights [for the brief time they're open] ).
__ That std.DESMO-cam is very quite wild in the 250-engine, pretty-wild in the 350, and still fairly wild even in the 450.
It's my fair opinion that the 'std.DESMO' cam-model is too wild for either the 250 or 350 for normal street-use, cuz that cam combined with a muffler doesn't let the engine take full advantage of that cam's extended valve-timing that's intended to perform optimally at high-RPMs,, and while a muffler may not restrict too much at lower-revs, the D.cam is too wild to allow for also producing strong power during such low RPMs. _ In a 450 though, it's not as bad of a compromise.
__ I hope this reply/response to your question has now covered whatever you were actually interested to learn of.
If not though, then please clarify your inquiry, (as Duke-cam.model info has always been one of my favorite topics about Duke-models!).


Duke-Cheers,
DCT-Bob

[Muzz350]

Hi Bob
If I change the existing cam to a milder profile would I have to change the ignition timing to suit ? For instance, with the existing cam the plug fires 2.5 to 4.0 BTDC but if I fit a milder cam from a different model would I adjust the ignition timing to suit that model? (remembering also I have a 40mm inlet valve and 10 :1 compression.)
Muz

[DewCatTea-Bob]

" If I change the existing cam to a milder profile would I have to change the ignition timing to suit ? "

____ No,, generally, when ya change a camshaft, NOTHING-else NEEDS to be changed, (except of-course the valve-clearance will LIKELY need to be readjusted).
__ However, if your carburetion-jetting was very finely tuned specifically to the cam & exhaust-system you had, THEN readjustment of the carb.jetting may be required (in order to once-again get that fine-tuning reset back to about where it had been).
____ Since your camshaft-model is not the crazy-wild Rapido-version,, if your address were here in the U.S., then I-myself would offer to trade you a more suitable cam.model.
Have you found any acceptable prospect for an-other/milder camshaft yet ?
I'd suggest your best-choice would be the w-c.250Mark-3 cam.model, but the w-c.250Scrambler-cam would be just a little better for a bit more low-end power.
It would not be worth your trouble to swap for a Green&White-cam, as such a cam.model is not significantly milder than your Lento-version.


Hopeful-Cheers,
-Bob

[Muzz350]

Hi Bob
I went through my books and found the 860 GT/GTS and 900GTS had Inlet- 48 BTDC -83 ABDC, Ex 83 BBDC -48 ATDC. These models only had one coil type valve spring and reved to 7500.They also had 32mm carbs.
I have 3 workshop manuals and 2 of them ( both published by Clymer)say when measuring valve timing to first set the correct gap then insert a 0.1mm feeler gauge between the rocker and valve and rotate the engine untill the feeler is held tight by the valve and measure the degree wheel at that point. If I do it that way I get a totally different readings than if I set the gap at 0.1 rotate the engine untill the valve just starts to lift and take my reading there? The Clymer method gives readings close to those in the Spanish manual but the later method seems more realistic? Bob, you must have had the patience of Job to mess around with valves and timing. There seems alot of trial and error in it.
Muz

[DewCatTea-Bob]

" I have 3 workshop manuals and 2 of them ( both published by Clymer)say when measuring valve timing to first set the correct gap then insert a 0.1mm feeler gauge between the rocker and valve and rotate the engine untill the feeler is held tight by the valve and measure the degree wheel at that point. "

____ Alright then, but what's actually meant by: "first set the correct gap" ? _ If that's meant to mean the normal running valve-clearance, THEN I'd assume that direction to be faulty, because then the clearance-ramp may become involved with the intended v.timing-reading (and cause exaggerated lift-durations).


" If I do it that way I get a totally different readings "

____ Okay then, right,, then indeed that likely means you're then getting the 'clearance-ramp' (prior to the actual intended valve-lifting lift-ramp) of the cam-lobe involved with your measurement-readings, which is not fair because that's not the intended timing-points when the valve is actually expected to be lifted-off & away from it's seat.


" than if I set the gap at 0.1 rotate the engine untill the valve just starts to lift and take my reading there? "

____ If the normal running valve-clearance is .05mm/(.002"), (which ought to be about/near the height of the clearance-ramp), then resetting the v.clearance to .1mm/(.004"), ought to then allow for bypassing the clearance-ramp and thus prevent that (minor) ramp's unknown-duration from falsely-effecting the actual-intended measurement-readings.
__ However I'm thinking that rather than trusting your eye to discern exactly when the valve is actually starting to get lifted, it could quite possibly be better to instead reset the v.clearance to .005" (or .006"), and place a .001" (or .002") feeler-gauge under the rocker-tip and-then take your reading at the very-point when the feeler becomes clamped & held too tightly to slip/slide between. _ As at THAT point, the valve would've THEN (normally) been lifted-off from it's seat (and thus-THEN 'fairly' begin to have an effect on internal cylinder-pressure).


" The Clymer method gives readings close to those in the Spanish manual but the later method seems more realistic? "

UPDATED ---
____ It would've been helpful if you had mentioned the variances of the resulted timing-figures which you had obtained with each method you tried.
__ First,, the Clymer-method ought to be "realistic", but it needs to be known exactly what amount of recommended clearance is supposed to be used for taking the readings (when a ".1mm"/[.004"] feeler-gauge is directed to be employed for the job),, cuz if the valve-clearance is set at .1mm/(.004"), then that would cause the measurement-reading to include the 'clearance-ramp', (with assumption that it would be fair to include the clearance-ramps as part of the actual cam-lobe lift-ramp). _ BUT since the clearance-ramps are really NOT intended to actually LIFT the valve off it's seat, the inclusion of the duration-length of the clearance-ramps would completely mask & exaggerate the REAL/intended valve-lift duration, (and therefore the v.timing-readings would then not be 'fair').
__ Second,, I-myself am unsure of the exact/actual direction for taking the measurement-reading, as (supposedly) given by the Spanish-manual, AND I've never seen any English-publication giving the actual factory-recommend clearance-settings for those extra-wild Vento-cams. ...
Earlier in this thread, it seemed to have been suggested that the 'checking-clearance' should be set to ".1mm", (and that the normal running-clearance is: ".05 to .07mm"/[.002" to .00275"] ), which seemed to be sensible enough,, but that ("later") method didn't get completely ironed-out, and-so while it SHOULD work-out with identical results (as that of the Clymer-method), I guess we ought-not be too surprised that it's non-detailed instruction could possibly lead to results which don't match (the Clymer-method's).
(I've already suggested a way to possibly improve on the "later" method, [using a .001" gauge].)


" you must have had the patience of Job to mess around with valves and timing. There seems alot of trial and error in it. "

____ NOW, I can tell that you definitely indeed have gotten your feet wet with this tedious work...
Yes I recall having spent many frustrating hours trying to obtain trustworthy measurement-readings, in hopes of identifying unknown camshafts (by their v.timing-specs*). _ So that's why I was somewhat surprised that YOU seemingly had had a relatively easy/straight-forward time of it.
(* It's a good-thing that a +/- 5-degrees of tolerance is allowed for this timing-check work.)
It can be somewhat fun at first, but when things don't go right, THEN it can get very upsetting,, but after all has been worked-out, then some satisfaction can be put under your belt.


Dukaddy-DUKEs,
DCT-Bob
PS. - I'm quite sorry I had previously left this post with one of my paragraph's wording making a relatively great error in proper sense !
My mistake was not correctly realizing what Muz had actually meant by "later method"... As I misinterpretedly HAD assumed that the Clymer-method must be the "later" method, (since it got brought-up secondly in this thread).
So now after reading his post again, I NOW got-it right,, and have now adjusted my previous wording accordingly.
SORRY about that !

[Muzz350]

Thanks again Bob
The "Clymer" instructions did not seem logical and seemed to guarantee that I measured the clearance ramp in my V-timing readings but there it was in black and white so i thought I was missing something. I do like the rocker gripping the feeler gauge principle so increasing the clearance then inserting a feeler gauge which leaves the recommended clearance plus the clearance ramp is a very good idea.

Updating my electrical problem, it was the "NEW" coil. I replaced the coil and it works perfectly. I think that is a rare occurance.
Muz