Wanted Ducati 250 Clutch

[Rocla]

Hello Bob,

Your answer is interesting and raises some remarks and questions (don't consider my last post):

-diameter or cirumference, it is the same source, given you know the formula to calculate the second from the first one. I guess, if you emphasize on the second, is it because it is more specific and reliable to measure?
- my Scrambler comes from Barcelona in Spain, and it is in theory the same model than the ones we can see in France (I am French) and UK but there are so many combinations, it is a big mess, Mototrans, that was the maker in Barcelona, happened to modify many things, and not only on the body, but on the engine too. Except for the 1974 models, because Mototrans was the only maker for all the Scrambler engines, including for Italian market ! So, I have a kind of certainty that my engine is the same of every 1974 Scrambler in Europe. I would be prone to add "and for American market too" but I don't really know, may be there are some legal or cultural constraints?
- the current combination is 47x15 and, when I came from Barcelona (I was brave to tempt coming back with the bike just after buying it, but it worked perfectly) my feeling was, if I rely on my ears, to run 90 km/h at about 5000 rpm. I probably confused between 47 and 57 (!) but on my excel file, with 47x15, I actually get 19,38 km/h at 1000 rpm, and as a result 96,9 km/h at 5000 rpm. That means for me that the best combination is 45x16 (108 km/h at 5000) or 47x17 (110 km/h at 5000), with in this last case the advantage of requiring to change only the front sprocket...
- I introduce an another topic, to take benefit from your knowledge: I've noticed that the exhaust seal at the head cylinder exhaust port is with a lower diameter than the port itself (4mm less). I will enlarge it and the beginning of the exhaust pipe too. I think, in addition with the conical air filter, thanks to that, I can grab some additionnal power without lossing torque. I don't want to modify the ports timing and moving the cam for a more agressive one, it is the best mean to loose torque (given the number of miles on the clock, 44 000 km, high speed engine is not recommended any more). Do you think the conical filter plus the increase in the exhaust port diameter could help the engine a little bit?
- another additionnal topic: I was told that all the revel single Ducati engines were noisy. Is it because the conical sprocket on the top cylinder? I am wondering about sticking a rubber layer inside each head cylinder lid. Rubber is very efficient for noise isolation
-last question: do you think electronic ignition is significantly profitable for a 12v Scrambler performance?

[DewCatTea-Bob]

[quote= Rocla ...
" diameter or cirumference, it is the same source, given you know the formula to calculate the second from the first one. "

____ But of-course indeed-so... as by the inclusion of the factor of 'Pi' -(3.14). _ But as I've already-before indicated, the working-RADIUS is more important than the outer-diameter, due-to tire-compression under weight !
But rather than measure the height from the center of the axle to ground-level (and multiply by: '2Pi'), it's even more accurate to measure the rolled-length of the 'working-circumference' (which is a slight-bit less than the 'actual-circumference') !


" if you emphasize on the second, is it because it is more specific and reliable to measure? "

____ YES INDEED ! _ Because the tire naturally gets it's diameter COMPRESSED somewhat (when taken-down off the center-stand and made to carry weight) ! _ So therefore your "66cm.diameter" MAY actually be only-just 64.5cm, (which would thus-then make your rear-wheel's ACTUAL-circumference of 207cm, to become shrunk-down to a rolling-circumference of only about 202cm).
So-therefore you must measure the 'working-circumference' of your wheel, rather than perform your calculations using the 'calculated-circumference' -(which results with incorrect-calculations) !



" I have a kind of certainty that my engine is the same of every 1974 Scrambler in Europe. I would be prone to add "and for American market too" but I don't really know, "

____ For the year-1974, the USA only got the 450-models imported, (and 750s, but no 350s).


" cultural constraints? "

____ Yes,, in a way, sort-of...
Our U.S.importer -(Berliner), did-not like Ducati's own marketing-designs, and-so required Ducati to do things as Berliner saw-fit. _ And besides the Scrambler-look with the high-rise handlebars, Berliner also wanted a motorcycle that would appeal to ALL sects of American-riders !
So for mid-1968, they conceived-of the '350SSS', which was basically a 350-Scrambler with the Green&White-camshaft ! - (In my-own opinion, a very stupid conception made to appeal to common-motorcyclists rather than Ducati-loyalists.)
So that's how Ducati's 350Scrambler models came to not include the 'scrambler-cam'.
__ Your confirmation of a scr.cam in a 350, helps confirm my long-suspected suspicion that it was-NOT Ducati's-own dumb-idea to put racing-cams into scrambler-type motorcycle-models.



" the current combination is 47x15 "

____ Okay then, I now gather that it was-NOT the "47" which was your typo-error, but rather it was your "57" which was your actual mistake !?
This revelation means that when I had come-up with "10.1-MPH per 1k-RPM", that the ACTUAL calculation-result should've really been: '12.2-MPH per 1k-RPM' . - (Equaling 99-k/h @ 5k-RPM).
And with the circumference-size discrepancy correction also applied, that thus corrects the speed down-to 97-k/h @ 5k-RPM !
__ And now with the expected rolling-circumference correction ALSO applied, that then corrects the expected calculated speed down-to 95-k/h @ 5k-RPM ! _ And is THAT not the very-SAME RPM/speed-ratio -("5000 t/mn, 95 km/h") which you-yourself had FIRST estimated !?!
SO, it now SEEMS that you were somehow ALREADY aware of your exact speed/RPM-ratio even before we've come-to determine it's approximate value !
__ So does ESP run in your family, or what ?
I guess we should double-check ALL minor-details before jumping to such amazing conclusions (that this is working-out as it seems to be).


" my feeling was, if I rely on my ears, to run 90 km/h at about 5000 rpm. "

____ Those must-be SOME-KIND of "ears" you have on your-head !
__ Later (after you've checked your 'ROLLING-circumference), we'll then do the-math (to a greater/finer-degree), and determine which is actually closest, ("90" or "95" km/h @ 5k-RPM).



" I probably confused between 47 and 57 "

____ Well at-least we got to play with the-math a little-more, that way.



" but on my excel file, with 47x15, I actually get 19,38 km/h at 1000 rpm, and as a result 96,9 km/h at 5000 rpm. "

____ And with my-own (unchecked) figuring, I got 97.0-k/h @ 5k-RPM.
__ But to-be most accurate, you should check your wheel's actual 'rolling-circumference'.



" That means for me that the best combination is 45x16 (108 km/h at 5000) or 47x17 (110 km/h at 5000), "

____ The math-itself on those figure-results is correct but, those resulted-answers are probably-not exactly 'actual'.
And while those sprocket-ratios will indeed raise-up your overall-gearing a considerable amount, they'll still be a bit lower than that which Ducati had chosen for their road-models.


" with in this last case the advantage of requiring to change only the front sprocket... "

____ That seems to-be your smarter choice to try-out first, before then possibly going-ahead & choosing a new 40 to 45t rear-sprocket.




" I introduce an another topic,
Do you think the conical filter plus the increase in the exhaust port diameter could help the engine a little bit? "

____ Yes, but merely-JUST "a little bit",, nothing you'll feel the difference of.



" I was told that all the revel single Ducati engines were noisy. Is it because the conical sprocket on the top cylinder? "

____ What,, "conical sprocket", ? _ I don't think that the 'bevel-gear' itself is mainly responsible for all the noise.



" I am wondering about sticking a rubber layer inside each head cylinder lid. Rubber is very efficient for noise isolation "

____ You could get some of the rubber-block pieces that Jap.bikes use in-between the fins on their cyl.heads, and fit them into yours.



" do you think electronic ignition is significantly profitable for a 12v Scrambler performance? "

____ No, not really "significantly".



Duke-Cheers,
-Bob

[graeme]

Hello Rocla
Where did you hear this?
" Mototrans, that was the maker in Barcelona, happened to modify many things, and not only on the body, but on the engine too. Except for the 1974 models, because Mototrans was the only maker for all the Scrambler engines, including for Italian market ! "

I haven't heard that before.
I have a 74/75 450 Scrambler that has made in Italy, and is the same as a 74 Desmo from the cylinder down.
I don't care where it was made, but I haven't heard that all SCR engines were made in Spain for 1974 on.
Or is this just the 350 engine?

Regards
Graeme

[Eldert]

in 1974 when Ducati stopped production of the singles some Italian built singles had Spanish engines .

i have seen blue and gold Mark 3 350cc with Mototrans engines . but this only happened when the supply of Italian engines dried up

Eldert

[Rocla]

Hello Bob, Eldert and Graeme,

I've read or heard that (with the sources of such pieces of information):
- Mototrans produced all the engines since 1974 (or 1973 ?) for all the markets including Italy (Ducati or Mototrans official website, I don't remenber). Myabe it confims what you say about the stop of the italian maker?
- Mototrans used to feel free with many details e.g. the wheels and tyres (strongers, with a 19' front wheel, not a 18'), the deco (no black strike on the middle of the tank and mudgards), (it is written womewhere in Motoscrubs forum and it is easy to check on Google image if you enter "Scrambler Mototrans" and you can check the genuine model that I've bought here too: http://strv.pagesperso-orange.fr/motode ... Ducati.htm )
and sometimes the engine (but I was told by a friend, I can verify)
- As yo ucan see, there are many combinations, probably a mixture of the last parts in warehouse, about the tool box, the seats, the fork, the colors...

BUT EVEN FOR THE SPANISH MODELS, IT IS WRITTEN ON THE ENGINE HOUSING "MADE IN ITALY". My engine is "made in Italy", from Barcelona... How can you be sure of the origin of your 450 Greame? I've red on Motoscrubs and somewhere else that the engraved code on the frame is the most reliable clue to identify if it is an Italian or a Spanish built: MD followed by numbers means "Mototrans Ducati". I guess the others have only a D and the figures...

[Jon Pegler]

It's not quite so simple with Mototrans engine and frame numbers.
Quite often, the information written in books is incorrect and just keeps getting re-written incorrectly on forums like this.
Graeme will be correct in thinking his 450 is Italian, as Mototrans never built any of the 450 motors or complete bikes.
Equally, Mototrans never produced any of the Desmo single motors, so if you own a late 250 or 350 Desmo, you can be sure that it was made in Italy.
However, many of the last 250 and 350 motors used in both the Mark 3 and Scrambler models were made in Barcelona.
Many of these motors have 'Made in Italy ' cast into the outer engine case, but are readily distinguished by their Spanish head casting, assuming it is an original motor.
Some late Spanish timing covers had 'Made in Spain' cast into them.
Most narrowcase timing covers produced in Spain just have the large 'Ducati' cast into the side casings.
When it comes to numbers, most of the narrowcase Mototrans machines do have the engine and frame number prefixed by MD -Mototrans Ducati, unlike the Italians who used DM - Ducati Mechanicca.
The narrowcase Spanish models also use different engine and frame number series compared to the Italian models.
By the time Mototrans started producing widecase single motors in early 1973 they started to stamp many engines DM 250 or DM 350 like the Italians, so it can be quite confusing deciding just where your motor came from.
Spanish frame numbers nearly always start with the prefix MD however.

Jon

[Rocla]

Thanks Jon,

It is clear that it is not simple
About deco, it seems as much as tricky... Is there a book of references with all the kinds of models? When I started the restoration of my 350 Scr, I decided to observe the Mototrans strips (no central strip like for the italian one, but 1 on each side of mudgards) but to change the color (I replaced the blue by the genuine ochre), the headlamp and the rear light (I've bought the italian style ones)...
I think it is not perfectly orthodox (in fact, my first criterion was the aesthetic) but how to proceed if there is no bible with all the deco combinations?
And is it true that Mototrans are less valuable than the italian ones? Even, as you suggested in a forum, I think the Mototrans wheels are most beautiful, stronger and with a bigger dimension on the front wheel. As I see it, a Mototrans very well restored should be as much interesting as the Italian one, is not it? Maybe more because they are less numerous?
I have no idea about that, and maybe it depends on each country: USA, UK, Italy, Spain and France have maybe their own preferences?

[DewCatTea-Bob]

[quote= Rocla ...
" (don't consider my last post): "

____ As you had requested, I had ignored responding to your previous-post (at the bottom of the previous-page),, but I found things within it which I felt were worth replying-to, so here's what I've got to say (so far) about those particulars.

by Rocla » Fri May 24, 2013 8:21 am
Hello Bob,

. Maybe there was a confusion between 47 and 57 but it is 47 teeth on the rear and 15 teeth on the front sprocket. I don't catch anymore. Could you confirm the speed at 1000 rpm in 5th speed with a 47x15 and 350 Scrambler genuine engine? Is it about 16 or 18km/h?

- I don't have the sufficient knowledge to introduce air penetration forces but your top speed estimation seems OK to me, and it won't be so far from the genuine top speed (130 !). My objective is to be somewhere between 105 and 110km/h at 5000 rpm. The only information I need to order new sprocket and crown is to know my actual speed at 1000 rpm (or 5000)... By mails, it is not easy to communicate, but at last we will find the solution

" Maybe there was a confusion between 47 and 57 but it is 47 teeth on the rear and 15 teeth on the front sprocket. "

____ Well a 10-tooth difference is quite a sizable discrepancy to allow going left unchecked more than once or twice, so that's why I hadn't much suspected your repeated "57" as being any typo-error.



Could you confirm the speed at 1000 rpm in 5th speed with a 47x15 and 350 Scrambler genuine engine? Is it about 16 or 18km/h? "

____ Okay, for determining the speed at 1k-RPM,, it's really-not too complicated to determine, once the overall gear-ratio & rear-wheel rolling-circumference figures are known. ...
__ The 350's internally-resultant 5th-gear ratio is 2.043:1, and your sprockets of 47/15t provide a ratio of 3.133:1, which results with an overall-ratio of 6.40:1, (which of-course is also the number of times the eng.crankshaft turns for each rotation of your rear-wheel). _ So at 1k-RPM, that means the wheel turns only 156.25 times a minute, which is 9375 times per hour.
Your rear-wheel is figured to be 81-inches in (virtual)- circumference, so that means it rolls 759,375 inches per hour,, and since there's 63360 inches in a mile, that therefore means your wheel rolls at 12-MPH at 1000-RPM , which converts to about 19.4-k/h -(about 97-k/h @ 5k-RPM).



" I don't have the sufficient knowledge to introduce air penetration forces but your top speed estimation seems OK to me, and it won't be so far from the genuine top speed (130 !).

____ I haven't before/yet suggested any attainable TOP 'top-speed' for your 350-Scrambler but, it's certainly got to be greater than merely-just "130"k/h -(81-MPH) ! ...
I believe a 350-model such as yours should be able to reach about 95-MPH -(at-least 150-k/h). _ But in order to reach it's possible actual TOP-speed, it requires a gear-ratio which happens to exactly match-up the engines maximum/peak-HP against the greatest wind-resistance/speed that that amount of eng.power can possibly cope with/against.
__ So then, if we figure (& assume) that your engine produces it's max.power at 7200-RPM, then we'd desire a gear-ratio (either 4th or 5th), that allows the engine to rev near 7k-RPM around 150-k/h. _ So with your rear-wheel's circumference being about 82-inches (at those higher speeds), that means with your current 47/15t.gearing, your engine would have to spin/rev over 7.7k-RPM to reach 150-k/h,, and with that-RPM being 500-revs past (the supposed) 'peak-power', it's then unlikely that your top-speed will be very-much higher than 140-k/h, (without any assisting tail-wind).
So this means that the overall gear-ratio needs to be raised-up 7 to 10%,, and a 47/16t sprocket-combo happens to provide an overall-ratio which almost falls-into that requirement, thus-then providing 150-k/h at 7250-RPM. _ However it's likely possible that slightly higher/taller-gearing could still-yet increase top-speed further-yet...
A 45/16t sprocket-combo would come-close (to the expected top-speed of near 96-MPH), yielding 156-k/h @ 7.2k-RPM,, while 48/17t would yield 155-k/h near the 7200-RPM figure.



" My objective is to be somewhere between 105 and 110km/h at 5000 rpm. The only information I need to order new sprocket and crown is to know my actual speed at 1000 rpm (or 5000)... "

____ Your present 47t wheel-sprocket with a 17t drive-sprocket would provide an additional 1.3-MPH at the '1000-RPM', for an increased speed/RPM ratio of 13.3-MPH per 1k-RPM,, which is equal to about 109.7-k/h, at the '5k-RPM'.
__ So it seems that all you need to do is replace your 15t with a 17t drive-sprocket,
(which also may just-happen to match-up your engine's 'peak-power' RPM-range with the highest attainable top-airspeed, [if it's peak-power is rather actually lower, near about 7k-RPM] ).

____ Please let us know what sprocket-combo you next try, and how you then like it.
__ If you choose to go-with the 47/17t.combo and then-next come-to find-out that 5th-gear actually indeed happens to provide the highest possible top-airspeed (for your 350 & yourself), but-yet STILL wish to further calm-down eng.vibes for during your most-often chosen cruising-speed,, then since 4th-gear is about 14% lower than 5th-gear, you could raise your overall-gearing about the same 14%-amount by replacing your 47t with a 41t.wheel-sprocket, so that you could then pretty-much retain the SAME 'top-speed' (in 4th-gear), and yet ALSO lower your cruising-speed RPMs (in 5th-gear), for attaining a more settled-down & pleasurable ride.
__ However, you couldn't then expect to run right-at 'TOP-speed' whilst in 5th-gear any-longer, because the RPMs would then be lowered-down to just 6150-RPM, at-which eng.power would then happen to-be too-low to fight-against the wind-resistance of speeds near 150-k/h.
But with the resulted 4.927:1 overall gear-ratio (of the 41/17t.combo), your 350 would then cruise at 126-k/h at 5000-RPM, (while 4th-gear would retain your desired 108 to 110-k/h @ the 5k-RPM).


Hopeful-Cheers,
-Bob

[Rocla]

Thanks for this analysis, despite for me the topic was over, I've made my decision: 17x47 or 16x45 (according to the availibility of parts) given my objectif is to cruise at a normal speed (108/110 km/h) without burning the engine beyond the 5000 rpm threshold.

But I think you are optimistic about the expected max speed for the Scrambler 350. Maximum speed is due to the power, not the displacement. As you know, most of 125cc are around 11HP to 15HP in Europe and can reach respectively 105 km/h to 125 km/h. My 250 is expected to have a 21HP genuine output and has it maximum speed at 130km/h. The mine one, which is now deeply modified (but mainly for torque and acceleration) has probably a 22HP output, and barely exceeds 130 km/h...

So, if the Scrambler is expected to develop 24HP, as a result, it cannot exceed something like 135km/h (higher the speed to be exceeded is, bigger the additionnal power is required, probably because of a square root relationship between air penetration and speed, if I remenber well)

It is clear for me that 150 km/h is out of reach for a Scrambler engine, even if it is possible for a 350 Mark one, significantly more powerfull (34 HP ?).

Unless documents we know about the Scrambler show wrong specifications and wrong output?

[DewCatTea-Bob]

[quote= Rocla ...
" Thanks for this analysis, despite for me the topic was over,

____ Much of what I had to add was already thought-of, but left-out of my prior previous-post because your updated-post didn't include ALL the same topic-matter.
And besides, I figured that other 350Scrambler-owners would also find that left-out info to be of fair interest as well.



" But I think you are optimistic about the expected max speed for the Scrambler 350. "

____ Of-course that may be a possibility under a number of various conditions...
For instance, the rider's bulk-size can possibly MUCH affect the wind-resistance which the eng.power must fight against.
And also, the muffler that's employed may curtail eng.power with too-much back-pressure.
And of-course as already before noted, most 350-models are-not properly 'geared' to well MATCH 'peak-power' against the max.wind-resistance that's possible to be coped-with (by the available max.peak-power).
__ So indeed there are a number of conditions which all have to come-together, in order to actually reach the maximum-speed that's actually possible !
I know for certain that a 350-Sebring (with small carb, port & valves) can be re-geared (not even OPTIMALLY) to reach 90-MPH, and-so a 350-Scrambler (with 3 more HP) ought to-be able to reach 96-MPH (once 'optimally-geared' to do so).
__ As Duke-models came stock from the factory, their gearing was set either too-low (45/15t, for Scr.models), or too-high (45/17t; 40/15t, for road-models), in-order to-be able to match peak-power with the maximum possible top-speed.
So now that YOUR 350's gearing will be closer to being optimally-set,,
if YOU aren't bigger than 5'7" & 150lbs in size, then you really ought-to be able to at-least get your 350 up-over 140-k/h !



" My 250 is expected to have a 21HP genuine output and has it maximum speed at 130km/h. "

____ So you have a "250" as well ? _ Or is that a typo-error ?



" The mine one, which is now deeply modified (but mainly for torque and acceleration) has probably a 22HP output, and barely exceeds 130 km/h... "

____ That seems about-right for a 250 with unoptimized overall-gearing.



" So, if the Scrambler is expected to develop 24HP, as a result, it cannot exceed something like 135km/h "

____ Well actually, stock 350Scrambler-engines are known to be able to reach up-to near 90-MPH -(145-k/h) !



" (higher the speed to be exceeded is, bigger the additionnal power is required, probably because of a square root relationship between air penetration and speed, if I remenber well) "

____ Actually, I believe its really 'twice doubled-up',, in other-words, for example, the wind-resistance at 80-MPH, is 4-times greater than at 40-MPH (and not merely-just doubled).



" It is clear for me that 150 km/h is out of reach for a Scrambler engine, "

____ I gather that YOU are a rather large person then ?



" even if it is possible for a 350 Mark one, "

____ Mark-3 350-models are known to reach 95-MPH with stock-gearing, (and can reach 105-MPH with optimized-gearing).


" significantly more powerfull (34 HP ?). "
____ Only the camshaft is different -(wilder), and 350Mk3-eng.power is expected to-be about 29-HP.



" Unless documents we know about the Scrambler show wrong specifications and wrong output? "

____ It's well-known that HP-figures are rather vastly inconsistent, and therefore can-not be trusted for comparison (from one document to another) !


____ Please let us know when you've changed your 350's gearing.


Dukaddy-DUKEs,
-Bob