Tuning a Mototrans 250cc

[LaceyDucati]

Bob

I have a bare Spanish 69mm 250 head here and unlike Elderts head it has the flat top.

Inlet port measures 27mm and the seat throats are 32mm inlet and 27mm exhaust. Looking at the seats I guess the inlet valve was possibly 35mm and the exhaust 30mm. Exhaust side looks original, but I'm not sure the inlet has not been played with (it's been blast cleaned so not eay to see).

It's also surplus if required.

As an aside, on the race engine I built that Eldert mentioned, I had to cut a "window" in the top and plate it to allow a high lift race cam to fit. A lot of work went into the engine and it did actually produce more top end power than any standard stroke engine I have built. Valves used were 39mm inlet and 34mm exhaust. The chamber was remodeled with a flatter squish and the valves brought out further to form more drop on the ports. The longer valves were also re-angled slightly to avoid a clash in the middle due to the cam used. Unfortunately no pictures as it was pre digital camera's for me, how life changes!

Regards Nigel

[Jon Pegler]

I would guess that Elderts head has come from a very late n/c mototrans model.
Probably from a Road 77 12v.
I said earlier that the Road models were the most confusing bikes that Mototrans produced.
They produced 250s in both wide and narrow case format, with both 69mm bore and 74mm bore.
I think the 350s were all widecase, unless anyone knows otherwise.
The Road 77 12v was a narrow case machine only produced in 1977 and 1978, production stopping when the new Strada 250 was released in 1978.
It did have a number of unusual features, as production of castings was gearing up to make the Strada.
This included some machines appearing with the square shaped cylinder barrel (jug) more commonly seen on Stradas, Ventos and Forzas, but not all.
Equally, the earliest Ventos often did not have the square cylinder barrel.
I think Elderts head is from a late casting, similar to that used on a Strada, but machined to fit the narrower head bolt spacing and having a smaller inlet port.
The Road 77 12v had a 27mm Spanish Amal concentric carb as standard, and as its name implies 12 volt electrics.
I think most of the Road 77 12v must have stayed in Spain, because most of the export Ducati Roads are widecase.

Jon

[DewCatTea-Bob]

____ Thanks Nigel & Jon for your informative additional related info !
__ It must be a first-occurrence that you two top-notch members happened to submit your posts consecutively within the same thread and within the very-same hour's time !
__ I suppose you two have certainly talked together on the phone before, but I wonder if you've both ever met in person ? _ If so, I wish I could've overheard whatever you two guys talked about, as it no-doubt would've certainly been interesting topic-matter worthy of listening to !




By Nigel ...
" All the Green and white cams here in the UK are the same as far as I have seen, the ones with the lower lift.
I haven't come across this other G/W in the last 25 years of my involvement in Ducati singles, "

____ The two G&W.versions are very much the same and-thus fairly difficult to tell-apart, (which is probably why they were both allowed to be classified with the same color-code) ! _ So I still think it's probable that you've possibly once had both versions pass-through your possession and had just assumed they were all the same common G&W.cam-model.
But I've personally handled several examples of each (taken from 350 w-c.engines), and the two versions are consistently distinctive and certainly not of the very-same cam.grind-model !
However it's no-doubt probably indeed the same over-there as it has been over-here in the U.S., with the quantity of the 250F1-G&W.version out-numbering the 350Mk3.version by about 5 to 1.
And-also, most made-for-USA w-c.350 parts-books rather indicate the part-number of the 250F1-cam.model.
__ If you have a collection of 350w-c.owner's-manuals (as I do), you can look-up the contained/listed camshaft-specifications which will ether display the valve-timing of the 350Mark3-cam.model (within pre-69 manuals) or that of the 250F1-cam.model (within 1969/70 350-manuals). _ The notable-difference between the two cam.versions being that the 350-version has it's ex.valve closing at 50-degrees after TDC, while the 250F1-version has it's ex.valve closing at 65-degrees after TDC !
Besides reduced duration (for a nonracing-cam), the 350-version also logically has the higher lobe-lifts -(10 & 8.5mm), as it isn't expected to rev as high as a 250F1 racing-engine !
__ It ought-to already be realized that the std.DESMO-cam.model was based on the 250F1-cam.model, thus those two cam.models have nearly the same (opening-lobe) cam-specs.




[quote= Jon Pegler ...
" I would guess that Elderts head has come from a very late n/c mototrans model.
Probably from a Road 77 12v. "

____ So then I've been incorrectly led to believe that the 24-Horas was the only 250-engine/model made with the 69x66-B&S ?



" They produced 250s in both wide and narrow case format, with both 69mm bore and 74mm bore. "

____ Wow, this is pretty-enlightening news for me ! _ Do you really mean that there were actually Wide-Case 250-models made with w-c.engines that also employ the 69x66mm bore & stroke as well ?


Enlightened-Cheers,
-Bob

[Jon Pegler]

Sorry Bob,

I should have chosen my wording more carefully.
Mototrans made the 250 Road model as a narrowcase with a 69mm bore, but also produced a widecase 250 Road which had the 74mm bore, not 69mm as you presumed from my original post.
By far the largest number of 69mm bore 250s made by Mototrans was the 250 De Luxe.
In production from 1963 to 1974 in both 4 and 5-speed versions (from 1970), approximately 8000-9000 were made.
24 Horas models only numbered about 1500.
Road 77 12v models numbered in the hundreds.

Jon

[LaceyDucati]

Bob

Eldert and I do know each other and have met on numerous occasions at race meetings around Europe. For a number of years through the 90's I raced in the Netherlands sometimes a couple of times a year. We have actually been in the same races, but mostly I raced against Elderts Brothers Jan and Peter, some of my most enjoyable racing. Haven't bumped into Eldert in recent years, but do communicate from time to time.

Regards Nigel

[DewCatTea-Bob]

[quote= Jon Pegler ...
" Mototrans made the 250 Road model as a narrowcase with a 69mm bore, but also produced a widecase 250 Road which had the 74mm bore, not 69mm as you presumed from my original post. "

____ Okay then, thanks Jon !
I now gather that Mototrans never made ANY wide-case 250-engine with the 69x66mm bore & stroke.
And-also now gather that in addition to the DeLuxe & 24-Horas 250-models, Mototrans also made the n-c.250-Road with the 69x66-B&S,, (so that's just three Mototrans-models in all, that they made with the small-bore 250-engine ?).
__ Just to confirm that I haven't been wrong to have believed-so,, but isn't it true that (sometime before 1971), Mototrans also made narrow-case 250-motors with the 74x57.8-B&S, as well ?



" By far the largest number of 69mm bore 250s made by Mototrans was the 250 De Luxe.
In production from 1963 to 1974 in both 4 and 5-speed versions (from 1970), "

____ So then may I assume/gather that ALL 69x66-B&S models were only 4-speeders (until 1970) ?

I would guess that Elderts head has come from a very late n/c mototrans model.
Probably from a Road 77 12v.

____ I certainly agree that his example has to be from a latter-type head-casting, (probably after Mototrans also began producing w-c.motors).
So do you happen to know which other 69-bore/square-pattern 250-heads came with that rather std.type/27mm intake-port,, and/or, which 250-model(s) came with the extra-small in.port ? -- Did the Deluxe AND the 24-Horas 250-models both come-with the small-port ? _ Or do you think that Mototrans was-not loyally model-consistent with such cyl.head traits ?

____ And BTW, do you happen to know whether Mototrans ever made a 76x66mm-B&S 300cc-engine ?
__ I also wonder where you've lived all those past years, to have gained such enlightened/extensive knowledge about 1963 & newer Mototrans-models ? _ Did you ever reside within Spain itself at-all ? _ Or did you merely once live in a country which imported most-all Mototrans-models ?


Enlightened-Cheers,
-Bob

[Jon Pegler]

In answer to some of your questions, Bob.

The first 5-speed n/c machines to come out of Spain appeared at the end of 1966, the 1967 model year.
This was a 200cc 5-speed Elite, replacing the previous 4-speed Elite. The new model was known as the Elite V5.
At the same time, the existing 4-speed 175 was replaced by a new 200cc 5-speed model, the 200TS.
Also produced at the same time was the 24 Horas, 5-speed again.
The 250 De Luxe continued in 4-speed form until about 1970 when it also gained the 5-speed motor.

I can't remember what the valve and inlet port sizes are for all these different models, without dismantling some of my own bikes to measure them.
I seem to remember that they are nearly all on the small size.
I'm going to have a V5 Elite motor apart in the next few weeks, so I'll measure a few things whilst it's apart.


I don't think there was ever a n/c 250 with a bore and stroke of 74x57.8
There was a couple of prototype oddities shown at the Barcelona motorshows in the early 1970s.
There was a n/c machine called the Electronica with a 300cc motor.
The earliest Forza was shown as a 300cc machine in w/c form with a bore and stroke of 75x76mm.(335cc?)
By the time the Forza went on sale in early 1977 it was 76x75mm
I haven't found any evidence that the 300cc n/c Electronica ever went into general production.

With the published material on Mototrans machines being either very limited or even wrong, I started making my own notes whenever I came into contact with them.
Together with a collection of Handbooks and Parts books covering most of the Mototrans machines, I think I am starting to get to grips with all the strange things they did before the end in 1983.
The Road models, together with their odd engine and frame numbering system is still confusing, though.

Jon

[NewKidOnTheBlock]

Back again! I've been keeping up with all the posts here although not posting myself as I didn't feel I had anything useful to add but all very interesting discussion.

I received my piston today! Exciting times as it's the first part to arrive. I've taken some photos (Bob - you may find my lighting peculiar again, forgive me!) http://imgur.com/a/YqGu7. The recesses on the top measure 34mm for the exhaust and roughly 37-38mm (Although I have no proper measuring equipment to hand so will recheck this once I have the opportunity).

I weighed both pistons with rings and pin and the new one comes in at 290g wheras the original came in at 325g so that's a bonus. I am not certain whether it's forged or cast, the non-machined faces in the underside are of very smooth finish so possibly die cast? Although it's Wossner branded and their website claims '"Manufacturer or forged pistons" although this does not explicitly state they only produce forged pistons.

I've spent more time thinking about this and reading and I'm leaning back towards the 'scrambler' cam, and weighing up whether it's worth taking the plunge and having a forged conrod fitted as that's the weak link and once I've had one fitted, with the mileage I'm likely to do I don't imagine having to touch the bottom end again.

[DewCatTea-Bob]

[quote= Jon Pegler ... "
" The first 5-speed n/c machines to come out of Spain appeared at the end of 1966, the 1967 model year.
Also produced at the same time was the 24 Horas, 5-speed again. "

____ And here I had always before thought that the 24-Horas was an oddish model only made for just a year or two around 1970.
So there weren't ever any 4-speed 24-Horas (and made before 1967), were there ?



" The 250 De Luxe continued in 4-speed form until about 1970 when it also gained the 5-speed motor. "

____ Okay, I now realize/gather that it was ONLY the DeLuxe-model which remained with the 4-speed motor after most-all the other n-c.250-models had previously switched-over to 5-speed motors long-before 1970 (and possibly ALL-others after 1966).



" I can't remember what the valve and inlet port sizes are for all these different models, without dismantling some of my own bikes to measure them. "

____ It's fairly certain now that the 250-Road cyl.heads all have the std.port-size (along-with 27mm-Amal).
Do you happen to have both the Deluxe and the 24-Horas 250-models ? _ If so, can you at-least tell us what carb.models are on them (if they both still have the stock carb.size) ?



" I don't think there was ever a n/c 250 with a bore and stroke of 74x57.8 "

____ I've seen a friend's book (covering Ducati & Mototrans Duke-models) which I recall listed some Mototrans 250-models with the short-stroke 250-engine, but I think it rather indicated the year without also mentioning whether n-c or w-c versions. _ So I may've simply assumed that some of their listed short-stroke 250-engines were n-c.type (as Ducati's own were).
I'll try to find-out about that again, cuz I was pretty-sure that there was at-least one 74x57.8/short-stroke narrow-case 250-engine listed under the Mototrans-models section of that book.




" There was a n/c machine called the Electronica with a 300cc motor.
The earliest Forza was shown as a 300cc machine in w/c form with a bore and stroke of 75x76mm.(335cc?)
I haven't found any evidence that the 300cc n/c Electronica ever went into general production. "

____ I seem to recall also seeing listed in that book I mentioned, an 'Electronica' model with a 75x76-B&S engine,, but I had assumed that those figures were just a mixed-up misprint.
__ This also seems to remind me that that book's Mototrans-section also listed a 225cc-model of some sort, or maybe an undersized 250-model with a 72mm-bore,, (my memory is no-doubt confused about whatever that extra-strange single actually was).



" I think I am starting to get to grips with all the strange things they did before the end in 1983. "

____ Is that when Mototrans stopped making Duke-models, or is that the year when Mototrans-itself went kaput ?


____ THANKS for all the extra info you've included, Jon !


Duke-Cheers,
-Bob

[DewCatTea-Bob]

[quote= NewKidOnTheBlock ...
" I've been keeping up with all the posts here
all very interesting discussion. "

____ I've been wondering if you've been doing-so, and have understood the stuff about your intake-port's size and it's effect combined with the wild-cam (which your motor is supposed to have).



" I received my piston today!
I've taken some photos (Bob - you may find my lighting peculiar again, "

____ No, not really (this time),, as this batch appears rather normal looking (and not appearing as if lite by mere moonlight).
__ It's a rather strange (but also smart) looking piston. _ Does it not include any notch-way for the sparkplug-tip within it's rather steep & tall crown-face ? _ If not, I hope there's still room left for a plug with an extended-nose/tip.
What's it's comp.ratio claimed to be ? _ With that rather small & high flat-plane atop it's crown, it thusly ought-to have a rather high-CR !



" The recesses on the top measure 34mm for the exhaust and roughly 37-38mm "

____ So then we can now expect that you may choose to install rather large valves.
However, it seems to me that if those valve-reliefs are as large as you've indicated, that at-least the intake-side's outer-boundary/cut-away would then protrude a bit into the squish-band area as well, since that piston is supposed to be no larger than 70mm.
So you ought-to check that all fits well, with the piston-crown placed into the combustion-chamber with your intended over-sized valves set at your intended camshaft's overlap-position.



" I weighed both pistons with rings and pin and the new one comes in at 290g wheras the original came in at 325g "

____ Can you post a picture showing both pistons side-by-side (preferably laying-over with a rist-pin aligning their pin-holes) ?



" I've spent more time thinking about this and reading and I'm leaning back towards the 'scrambler' cam, "

____ How-come exactly ?
__ I do agree that the Scr.cam combined with the small-port & long-stroke would all gang-up together to provide a more fun ride, (if you're much like myself who prefers the power-characteristics of a single-cylinder engine).
__ Such an increased low-end torque 250-engine combined with the lighter weight of your intended 160-chassis, would be a very impressive 250-bike taking-off from standing-starts and likely even at higher roll-on speeds as well. _ And-so you could then certainly expect to out-accelerate most any other 250-Duke (at speeds under 60-MPH).
____ I've had a 'higher-torque' 250Scr.project (with Monza-head), of which I installed a 22mm-carb (from a 160) mounted on a non-stock manifold that had an extended 22mm inlet-tract,, and not-only was it's low-end torque improved as expected, but also the mid-range power didn't suffer any, (if it wasn't also increased a bit) ! _ It was the extra fun ride I had expected it to be ! _ (If-only I could've also had it with the long-stroke crank, as well,, I sure would've !)
__ Those who race on tracks where 1st.gear gets much use,, really ought-to try tuning an engine for low-end torque, rather than for high-RPM performance,, as such uncommon tuning can actually provide a bit of advantage against the pack (of regularly-tweaked hopped-up racers) !
It's just more fun to race & ride with rather instant power on tap, than having-to wait for revs to build-up sky-high (just to get an extra HP or two) !


Hopeful-Cheers,
-Bob