Tuning a Mototrans 250cc

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NewKidOnTheBlock
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Re: Tuning a Mototrans 250cc

Postby NewKidOnTheBlock » Mon May 19, 2014 7:54 pm

Thank you all for your replies. It would seem that I am about ready now to begin the work, once my piston arrives I shall start getting everything else in place. I will endeavour to update you on here.

DewCatTea-Bob
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Re: Tuning a Mototrans 250cc

Postby DewCatTea-Bob » Mon May 19, 2014 8:01 pm

[quote= LaceyDucati ...
" He does have the green and white profile, but I wouldn't bother as it won't be suitable. "

____ I wonder WHICH Green & White cam-profile !? ...
I'd agree that the '250F1' G&W.cam would be unsuitable, (for anything other than racing on circuits which don't ever call-for reengaging 1st.gear),, however the 350Mk3.G&W version is just a step hotter than the M1/Gray-cam, and not so awfully wild.
It's really too-bad that Ducati ever allowed these two (only somewhat-similar) cam-models to become color-coded the same !


Dukaddy-DUKEs,
-Bob
PLEASE NOTE... If this-post is not-yet signed-off with '-Bob', then I'm still in the process of completing it,, and if not also included with 'DCT' near bottom as well, then I may edit this post's wording at a later time. - Dct.Bob

DewCatTea-Bob
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Re: Tuning a Mototrans 250cc

Postby DewCatTea-Bob » Mon May 19, 2014 8:21 pm

DewCatTea-Bob wrote:[quote= NewKidOnTheBlock ...
" see the photos on this link, they will probobaly help to answer more questions than I have with words alone: "

____ I scrolled-through about 18-pix
I'll
see what I can do to make their subject-targets more visible.
____ I've chosen the most useful pix you had, and will now soon post their subject-targets within this post (and perhaps another as well).


____ After seeing the picture of your 200/250-cyl.head and noticing it's finned-top, I then realized that I've forgotten of something which I've always been well aware of...
Those 200-type cylinder-heads rather have 'FLAT-tops' which don't have the rounded/lifted-dome that the newer head-design employs so as to create additional cam-lobe cavity-volume for the cam-followers of the rocker-arms (which may have-to work with cams that have higher lobe-tops) !
__ So another possible issue with fitment of newer n-c.cams, is possible insufficient clearance between the cam-followers & the cavity's overhead-ceiling.
However a simple solution for such issue, is to simply grind-off (& polish of-course) up to .5mm from the top-sides of the followers, (for your Scr.cam).
__ I wouldn't have thought of this as being much of a concern,, but obviously Ducati had, or-else it seems they wouldn't have bothered with replacing their nicely designed fins with the rather bare-dome atop their later head-designs.
__ But still this overlooked concern shouldn't be any issue for adapted-installation of w-c.cams,, as THEIR base-circle diameters are about 2.5mm smaller, thus compensating for taller cam-lobes.
You do not have the required permissions to view the files attached to this post.
PLEASE NOTE... If this-post is not-yet signed-off with '-Bob', then I'm still in the process of completing it,, and if not also included with 'DCT' near bottom as well, then I may edit this post's wording at a later time. - Dct.Bob

LaceyDucati
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Re: Tuning a Mototrans 250cc

Postby LaceyDucati » Mon May 19, 2014 9:15 pm

Bob

The G/W he does is the mark 3/ SCR cam.

My experience is that this cam is okay for a 250 race bike, not the best but reasonable top end. Nothing special in a 350 race bike and lacking midrange for the road in either (even with an open exhaust). The other G/W is not well known in the UK, so no experience.

Nigel

Eldert
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Re: Tuning a Mototrans 250cc

Postby Eldert » Mon May 19, 2014 9:40 pm

i posted this before in another topic but here it is again

a Mototrans 69 bore head but it looks like they modified the mould to accept a high lift camschaft or it could be a differend casting .

Image

Eldert

DewCatTea-Bob
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Re: Tuning a Mototrans 250cc

Postby DewCatTea-Bob » Mon May 19, 2014 10:07 pm

[quote= LaceyDucati ...
" The G/W he does is the mark 3/ SCR cam.
The other G/W is not well known in the UK, "

____ I've covered details about this before, so I gather that you either missed them or didn't absorb or remember the info.
__ There are slight lobe-height/lift differences between the two G&W.versions (however tolerance-differences blur the base-figures)... intake - 10mm vs. 9.85mm ; exhaust - 8.5mm vs 8.35mm,, and the greatest difference between the two versions is the 'overlap' valve-timing, of which the 250F1-version has 135-degrees (at-least 15-degrees more than the 350Mk3.cam).
__ That BOTH these camshafts got factory-installed into 350-Scrambler models, is likely the fault of Berliner -(U.S.importer), as I understand that a white-cam was LOGICALLY installed in 350Scr.models for some other countries.
As I think I've determined, it seems that it was late-1968 when the G&W switchover from the 350Mk3 to the 250F1 version occurred,, SO if your country got 350-Scramblers with such non-scrambler/G&W.camshafts all the years since w-c.models became produced for 1967, then you also ought-to have examples of both G&W.versions !
So I hope you have a collection to check-out & see if you happen to have both versions.
In the past, Eldert has (separately) posted the specs of both example-types he's measured, so I gather that HIS country has gotten both G&W.versions as well.


Hopeful-Cheers,
-Bob
PLEASE NOTE... If this-post is not-yet signed-off with '-Bob', then I'm still in the process of completing it,, and if not also included with 'DCT' near bottom as well, then I may edit this post's wording at a later time. - Dct.Bob

DewCatTea-Bob
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Types of 250-heads with the Square Bolt-pattern

Postby DewCatTea-Bob » Mon May 19, 2014 10:30 pm

[quote= Eldert ...
" a Mototrans 69 bore head but it looks like they modified the mould to accept a high lift camschaft or it could be a differend casting . "

____ Until I saw NKOTB's picture of his Mototrans 250-head, I had assumed that his example was the same as Eldert's posted head-casting.
Eldert's square bolt-pattern 250-head must be a newer casting, as it has added casting-space for optional machining of the wider rectangular bolt-pattern as well.
__ Also, it seems to appear that Eldert's cyl.head may have the standard inlet-mouth dia.size as well.
Eldert, can you confirm the dia.size of it's in.port,, and also, tell us what size the stock valves were in your Mototrans 250-head ?
__ I'm still sort-of surprised that the older Mototrans-head has an intake-port that's well under 25mm.
However I've been aware of (non-Ducati practiced) theory for matching-up wild-cam/valve-timing along-with rather narrow intake-porting. ...
Back in the '70s, MotoGuzzi (who's cyl.heads had overly large intake-ports), had discovered that reducing the diameter-size of their in.ports, actually INCREASED max.HP at top-RPM (rather than reduce power, as would be common-sensibly expected).
The related theory is that at higher RPMs, there's then no time for engines to take-in a 'big-gulp' of atmospheric-air,, so-thus BETTER to take advantage of the rather full RAM-effect (with an optimally-narrow in.port), so as to stuff the cylinder to a fuller degree (than otherwise might be attained with an in.port that's too-wide).
__ So since the Mototrans 250-head has such an extra-small intake-port that's expected to work together with a camshaft which has such extra-WILD valve-timing, that seemingly odd combination seems to be TOO-much of a peculiar circumstance to have come-together without any consideration of the probable outcome !
So it seems rather likely, (now that I've thought about it), that Mototrans had quite possibly 'tuned' their chosen port-diameter & camshaft/valve-timing combination to reach a certain compromise which Mototrans had deemed to be best overall, (combined with whatever exhaust-system was supposed to-be employed along-with).
__ Am I giving Mototrans too much credit ? _ I once would've thought-so,, but the overly peculiar extremes of cam & port, would seem to indicate NOT !
What does anyone-else think ?


Dukaddy-DUKEs,
DCT-Bob
You do not have the required permissions to view the files attached to this post.
PLEASE NOTE... If this-post is not-yet signed-off with '-Bob', then I'm still in the process of completing it,, and if not also included with 'DCT' near bottom as well, then I may edit this post's wording at a later time. - Dct.Bob

LaceyDucati
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Re: Tuning a Mototrans 250cc

Postby LaceyDucati » Tue May 20, 2014 3:34 pm

Bob
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 had seen the previous imformation, but as I haven't come across this other G/W in the last 25 years of my involvement in Ducati singles, there seemed little point "absorbing" the imformation! If I need it I will use the search :-)

Personally my Brain is fully absorbed trying to run a business and what seems like the Worlds Ducati single requirements and problems via the wonders of email. Can't really complain as it is good to be busy :)

Good job this site is here otherwise the situation may be worse!

Regards Nigel

Eldert
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Re: Types of 250-heads with the Square Bolt-pattern

Postby Eldert » Tue May 20, 2014 8:13 pm

DewCatTea-Bob wrote:Eldert, can you confirm the dia.size of it's in.port,, and also, tell us what size the stock valves were in your Mototrans 250-head ?


Hi Bob

the intakeport is a little over 27 mm . there are no valves in the head to measure

Eldert

DewCatTea-Bob
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Re: Types of 250-heads with the Square Bolt-pattern

Postby DewCatTea-Bob » Wed May 21, 2014 11:29 am

[quote= Eldert ...
" the intakeport is a little over 27 mm . there are no valves in the head to measure

____ THANKS Eldert !
__ I had thought perhaps that you would've also had the valves & cam, etc which came with that 69mm/small-bore 250-head.
I'd assume that it's valves were likely std.type 36 & 33mm items.



____ Since Eldert didn't mention anything about the std.type intake-port appearing as possibly being non-factory looking,, and-also, since the fact that his presented small-bore/square-pattern 250-head is a newer casting than the older/200-type example with the finned-top,,
then either Mototrans later abandoned their practice of small-ports with wild-cams, or-else the newer small-bore 250-head is from a DIFFERENT long-stroke 250-model, (which probably came with a different camshaft also).
In either case, mystery abounds with these small-bore/long-stroke 250-engines !
__ I sure wish Ducati had also built all the strange motor-models that Mototrans did, cuz then I'd have still more interesting stuff to know about and not be so mysterious to me.
Too-bad that there's not an English-speaking counterpart to myself who I could deluge with questions about Mototrans Duke-models !
____ Anyhow, I'm now thinking that rather than going-through all the work of porting-out the older finned-top cyl.head,, it would be preferable to keep it as stock, and also acquire another small-bore 250-head like Eldert's example. _ As such an example ought-to be found cheaply enough in Spain, (if Eldert is unwilling to part with his), and-thus could possibly save it's worth in porting-work.


Dukaddy-DUKEs,
-Bob
PLEASE NOTE... If this-post is not-yet signed-off with '-Bob', then I'm still in the process of completing it,, and if not also included with 'DCT' near bottom as well, then I may edit this post's wording at a later time. - Dct.Bob


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