Tuning a Mototrans 250cc

[DewCatTea-Bob]

____ Thanks a lot for your useful post Jon !

The most common camshaft fitted into the 250 De Luxe had the following events-
Inlet opens 45 BTDC
Inlet closes 85 ABDC
Exhaust opens 65 BBDC
Exhaust closes 45 ATDC

The 24 Horas motor had the following events-
Inlet opens 55 BTDC
Inlet closes 90 ABDC
Exhaust opens 85 BBDC
Exhaust closes 55 ATDC

____ If Mototrans relates their valve-timing figures with the exact-same method as Ducati, then those are some really hot/wild cams !
It would be of real interest to see the profile of either of those cam.models !
__ Do both of those motor-models employ the long-stroke 69x66 bore&stroke engines ?
I thought the '24 Horas' was the only motor which has the long-stroke 250-engine.



" The 24 Horas cam was also fitted into a few n/c 250 Road models so may appear in the US occasionally. "

____ I think not unfortunately, as Mototrans-DUKEs weren't imported into the U.S. before producing the wide-case ROAD-model versions in late 1971.
If they had imported Mototrans n-c.models over-here, then I'd sure know lots more about them !



" Some of the Spanish cams were not too clever to begin with. "

____ Not sure what you mean by "cleaver" exactly, but
it wasn't very logical for Mototrans to match their 69x66-engine with such wild cam.timing, when that long-stroke engine is otherwise so low-tuned for low-end torque (rather than high-end power), compared-to the short-stroke 250.
Didn't Mototrans also make n-c.250-motors with the 74x57.8 bore&stroke engines ?


Dujaddy-DUKEs,
-Bob

[Bevel bob]

Sounds like my comments were not far off the mark. What i really mean is that the level of tune of the 4 speed American spec Dianna's is about as far as I would go. The higher level of tune found on the Mach 1 and late M3 narrow case or 24Hours does not make a better bike (in my opinion). Parts for Mototrans are not going to be as easy (!) as Ducati . Some Mototrans parts were substandard and got a bad rep in the UK.If the cam is as wild as Dct- BOB says drastic porting mods are likely to raise the rev range into grenade territory , Which is pretty much where my motor is.

[DewCatTea-Bob]

[quote= Bevel bob ...
" Sounds like my comments were not far off the mark. "

____ I pretty-much agreed with your advice to not get carried-away too far with the modification-specs. _ However I wouldn't have expected anyone wishing their project-Duke to remain street-legal, to go-forth to the modification extent that Eldert has.



" What i really mean is that the level of tune of the 4 speed American spec Dianna's is about as far as I would go. The higher level of tune found on the Mach 1 and late M3 narrow case or 24Hours does not make a better bike (in my opinion). "

____ I'd agree with that.
__ However when you've stated "Dianna", I'm assuming you really mean the 'Mark-III' model, because the 'Diana 250' was a 4-speed model which employed the SAME motor as the 250-Monza (with same mild-cam & 24mm-carb) !



" If the cam is as wild as Dct- BOB says "

____ Not knowing what cam-grinds come in n-c.Mototrans-models, I was figuring that a 250-engine model which comes with such small valves would naturally have a rather mild camshaft (much like the w-c.250ROAD-model), to go-with. _ But if the specs that Jon has posted are representative of the camshaft in question, then ya need-not take my word for it that it's valve-timing is 'wild', as ya can compare the figures for yourself...
I believe the valve-timing figures for the F1/G&W.cam are as follows...
Inlet opens 70 BTDC & closes 84 ABDC ,
Exhaust opens 80 BBDC & closes 65 ATDC ,
so ya can see that Jon's posted figures are-not too much different.



" drastic porting mods are likely to raise the rev range into grenade territory "

____ If the inlet-mouth is as overly small as said to-be, then porting-out the intake-port will indeed allow a relatively great power-increase at the higher-rev.range !
__ But why would any factory combine such wild cam.timing with such a small intake-port, in the first place ?



" Which is pretty much where my motor is. "

____ So then Bob, are you still looking to find a milder camshaft and-also considering getting a cam reground to your chosen specs ?


Duke-Cheers,
-Bob

[NewKidOnTheBlock]

Bob – cutting hardened steel is no issue as I have access to a wire EDM at work which should find it no issue. A white cam is however, exactly what I was after, I am unsure if I want to get rid of the stock cam, at least until I’ve rebuilt and proven the engine, would you consider selling your white one? I do have another unidentified cam which I would be more willing to part with which I can take some measurements from if you’re interested?
I have a spare 28mm amal which I was planning on using with this engine so the intake wouldn’t be any larger than that certainly, I would plan to match the intake to the carb and manifold.
Onto valve sizes I was considering 36mm intake /33mm exhaust, however I cannot obtain a 36mm intake and wondered if 37mm is just too large. As I have no expertise in this area I would love to know what others have fitted and how well they ran?
The crown of the piston – I do not yet know, I have one on order from Spain but have yet to see it!
I do agree, starting with a scrambler engine would perhaps have saved me much work, it was an issue of availability over here. I almost bought 2 on different occasions from the states but trans-Atlantic shipping made it unreasonable. However, I’m never one to shy away from a challenge so, regardless of how the results compare to others I would like to make this engine the best I can without spending the earth on it.

Jon – Thanks for the cam information, I believe my engine is a De Luxe. I’ve already found sourcing parts specific to the mototrans difficult .

[DewCatTea-Bob]

[quote= NewKidOnTheBlock ...
" cutting hardened steel is no issue as I have access to a wire EDM at work which should find it no issue. "

____ Then the job could be rather fun for you, (if still a bit risky).
However with access to such a shop, you might rather be able to produce a 5.5mm shim-plate to place between the head & bearing-support/cap-cover, so as to allow the installation of the longer camshafts (so that you then wouldn't ever have-to cut-down another standard-length shaft) ! _ Or modify the bearing-support so as to be able to sink the 6202-bearing 5mm deeper into the cap.
I'd think that these solutions would be preferable to cutting-down camshafts at-least 5mm !



" A white cam is however, exactly what I was after, "

____ I think one of us is confused about something...
You had mentioned that you wanted "a slightly more aggressive cam", yet a scrambler-cam is very-MUCH MILDer than the cam.model which your engine is supposed to have.
So what is your actual goal as far as engine-performance goes,, more mid-range, more peak-power, or what ?
__ From my-own experience, I know that a milder-cam (than those two noted by Jon) would be a better match to go-along with your long-stroke motor,, so I'd agree with choosing to install a more appropriate cam.model.
__ Another concern is, the 'White' cam.model designation was unfortunately used for at-least 4 significantly different Scrambler-camshafts !
Do you know which specific one you most desire ?



" I am unsure if I want to get rid of the stock cam,
would you consider selling your white one? "

____ I have a collection of most-all Duke-camshafts, of which the one I'd trade is part of,, but it's only for-trade for any cam.model that's not yet in my collection.
I deem having Duke-camshafts as better than having cash-money, so I really don't wish to sell any (before I ever become cashless).



" I do have another unidentified cam which I would be more willing to part with which I can take some measurements from if you’re interested? "

____ Perhaps but, lets get it identified ASAP !
Can you post some pix of it (mainly showing it's cam-profiles) ?



" I have a spare 28mm amal which I was planning on using with this engine so the intake wouldn’t be any larger than that certainly, "

____ That's a pretty-reasonable goal !
Have you yet checked to see exactly how much porting-work that would require ? - (I can't hardly believe it's so much as you've indicated, and think you shouldn't have-to remove much more than just 1mm.)



" I was considering 36mm intake /33mm exhaust, however I cannot obtain a 36mm intake and wondered if 37mm is just too large. "

____ If your 69-bore 250-head is actually the same as a std.200-head, (as I think it should be),, then a 37mm intake-valve is not too large. _ But I think your 250-head OUGHT-to already have 36 & 33mm valves in the first place, (or at-least 33 & 32) !
__ Have you checked to measure the exact size of those stock valves yet ?



" The crown of the piston – I do not yet know, I have one on order from Spain but have yet to see it! "

____ Exactly what kind/type of piston did you order ?
In any case, I expect it will have a 38mm cut-out/relief valve-pocket in the crown-top.
Let us know the exact size when you get it.



" starting with a scrambler engine would perhaps have saved me much work, it was an issue of availability over here. "

____ Too-bad you're so far away, otherwise I'd swap a 250-Scr.motor for yours !



" but trans-Atlantic shipping made it unreasonable. "

____ You're certainly right about that ! ... I've had a couple boxes of bike-mags shipped over from your country, and the shipping-cost was indeed unreasonable to the point of being ridiculously atrocious !
So I ended-up letting the seller keep the other two boxes which had yet to be shipped.



" I’m never one to shy away from a challenge so, regardless of how the results compare to others I would like to make this engine the best I can "

____ That's the right attitude to have, and there's a certain reward attained by doing just the work in itself ! _ And afterwords you then finally have a very unique completed project to be proud of.



" I believe my engine is a De Luxe. "

____ According to Jon's posted data,, it's my good-opinion that that model has the PREFERABLE cam/valve-timing ! _ But still it's not what I think would work best.


Hopeful-Cheers,
-Bob

[NewKidOnTheBlock]

I hadn't yet looked at where the cam would need shortening, but if as you say it's on the bearing support end then yes, a shim does sound like a reasonable solution. I have spoken to Kent cams which are able to reprofile cams. They said that they're able to replicate another profile, however they requested a cam to work from, has anyone any experience with reprofiled cams willing to comment on them?

[DewCatTea-Bob]

[quote= NewKidOnTheBlock ...
" I hadn't yet looked at where the cam would need shortening, "

____ The camshaft-dimensions are all spread-out the same except that the left-side of the shaft-itself got it's length increased and-thus extended it's tip-end 6mm further outward (above the sparkplug-hole).
__ When Ducati designed their first 250,, instead of lengthening the shaft, I think they should've kept all the camshafts the same length and rather should've lengthened the snout-extension of the bearing-support, (like they did the 160's).



" a shim does sound like a reasonable solution. "

____ You could use a gasket (made for the support/cover) as a template to copy for forming a piece of 7/32" aluminum sheet-plate into a spacer-shim for the space-extension modification.
You'd then also just need to inwardly widen the oil-passage/hole (in the snout of the bearing-support) about 3.5mm, as well.
This ought-to be a rather fun little project,, and if I were in that shop (that I imagine you have access to), I'd certainly offer to do all the involved work for you.
__ Also don't forget to throw-out the four worthlessly short stock 15mm-long Allen-screws and substitute them with 25 or 30mm long (preferably aluminum) replacements.



" I have spoken to Kent cams which are able to reprofile cams. "

____ That would be great for n-c.Scrambler & Monza camshafts (which have over-sized base-circles to work with) !



" They said that they're able to replicate another profile, however they requested a cam to work from, "

____ While I'm sure they possibly could simply cut-out a mild-profile from a wilder one,, I'm having some doubt that they could make-up any wild-profile, (even from a Monza-cam), without first welding-up the existing cam-lobes.
__ So are you saying that they need one camshaft to work-on & reform,, and ANOTHER-one to model after, as well ? _ Or do they just need one camshaft (because they can't make a complete one from scratch) ?
OR rather perhaps,, they indeed can make-up a camshaft from scratch, but just need an example to model & copy measurements from ?
__ Whatever the case, what kind of pricing are they talking ?
I might have some interest in involvement with such.


Hopeful-Cheers,
-Bob

[NewKidOnTheBlock]

Okay, I got my calipers out and measured everything again, here's what I have:

The Moto trans head as I received it has as 23.6mm dia. inlet (measured where the manifold bolts on) and was fitted with a 32mm inlet valve and a 30mm exhaust valve, these are 88(ish) mm long but were very coked up on the cylinder side so the measurements are rough. The cam fitted to the mototrans head has 25mm base circles on both lobes, inlet measured 32mm at the peak and exhaust measures 32.2mm at the peak.

The 'spare' head I have which housed my mystery cam has a 36mm inlet valve and 33mm exhaust, both measuring 83.5/83.6 long. It has a inlet to the head of 28mm from the manifold, the cam fitted to that, my 'mystery' cam has a base circle of 24.4mm, inlet peak of 32.2mm and exhaust peak of 32.1mm. I was sold the head as a 'scrambler' head hoping to use the cam but from the measurements I don't believe the cam was a scrambler part although the rest of the head seems to match. I have not measured any timing of any of my cams as I do not have the facility to check at the moment.

With regards to what I want, I would like the engine to provide as much useable power as reasonably possible without loosing reliability or spending a fortune on it. I am intending to use the stock con-rod for now as a replacement forged item is prohibitively expensive for me, therefore I wish to remain on the safe side of broken/bent con-rods.

With regards to the cam re-profiling, they require one cam with the desired profile, and one cam to replicate that profile onto. They claim to be able to build up material, presumably weld, and grind that back *IF* the profiles are fairly similar, they would like to see both together before confirming that is possible though. The cost for 2 lobes is £100+VAT, so £120. This comparing to £280+VAT = £336 for a new reproduction cam

This photo is of the cam taken from the bearing support end, apologies it's a little blurry but I only had a mobile phone with me at the time http://imgur.com/tNKzcMw

[Jon Pegler]

E-bay item 321337317204 is a camshaft that would fit an A series 175 or 200.
Part number 0400.029.010
Translates as 175 DS 51in the old parts numbering system.
A 175 DS 51/2 would be better, but that number was never carried over into the newer numbering system, so 0400 029.010 may be the only cam produced after 1961 as a replacement for 175 DS 51/2.
Might save you some money, although customs will probably charge you duty on it once it gets to the UK.

[Eldert]

you might wanne check out Phil Joy . he does reprofiling Ducati single camshafts to and has a few profiles he can put on.

Eldert