Mototrans 250 help / advice wanted.

[Jeb]

This is my first post here, so I would like to say hello to you all first.
I am restoring a Mototrans 250 scrambler. I brought this a couple months back as a four speed N/C with Ducati OC UK dating certificate of 1973 ? with a known gearbox fault ( strange noise in second gear and no drive ) I was told it had a new piston fitted recently, ( while in Spain ) the engine had obviously been apart by the look of all the new gaskets. The seller couldn't tell me much about it as I think he had brought it in a 'job lot' to import to UK.
Any way, I took a gamble on purchase as I suspected that whoever took the engine apart would not have fitted a new piston if they knew there was something damaged in the gearbox, and I suspected they had just assembled it incorrectly .
I stripped it down, and yes, it has a new piston, original size 69mm and bore is very good, no wear. Gearbox had been assembled incorrectly, with shims and spacers missing or not in the correct place. It also turned out to be five speed not four, and would only select four because of the wrong assembly.
Having now done a trial assembly with correct shimming etc, all gears select and seem ok, and apart from slight damage to second gear dogs ( which I have been told is not uncommon on Ducati's ) where it had not been engaging properly I think it should be ok.

Now to my question. The camshaft is quite badly scored as are the rockers, and I want to get them reground. What I need to know are the cam timing periods for the Mototrans engine. Ducati workshop manual gives the timing for all the Italian engines but as the Spanish engine has different bore / stroke and smaller inlet / exhaust valves I would think that timing will be different also to any Italian engine.

Hoping some one can help please.

John

[Jon Pegler]

Hi John,

The camshaft figures for most of the Spanish 250s is as follows
Inlet opens 55 btdc
Inlet closes 90 abdc
Exhaust opens 85 bbdc
Exhaust closes 55 atdc

Hope that helps.
Who are you getting to reprofile your cam and rockers?

Jon

[LaceyDucati]

John

My experience is that Phil Joy (Joy Engineering) is the best guy in the UK for Nickel stellite repairs. Not the quickest, but does a good job. He repairs cams too

I and some of my customers have used a few others (who will remain nameless) who have best part wrecked the rockers.

Nigel

[DewCatTea-Bob]

[quote= Jeb ...
" This is my first post here, "

____ Welcome as our second-newest member !



" The camshaft is quite badly scored as are the rockers, and I want to get them reground. What I need to know are the cam timing periods for the Mototrans engine. "

____ I believe that it's next to impossible for ya to find anyone in the world who will accurately duplicate the exact original cam-specs of any camshaft-model, even when you supply them with the precise cam-specs,, (unless perhaps you also provide them with a good sample camshaft to copy) !
So I'm thinking that you may as well not bother to try getting any particular camshaft-model's specific cam-specs, and rather settle for a suitable-range for the specs to end-up falling within.
__ I assume that the reason for why Jon only provided just one set of 250-Mototrans cam valve-timing figures, is because he chose the specs of the only Mototrans-model with a 250-motor that includes both the 69mm-bore and a 5-speed transmission, (as I'd guess that's probably a unique-combo within a '250-Mototrans' motor-model).
If only all Mototrans-models had also been imported into the USA as well, I then no-doubt would possess a rather complete list of all their cam.model-specs too. _ But since not, I sadly don't recognize the cam.specs listed by Jon, as being those of any 250-model.
The particular cam.specs which I happen to have for one of the 250-motors with the 69mm.bore, are for the '250 De-Luxe' model,, which so far as I know, only came with just a 4-speed trans.
Those cam-specs are as follows...
Inlet opens 45 before TDC
Inlet closes 85 after BDC
Exhaust opens 65 before BDC
Exhaust closes 45 after TDC
Apparently the 'De-Luxe' 250-motor model employs milder valve-timing than whatever 250-Mototrans model Jon's provided cam-specs are intended for.
__ So what you need to do before having any cam.work done,, is decide whether you prefer eng.power-characteristics that closer relate to spirited high-eng.reving, or relatively civil-ized riding.
While neither set of the given v.timing-figures are considered as 'mild' for a 250-single, the De-Luxe figures would provide the better low-end power-production !
So, if you want wild eng.power-characteristics, then request that your cam-specs fall into a 'range' between those two spec.sets. _ And if you rather want mild eng.torque, then request cam.specs that 'range' about the same amount, but rather in the opposite-direction. _ (Which means you'd end-up with in/ex cam-specs near-around 40bt - 82ab / 55bb - 40at [which still wouldn't be considered as really 'mild' valve-timing].)
__ Whatever,, don't make the mistake of choosing wild timing combined with a baffled-muffler,
as such a combo will certainly make your Duke a dog at both high-end and low-end power-ranges !


Duke-Cheers,
-Bob

[Jeb]

Thank you all very much for the welcome and suggestions.

I would like to end up with an engine that produces reasonably good low end torque, rather than high end power, and as I will be retaining the original valve sizes of 35mm inlet and 30mm exhaust combined with 27mm inlet tract and Amal concentric carb I think the mildest cam profile will be in order.

Nigel, do you have contact details for Phil Joy please ?


John

[DewCatTea-Bob]

[quote= Jeb ...
" I would like to end up with an engine that produces reasonably good low end torque, rather than high end power, and
I think the mildest cam profile will be in order. "

____ So-then perhaps you should rather shop for a 175/200-camshaft from a milder road-mannered Duke-model.
Cuz a really mild-cam would have v.timing something like 10bt - 40ab / 30bb - 15at, but Ducati didn't produce any that mild !
__ It wasn't too awfully long ago that a 200-cam was listed on eBay.


Hopeful-Cheers,
-Bob

[LaceyDucati]

Hi John

Phils number is 01279 730682

His work is accurate but he would either need to have a master or a good cam to copy. He can sometimes pick up the profile from a thin unworn section if it still exists, but obviously once it's mullered you are snookered without a reference. Mostly he has the "hotter" or race profiles, but it's worth a call he may well have something suitable.

Nigel

[Jeb]

____ So-then perhaps you should rather shop for a 175/200-camshaft from a milder road-mannered Duke-model.
Cuz a really mild-cam would have v.timing something like 10bt - 40ab / 30bb - 15at, but Ducati didn't produce any that mild !
__ It wasn't too awfully long ago that a 200-cam was listed on eBay.

Good advice thanks Bob. I will keep a look out for any that show up, but in the meantime I think I will have to see if my original can be cleaned up. It would be preferable to me, to avoid having to re-jet carb.

Phils number is 01279 730682

His work is accurate but he would either need to have a master or a good cam to copy. He can sometimes pick up the profile from a thin unworn section if it still exists, but obviously once it's mullered you are snookered without a reference. Mostly he has the "hotter" or race profiles, but it's worth a call he may well have something suitable.

Thanks Nigel. Fortunately the cam only appears to be scored in the centers of lobes, so hopefully Phil would be able to pick up the original profile from unworn edges.

One further question.

Is it worth while fitting a high capacity oil pump ? Would it help in preventing future camshaft wear. I realise the old cam could have worn due to lack of oil changes, or over revving from cold starts. ( which it will not suffer from in future use) but if it is a worthwhile modification for a road bike then I would consider fitting one.

John

[DewCatTea-Bob]

[quote= Jeb ...
" I think I will have to see if my original can be cleaned up. "
" Fortunately the cam only appears to be scored in the centers of lobes, so hopefully Phil would be able to pick up the original profile from unworn edges. "

____ If the cam-figures that Jon has listed are actually the correct specs for your particular 250 engine-model,, you should be advised that such a cam is not-only wilder than a Mark-III cam, but pretty-much as a racing-cam for any 250-engine !
So if your cam.model is indeed an example of such, then you no-doubt really wouldn't want to have it's exact-same/original profile fully restored.
(A cam that provides the kind of power-delivery which you're more interested in, would have timing-figures more like: 30bt - 75ab / 60bb - 35at !)
__ Fortunately, with wild-cams (normally having relatively large lobes),, it's possible to 'regrind' their lobes down-to milder versions ! _ So you may wish to inquire about such.
If you could post a picture of your camshaft, then we should be able to confirm whether your particular cam is a 'wild' verson or not.



" It would be preferable to me, to avoid having to re-jet carb. "

____ Re-jetting of the carb merely due-to a camshaft-profile change,, isn't really an important concern, except for possibly achieving small gains in race-tuning.



" Is it worth while fitting a high capacity oil pump ? "

____ No, not really,, (but if you happen to have one laying-around, then you may as well install it).



" Would it help in preventing future camshaft wear. "

____ Probably not much, but it sure wouldn't hurt.
__ Rather than pumping more oil,, you could rather instead increase oil-volume out-through the cam-lobe pinholes, by partially plugging the oil-passageway of either or both the crankshaft and camshaft.
This trick is usually done by pressing a suitably sized split/drift-pin into the center-hole of the right-side tip-end of the camshaft,, thus positively re-proportioning the amount of oil that exits the camshaft rather through the cam-lobes themselves, (whilst leaving less to bleed-out the bevel-gear end) !



" I realise the old cam could have worn due to lack of oil changes, or over revving from cold starts. "

____ Those possibilities are less common than fuel being allowed to leak down-through into the oil-sump (and dilute the oil), or the oil-pump getting busted due-to the oil-strainer not being reinstalled correctly (and allowing junk to get sucked into the pump-gears) !


Dukaddy-DUKEs,
-Bob

[Jeb]

My appologies for not replying earlier, I have been laid up for a few days, and made use of my idle time in reading through previous posts. Most of my questions it seems have been asked, and replied to before.

If you could post a picture of your camshaft, then we should be able to confirm whether your particular cam is a 'wild' verson or not.

No pictures of my cam yet, as I can't get to my workshop at the moment, but it does appear to be similar to one shown in a previous post of a MotoTrans 250 scrambler cam, so I can assume it is a fairly wild cam as that one was thought to be.

" Would it help in preventing future camshaft wear. "

____ Probably not much, but it sure wouldn't hurt.
__ Rather than pumping more oil,, you could rather instead increase oil-volume out-through the cam-lobe pinholes, by partially plugging the oil-passageway of either or both the crankshaft and camshaft.
This trick is usually done by pressing a suitably sized split/drift-pin into the center-hole of the right-side tip-end of the camshaft,, thus positively re-proportioning the amount of oil that exits the camshaft rather through the cam-lobes themselves, (whilst leaving less to bleed-out the bevel-gear end) !

My cam does have a split / drift pin in the drive end allready.

I have been thinking, it may be best for me to do a trial assembly of the engine, and set up to take measurements of the cam timing periods. I realise that it is not likely to be perfectly accurate, but it will give me a better idea or which cam it is, by comparing with the figures previously given for the cams fitted to MotoTrans engines.

When I can get back to my workshop, I will take pictures of the engine etc, and post

John