blowback with green white

[Bevel bob]

When I checked my cam timing at a friends house I did not use the normal procedure (unhelpfull!) , with running clearances of 7 thou I read the closing and openening when the valve caps were just gripped. This gave me timings that were closest to the green white than anything else, but gave figures approx. 6 degrees out on average , opening early and closing late.( mind you the figures I have for a green white are nothing like whats posted on this site) ,but its what I would have expected doing it this way. In order to reduce the blowback I'm getting I am thinking of running larger clearances to open later and close earlier. Any sugestions as to clearances to try?.What cam would have the following timing?,inlet 70 open 84close,ex 80 open 64 close,thats what I think I have.Seems to be a 250f-1 spec,If so I would think about swopping it for a Mach1 cam.

[DewCatTea-Bob]

When I checked my cam timing at a friends house I did not use the normal procedure (unhelpfull!) , with running clearances of 7 thou I read the closing and openening when the valve caps were just gripped. This gave me timings that were closest to the green white than anything else, but gave figures approx. 6 degrees out on average , opening early and closing late.( mind you the figures I have for a green white are nothing like whats posted on this site) ,but its what I would have expected doing it this way.

____ Most-all of your wording leaves a LOT of things to be assumed by the reader, of whatever you may've ACTUALLY been meaning to convey. _ So if you expected any of the above to be importantly understood CORRECTLY (as you had actually intended), then please try wording your thoughts again in other-words.



" In order to reduce the blowback I'm getting I am thinking of running larger clearances to open later and close earlier. Any sugestions as to clearances to try?. "

____ Certainly no larger than .006" intake and .008" for exhaust ought-to be purposely tried-out, (as that's about 3-times greater than the recommended-minimum for the G&W.cam).



" What cam would have the following timing?,inlet 70 open 84close,ex 80 open 64 close,thats what I think I have.Seems to be a 250f-1 spec, "

____ Right, that's indeed the FACTORY valve-timing of the '250F1-cam' .
The other (less wild) G&W.cam closes the ex.valve earlier, at around 50-degrees after TDC, (about the same as the Mach-I cam does).


Duke-Cheers,
-Bob

[Bevel bob]

Thanks , I must have picked up the wrong information from somewhere, At least I now know why I've been struggling with identification!, and running cleanly with anything resembling a silencer. I appear to have the 250 F-1 cam or a copy. I expect it will be pointless long term to carry on with this. Finding a decent M1 cam will not be easy.In the meantime I will try increasing the clearances ,do we know the running clearances for this cam.? When I first rebuilt this motor I tried it on 3 and 5 thou and could not get it to rev, changing exhaust,fuel level and increasing clearances made a vast difference , I think I will experiment a bit more while looking for something sensible.I do not have access to the bike or a safe workshop at present,so I can't give any usefull information,however I hope to get the bike back in time for a Boxing Day run ,may just have time for a tinker.If I take the bike to bits there is a real risk of it never getting back together in my life, Don't want to risk that.From memory the cam lift was similar to a grey white, ie not big, but that now makes sense with the long duration I seem to have.

[DewCatTea-Bob]

[quote= Bevel bob ...
" I must have picked up the wrong information from somewhere, "

____ What info is it that you suspect to possibly be wrong



" At least I now know why I've been struggling with identification!,
I appear to have the 250 F-1 cam or a copy. "

____ Perhaps you may actually have some aftermarket all-out racing-cam.
I'm left to gather that YOUR measured v.timing-figures were "6" degrees even-greater on either side of the F1-cam's factory-figures, (thus-then reading 76 to 90 & 86 to 70).
With intake-timing that wild, a muffler would certainly cause some exhaust-gas to partially also get expelled out-through the intake-tract at lower RPMs.



" I expect it will be pointless long term to carry on with this. "

____ By "this", I'm left to assume that you may mean your wild-camshaft.



" Finding a decent M1 cam will not be easy. "

____ Either a Mark-III cam or a 350Mk.3-cam would also be preferable to that which you now have.



" In the meantime I will try increasing the clearances "

____ Only your intake-clearance setting should affect your (ex.gasses leaking-out the inlet) issue.
__ Perhaps someone has matched-up a G&W.cam along-with rocker-arms which have had the radius of their cam-follower faces increased.
In any case, you could optionally install an intake-rocker which has had it's follower-radius rather reduced, thus-THEN decreasing the inlet-duration ! _ If done just-right, you could possibly cause a F1-cam to produce v.timing-figures fairly close to that of a M1-cam.



" do we know the running clearances for this cam.? "

____ I believe the recommended normal running-clearance for a G&W.cam is .002" to .003" -(intake) & .0025" to .0035" -(exhaust).
__ I've found neglected (G&W equipped) w-c.350-engines running with valve-clearances as loose as around .018", (without any resulting damage) !



" I tried it on 3 and 5 thou and could not get it to rev, "

____ Do you mean after the engine was fully warmed-up
If you had CORRECTLY set those v.clearances right at TDC, then your camshaft is probably not an authentic Ducati factory-made product !



" I think I will experiment a bit more while looking for something sensible. "

____ In-place of another camshaft, consider having some partially worn-out rocker re-radiused down-to between 28 to 20mm, (from the stock 32mm-radius).



" From memory the cam lift was similar to a grey white, "

____ What's a "grey white"
The only Gray&White-cam I know-of, is the special-450D.cam !
__ The 250F1-cam's ex.lift is 8.35mm.


Hopeful-Cheers,
-Bob

[Bevel bob]

Hi Dct-Bob, The timings I was given for a Green-white were in fact for a 250F-1, did not help, I was also told by the PO that the motor was fitted with a green-white,not true,did not help. Surely a grey white is the Mach1 cam?, I had assumed (wrongly) that a race cam would have a high lift ,whereas the 250F-1 does not ,which is why I did not consider it to be what it most likely is.I would have thought that bigger clearances on both valves would help ,ie inlet opens later, exhaust closes earlier. It is possible that the 250f-1 cam was run with larger clearances than normal road cams, unless you know better?.

[DewCatTea-Bob]

[quote= Bevel bob ...
" The timings I was given for a Green-white were in fact for a 250F-1,
, I was also told by the PO that the motor was fitted with a green-white,not true, "

____ But that F1-cam IS a Green&White-cam (according-to the w-c.parts-books !) !
(Seems-like YOU ought-to have been one of us long-established members who has already learned long before now, what the actual story really is concerning the two different G&W.camshaft-models !)



" Surely a grey white is the Mach1 cam?, "

____ NO, the Mach-I cam is ONLY color-coded just 'GRAY' !



" I had assumed (wrongly) that a race cam would have a high lift ,whereas the 250F-1 does not , "

____ A race-cam's lobe-lift is dependent on the engine it's best suited for,, for example, the Special-450Mark-3 cam has a 12mm lobe-lift, yet significantly less duration than the 250F1-cam, (because the 450 can't rev as high as a 250 !) ! _ Where-as the 250F1-cam can allow the 250-engine to rev so high that duration is then more important, and too-much lift would then put the valve-train in greater jeopardy ! _ That's why the 250F1 race-model employs (stronger !) F1.type valve-springs along-with exhaust-valve lobe-lift that's not quite as tall as that of the 350M3-G&W.cam.
Besides,, of all the various std.production camshaft-models, the 250F1-cam's lobe-lift is close-seconded only compared-against the G&W/350M3-cam ! ...
__ Have you not-yet been following the other recent thread concerning related-info ? - viewtopic.php?f=3&t=1609



" I would have thought that bigger clearances on both valves would help ,ie inlet opens later, exhaust closes earlier. "

____ But if you ALSO cut-down the exhaust-timing as well, THEN the exhaust-pressure will STILL tend to remain pretty-much the SAME higher relationship with respect to the intake-pressure. _ So to BEST help solve your-issue (without making your valve-lash TOO-loose), you should only wish to decrease JUST the inlet-duration. _ Cuz you see if you also reduce the exhaust-duration as well, then you will REDUCE the effectiveness of your intended-effort on the INTAKE-side ! _ So let the exhaust-side CONTINUE to over-breath & thusly reduce cyl.pressure, whilst just curtailing ONLY the intake's breathing-duration. _ Cuz you prefer the ex.gasses to have a substantially EASIER-time getting pushed-out the exhaust-tract, rather than the inlet ! - Right ?



" It is possible that the 250f-1 cam was run with larger clearances than normal road cams, ?. "

____ By 1969, Berliner was (STUPIDLY !) having Ducati install the 250F1-cam within their 350-Scr.engines,, so all the related valving-specs ought-to be the very-same as that given within the related manual-books !


Dukaddy-DUKEs,
DCT-Bob

[Bevel bob]

I'll try it your way first with the inlet. Seems crazy and inconsistent to have colour codes to denote particular cam grinds and then produce green whites with wildly differing grinds. Still that's what we have.

[DewCatTea-Bob]

[quote= Bevel bob ...
" I'll try it your way first with the inlet. "

____ That's your best-chance* of having any notable positive-effect against your reverse inlet-charging issue,
(* by increasing inlet-v.lash).
So keep the ex.lash set at std.spec, (no looser than .003"), and only loosen-up just the in.lash to somewhere between .005" & .010",, (although I really don't expect any worthwhile duration-difference that'll have a noticeable effect with that tight of valve-lash.)
__ If you do get some noticeable reduction in the reverse-flow through the intake-tract, you ought expect to kill-it once you ALSO loosen-up the ex.lash ! _ Cuz that would then curtail exhaust-flow out-through the ex.tract and thusly raise cyl.pressure, and once-again make the in.tract a rather attractive escape-route for compressed cyl.pressures, (during low-RPM).



" Seems crazy and inconsistent to have colour codes to denote particular cam grinds and then produce green whites with wildly differing grinds. "

____ I certainly quite very-much AGREE !
But that's the kind of $#!+ we can expect from people in charge who are-not like-minded with those like myself who are keen to being concerned with detailed-details !
__ I believe that the Green&White designation was allowed to represent both camshaft-models because, (like all the 4 or 5 real Scrambler-cam models, which are all represented by just the 'White' color-code), they are both so very-similar in cam.specs. _ As the only really notable difference is with their respective 'overlap-duration' - (the F1-cam being somewhat considerably wilder) !
It seems that we have the penny-counters -(the Italian-gov) at the time, to thank for the consolidation of the production for the two G&W.camshaft-models,, and-so ONE had to be chosen as the sole-successor for both cam.models.
And unfortunately whoever made the decision, must've been some common-reasoner who (wrongly) thinks that wilder-is-better/faster, and-thus preferred & chose the F1-cam, (which is pretty-much worthless for most of US !).


Dukaddy-DUKEs,
-Bob

[Bevel bob]

They probably made that decision based on the fact that they had a large bin full of that type of cam. This cam in my 250 is currently running on about 7 thou clearance IN and EX with a 6 thou feeler packing on the ex side . ,in effect I'm already doing what you suggest(nearly) . I was thinking of running 10-12 thou on the inlet (noisy!!). Another option may be to get my local cam manufacturer (Newmans ) to re-profile the cam to Mach1 spec. May not be able to achieve the full Mach1 lift?.A new cam from Lacey is a bit out of my price range sadly.

[DewCatTea-Bob]

[quote= Bevel bob ...
" I was thinking of running 10-12 thou on the inlet "

____ For just trying-out a test (to see if you can possibly notably address your-issue in this manor),
you could try increasing the in.lash out-to near .020". _ (But even that loose, I still have doubts that it would fully solve your-issue.)



" Another option may be to get my local cam manufacturer (Newmans ) to re-profile the cam to Mach1 spec. "

____ That would be a certain waste ! ...
Rather, (if you do go that route), you ought-to have it done to roughly-equal specs
set to nearly in-between the M1-cam & 350M3-cam valve-timing specs. _ That way, you'd then have a HOT gray-cam (rather than just a run-of-the-mill example).
BTW, the 350M3-cam was deigned to do for the 350-engine that which the gray-cam famously did for the 250-engine.



" May not be able to achieve the full Mach1 lift?. "

____ Why not retain the lift-height of the G&W.cam ? ...
While both cam-models have nearly the same (8.35/8.5mm) ex.lift, the G&W.cam's in.lift is near 1mm higher than the M1/gray-cam's 9mm-in.lift !


____ Here-follows a link to a related thread from back when you probably weren't interested enough then to remember the related stuff within it Bob - viewtopic.php?f=3&t=195&p=2221#p2221
____ Taking into account all the associated valve-timing figures, I'd most recommend a cam-regrind (for YOU), with the following timing-figures ...
intake ____ 62BT - 75AB
exhaust ___ 75BB - 55AT
Those timing-figures combine the wildest of both the gray/M.1 & red/Mk-III camshaft-models (without getting so wild as either of the G&W.cams !).


Hopeful-Cheers,
-Bob