1968 250 MK3D rebuild - ex W/C Oil Pump

[DewCatTea-Bob]

" i did some work on a guys 350 Desmo last year . when i had the cam out of the head i took some measuremends
intake lift was 9.05 mm and exhaust lift 8.45 mm . "

____ Now that you've stated these DESMO lift-figures Eldert, come to think of it, that seems to spark-off a very-vague memory (of one) of the first DESMO-cams I ever measured (back in the early-70s),, which was from a 1968-350Mk3D model.
But I'm sure that all other B&W-D.cams I've measured (since way-back then) from other (newer) stock 350 & 450 DESMO-models, had lift-figures pretty-close to (within less than .2mm) 10.0mm -(in.lobe) & 9.0mm -(ex.lobe).
And after-all, the B&W D.cam was supposed to have been modeled after the '250-F1 cam' (which was the 250 factory-racer camshaft with very-similar specs!).
__ Do you know what model-year THAT 350-DESMO was ?
____ Hopefully, Kev's 450-friend will allow Kev to measure his DESMO-cam, as well ! _ As it should be at least a year newer than Kev's D.cam.


Dukaddy-DUKEs,
-Bob

[wcorey]

According to Jim Pianetta's cam data sheet 9/8.4 is right around what what was measured from 4 different b&w cams and 10.17/9.7 was found in a very early 350 MK3D.

Kev, sounds like you need to either or both make the pocket deeper in the spring retainer or take some more off the collet, better than the alternative of making the valve seat deeper or valve face thinner, lol. Hopefully Bob is right that parts just got swapped around.
What would concern me is the .38 difference in lift of the exhaust opener and closer on your cam, though I can't quite envision what the exact result of that would be...

Bill

[DewCatTea-Bob]

" sounds like you need to either or both make the pocket deeper in the spring retainer or take some more off the collet, better than the alternative of making the valve seat deeper or valve face thinner, "

____ All certainly true, however (assuming he has the thicker-version), his spring-tie also could be flatened/thinned-down (where the closing-rocker makes contact against it), or he could possibly make better use of the newer-type D-valves which his friend has ! - (But we understand that THAT should not actually be a necessary solution!)

" Hopefully Bob is right that parts just got swapped around. "

____ If I am wrong about that (intake & exhaust parts mix-up) possibility, then it would seem that either the original closing-rocker gained some excess material, or some OTHER parts swapping was since done somewhere, possibly without Kev being made aware of it.


" What would concern me is the .38 difference in lift of the exhaust opener and closer on your cam, though I can't quite envision what the exact result of that would be... "

____ I'm sure you actually could Bill, (if you bothered to take the time to think-it-out).
__ That max.difference means that when the opening-lobe is at max.lift, the closing-rocker shall already have a preset clearance advantage equal to 15*thousandths of (possibly extra) slop-clearance, (to help towards avoiding negative-clearance, [at that particular point] ).
EDIT-NOTE: _ I've needed to alter my wording above-here, cuz my previous-wording was unintentionally misleading - so as to have biased the reader's thinking towards a particular mind-set which tended to block proper reasoning on the issue. _ (Sorry about that!)

*UPDATE-NOTE: From Kev's corrected lift-figure, the .015" space-amount should've actually been figured as .009", instead.


Dukaddy-DUKEs,
-Bob

[wcorey]

...spring-tie also could be flatened/thinned-down (where the closing-rocker makes contact against it)...

Ah, that's an obvious solution I hadn't thought of, and potentially much easier than boring out the pocket. I would assume those are through hardened and not case hardened?

I had a very similar situation with mine when I put in a different exhaust valve that had more/thicker material on the face (which is why I replaced the original thinning one). It was a very small amount needed though and I just stoned down the collet.

That max.difference simply means that when the opening-lobe is at max.lift, the closing-rocker will then have .015" of slop...

What happens 180 degrees from that, when the closer is at max lift?
So if it was the other way around (closer having more lift than the opener), then it would bind?
Or maybe that would be from variance in concentricity from the center/base circle or the two being out of sync by degrees of rotation?

I'm sure you actually could Bill, (if you bothered to take the time to think-it-out).

It's difficult for me to work this out in my (own) head without having the (450) head in front of me (it's disassembled (the 450 head that is) but in the frame for fitment purposes ). I suppose I could draw it. It's much easier to have someone else to think it out for me though...


Bill

[machten]

My apologies up front for the length of this post, but there's getting a bit to it now. I guess the original title is now totally misaligned with the content, so if Jim wants to change it, please feel free to do so.

See my replies embedded below:

So it makes fair sense that your particular B&W D.cam may actually be specifically a '250 DESMO-cam', (and thus not so suitable to be transferred into a larger DESMO-engine). This is of course a disconcerting notion for myself, but (from all the info you've given), I'd reach this conclusion before I'd more suspect that your cam-lobes were worn-down (so much) by the worn-rockers & your stoning-work, to result with such reduced lift-figures.

Certainly my stoning work was in the microns range. Original cam lobe wear see some cam comparisons below.

It makes me need to ask you the question - (aside from your rocker-arms), are you absolutely positive that none of your parts which came-out of your 250D-head, were not switched/swapped with parts from another source ?

Absolutely postive. All work other than the new valve guides and refacing of the valves has been done in my own garage by me. Only the bare head and valves have left my garage, and this is the only single I'm working on. i.e. if there is a parts swap issue it is between the bikes own parts and the culprit looks at me from a mirror!

If I have correctly interpreted your wording, then in this particular case I'd first suspect that you've possibly gotten the exhaust & intake spring-tie and/or v.keeper-retainer mixed-up/switched-around. _ Cuz those two parts, (especially the C-clips "retainer"), will vary in thickness !

You could be onto something there, Bob! I had bagged and labelled them seperately, but there was one occasion where I had them both out at the same time and became uncertain which one was which when I was putting them back. The spring tiedowns are different thicknesses by about 2mm (as you correctly alerted as a possiblity - Is it standard out of the factory to have different sizes? I could only find one part number reference.) Both intake and exhaust collet retainers are approximately the same size.

____ Well if I'm right about what likely happened, then if you had gone-forth, you probably would've discovered (all on your own) the source of your issue, at that time.

Indeed! Just ran out of time Tuesday night, otherwise I would have done that. I have retreived the valves and will test out your theory tonight, all going well. I hope you are right!

sounds like you need to either or both make the pocket deeper in the spring retainer or take some more off the collet, better than the alternative of making the valve seat deeper or valve face thinner, "

____ All certainly true, however (assuming he has the thicker-version), his spring-tie also could be flatened/thinned-down (where the closing-rocker makes contact against it), or he could possibly make better use of the newer-type D-valves which his friend has ! - (But we understand that THAT should not actually be a necessary solution!)

Thinning the spring tie down was definitely an option I was considering if required. I also have 0.5mm on the valve I can easily lose, but would rather not, and the collet retainer could also lose 0.5mm if need be. Hopefully none of that will be necessary, and to be honest, if it is, I'd rather source a better fitting valve.

____ Hopefully, Kev's 450-friend will allow Kev to measure his DESMO-cam, as well ! _ As it should be at least a year newer than Kev's D.cam.

Ask and ye shall receive!! Here is the collected camshaft data. Mine and two camshafts from one of my friends. One is an unused camshaft from Old Racing Spare Parts, the other is a lightly used camshaft from Road & Race. I don't know who the camshaft manufacturer is (Ducati original or otherwise), but his, from two different sources, are identical within my margin of measuring error, I reckon.

Camshaft 1 - Kevin's '68 250 M3D
EC IO EO IC
Max 41.05 31.15 29.93 41.16
Min 32.54 21.96 21.65 31.94
Lift 8.51 9.19 8.28 9.22
Valve (Closer - Opener) Exhaust 0.23 Inlet 0.03

Camshaft 2 - New from Mario Sassi
EC IO EO IC
Max 40.14 30.08 29.48 40.14
Min 32.09 21.1 21.1 31.29
Lift 8.05 8.98 8.38 8.85
Valve (Closer - Opener) Exhaust -0.33 Inlet -0.13

Camshaft 3 - Lightly Used From Road & Race
EC IO EO IC
Max 40.59 30.53 29.9 40.63
Min 32.54 21.56 21.56 31.75
Lift 8.05 8.97 8.34 8.88
Valve (Closer - Opener) Exhaust -0.29 Inlet -0.09

" What would concern me is the .38 difference in lift of the exhaust opener and closer on your cam, though I can't quite envision what the exact result of that would be... "

____ I'm sure you actually could Bill, (if you bothered to take the time to think-it-out).
That max.difference simply means that when the opening-lobe is at max.lift, the closing-rocker will then have .015" of slop (for avoiding any binding-issue with, [at that particular point] ).

That also suprised me a bit, Bill. Note the Valve (Closer - Opener) figures for each camshaft. Perhaps my cam is exhibiting some wear on the opener lobe tips (although it isn't obvious by inspection)?

Anyway, with luck I'll have another go at assembly tonight and report back. More garage fun!

Kev

[DewCatTea-Bob]

" I guess the original title is now totally misaligned with the content, so if Jim wants to change it, please feel free to do so. "

____ I'd like to take-care of that myself, and also adjust your data-listing spacing as well.


" Certainly my stoning work was in the microns range. "

____ Certainly so, and that's why I've begun to consider that the earlier B&W-D.cams only had lift-figures roughly equal to the Mach1-cam.


" All work other than the new valve guides and refacing of the valves has been done in my own garage by me. Only the bare head and valves have left my garage, "

____ So then I must assume that you had taken steps to assure yourself that you would be able to surely-recognize your very-own parts once returned-back to you ?


" The spring tiedowns are different thicknesses by about 2mm
Is it standard out of the factory to have different sizes? "

____ I'm sure it's not standard-practice, at least I-myself have never seen unmatched/differing-thickness versions of spring-ties*, both installed within the very-same cyl.head !
(* the factory-given name for the 'collet-receptor/valve-lifter/spring-tiedown' part, which the closing-rocker lifts directly against)
I've only noted that (fairly unknown) variance from having compared parts between two separate DESMO-head part-sets (which MAY have been 350 vs 450, I don't really recall).
__ Since you have BOTH size-types of spring-ties for your one cyl.head, THAT possible mix-up is most likely the (main) source of your particular fitment-issue.


" Both intake and exhaust collet retainers are approximately the same size. "

____ Now that is usually a far less likely occurrence, as those v.keeper-retainer/shim-collets (are well known to) come in a number of thickness-sizes ! _ And (when they're both not the same size), having them get switched-swapped could certainly lead to such a fitment-issue as you've ran-into !


" Here is the collected camshaft data. Mine and two camshafts from one of my friends. "

____ I was hoping that you'd get the lift-figures from the original D.cam which came from a stock-450 DESMO-head.
__ I should still have my own recorded figures around somewhere but, I haven't seen them for many years back before I moved.


" I don't know who the camshaft manufacturer is (Ducati original or otherwise), but his, from two different sources, are identical within my margin of measuring error, I reckon. "

____ Yes, and it seems (from the given figures) that all three are Ducati-factory Blue&White D.cams . _ Although it seems that all the stated figures make YOUR D.cam continue-on to stand-out (from those other two), by more than just having that extra/5th-hole !


Hopeful-Cheers,
DCT-Bob

[machten]

____ I was hoping that you'd get the lift-figures from the original D.cam which came from a stock-450 DESMO-head.

I can't be certain that is the original cam in it either and it has recently been lunched by an oil issue too (that's why he has sourced the others). At the moment it's still in the head. After it's been extracted I'll measure it. It looked in far worse shape than mine did, but then mine cleaned up pretty well. I'll be interested to see how it mikes up myself.

Kev

[DewCatTea-Bob]

By: wcorey...
" I would assume those are through hardened and not case hardened? "

___ I'm really not too sure about the degree of hardening but, it ought not matter too much since there should be oil between there and the actual pressures exerted are relatively quite low.


" I had a very similar situation with mine when I put in a different exhaust valve that had more/thicker material on the face .
It was a very small amount needed though and I just stoned down the collet. "

____ For such small changes as that, ya should only have to remove a shim-washer ! ...
It's fairly unusual (but it does happen, rarely!), that only a collet-retainer/shim alone is needed for obtaining proper closing-clearance (without any added washer-shims placed underneath it, within the spring-tie). _ So I'm somewhat surprised that you found the need to have merely "stoned down" a collet-shim, to get your desired added-clearance.


" What happens 180 degrees from that, when the closer is at max lift? "

____ At such point (180-degrees from maximum valve-lift, [which is getting near TDC] ), ya then of course simply have clearances as they've happened to have been manually set to !


" So if it was the other way around (closer having more lift than the opener), then it would bind? "

____ Didn't you actually mean to ask: "(OPENER having more lift than the CLOSER)" ? _ Since the opposite circumstance has already been addressed.
__ Well actually in any case, since there's at least 10mm of space between the valve-end tips of the closing & opening rockers, any such small differences in these particular areas of concern, are easily absorbed-up by the relatively large space-adjusting selection of opening & closing shims, (to then obtain whatever proper clearance-settings are required with a particular D.camshaft) !


" Or maybe that would be from variance in concentricity from the center/base circle or the two being out of sync by degrees of rotation? "

____ Now with those two thoughts combined, you're getting a bit 'deep' Bill ! _ So I'm not sure of exactly what you're meaning, but I'm not thinking so,, as regardless of whether these (negative or positive) figures seem to present reason for concern, their relatively small amounts are well within that which can be adjusted-away (and thus little-doubt, out of contention) !
__ I must add that those more recently listed closing & opening lift-figures (which indicate negative-results) would seem to imply certain binding/negative-clearance near full valve-lift, therefore I have to assume that the closing-rockers must have a greater 'rocker-ratio' than that of the opening-rockers -(which I think is '1:1.04').


Dukaddy-DUKEs,
-Bob

[machten]

DCT Bob said...

If I have correctly interpreted your wording, then in this particular case I'd first suspect that you've possibly gotten the exhaust & intake spring-tie and/or v.keeper-retainer mixed-up/switched-around. _ Cuz those two parts, (especially the C-clips "retainer"), will vary in thickness !

I said..

You could be onto something there, Bob! I had bagged and labelled them seperately, but there was one occasion where I had them both out at the same time and became uncertain which one was which when I was putting them back. The spring tiedowns are different thicknesses by about 2mm (as you correctly alerted as a possiblity - Is it standard out of the factory to have different sizes? I could only find one part number reference.) Both intake and exhaust collet retainers are approximately the same size.

Anyway, with luck I'll have another go at assembly tonight and report back. More garage fun!

Well....give the man a coconut. That was the problem. Brilliant piece of remote diagnosis, Bob! Thanks.

Ran into my next little problem. The exhaust closer isn't sliding neatly over the new guide despite the rocker being shimmed correctly, so a little bit of a tidy up to do there, but no big deal.

The learning continues. Thanks to all for your help so far.

Kev

[DewCatTea-Bob]

" That was the problem. "

____ And a very unusual one, (since it was actually the spring-tie and not the coller-shim), which I had never ran-into before !
So it's now even more evident that someone once before replaced some parts or other, within that D.head...
As such mismatched parts shouldn't have been found within the very-same cyl.head.
__ You had mentioned that you had a valve which had it's C-clip/v.keeper-slot spaced 2mm further-down from the valve-stem's tip-end, (compared to a 450's)... Was that the exact-same case with both your valves? ...
Cuz I'm now wondering if rather than someone (in the past) having had installed a new-cam (but not the rockers), had actually in fact, instead robbed that D.head of it's original good-rockers and substituted their old worn-rockers, and then used other non-original parts so as to help allow them to work (well enough) that way. ?


Hopeful-Cheers,
-Bob