1968 250 MK3D rebuild - ex W/C Oil Pump

[machten]

I installed the "Road & Race" supplied stock Blue and White camshaft detailed in the camshaft data provided earlier in this thread. I took a few photos to illustrate the slight differences between the closer cam profiles of my cam and that one (which is the same as others I have seen and measured).

My cam is the five hole one.

Exhaust Closer Comparison.jpg

Intake Closer Comparison.jpg

In any case, the same problem ocurred with binding, so I'm now sure the rockers have been incorrectly radiused. I'll be chasing that up tomorrow.

Kev

[wcorey]

Well that sucks... At least if it's the rockers, they can be remedied by whomever did them, and you did say you enjoy shimming.
As the issue occurs on both cams, it would seem evident that the rockers must be the cause. But why only on the exhaust side, wouldn't the problem then exhibit itself on the inlet side also?

Bill

[DewCatTea-Bob]

" the same problem ocurred with binding, "

____ First I must say that I really can't believe that I somehow completely missed noticing all of the last four posts added to this thread, before this time !!
__ Anyhow, I'm sure I know what the real cause of this (fairly common!) binding-issue actually is, (and Jordan has already given the best clue so far).
If I had only noticed Kev's first post (mentioning his current binding-issue) soon after he had posted it, I then would've instantly asked: At exactly what crankshaft-point do you choose for adjusting your closing-clearances at? - TDC or what ?


" so I'm now sure the rockers have been incorrectly radiused. "

____ Of course a distinct possibility but, the type of clearance-issue which you've encountered is a fairly common one, with a simple cure.


_________ From the previous-page post .....

" and ran in to a tight spot (like very tight). I thought I tested at least a complete camshaft rotation before, but now recall I only did that with the inlet opener and closer and the exhaust closer (only) shimmed. "

____ One fine example of why I told you that ya really ought to perform "(at least) a tripple-check" before ya can then be (more) absolutely certain that all clearances are still exactly what ya first figured them to be !


" Closer investigation revealed that the exhaust opener and closers were conflicting and causing the bind. "

____ And you had seemed to have made it clear that you were certainly aware that that's the exact reason for completing the final clearance-check (complete camshaft-rotation) procedure (AT LEAST once, afterwords).


" next suspect was a dud rocker radius (and that may still be a possible contributing factor). I then swapped the opener rockers between inlet and exhaust. Binding still happens on exhaust, inlet fine. Next I swapped the closing rockers - same issue on exhaust, no problem on inlet.
So now I'm suspecting the camshaft or a rocker radius/camshaft combination.
I think my next step is to try one of the other B/W cams and see what happens. "

____ An even more important test (in your case with the refaced-rockers), would be to try a pair of stock/unaltered D.rockers (with your own D.cam) !


" I wonder if this is indicative of the cause of the rocker damage? "

____ It's certainly doubtful that all that o.rocker-face damage (which appears between .030 to .045") could've occurred and yet your rocker-pins still fit snugly within their holes in the D.head. _ Cuz whenever this kind of negative-clearance issue occurs, those r.pin-holes get worn-open/loose, (and besides the c.rocker-faces would've then also suffered pretty-much the same amount, due to any such opposition-interference).


" wcorey had also raised the possibility of issues with the exhaust closer lift being greater than the opener lift (I was wondering the same!). Not sure if that impacts anything of itself. "

____ I had already-before eliminated that as being of any concern... Cuz you must certainly understand that if the closing-lobe has pre-required the creation of it's certain-amount of leeway/space -(due to it's preset lift-height), which happens to be greater than that which the opening-lobe can fill-up (with it's max.lift-peak), then there cannot be any conflict (with the left-over spare-space), that is, at 'max.lift' at least, (and with proper clearance-shimming of course) !
So all that would impact, is provide an easier preset circumstance for whatever final-readjustment (possibly affecting that relationship).


Fun-Cheers,
-Bob

[DewCatTea-Bob]

saved space for previously expected update

[machten]

At exactly what crankshaft-point do you choose for adjusting your closing-clearances at? - TDC or what ?

Yes, I set them at TDC compression, but I rotate around the cam to check. i.e. I always set my clearance to the minumum point. In the case of the replacement B&W cam I set a "minimum" closer (which was the same as what it was at TDC) of 0.13 (for the purposes of testing). After fitting the opener, I still needed a gap of (from memory, i don't have my notes with me) of 0.63 on the opener to remove the bind. (so the issue is in fact even more accentuated with this cam). I'm battling to see that it can be anything other than rocker radii, but I'm happy to be shown otherwise (cause that is going to be a pain). Basically, the rocker radii seem to be not set to give the required mirror action on openers and closers.

I'm going to take it to an ex Ducati mechanic tonight to get a fresh fair of eyes on it just to make sure I'm not doing something stupid. I'm not sure if i can get hold of a set of rockers. It'd be nice if i could and I'll ask around the locals to see if i can.


Kev

[wcorey]

Not sure if it would help or not but it's at least easy to do...
I took one of my stock closers and figured out the radius to be 35 mm. You can set your digi calipers to that and use the inside measuring points to scribe said radius (you obviously don't need the whole circle) into a piece of hard plastic or aluminum sheet and line the rocker face up to it and see if the radius looks ok (bigger, smaller, compound). With a bit of magnification I could easily see the deviation if the scribed radius was made a few mm larger or smaller. You could also just draw it on paper but a scribed line is much more clean/concise.

To measure for relative orientation, with the rocker held in place on the first scribe line, scribe a circle around the inside of the rocker shaft hole and measure from the center of that one to the center of the 35mm radius (the pivot point from the caliper, would be the middle of a 70mm circle). Mine was 48 mm in that dimension.

Bill

[DewCatTea-Bob]

" Yes, I set them at TDC compression, but I rotate around the cam to check. i.e. I always set my clearance to the minumum point. "

____ I'm not too sure exactly which you actually do, cuz that wording seems self-contradictory.
__ OPENing-clearances are always set while at TDC (prior to power-stroke) of course, however, for closing-clearance setting, the factory-suggested 'zer0' clearance-spec MUST be set at WHATEVER cam rotational-point happens to provide the LEAST clearance-space ! - Which very well may not be at TDC !
The manuals which seem to suggest that it should be done & completed right-at TDC are understandably of-course incorrect (especially concerning the later D.cam-productions) ! _ And because many desmo-want-to-be-mechanics in the past have believed that poorly worded instruction, many D.heads have had their r.pin-holes expanded !
__ I think you ought to reread all the posts on this topic within this thread, as it may be that points which didn't make perfect sense to you on your first read-through, ought now be more clear to you. ...
For instance, a sloppy closing-rocker at TDC doesn't necessarily indicate that it's in any real need of being reset closer to spec !
Ducati must've realized that once the valves have been closed (out of harm's way), the valve-springs will then surely keep the valves shut, and so must've relaxed the tolerances for their D.cams,, cuz (as you've certainly found), their D.cams are fairly far from being consistently standardized.


" In the case of the replacement B&W cam I set a "minimum" closer (which was the same as what it was at TDC) of 0.13 (for the purposes of testing). After fitting the opener, I still needed a gap of
of 0.63 on the opener to remove the bind. "

____ Of course the opening-clearances much more-so NEED to be set at proper clearance-specs, therefore it's the closing-clearances which instead must be relaxed in order to avoid any such conflict-binding !


" I'm battling to see that it can be anything other than rocker radii, but I'm happy to be shown otherwise "

____ It's been known (by those who have adjusted many different DESMO-heads), that some of them require that the closing-clearance be left notably looser at TDC than others (due to the factory variances between cams). _ And so it's not really important to try to make sure that the closing-lobes are holding the valves completely shut at ALL points where the opening-lobe allows so.
Therefore ya just have to be content that your closing-ramps have performed the main-function of the DESMO-cam, and set the CLOSING-clearance (rather than the opening-clearance), as loosely as is needed so as to "remove the bind" ! _ I've before noted up to about .020" of closing-slop at TDC, so as to fully-avoid any conflict-binding, (although still achieved a near zer0 closing-clearance).


" As a test, I progressively reduced the exhaust opener shim to see what clearance would remove the bind. (Note the closer shimming is at 0.04mm). The binding ceases with an exhaust opener clearance of 0.43mm. At this setting I have an opener clearance of zero at the bind point for about 15 cam degrees. "

____ So now you ought to understand that it's within that same "15 cam degrees" area which is actually the point where you need to set your chosen closing-clearance at, (not TDC).
And I figure that you'd then end-up with only about .012" of closing-rocker slop at TDC, (which actually isn't half bad!).


" Basically, the rocker radii seem to be not set to give the required mirror action on openers and closers. "

____ On the less optimistic side, of course the binding-issue could still be an improper rocker-facing.


" I'm going to take it to an ex Ducati mechanic tonight to get a fresh fair of eyes on it just to make sure I'm not doing something stupid. "

____ It ought not be very productive to present your rather complex issue to anyone-else who hasn't had prior chance to have been already brought up-to-speed on it, so let him ponder it a while alone, before then expecting any good-answer from him. _ Otherwise, he's more apt to just accept & co-promote the very-same thoughts which you will have presented to him.


" I'm not sure if i can get hold of a set of rockers. It'd be nice if i could and I'll ask around the locals to see if i can. "

____ If you picked-up the gem at this link... http://cgi.ebay.com/Ducati-Single-Desmo ... 27b962f304
you could no-doubt later resell it at a profit, after you've tested with it.


Hopeful-Cheers,
-Bob

[machten]

____ If you picked-up the gem at this link... http://cgi.ebay.com/Ducati-Single-Desmo ... 27b962f304
you could no-doubt later resell it at a profit, after you've tested with it.

DCT Bob...Thanks for the tip. I secured that at a good price (and won't be selling it for a profit!!!)

Not sure if it would help or not but it's at least easy to do...
I took one of my stock closers and figured out the radius to be 35 mm.

Bill... thanks. I appreciate your effort and I will definitely use that info to check out my rockers. Exactly what I was looking for. It helps a lot. Once again, thanks.

I'll come back and respond to DCT Bob's last post in more detail later. Busy at work, so it might take a day or two. At this stage, let me just say that I am quite sure the issue is not about where the closer clearance is taken on the cam. (TDC vs anywhere else) I too have set some desmo closers in my 30+ years of desmo ownership and i know to set them at the point of minimum clearance. (wherever that might be - I just do my first reading at TDC). My experience tells me that the unusually large clearances required to prevent binding across two different desmo cams and the fact that the rockers have just been repaired is unlikely to be coincidental. We'll see.

Kev

[DewCatTea-Bob]

" I secured that at a good price "

____ That's great, as I've seen USED one's sell many times on eBay for between 150 to 200$US a piece !
__ (Also note that you're not one of the many stupid eBay-bidders who bid-up things ahead of time ! _ Smart !)

" i know to set them at the point of minimum clearance.
My experience tells me that the unusually large clearances required to prevent binding across two different desmo cams and the fact that the rockers have just been repaired is unlikely to be coincidental. "

____ I'd certainly agree with that IF by: "unusually large", you were actually referring to over 1mm, rather than just ".43",, especially since it's now known for sure that you actually set your (.04mm/.0016") closing-clearance correctly at other than TDC !
YOUR experience may have been with a fair number of newer DESMO L-twins, but does it also include as many old DESMO-singles ? _ (I'm thinking not so much.)
__ Hopefully you'll soon get your new c.rocker and can then try it out to see if IT helps-out with your issue. _ Although I'm currently doubting that it will, sufficiently (to YOUR expectations).
However, if it still doesn't fully satisfy you, there's really no good reason to not be satisfied with the closing-clearance being reset another .3mm/.012" looser ! _ Since the v.springs have the 'valve completely held-closed function', fully well covered !
(Desiring the closing-lobe to ALSO HOLD the valve shut, is fairly akin to using a circuit-breaker to turn-off a light which also has it's light-switch already turned-off.)


Hopeful-Cheers,
-Bob

[machten]

YOUR experience may have been with a fair number of newer DESMO L-twins, but does it also include as many old DESMO-singles ? _ (I'm thinking not so much.)

You're on to me! I'm sure glad this forum exists!

However, if it still doesn't fully satisfy you, there's really no good reason to not be satisfied with the closing-clearance being reset another .3mm/.012" looser ! _ Since the v.springs have the 'valve completely held-closed function', fully well covered !

Worst case I'll have some piece of mind and a spare closer rocker (and if things go to plan, a spare opener too). And on the bright side out of all this, I've done some good learning and I can now assemble a desmo single head in my sleep!

I'll report back when I've had the chance to compare mine against Bill's measurements and later, the original(s).

Kev