1968 250 MK3D rebuild - ex W/C Oil Pump

[machten]

__ 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? ...

Comparing the inlet valves: same length overall, with my c-clip recess 2mm closer to the valve head
Comparing the exhaust valves: My valve was 2mm longer overall, with my c-clip recess 1mm further from the valve head (the head being the the valve seat end)

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. ?

You may well be right. I just don't know the history of this bike. I'm going to try and track it down when I get a chance.

The head is now assembled and the valves shimmed. All feels good. Just got the bevel gear assembly to fit and it can go on this weekend (or maybe even tonight if I can wangle another night in the garage!)

Head Stage 1.jpg

Kev

[DewCatTea-Bob]

" Comparing the exhaust valves: My valve was 2mm longer overall, with my c-clip recess 1mm further from the valve head "

____ It's been a very long time for me but I really don't recall ever before noting DESMO-valves being made in more than one standard-length (from Ducati), nor differing locations of the recess-slot.
I'd expect the shorter valves being easier to get properly shimmed-up after any future valve & seat work.


" The head is now assembled and the valves shimmed. "

____ So what clearance-settings did you end-up with? - (It's a good-idea to make-note & record each of your four separate set figures, for future reference.)
__ When you were pulling/reinstalling the four rocker-pin/spindles, did you need to use a puller-tool on them all, or (at the other extreme), did they all simply drop right in & out of their locations within the head?
Again for possible future reference, that ease of fitment info also ought to be kept noted & recorded, for each one of their four locations, (especially so noted of the closer-pin/spindle locations).


Hopeful-Cheers,
-Bob

[machten]

____ So what clearance-settings did you end-up with? - (It's a good-idea to make-note & record each of your four separate set figures, for future reference.)

I record everything I do on all my bikes. I have a file including a service log for each duc I own (some of them are getting rather fat!)

Openers are set at 0.10mm (I) and 0.12(E) closers both at 0.04mm. I'll check them again after 500km when i drop the oil for a looksee.

I used a spindle puller tool on all spindles. They were snug but not overly tight - what you would expect from a good condition head.

There is a little bit of play in the rocker bushes, but nothing to worry about. If I had some around or could easily get them, I'd have replaced them seeing as I was in there, but I couldn't easily lay my hands on any, so I'll order some and do it at next shim change.

Kev

[DewCatTea-Bob]

" I record everything I do on all my bikes. "

____ Since you're such a good DUKE-mechanic type, did you also make note of what all the clearances were previously at, before you tore-down that 250-D.head ?
(I myself always do such, so as to get some added insight on such used things I get.)


" Openers are set at 0.10mm (I) and 0.12(E) closers both at 0.04mm. "

____ So then you have the intake set at .004", the exhaust set at .005", and both closers set a .0016" ...
That makes it seem to me that you must likely have an excellent selection of valve-clearance shims to pick from, as your clearances seem uncompromised.
__ When ya have your closing-clearances set so close, then best to (at least) triple-check that they actually are at what they first seem to be set at !


" I used a spindle puller tool on all spindles. They were snug but not overly tight - what you would expect from a good condition head. "

____ That's good, you're lucky ! _ Cuz whenever ya find that the closer-pins slip right-out, you can then be fairly sure that someone in the past had set the closing-clearance at zer0 and likely didn't bother to double-check his work.
__ Since it's really not necessary for the closing-rockers to be set under .002", it's just safer (for all the involved parts), to keep those clearances between .004 & .008" .


" There is a little bit of play in the rocker bushes,
If I had some around or could easily get them, I'd have replaced them
but I couldn't easily lay my hands on any, so I'll order some . "

____ For a modified DESMO-head I have, (which doesn't make use of the 'hairpin-springs' but rather employs the 'special' rocker-type closer-springs), I have substituted those std.bushings with 8x10mm caged needle-bearings.
I also once used sets of 1mm (un-caged) needle-rollers, (which seemed the stronger set-up to trust).


Dukaddy-DUKEs,
-Bob

[machten]

____ Since you're such a good DUKE-mechanic type, did you also make note of what all the clearances were previously at, before you tore-down that 250-D.head ?

Now I think you're just teasing me, Bob . I confess I didn't. I do keep records of both clearances set and the shims installed so that I know what's happening on the valve seats over time. In this particular case, knowing I was going to be repairing the rockers and recutting the seats, there didn't seem much point in recording things.

That makes it seem to me that you must likely have an excellent selection of valve-clearance shims to pick from, as your clearances seem uncompromised.

Well, yes....and....no. As you are aware my Duc background is in bevel twins and I have 4 of them. I have therefore had many years opportunity to collect the opener shims which are the same as the single openers. I also live in the same city that VeeTwo was domiciled in. When VeeTwo were shutting down their Ducati parts operations, they had a bit of a fire sale. I had often been frustrated by having "not quite" the right sized shim (usually because the closest one is in another bike or the other head!), so when the opportunity came up to buy a complete set of opener shims from 2.00mm to 6.95mm in 0.05mm increments at a few bucks a piece, I went for it. I similarly stocked up on twin closer shims. Between those (which I try not to stone) and my own collection - which I'm happy to stone, I think I can safely say "Yes, I have a good selection".

Shims.jpg

Of course, being new to Desmo singles, I have had no such opportunity to assemble closer shims for singles. I had what was in the bike (about 6), a few that a friend had and I extracted 5 from Phil Hitchcock at Road and Race. In setting up the closers in fact, I just got very lucky! I'm on the lookout to improve my selection.

When ya have your closing-clearances set so close, then best to (at least) triple-check that they actually are at what they first seem to be set at !

I'm pretty comfortable working to these tolerances having worked to them on my desmo twins for a long time - and yep - I check them alright. I too don't set them to absolute zero so that I can easily test positively for the little clearance there.
Kev

[DewCatTea-Bob]

" Now I think you're just teasing me, Bob "

____ No Kev, not teasing at all really ! _ You of course must already realize that recording the 'befores' is going to be of little use if ya don't also later take note of the 'afters' as well, (when the later-times finally come). ...
__ I asked about the previous clearance-settings cuz if you had bothered to note them at the time, we'd then possibly have a way to confirm whether or not that rocker-wear all took place after (or before) the last time the clearances were set, thus then providing some idea of how much wear was taken from the follower-faces, (of course assuming that the clearances were previously set acceptably close to std.specs), and/or whether those rockers were installed already so worn, etc.
__ And besides being useful for that kind of help, I myself have so noted that (without exception), in most every used DESMO-head I've so (pre)-checked, I've always found the closing-clearances to be somewhere between 15 to 40 thousandths loose (averaging around .025") at TDC !
Unfortunately, I had never taken an opportunity to so check a factory-new D.engine, to make sure that the factory-itself had them properly set to the standard '0.0mm' closing-spec, in the first-place.
Wish I had gotten that notion way-back then, cuz then I'd now have that useful data to report from at least the ex.side of over a dozen DESMO-models.


" I too don't set them to absolute zero so that I can easily test positively for the little clearance there. "

____ Whenever I did the work for a DUCATI-shop, I'd set for zer0 closing-clearance...
I'd figure I had the zer0 setting when I couldn't slip-slide a .0005" feeler through-between, yet I could still easily twist the collet-shim with my finger-tips (at ANY point of camshaft rotation).


____ BTW, I've since dug-up a pair of DESMO-valves (which I don't happen to know if both were removed from the very-same D.head), and noted (by eye) that the INTAKE-valve is actually 1mm (or possibly up to no more than 1.5mm) longer overall than the exhaust-valve, and also that the IN.valve's recess-slot is (roughly) 3mm further from it's valve-head face.
If this pair of valves (which I found in a box of old used engine-parts), are exactly the same as all the new D.valves I've ever handled before, then I guess I never really bothered to note these particular variances to memory.


Dukaddy-DUKEs,
-Bob

[machten]

__ I asked about the previous clearance-settings cuz if you had bothered to note them at the time, we'd then possibly have a way to confirm whether or not that rocker-wear all took place after (or before) the last time the clearances were set, thus then giving us some idea of how much wear was taken from the follower-faces, (of course assuming that the clearances were previously set acceptably close to std.specs), etc.

I didn't note them down, but I can tell you they were all high, especially the closers - so some signal there I guess that the rocker damage was an earlier event. It wasn't like it was really noticably rattling in the top end or anything, or i wouldn't have rode it the 150km I did defore inspecting. On reflection i don't think the clearances were low enough to indicate that the damage took place since last shim set. Plus I found zero detritus anywhere at all.

If you look at the earliest photos of the rockers you can get some idea of the wear because the predamage edge of a few of the rockers is apparent.

This pic probably shows it best...

rocker2.jpg

____ Whenever I did the work for a DUCATI-shop, I'd set for zer0 closing-clearance...
I'd figure I had the zer0 setting when I couldn't slip-slide a .0005" feeler through-between, yet I could still easily twist the collet-shim with my finger-tips (at ANY point of camshaft rotation).

Yep. That's exactly how I set my bevel twin closers. The finger twist test. Although If it is a newly rebuilt engine or head, I like to deliberately set both openers and closers a bit higher, knowing I'm going back for a look in 500km (I enjoy shimming anyway!). I know the natural tendancy of the closers will be to open up further, it's just my paranoia, i guess. We can also run our engines in some higher ambient temperatures in Perth, so if i have to make a shim choice I tend to lean towards more gap - particularly on the exhaust opener.

____ BTW, I've since dug-up a pair of DESMO-valves (which I don't happen to know if both were removed from the very-same D.head), and noted (by eye) that the INTAKE-valve is actually 1mm (or possibly up to no more than 1.5mm) longer overall than the exhaust-valve, and also that the IN.valve's recess-slot is (roughly) 3mm further from it's valve-head face.
If this pair of valves (which I found in a box of old used engine-parts), are exactly the same as all the new D.valves I've ever handled before, then I guess I never really bothered to note these particular variances to memory.

Interesting! I'm getting another set of brand new valves next week to compare. I'll let you know what I find out.

Kev

[Jordan]

____ For a modified DESMO-head I have, (which doesn't make use of the 'hairpin-springs' but rather employs the 'special' rocker-type closer-springs), I have substituted those std.bushings with 8x10mm caged needle-bearings.
I also once used sets of 1mm (un-caged) needle-rollers, (which seemed the stronger set-up to trust).
Dukaddy-DUKEs,
-Bob

I like the idea of the needle rollers instead of bushes for the rockers. Possibly not recommended with the strong standard springs that even the desmo singles use, but in my 350 I have no springs at all. Loads would only be from inertia, and hopefully not great.

Jordan

[machten]

Disappointing news.

After fitting the bevel gear and shaft I was rotating completely (dots aligning, all the way to dots aligning again) around the bevel gears to check the meshing 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. Idiot! Initially I thought it was a bevel shimming issue, so I backed off the bevel shaft and still had the problem. Closer investigation revealed that the exhaust opener and closers were conflicting and causing the bind. Inlet is fine.

Hmm..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. The binding point on the exhaust closer lobe can be seen in the photo below. You may recall I previously identified the "sharpness" of this point as point of difference between other B/W cams I have been looking at.

Cam Binding.jpg

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. It would seem all dependant on the relative opener/closer lobe timing. (But right now, my head is spinning so that could well be a load of ....!!!)

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.

I think my next step is to try one of the other B/W cams and see what happens. I wonder if this is indicative of the cause of the rocker damage?

I'm going for a cup of tea - or maybe something stronger.

Kev

[Jordan]

Yoiks! That underscores the need to find the tightest spot, and adjust by shimming for that. A perfect desmo system is a nice idea, but they probably all vary from ideal to some degree. Even with more play than theoretically ideal at some points, the desmo will do its main job of preventing tangled valves and piston contacts.

Jordan