Following up on the damaged rockers and oil pump inspection (see pics at the top of this thread)...
The oil pump turned out to be in top condition - close to new condition, in fact and all oil ways were clear. I took the opportunity to inspect the piston and barrel, and they too have little signs of use. The bottom feels perfect as far as can be told in situ. So either the engine was overhauled , but for some reason the rocker's weren't repaired (which seems the more likely, as I found almost zero metal/hard chrome fragments anywhere), or it is a longer term fuel contamination of the oil.
I had the rockers resurfaced to stock radii and they came back looking a treat:
Unfortuately, my much anticpated VeeTwo camshaft fell through, which was disappointing, as I was looking forward to testing that. I was able to recover the existing camshaft with some very light stoning. Not sure how much hard chrome is on there, but I was gentle and there are no signs of wear through, so I'll give it a go and keep my eyes open for a Vee Two camshaft to try. Certainly the rockers did most of the sacrificing.
I think this is the stock Ducati cam, but I can't be sure. Here's a profile of the cam.
More to follow...
Kev
1968 250 MK3D rebuild - ex W/C Oil Pump
Moderator: ajleone
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machten
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W/C Oil pump and top end recovery
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machten
- Posts: 507
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Re: W/C Oil pump and top end repair
Continuing from previous post...
And seeing as I'm in there....
The valve guides were at wear limits, so the head was treated to some new guides...
Refaced the valves...
And recut the valve seats
Planning to reassemble over the next week and with a bit of luck will be able to fire it up next weekend. Yahoo!
Kev
And seeing as I'm in there....
The valve guides were at wear limits, so the head was treated to some new guides...
Refaced the valves...
And recut the valve seats
Planning to reassemble over the next week and with a bit of luck will be able to fire it up next weekend. Yahoo!
Kev
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DewCatTea-Bob
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Re: W/C Oil pump and top end recovery
____ Thanks for your interesting update-report, Kev !
" So either the engine was overhauled , but for some reason the rocker's weren't repaired
or it is a longer term fuel contamination of the oil.
Certainly the rockers did most of the sacrificing. "
____ Since it seems the cam-lobes were not worn even close to the amount of damage which the rockers had, I'd now more suspect that the camshaft had been replaced (after having been run with a bad oil-pump), and who-ever did the work just couldn't find any better DESMO-rockers to go-with.
" I had the rockers resurfaced to stock radii and they came back looking a treat: "
____ That's great ! _ Where did you find the place to do that resurfacing-work, and how much did they charge for it all ?
" I was able to recover the existing camshaft with some very light stoning. Not sure how much hard chrome is on there, but I was gentle and there are no signs of wear through, so I'll give it a go and keep my eyes open for a Vee Two camshaft to try. "
____ It really is too bad that you don't have that V-2 D.cam you wanted, to try-out at this convenient time !
Anyhow, your-own questionably worn D.cam ought to fair-out just fine, just so long as it gets plenty of lubricant in the future ! _ And in such case, your-own resurfacing-work on it should've only really been just required merely for keeping your rocker-arms' new follower-faces in top-condition, (since there's really not too much related pressure-friction generated (relatively) within those DESMO-type mating-surfaces).
" I think this is the stock Ducati cam, but I can't be sure. "
____ Before you reinstall it back into the cyl.head, you really ought to mike-it-out... So please then let us know what measurements you get for the base-circle & opening-lobes.
THEN we can become reasonably sure that it's indeed a 'Blue&White' DESMO-model D.cam .
" The valve guides were at wear limits, "
____ Did you note whether the O-ring valve-guide seals were still intact within the old guides ?
Exciting-Cheers,
-Bob
" So either the engine was overhauled , but for some reason the rocker's weren't repaired
or it is a longer term fuel contamination of the oil.
Certainly the rockers did most of the sacrificing. "
____ Since it seems the cam-lobes were not worn even close to the amount of damage which the rockers had, I'd now more suspect that the camshaft had been replaced (after having been run with a bad oil-pump), and who-ever did the work just couldn't find any better DESMO-rockers to go-with.
" I had the rockers resurfaced to stock radii and they came back looking a treat: "
____ That's great ! _ Where did you find the place to do that resurfacing-work, and how much did they charge for it all ?
" I was able to recover the existing camshaft with some very light stoning. Not sure how much hard chrome is on there, but I was gentle and there are no signs of wear through, so I'll give it a go and keep my eyes open for a Vee Two camshaft to try. "
____ It really is too bad that you don't have that V-2 D.cam you wanted, to try-out at this convenient time !
Anyhow, your-own questionably worn D.cam ought to fair-out just fine, just so long as it gets plenty of lubricant in the future ! _ And in such case, your-own resurfacing-work on it should've only really been just required merely for keeping your rocker-arms' new follower-faces in top-condition, (since there's really not too much related pressure-friction generated (relatively) within those DESMO-type mating-surfaces).
" I think this is the stock Ducati cam, but I can't be sure. "
____ Before you reinstall it back into the cyl.head, you really ought to mike-it-out... So please then let us know what measurements you get for the base-circle & opening-lobes.
THEN we can become reasonably sure that it's indeed a 'Blue&White' DESMO-model D.cam .
" The valve guides were at wear limits, "
____ Did you note whether the O-ring valve-guide seals were still intact within the old guides ?
Exciting-Cheers,
-Bob
PLEASE NOTE... If this-post is not-yet signed-off with '-Bob', then I'm still in the process of completing it,, and if not also included with 'DCT' near bottom as well, then I may edit this post's wording at a later time. - Dct.Bob
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wcorey
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Re: W/C Oil pump
The cam doesn't look quite like mine with the 5 holes but it's in pretty good shape considering the rockers, I've seen desmoquattro cams that looked worse brand new, lol. Like Bob, I find it hard to believe that cam did that much damage to the rockers and came through that well. One thing to watch if the profile got slightly altered from the cleanup is binding, the openers/closers have to match very well or there can be conflict between the rockers.
Here's a pic of my 450 cam, you can see that the closer lobe closely matches the size and radius of the tunnel, even more so than it appears in the angle of this shot. I can see where a higher lift cam could require additional clearance to fit, unless the base circle is reduced to get the increased lift.
Bill
Here's a pic of my 450 cam, you can see that the closer lobe closely matches the size and radius of the tunnel, even more so than it appears in the angle of this shot. I can see where a higher lift cam could require additional clearance to fit, unless the base circle is reduced to get the increased lift.
Bill
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machten
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DESMO camshaft comparisons
Bill,
Thanks for the photo. I was comparing my cam last Tuesday night with a supposed Blue/White slightly used, and a new one. Both had only four holes and the lobes looked like yours. Mine has a noticably harder edge at the fifth hole in my pic (the one you don't have). The opener lobes were also ever so slightly different in profile. I suspect you and Bob are right and the cam has been changed, but this one was also subjected to some pretty serious heat at some stage in it's life. My cleaning up of this cam has been extremely gentle, with the object only (as Bob correctly surmised) to remove any burrs that might put any nicks on the new rockers (and to clean up the surfaces a bit to allow me to better inspect them).
I've checked the radii of the rockers and they appear perfect (as best i can tell). I'll be installing them without springs and will shim them tight to check for binding before backing out to factory settings. Fingers crossed!
Kev
Thanks for the photo. I was comparing my cam last Tuesday night with a supposed Blue/White slightly used, and a new one. Both had only four holes and the lobes looked like yours. Mine has a noticably harder edge at the fifth hole in my pic (the one you don't have). The opener lobes were also ever so slightly different in profile. I suspect you and Bob are right and the cam has been changed, but this one was also subjected to some pretty serious heat at some stage in it's life. My cleaning up of this cam has been extremely gentle, with the object only (as Bob correctly surmised) to remove any burrs that might put any nicks on the new rockers (and to clean up the surfaces a bit to allow me to better inspect them).
I've checked the radii of the rockers and they appear perfect (as best i can tell). I'll be installing them without springs and will shim them tight to check for binding before backing out to factory settings. Fingers crossed!
Kev
Last edited by machten on Wed Mar 23, 2011 7:02 am, edited 2 times in total.
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machten
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DESMO top end repair
In answer to DCT-Bobs post so far...
I think that assessment is probably correct (concurrs with wcorey's), but this cam had also been subjected to some significant heat leading to some blueing in places. In any case, I'm happy it will work fine for quite some period of time. (but i still want to test one of those VeeTwo cams, cause I like the specs of them!) Given my experience of trying to find Desmo rockers, i can well understand the possible approach (see below).
They were done through Phil Hitchcock at Road and Race. He has them the done by a shop in Queensland (R&R is in New South Wales) but I don't know who (although I plan on finding out!). It cost an arm and a leg, but as noone was thowing desmo rockers at me at the time (despite my best spruiking), I didn't feel I had too many options. The cost was AU$110 a rocker (just for the cam contact surface). I thought that was right up there, but on reflection, when you consider what's involved in the process, it's probably not an unfair price at all.
If I can, I will. (I get kind of twitchy when I have all the bits ready to reassemble!
)
Yes, I always carefully examine these. A key piece of info. The o-rings were intact, but the inlet o-ring had been nicked during initial fittment. Fortunately, not enough to allow any noticable leakdown. I've seen this a lot. My bevel mechanic mentor of many years experience has taught me to put a very light chamfer on the valve stem surfaces that cause this, and to do the initial fitment of valves with my hand cupped over guides to catch any o-ring nicks. Then I'll know I have to replace the o-ring and try again.
Kev
Since it seems the cam-lobes were not worn even close to the amount of damage which the rockers had, I'd now more suspect that the camshaft had been replaced (after having been run with a bad oil-pump), and who-ever did the work just couldn't find any better DESMO-rockers to go-with.
I think that assessment is probably correct (concurrs with wcorey's), but this cam had also been subjected to some significant heat leading to some blueing in places. In any case, I'm happy it will work fine for quite some period of time. (but i still want to test one of those VeeTwo cams, cause I like the specs of them!) Given my experience of trying to find Desmo rockers, i can well understand the possible approach (see below).
I had the rockers resurfaced to stock radii and they came back looking a treat: "
____ That's great ! _ Where did you find the place to do that resurfacing-work, and how much did they charge for it all ?
They were done through Phil Hitchcock at Road and Race. He has them the done by a shop in Queensland (R&R is in New South Wales) but I don't know who (although I plan on finding out!). It cost an arm and a leg, but as noone was thowing desmo rockers at me at the time (despite my best spruiking), I didn't feel I had too many options. The cost was AU$110 a rocker (just for the cam contact surface). I thought that was right up there, but on reflection, when you consider what's involved in the process, it's probably not an unfair price at all.
Before you reinstall it back into the cyl.head, you really ought to mike-it-out
If I can, I will. (I get kind of twitchy when I have all the bits ready to reassemble!
)Did you note whether the O-ring valve-guide seals were still intact within the old guides ?
Yes, I always carefully examine these. A key piece of info. The o-rings were intact, but the inlet o-ring had been nicked during initial fittment. Fortunately, not enough to allow any noticable leakdown. I've seen this a lot. My bevel mechanic mentor of many years experience has taught me to put a very light chamfer on the valve stem surfaces that cause this, and to do the initial fitment of valves with my hand cupped over guides to catch any o-ring nicks. Then I'll know I have to replace the o-ring and try again.
Kev
Last edited by machten on Wed Mar 23, 2011 7:04 am, edited 1 time in total.
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DewCatTea-Bob
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- Location: Near SE side of Lake Michigan
DESMO Valve-Gear
" I'll be installing them without springs and will shim them tight to check for binding before backing out to factory settings. "
____ It's fairly doubtful that you'll be able to obtain non-binding tolerances as closely slim as that which could be obtained with new STOCK items, since being the case that both the rockers AND the cam have been somewhat retouched.
__ Also, the factory-specs call for zer0 to .002" of closing-clearance...
But actually, while zer0 can indeed actually be done, I advise to never try for that slim of a setting (even when running without valve-springs) ! _ As that just isn't really necessary.
In fact, providing that ya can get the closing-clearance set between .002" to .010", that's close enough to still work quite well enough, (even without springs, since momentum & compression will close-shut the valves the final amount). _ Because ya really don't want to have to be concerned with your preset zer0-clearances possibly becoming negative-clearances ! _ Which ya must understand is far,far more undesireable !
" If I can, I will. "
____ I should think that you'd really want to know for sure if your D.cam is actually a stock-type B&W-model or not (since there exists substantial reason to wonder) !
__ The Blue&White-cam was mainly intended for the 250, and you really shouldn't want (or have any good use for) any wilder of a cam in such a small cylinder-size ! _ As the B&W already has racing-cam specs.
" The o-rings were intact, "
____ To me, that means that the cyl.head has low-milage since it's last assembly...
Cuz every single DESMO-head I've ever torn-down, (even those which I had redone myself, years prior), had those (stock) O-rings ENTIRELY & completely GONE !! _ I really don't know where they go to but, I dread to think of it !
__ I've been meaning to ask Eldert & others what their experience is with this missing v.guide-seal mystery. - So what do any of you other DESMO-mechanics think ?
" My bevel mechanic mentor of many years experience has taught me to put a very light chamfer on the valve stem surfaces that cause this, and to do the initial fitment of valves with my hand cupped over guides to catch any o-ring nicks. Then I'll know I have to replace the o-ring and try again. "
____ He's a smart enough fellow but, I've never had such shred-clipping occur with my-own technique,, as I have always first inserted a spray-lube into the valve-guide and coated the v.stem-tip with grease, and also twist the valve while lightly pressing it in-through & past the (somewhat compressed) O-ring . _ That method has always worked just fine for me, and it's a nice little treat to FEEL the passage of it.
Fun-Cheers,
-Bob
____ It's fairly doubtful that you'll be able to obtain non-binding tolerances as closely slim as that which could be obtained with new STOCK items, since being the case that both the rockers AND the cam have been somewhat retouched.
__ Also, the factory-specs call for zer0 to .002" of closing-clearance...
But actually, while zer0 can indeed actually be done, I advise to never try for that slim of a setting (even when running without valve-springs) ! _ As that just isn't really necessary.
In fact, providing that ya can get the closing-clearance set between .002" to .010", that's close enough to still work quite well enough, (even without springs, since momentum & compression will close-shut the valves the final amount). _ Because ya really don't want to have to be concerned with your preset zer0-clearances possibly becoming negative-clearances ! _ Which ya must understand is far,far more undesireable !
" If I can, I will. "
____ I should think that you'd really want to know for sure if your D.cam is actually a stock-type B&W-model or not (since there exists substantial reason to wonder) !
__ The Blue&White-cam was mainly intended for the 250, and you really shouldn't want (or have any good use for) any wilder of a cam in such a small cylinder-size ! _ As the B&W already has racing-cam specs.
" The o-rings were intact, "
____ To me, that means that the cyl.head has low-milage since it's last assembly...
Cuz every single DESMO-head I've ever torn-down, (even those which I had redone myself, years prior), had those (stock) O-rings ENTIRELY & completely GONE !! _ I really don't know where they go to but, I dread to think of it !
__ I've been meaning to ask Eldert & others what their experience is with this missing v.guide-seal mystery. - So what do any of you other DESMO-mechanics think ?
" My bevel mechanic mentor of many years experience has taught me to put a very light chamfer on the valve stem surfaces that cause this, and to do the initial fitment of valves with my hand cupped over guides to catch any o-ring nicks. Then I'll know I have to replace the o-ring and try again. "
____ He's a smart enough fellow but, I've never had such shred-clipping occur with my-own technique,, as I have always first inserted a spray-lube into the valve-guide and coated the v.stem-tip with grease, and also twist the valve while lightly pressing it in-through & past the (somewhat compressed) O-ring . _ That method has always worked just fine for me, and it's a nice little treat to FEEL the passage of it.
Fun-Cheers,
-Bob
PLEASE NOTE... If this-post is not-yet signed-off with '-Bob', then I'm still in the process of completing it,, and if not also included with 'DCT' near bottom as well, then I may edit this post's wording at a later time. - Dct.Bob
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machten
- Posts: 507
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DESMO Rocker clearances and valve differences
let me report back on my homework assignment:
These measurements were taken using a digital vernier (or "very near" as my buddy refers to it as) so bear that in mind. I've taken readings at various places on the cam running surface. Generally speaking there isn't much variation edge - middle - edge
Inlet Closer Max - 41.16
Inlet Closer Min - 31.94
Lift 9.22
Inlet Opener Max - 31.15
Inlet Opener Min - 21.96
Lift 9.19
Exh Closer Max - 41.05
Exh Closer Min - 32.54
Lift 8.66
Exh Opener Max - 29.93
Exh Opener Min - 21.65
Lift 8.28
And now for something a little more bizzare. (and if that is an "odd" cam it might be involved in this scenario, so I'm interested to hear what people think about it.)
And this I did (which is where it got interesting). I was able to compare visually the repaired rockers with some brand new ones a friend has. As best I could tell, they look a perfect profile match (but that is an imprecise science!). I installed the refaced original valves, the repaired inlet rockers and the cam and the closer shim arrangement (collets and retainer - but zero shims at this stage and no springs) and tested the rotation of the cam. Guess what? The inlet cam reached the valve seat before maximum closer lift was reached on the cam. Bear in mind these are not new seats and I have just recut them, so they have been cut at least twice. There were only three logical explainations to me...either the rockers had a whole lot more material on them than spec after the repair (which didn't appear to be the case when I looked at them - but it ain't easy to be sure) or the inlet valve is too short in the distance from the valve head to the valve stem collet recess, or both.
I did notice when I dismantled the assembly, the intake closer had zero shims installed and I now suspect the collet retainer has been machined down too. Never having worked on a desmo single before I'm not familiar with the specific dimensions of the valves. I got a friend to take my valves with him to compare against his 450 desmo valves. I don't think they are original either, but he reported back that my inlet valve overall length was exactly the same as his, but the distance from the valve head to the collet recess is 2mm greater than on my valve.
I didn't get onto the exhaust side last night as i was trying to get my head around this lot.
If anyone has a set of old Ducati 250 Desmo valves sitting around, I'd very much appreciate finding out overall lengths and a reference point for the collet recesses for both valves.
The amazing thing is that, it's quite possible that the only thing that allowed the cam to rotate at all when the engine was last running was the material missing off the damaged rockers!!
Kev
____ Before you reinstall it back into the cyl.head, you really ought to mike-it-out... So please then let us know what measurements you get for the base-circle & opening-lobes.
THEN we can become reasonably sure that it's indeed a 'Blue&White' DESMO-model D.cam .
These measurements were taken using a digital vernier (or "very near" as my buddy refers to it as) so bear that in mind. I've taken readings at various places on the cam running surface. Generally speaking there isn't much variation edge - middle - edge
Inlet Closer Max - 41.16
Inlet Closer Min - 31.94
Lift 9.22
Inlet Opener Max - 31.15
Inlet Opener Min - 21.96
Lift 9.19
Exh Closer Max - 41.05
Exh Closer Min - 32.54
Lift 8.66
Exh Opener Max - 29.93
Exh Opener Min - 21.65
Lift 8.28
And now for something a little more bizzare. (and if that is an "odd" cam it might be involved in this scenario, so I'm interested to hear what people think about it.)
I'll be installing them without springs and will shim them tight to check for binding before backing out to factory settings.
And this I did (which is where it got interesting). I was able to compare visually the repaired rockers with some brand new ones a friend has. As best I could tell, they look a perfect profile match (but that is an imprecise science!). I installed the refaced original valves, the repaired inlet rockers and the cam and the closer shim arrangement (collets and retainer - but zero shims at this stage and no springs) and tested the rotation of the cam. Guess what? The inlet cam reached the valve seat before maximum closer lift was reached on the cam. Bear in mind these are not new seats and I have just recut them, so they have been cut at least twice. There were only three logical explainations to me...either the rockers had a whole lot more material on them than spec after the repair (which didn't appear to be the case when I looked at them - but it ain't easy to be sure) or the inlet valve is too short in the distance from the valve head to the valve stem collet recess, or both.
I did notice when I dismantled the assembly, the intake closer had zero shims installed and I now suspect the collet retainer has been machined down too. Never having worked on a desmo single before I'm not familiar with the specific dimensions of the valves. I got a friend to take my valves with him to compare against his 450 desmo valves. I don't think they are original either, but he reported back that my inlet valve overall length was exactly the same as his, but the distance from the valve head to the collet recess is 2mm greater than on my valve.
I didn't get onto the exhaust side last night as i was trying to get my head around this lot.
If anyone has a set of old Ducati 250 Desmo valves sitting around, I'd very much appreciate finding out overall lengths and a reference point for the collet recesses for both valves.
The amazing thing is that, it's quite possible that the only thing that allowed the cam to rotate at all when the engine was last running was the material missing off the damaged rockers!!
Kev
Last edited by machten on Wed Mar 23, 2011 7:05 am, edited 1 time in total.
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DewCatTea-Bob
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- Location: Near SE side of Lake Michigan
DESMO shim-clearance issues
____ All this is going to take a bit-extra to get all completely covered.
To start-out, I must state that I've never measured a DESMO-cam with such low 'lift' figures ! _ Although again, I should point-out that I've never measured a DESMO-cam actually removed from a '250'. _ And until now had assumed that the 250s come-stock with the vary-same 'Blue & White' D.cam as the larger cylinder models.
So I'm now figuring that you must have one of the very first production DESMO-cams produced, before 450 DESMO-engines were produced.
__ Your cam's lobe-lifts are considerably milder than any DESMO-cam I've ever miked !
As all the standard 350 & 450 D.cams I've measured had very near 10mm intake-lift & 9mm exhaust-lift.
So we can be pretty-sure that your DESMO-cam has to fall-under the 'Blue & White' type of D.cam.
__ Ducati has been known to produce a varying range of camshaft-models and yet for replacement-part purposes, (unfairly!) assign several similar cam-models to the very-same color-code colors ! - (The 'White' scrambler-cam designation being the best example of such.)
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.
__ Hopefully Eldert or someone here has some related experience with DESMO-cams pulled from the 250s !
" And now for something a little more bizzare. "
____ This does indeed seem to be a quite strange & disconcerting mystery !
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 ?
" I installed the refaced original valves, the repaired inlet rockers and the cam and the closer shim arrangement (collets and retainer - but zero shims at this stage and no springs) and tested the rotation of the cam.
The inlet cam reached the valve seat before maximum closer lift was reached on the cam. "
____ 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 !
__ Otherwise I'd only conclude:
" the rockers had a whole lot more material on them than spec after the repair " .
" the intake closer had zero shims installed and I now suspect the collet retainer has been machined down too. "
____ Concerning that part.....
As you must already realize, the 'C-clip' type valve-keepers are held into their recess in the valve-stem by the 'collet-retainer', and that particular part comes in a range of varying thicknesses (from 2 to 5mm, in .5mm increments, [I think]). _ So it seems (to me) that it's likely you've mistakenly installed a thicker one than the original which WAS used for the intake-side.
__ The varying-thickness washer-shims which fit under that part, are intended only for more finely adjustment of clearances, and few as possible of them should be used, therefore the need for a range of (more course) variances of that (dual-purpose) shim-coller !
__ The spring-tie/shim-holder also comes in at least two thicknesses, (with a 2mm difference [I think] ).
____ So whenever DESMO-heads are torn-down, ya should take-care to not allow any of these varying-thickness parts to become mixed-up & confused !
" I got a friend to take my valves with him to compare against his 450 desmo valves. I don't think they are original either, but he reported back that my inlet valve overall length was exactly the same as his, but the distance from the valve head to the collet recess is 2mm greater than on my valve. "
____ I've never before happened to note any such variance, although that's not to say I've never encountered such (unknowingly).
Unfortunately, I've never been able to accumulate DESMO-head parts, so as to have them all laying-about for possible comparison. _ Otherwise, I would've already been quite aware of the alternate location for the C-clips on the valve-stems.
There actually shouldn't be any alternate locations in the valve-stem (for the keeper-clips) due to whether the DESMO-head is made for a 250/350 or a 450 !
__ That your 250's valves are set-up with the shorter length from valve-head to keeper-slot, goes hand&hand with your low-lift D.cam ! _ And well correlates with my notion that older (pre-450) DESMO-models had a milder-lift D-cam.
" I didn't get onto the exhaust side last night as i was trying to get my head around this lot. "
____ 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.
" If anyone has a set of old Ducati 250 Desmo valves sitting around, I'd very much appreciate finding out overall lengths and a reference point for the collet recesses for both valves. "
____ If we could find another stock/original 250D-head, then it could be confirmed that there were indeed more than just one type of B&W DESMO-cam set-up.
" it's quite possible that the only thing that allowed the cam to rotate at all when the engine was last running was the material missing off the damaged rockers!! "
____ That could indeed be the case but, then the closing-rockers would've had to have had a good deal of worn-away material, and also someone would've had to have assembled them already well worn !
Hopeful-Cheers,
-Bob
To start-out, I must state that I've never measured a DESMO-cam with such low 'lift' figures ! _ Although again, I should point-out that I've never measured a DESMO-cam actually removed from a '250'. _ And until now had assumed that the 250s come-stock with the vary-same 'Blue & White' D.cam as the larger cylinder models.
So I'm now figuring that you must have one of the very first production DESMO-cams produced, before 450 DESMO-engines were produced.
__ Your cam's lobe-lifts are considerably milder than any DESMO-cam I've ever miked !
As all the standard 350 & 450 D.cams I've measured had very near 10mm intake-lift & 9mm exhaust-lift.
So we can be pretty-sure that your DESMO-cam has to fall-under the 'Blue & White' type of D.cam.
__ Ducati has been known to produce a varying range of camshaft-models and yet for replacement-part purposes, (unfairly!) assign several similar cam-models to the very-same color-code colors ! - (The 'White' scrambler-cam designation being the best example of such.)
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.
__ Hopefully Eldert or someone here has some related experience with DESMO-cams pulled from the 250s !
" And now for something a little more bizzare. "
____ This does indeed seem to be a quite strange & disconcerting mystery !
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 ?
" I installed the refaced original valves, the repaired inlet rockers and the cam and the closer shim arrangement (collets and retainer - but zero shims at this stage and no springs) and tested the rotation of the cam.
The inlet cam reached the valve seat before maximum closer lift was reached on the cam. "
____ 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 !
__ Otherwise I'd only conclude:
" the rockers had a whole lot more material on them than spec after the repair " .
" the intake closer had zero shims installed and I now suspect the collet retainer has been machined down too. "
____ Concerning that part.....
As you must already realize, the 'C-clip' type valve-keepers are held into their recess in the valve-stem by the 'collet-retainer', and that particular part comes in a range of varying thicknesses (from 2 to 5mm, in .5mm increments, [I think]). _ So it seems (to me) that it's likely you've mistakenly installed a thicker one than the original which WAS used for the intake-side.
__ The varying-thickness washer-shims which fit under that part, are intended only for more finely adjustment of clearances, and few as possible of them should be used, therefore the need for a range of (more course) variances of that (dual-purpose) shim-coller !
__ The spring-tie/shim-holder also comes in at least two thicknesses, (with a 2mm difference [I think] ).
____ So whenever DESMO-heads are torn-down, ya should take-care to not allow any of these varying-thickness parts to become mixed-up & confused !
" I got a friend to take my valves with him to compare against his 450 desmo valves. I don't think they are original either, but he reported back that my inlet valve overall length was exactly the same as his, but the distance from the valve head to the collet recess is 2mm greater than on my valve. "
____ I've never before happened to note any such variance, although that's not to say I've never encountered such (unknowingly).
Unfortunately, I've never been able to accumulate DESMO-head parts, so as to have them all laying-about for possible comparison. _ Otherwise, I would've already been quite aware of the alternate location for the C-clips on the valve-stems.
There actually shouldn't be any alternate locations in the valve-stem (for the keeper-clips) due to whether the DESMO-head is made for a 250/350 or a 450 !
__ That your 250's valves are set-up with the shorter length from valve-head to keeper-slot, goes hand&hand with your low-lift D.cam ! _ And well correlates with my notion that older (pre-450) DESMO-models had a milder-lift D-cam.
" I didn't get onto the exhaust side last night as i was trying to get my head around this lot. "
____ 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.
" If anyone has a set of old Ducati 250 Desmo valves sitting around, I'd very much appreciate finding out overall lengths and a reference point for the collet recesses for both valves. "
____ If we could find another stock/original 250D-head, then it could be confirmed that there were indeed more than just one type of B&W DESMO-cam set-up.
" it's quite possible that the only thing that allowed the cam to rotate at all when the engine was last running was the material missing off the damaged rockers!! "
____ That could indeed be the case but, then the closing-rockers would've had to have had a good deal of worn-away material, and also someone would've had to have assembled them already well worn !
Hopeful-Cheers,
-Bob
PLEASE NOTE... If this-post is not-yet signed-off with '-Bob', then I'm still in the process of completing it,, and if not also included with 'DCT' near bottom as well, then I may edit this post's wording at a later time. - Dct.Bob
-
Eldert
- Posts: 805
- Joined: Sun Nov 01, 2009 3:23 pm
- Location: Hazerswoude Rijndijk Netherlands
Re: W/C Oil pump
DewCatTea-Bob wrote:
__ Hopefully Eldert or someone here has some related experience with DESMO-cams pulled from the 250s !
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 . the lift figures where the same as the ones from the brand new
grey ( Mach 1 ) cam i have laying around .
the guy was the first owner of the bike and never swapped a camshaft
Eldert
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