desmo exhaust valve seals

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Spagjet
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desmo exhaust valve seals

Post by Spagjet » Sat Mar 21, 2015 7:30 pm

Hi,
just wondering if anyone knew if the smaller of the two cylinder head o rings were the same as the exhaust valve stem seal o ring. That's what I was told and that's what I was sent but I have tried for ages to install the new orings without the slightest success. I got the old seals out, they are a lot smaller in profile, I just don't see how you could put a thicker oring in it's place but I keep being told they are the same as the smaller head oring. Anyone got any knowledge on the subject?
cheers

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Craig in France
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Re: desmo exhaust valve seals

Post by Craig in France » Sun Mar 22, 2015 3:49 am

Dunno if this gonna help, but:

Well, in the 750SS-900SS (1975-6) parts book they have the same Ducati part number: 0400.17.030.

But, that said, the specification given in the description is not the same :? . For the cylinder head, it's OR 2031, for the valve guide it's OR 107. Strange ...

From here*, I see that the dimensions (ID followed by x-section) for OR 2031 are 7.65 x 1.78. But I cannot find OR 107 referenced either by this source, or anywhere else. So maybe OR 107 is no longer produced ...?

* http://www.argotmf.com/pdf/oring/OR_NWLIS.pdf

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Re: desmo exhaust valve seals

Post by Spagjet » Sun Mar 22, 2015 5:56 am

Hi Craig,
that's very interesting, I measured the section on the old o ring (1.5mm) against the new green o ring (1.7mm+), the oring groove in the valve guide just isn't wide enough to get the oring to seat in it, you can sort of squash (part of) it in with the side of a thin pin punch but it just comes back out when you move to a different part of the oring, the closest I got was putting the valve in till the top of the stem was level with the bottom edge of the groove to stop it the o ring jumping downwards when I tried to work it in but after ages carefully buggerizing around I admitted defeat, you just can't get it in the groove all the way round all at once let alone get it in and get the valve stem past it. I reckon even if you did it would be far too tight and just jam the valve anyway.

I was the one that installed new valve guides in this bike 15 years ago when it belonged to someone else and I remember getting semi-finished ones so I could set the interference myself on the lathe, I know how crucial it is and always err slightly on the side of tight (.0003" or so), heat the heads, dry ice the guides, have purpose made stepped drift ready and drive them in with 3 or 4 hits till they ring, and ream to suit the valve stem size. All standard practice but I remember these guides as being almost too tight and having to give them a half decent whack to get them all the way home. Wondering if I may have narrowed the oring groove by .2mm or so which certainly wouldn't be impossible but I think unlikely. The engine was assembled last time with much (external circumstances) drama very late at night but I still remember the exhaust orings being an issue (among many) back then. I ended up getting some skinnier orings off a Ducati mechanic mate to get out of trouble. they were still ok when I did the desmo clearances this time but I chopped them witht he edge of the collet groove getting the valves in and out (and in and out).

You mention the '75- '76 SS's but this SD is an '81, maybe in the later Bosch ign motors the seal was only 1.5mm section?

I am going to go hit the local bearing and seal shop in town tomorrow when I go in for deisel and dogbones but I am very dubious that even if they have got the size I want (which they probably will) it won't stand the heat of being an exhaust valve seal and just melt.

I've been trying to think of a way to neatly trim .2 off the thickness of the green o ring, I think it would work then but I'm dubious about performing any kind of effective surgery on o rings without just wrecking them. I'm very used to making and modifying things to make sure everything is just right but even I am baulking at trying to effectively change the dimensions of an o ring.

Thanks for the info, very much appreciated. I want to get the heads back together before I get the barrels back next week so I can get the whole plot back together from air cleaner to pipes over Easter. Who needs chocolate eggs?
Brett

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Craig in France
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Re: desmo exhaust valve seals

Post by Craig in France » Mon Mar 23, 2015 6:17 am

Spagjet wrote: You mention the '75- '76 SS's but this SD is an '81, maybe in the later Bosch ign motors the seal was only 1.5mm section?
Well, for a moment, I thought you might be on to something there, Brett ..

Because in 1980, Ducati DID change the valve guide O-ring. The new O-ring got part number 0799.92.395, a change from the previous part number of 0400.17.030 to (ref Tavola 6, 900SD Sport Desmo Darmah Edizione 1980). Unfortunately, the 1980 parts book doesn't give the size of this new seal, so it's not immediately evident what the change was.*

However, the valve guide part number was NOT changed - which it would have had to have been if the groove had been altered to take a different size O-ring. So I suspect the change was to the O-ring's material, not to its size. Also, a web search turns up numerous sites which claim that an O-ring that is much-used on modern Ducrappis, part number 88641181A, is a replacement for the 'new', i.e. 1980 seal. And the size of this modern O-ring? 7.66 x1.78, i.e. the same as the 'old' 0400.17.030 O-ring ... :roll:

So, if it were me, I'd mic up the groove as accurately as poss and then go buy the 'best fit' O-ring I could find. My preference would probably be for a looser fit than for something that's so over-size it won't go in properly. It's just gonna rip out otherwise, I'd have thought ...

Craig

* The only information I can find is from one of Ian Falloon's books where it is stated that the new seal was "OR 1000760". Unfortunately, this reference doesn't correspond to anything I can find.

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Re: desmo exhaust valve seals

Post by Spagjet » Mon Mar 23, 2015 2:51 pm

Hi Craig,
man, you must be up there with Falloon (or beyond) as far as arcane knowledge of bevels go. I ended up ordering some Viton orings (which apparently will stand the heat) with 1.5 section and 8mm i.d. I figure that even though the orig spec is 7.65mm they will still drag on the stem from bearing on the back of the groove. I'm only guessing as to the exact dimensions of the oring groove as it would be all but impossible to get anything down there to get an accurate reading (among the collection measuring sticks here anyway) without making a special go-nogo and that would only tell you width (which admittedly is the important one in this case). If (and from what you have told me I am believing more and more) the width of the groove never changed throughout the bevel run then I am back to my theory of slightly closing it with the last couple of dongs with the ball pein during installation, If that is true then the depth of the groove would be the same (within 4/5th of a beesdick anyway) with only the groove width being affected (narrowed). That means that if the section is 1.5mm and the i.d 8mm then once they are installed in a groove that was meant for an o ring with 7.66 i.d (but a section of 1.78mm) then it might be too loose or just drag very slightly on the stem. The orings that were in there up to now had been flattened on the contact surface with the stem (the 1.5mm section measurement I got was measuring the oring "across the groove" as it was much thinner (worn) looking at it across the section from the back of the groove to the stem, either because of wear and tear or being neatly "trimmed" by the sharp edge of the collet groove during the desmo clearance set up. Anyway, the next choices up and down as far as section goes on 8mm Viton orings is 1.0mm or 2.0mm so 1.5 it is. They'll be here in a couple of days so I will know soon enough once I put one in and slide a valve past it. I'm with you as far as choice of tight or loose (but still touching stem) goes, I reckon loose would be better, I'd much rather a bit of oil got past than sticking and ripping it out and jamming the valve with catastrophic results. If it was too tight you would just damage it with the collet groove during assembly anyway.

In the meantime I will give the Spaghetti Jet a big fat birthday, it has been sitting next to the Darmah sulking (and corroding) over all the intense attention not going it's way since the BIG DARMAH REBUILD (down to bare frame and back) got seriously underway at the start of December last year. I built myself a soda blaster to give the heads and barrels a much needed love up while apart (oil leaks and dirt roads) and learnt that baking soda dust in the air in NOT what you want floating around a bike workshop. After a couple of months it starts to etch it's way into all the polished alloy on all the bikes (yay), so the GTS can have today, I'll cuddle up to it with some kero, scotchbrite, metal polish and rags, by this arvo we should be friends again. By then the Bultaco will be swearing at me, at least I'll be in full polishing mode by then.

Thanks very much for the info, I also noticed that the back of the orings I pulled out had a pale yellow line around the o.d. might be discolouration from being pushed up against the groove in the bronze guide but I rather suspect it was some kind of colour coding as to material the oring was made out of.
Brett

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Re: desmo exhaust valve seals

Post by wdietz186 » Mon Mar 23, 2015 7:18 pm

I'm pretty sure the o ring in question is the same as the one used on the primary cover to seal the oil feed to the crank. It has been forever since I messed with the older style guides but I ran into the same problem.

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Re: desmo exhaust valve seals

Post by Spagjet » Mon Mar 23, 2015 9:02 pm

I just found and checked the dimensions on the oring in the clutch cover, it is exactly the same size as the exhaust seals (1.78mm x 7.65mm) but that doesn't mean it isn't the wrong one, I would have been the one to put it in and could have easily have used a cylinder head one or something. I have also realised that the valve guides were not Ducati parts so the width/depth of the oring groove is down to the vagaries of aftermarket manufacturing decisions and care as much as anything else. Not much good having the right oring for the wrong groove. I think you'd have to pound on a guide with a 4lb hammer to narrow the groove once in any measurable way once it's in the head casting but that's the only thing I could think of before I realised the grooves might be just shonky. It's all good, the orings I put in last time were 1.5mm section and the bike never blew smoke on start up or stunk of burnt engine oil and it used to get ridden hard and went like stink 180KPH+ for years so I figure if I put 1.5's in they will do the job again.

Thanks for the input though, it's much appreciated. I bounce ideas off the bull terrier all the time but he just gives me funny looks

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Re: desmo exhaust valve seals

Post by machten » Tue Mar 24, 2015 4:06 am

I seem to recall the valve guide o-rings were 8 x 1.0

Kev

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Craig in France
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Re: desmo exhaust valve seals

Post by Craig in France » Tue Mar 24, 2015 6:03 am

Good call I reckon, Brett. As you say, a bit of oil down the guides is better than none at all (of course it used to be (still is? Dunno ..) common practice to run race bikes with out any seals at all ..)

Air borne baking soda attacking exposed ali? Well, hadn't thought of that, but can well believe it. What's the ph of baking soda? 8.3? Yeah, that would do it, given time and a bit of moisture... :shock:

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Re: desmo exhaust valve seals

Post by Spagjet » Tue Mar 24, 2015 2:35 pm

yep, live and learn. The soda blasting cabinet I made was used inside the workshop the first time I tried it, after a couple of minutes I noticed it had pressurised the cabinet and was leaking out the lid seal, an industrial vacuum being involved didn't seem to work, too hard to juggle in and out pressure so I skull dragged the whole plot out into the yard and did the rest of what turned out to be endless hours (lots of days in a row, maybe 10) of blasting out there with the door shut. I had noticed a very slight mist in the air which I saw had settled on everything in the workshop (all the bikes were covered with sheets just in case but soda dust settles on every surface including ones under coversheets. I wiped my thumb across a few surfaces to see if it was on them (it was so light a dusting you had to do that to even see if there was soda dust on it), after 8 weeks or so there was a cyclone which provided the moisture in the air, 2 weeks later I ran my finger across some alloy again and realised it wasn't wiping off anymore but had starting etching in to the mirror polished surface generally and with little flowers of corrosion that looked like little white spots, some polished off with a bit of work, some had to be sanded off with 1000grit and then polished. It was hard to get off paintwork, seems to leave an oily, sticky residue that can be polished off but not straight away, several goes needed to get paint back to non-sticky, shiny surface. I have had to madly clean and polish every bike. All the non polished castings/cases were affected too, a finger run across comes away black and gritty. A scrub with kero and scotchbrite brings it back but another month or two and I reckon it would be a massive nightmare.
The soda blasting itself came up beautiful but it's a long process, nothing like sand or glass blasting but it's gentle enough to blast Dellorto bodies without even slightly affecting the tiny letters cast into the bodies.

I am madly polishing with my fingers crossed that when the Viton orings turn up and I put one in, the valve stem will drag on it, even very slightly, will be all good and the assembly will be off and running again. I used to work for a big engine rebuilding company in another life and we always took the view (with anything even remotely exotic, no one cared about stock car engines) that it was a good thing for a bit of oil to get past the valve seals to lubricate the stem rather than them never getting anything at all. It's always the problem, oil ends up gumming up the valve but bone dry ends up flogging out anyway. NO seals in race bikes, huh, makes perfect sense, I've heard they run only one litre of oil and were set up with zero clearance on both opening and closing and no keeper springs in the heads too. All makes sense (for racing). I'll just be happy if I can feel the stem drag slightly on the 1.5 section.

Slightly more optimistic after Kev said he thought they were 8 x 1.0mm from memory. 1.5 should work.

I'll let you know what happens. Another day of polishing soda etched mirror polishing stretches ahead, at least I can put loud music on and turn the brain off for that...

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Re: desmo exhaust valve seals

Post by machten » Tue Mar 24, 2015 6:24 pm

I may be mistaken on the 8x1, but I do remember fitting o-rings and them being a bit loose in the guide slots.

I remember looking for the o-ring standards that Ducati used in the manuals. That was the (now defunct) UNI standard of the Ente Nazionale Italiano di Unificazione. I've never found though a reference for OR107. OR106, yes, OR108, yes...but no 107.

There is some information on the sizes here though: http://mdmetric.com/or/corda1gb.htm and here http://www.thisoldtractor.com/o-rings_uni.html

1.78 mm was a standard Italian cross section, so it may well be that the 107 should be that c/s as well. It is probably valid to interpolate 107 as being somewhere between 106 and 108 in ID.

Kev

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Re: desmo exhaust valve seals

Post by Spagjet » Tue Mar 24, 2015 7:13 pm

all interesting. Craig told me the i.d was 7.65 or so (probably because the stems are 8mm so that is the interference on the stem) but there is only half mill nominal steps in Viton (probably all) oring range so 8mm x 1.5mm was as close as I was going to get. I am verging on the side of optimism though as the ones that came out after 15 years were still dragging on the stem (before I chopped them during desmo set up) and were definitely 1.5 when measured across the section, you really couldn't measure the section the other way as they had had a skin trimmed off by the collet groove by the time I got them out, they were a bit hard too, I busted them both removing them with a bent needle, never would have busted an oring that way if they were not hardened so it's probably a good move to put fresh ones in (I wouldn't have if they hadn't been damaged). That's a great little bit of info you saying you reckon 1.0mm section seemed loose in the groove and didn't seem to drag much, I am sure the grooves (for whatever reason) on this engine are too narrow for 1.78 so I am all but sure (shouldn't even say that out aloud) that 1.5mm will work. They should be here tomorrow.

In the meantime I am deep in the GTS de-soda-etching, it's really touch and go that it was too far gone to get back but I think it will be all good, I have just gone through all the pulled apart bike engines here on the strength of it and sprayed them all with WD-40 just in the short term, they were all sticky and gritty. Talk about live and bloody learn.......

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Re: desmo exhaust valve seals

Post by machten » Tue Mar 24, 2015 7:33 pm

you really couldn't measure the section the other way as they had had a skin trimmed off by the collet groove by the time I got them out
Yep! Been there. I put some white paper down on the bench and have a close look for any rubber nicks after pushing the valves through with a twist. I don't think it does any harm to lightly sand sharp edges of the collet grooves before fitting the valves either.

Re 1.5mm c/s, like you said earlier, all depends on the machining of the slots. All mine are aftermarket too now so who knows what fits any more?

Bit of a bugger about the soda! Hope it all cleans up OK.

Kev

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Re: desmo exhaust valve seals

Post by Spagjet » Tue Mar 24, 2015 8:34 pm

I thought about that but in the end didn't dare touch the collet grooves as they are really the only surface that sets the closing clearance. My guruwiz mate told me about the turning over of the collets during set up and having them on the looser choice so you had one last bite at the cherry if you went too far on the oilstone in the final fit, and how you had to be very careful to always put them in the same way up they came out etc (I marked them with a nikko pen), I figured every bit of material on the valve stem would be crucial as far as holding the clearance setting, I discovered that during set up you could get them real close and then dong the ends of the rocker shafts and the head casting itself in a few spots with the handle end of a big screwdriver and the feel would change (looser) so the rocker arm shaft/bush/collets/rocker/valve/camshaft bearings/etc all settled after a couple of love taps. Made me re-do the whole lot. My mate told me it should take a hour or so to do each valve properly, but he has done a million of them, it takes me days to set up desmo heads till I am 100% satisfied that they are right.

I fully understand why desmo set up is regarded as a black art. Micrometers only get you so close then it's all up to feel and instinct. I like. Big difference between right and nearly right with quite different results as far as how the bike ends up.

I also noticed the valve would get stuck getting it out not in so figured I could do final assembly with new orings safely. When I wondered why I figured that the collets would bear on the top of the groove in operation and so would have worn a sharp edge on that side of the groove. Serendipitous considering you are pushing the valve in during final assembly so are pushing the original 'unsharpened' side of the collet groove past the oring. All good.

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Re: desmo exhaust valve seals

Post by Spagjet » Thu Mar 26, 2015 5:38 pm

just thought I'd end up sharing what panned out with the exhaust valve seal drama.

I got hold of the 8mm x 1.5 Viton o rings, tried for ages and ages again but there was just no way they were going to fit in the groove. I could get 90% of the groove full of o ring right in the slot (with a bit of o ring standing proud of the groove which would have successfully dragged on the valve stem) but the last little bit doubled out of the groove (only a little bit) just stopped it from being a solution. I found out the next size down in Viton is 7mm x 1.5mm, they would have just been pulled out by the collet groove on assembly. The imperial sizes closest really weren't options for similar reasons. A 7.5mm x 1.5mm Viton o ring would solve the whole problem but that size does not exist.

I contacted my mate who knows pretty much all there is to know about the old bevels, he told me it was only the early Desmos that had the o rings in the exhaust guides, it was always a pregnant dog of a system and was only because the closing rocker destroyed the mushroom seal as there was just no room for both. He told me most of the older closing rockers had already been modified (ground away carefully to suit) nowadays to suit using an (inlet) mushroom seal, and Ducati modified the rocker themselves in the end by machining a wide groove across the back of the rocker where it fouled on the seal. I checked the Darmah closing rockers, both already were the ones with the groove so would take a mushroom seal, I inspected the end of the exhaust valve guide and saw there was no groove around the top of it on the outside to stop the seal jumping back off. The memories came back from 15 years ago when I put the guides in and the same drama came up. Anyway, stuck with a problem again, I ended up resorting to surgery on the installed exhaust guides with a dremel with a tiny little cut off wheel, it was nowhere near small enough to do the job so I had to hand grind the OD of the cut off wheel from an inch or so down to about 1/2" by using the pedestal grinder so the thing would fit in the space between the head casting and the top of the guide.
It took quite awhile but I have successfully "machined" the mushroom seal retaining groove in the top of both exhaust guides and checked them by putting a used mushroom seal on and installing the valve and pinching the seal on the valve stem with my fingers and try to pull the seal off. Can't pull it off, problem solved, assembly can continue.

Phew.

Thanks for all the replies and info offered, much appreciated. I'm writing this in case it helps someone else in the same boat. By the way, Mr. Elliott tells me it wasn't the fact that I had squashed the groove by pounding it with a hammer on installation, he struck several cases over the years of the same thing happening from after market guides having too small a groove. The fix 15 years ago would have been to machine the retaining groove for the mushroom valve into the guide before installation but I had already finished machining the semi-finished O.D. and installed and reamed the guides before realising the seal dramas back then so went to the oring groove out of sheer desperate necessity (it was well after midnight by then, we had the thing running by morning. The exhuberance of youth).

Time to do final assembly on both heads, hot coffee and a few deep breaths and I'm away.

cheers,
Brett

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