Shimming Valves

As those who have been unlucky enough to meet me in the flesh will testify, I’m slightly long in the tooth, but will readily admit, the world of the desmo is a fairly new one to me.

It’s not that I’m just a stingy old git, as more that I dont buy new parts if I can a machine up an alternative from bits in the scrap-box. So I need to lean on the experience of members who have ‘been there, done that, and know what works’ when it comes to getting the best from my air cooled Desmo lump……

I’m slowly but surely getting a pair of heads ready to allow the engine to make best use of a pair of FCRs and some HC pistons…… ports are done (well, they definitely flow more now!), suitable seals are waiting, and now there’s just the little matter of shimming the valves.

I’ve scoured the interweb thingy, watched the CA vids (very handy), and then set about the tasks…… and am now mildly confused, and so need some advice (even if it’s just someone to say “Yep, mine were that far out as well” )

Tappet/Shim clearances on old 4 stroke engines are usually, in my experience, around the 4 to 12 thou range dependant on engine type, valve layout, materials, cam drive, etc. I wasn’t totally surprised to see that Desmo’s should have tighter settings of 0.003” openers and 0.001” closers ……… until the heads I was checking gave me gaps of between 0.007” and 0.009” on the openers. I then used the ‘press down on closer and remeasure opener, then deduct orig. opener gap’ method, and got a further 0.010” to 0.023” gaps on the closers…… way too big, even if they were on an old Ford X-flow.

Now these heads came off a running engine…… so, either the 0.002” tolerances most advice gives before needing to change shims is way off, or these heads must’ve been very noisy, and the engine was probably lucky to even start - unfortunately I never got to hear it running, let alone check it for power.

Firstly, are these gaps common, or have I completely screwed up the measurements (I never discount human error) :laughing: . And secondly, has anyone tried to bridge these kinds of gaps with what would effectively be 8mm diameter inserts and 15mm washers for the opener/closer shims repectively. If the gaps were a couple of thou out then separate shims would be too thin to last any length of time, but on gaps of 20 thou, that’s tempting to make up some oversized (to ensure enough strength) inserts, and then polish the original shims down to required size. If you can see where my brain is leading here; if a supplier where to make up a batch of case hardened washers of 0.010”/ 0.25mm or 0.020” / 0.5mm, then it would just be a matter of picking the most suitable one and polishing down the original closer shims to suit…… think of all the old discarded thin shims that could be reused – there, biking can be environmentally friendly. :stuck_out_tongue:

So, has anyone else tried it? What grade material did you use? And was the end result a cheap fix or a shortcut to an expensive engine failure…… :astonished: ?!?

Not sure about clearances, but before going to the trouble of making inserts check with your nearest dealer. They usually swap valve shims for a niminal fee (or for nothing at all if you smile nicely :wink: ).
Ducati Manchester gave me a couple for my 250 single racer (same as 2-valve closing shims).



Hi Wilbert,
Many years ago (at least 25 or more) the then club membership sec’ Pete Fisher (There’s a blast from the past) had sets of hardened silver steel shims made up in assorted thickness’ to do just what you’re asking about…
The idea being that with a set of these Washers (for want of a better discription) and a slack handful of genuine closing shims the variations that you could achive would be almost infinate…
I didn’t buy them at the time because I worked as a Ducati mechanic and therefore had no problems obtaining genuine shims.
Over the years I’ve worked on quite a few old bevel bikes and have found these ‘Washers’ in a few motors, they seem to run with no problems…
To this date I’ve never found a broken one!
As you say if they are too thin (and Pete’s weren’t) they can and will break up, I’ve seen this when someone has just cut small steel shims of only a couple of thou, finding whats left of them floating around somewhere in the motor.
Pete wrote up all about this in the DESMO and Spaggy should have it in the archives somewhere?
They maybe on the club website by now?
However this sort of idea came about because Ducati dealers were few & far between, parts were hard to get hold of back then.
Which isn’t the case nowdays, I now buy my shims from EMS in California I order them online and they drop on my front doormat in normally less than 4 days, they’re better made than the genuine articals, they’re hardened all the way through, cheaper and come in smaller incriments!!
Here’s the web page…

I highly recommend their service, I’ve used it a few times and also know that top Ducati engine builders here in the UK use them as well.

You now owe me a beer!

Steve R (The Southern version )

Very interesting there Steve

Sounds like he borrowed the idea from the Singles Desmo motor where there were only 3 closer sizes but 6 washer sizes.

Mind you the single Desmo engines are a cheat as the hairsprings are still there and are quite strong.

Easy to convert to bevel twin style though, with no springs at all/ very light closer for starting.

Shims (common for all 2 valve motors) are still available from your local dealer in 0.05mm increments. 0.1’s with the old part numbers and .05’s with some new fangled numbers…

Many thanks for the replies lads.

Sounds like (a) the idea is not only a sound go-er, but has (as I’d imagined) been applied successfully in the past, and (b) there are easier ways to get the job done nowadays, especially as we now have access to a decent worldwide network of Duc workshops to source parts from … but not as much fun as making me own (told you I’m a born tinkerer) :stuck_out_tongue:

I’ll have to nudge Spaggy and see what’s lying at the back of the cupboards covered in dust :laughing:

and why am I not surprised to find that it’s easier to get stuff from the yanks … it still baffles me how under-appreciated these twins seem to be in Europe.

Thanks again - I’m off to get oily :smiling_imp:

Mind you the single Desmo engines are a cheat as the hairsprings are still there and are quite strong.

Easy to convert to bevel twin style though, with no springs at all/ very light closer for starting[/quote)

Hi Andrew,
I’ve had my 250 Desmo head converted to the bevel twin style closing springs by Tony Brancato.
A very neat job which involves machining the head and the closing rockers, I’d asked Nigel Lacey about this mod and he said it was very worthwhile and that Tony’s was the best place to get it done.

I also have a set of heads on my 900SS Bevel which I had converted in the early 80’s to eccentric rocker spindles with a screw slot and locknuts on the lefthand side cam support block.
You shim the heads in the central position of the eccentrics they take up any adjustments needed with the eccentrics using the usual feeler gauges, screw driver and a spanner…
Simplicity it’s self!
The same idea was used on the BSA Gold Stars and quite a few other British bikes.
This was another of Pete Fisher’s ideas, (To make it fit a Desmo) he’d done it on his then unique 750 longstroke Pantah motor, he had a special crank made for this bike.
He helped me find someone to do the machining work, make the special spindles and in the case of the bevel twins some new cam support blocks made to carry out the conversion…
These were turned up from a solid bar of top quality alloy and are beautifully made items, as was the rest of the work.
These were needed because the’re hollows were you need meat to machine on the original bevel support blocks and they can’t be welded up, we found this out when we tried to weld them the alloy was absolute Sh*te and completely unweldable!
The Pantah support blocks were/are solid and could be machined for the job easily.
All of this was writen up in the DESMO all those years ago and will be in the clubs archives somewhere.

Steve R (The Southern experimentor)

I actually still have the issue of Desmo with that article in kicking about somewhere in the loft :slight_smile: Never got around to doing it with my old Darmah or had the money to get it done , 20 odd years on and I’m now a jobbing machinist in a small engineering shop with a whole workshop to play with but sadly no Darmah :frowning:

Hi Paul,
I’ve still got most of the Desmo’s I’ve ever received some of them getting on for 30 years old.
I recently spent hours looking for an article that Jilly needed for an ex-member/racer…
Lifes too short to go through that again, but I did find lots of interesting stuff though.
Spaggy has started the very long process of transfering the old Desmo’s onto the club website, I haven’t looked of late to see how he’s getting on with that labour of lurve.

Steve R (South)

One thing about shimming that keeps popping up is differences in how to measure them. I know from the gaps what increases in thickness I need for each individual shim to get the gaps down to recommended 0.003" / 0.001", so it should be a doddle - pick a size and buy them… but No :imp:

Measuring openers isn’t a big problem because I’ve got a decent micrometer that fits inside the opener shims, and my measurements seem to be within the ranges being quoted for replacements, but when it comes to closers, I’ve tried the ‘measure the edges and take an average’, and ’ put feelers either side and subtract them from the reading’ methods… but neither puts my shims within the ranges being quoted either at dealers here or in the states for replacements… for ref. mine are between 0.306" (7.77mm) and 0.330" (8.38mm) top face to bottom face… sizes to order seem to be from 5.5mm to 8mm … do these dealer sizes relate to the ‘internal’ thickness, ie - taking into account the depth of the collet into the shim top? If so, is this depth standard and then can I deduct it from the measurements? …or, as with most things ducati, do I need to buy the ‘special tool’ inserts just to measure a bloody shim!!!

(yes, you’ve by now guessed, as an amateur mechanic of over 30 years I’m getting really infuriated when everytime I try to do what should be a simple little job on a Duc I discover they don’t even measure things like the rest of the world, so I need to buy special tool number 123XYZ… or of course, pay your local dealer stupid / hr for it :imp: )

Without measuring the new and old shims with the same method / instruments, how can you be sure you will get the right thickness when ordering through mail from the colonies? When we’re dealing here in adding between 2 and 16 thou (worst of the 4 closers by far!) to a shim, a potential error of up to 0.065" (collets thickness) makes a nonsense of even bothering…

A few intakes of breathe and a couple of cups of Tea later, and I’m determined not to be beaten by Duc and their ridiculous attempts to thwart my engineering - I set out to extract, AND WILL GET, 90rwhp out of this friggin thing WITHOUT paying a dealers mechanic to touch it :laughing:

The size of the closing shims is indeed read from the bottom of the 1/2 ring recess.
The depth of this recess isn’t constant across the shim range, it can be different on shims of the same ‘REAL’ size.
The easiest way is to get a measureing tool, like the one shown on the EMS website.
Tony Brancato sells a ‘Penny on a Stick’ tool*** (Other specialists sell a pair of buttons that sit inside the shims) that fits down inside the recess, you take your measurement then subtract the size of the tool, this along with the gap you’ve measured with your feeler gauges can then be used to order the correct size shim needed to get the new gap you need.
I’ve now got a large collection of shims, (For both 2+4 Valve motors) but when I need to fill any gaps in my set I usually buy a size larger then I use an oilstone to get the clearances spot on, rubbing the excess down using a figure of eight motion.

Steve R (South)

*** These tools don’t cost a lot of money.


I’ve spent the last hour or so in the garage (missus said the roast chicken will be another hour yet so why waste it watching Superbikes on telly :astonished: ) turning down a ‘button’ to help with the measuring … basically a stainless bar a with couple of mm at 8mm diameter (valve stem) and approx 5mm at 9.75mm, so it fits inside the collet recess in the closer shims … by inserting it alternately in the base of the shim, then in the collet recess end, and using a feeler gauge to ‘close’ the other end of the shim (was 1 1.0mm feeler but doesn’t matter what size as it’s a constant and becomes irrelevant in the calcs :nerd: ) I’ve ben able to accurately measure the ‘correct’ shim size… and guess what? The recesses all vary … for those who aren’t too bored yet, heres a summary of the results…

The collet recesses varied between 0.0626" and 0.0736" - as I’ve said before, when you’re looking to close gaps of only a few thou, that’s a BIG range…

The resultant shim sizes I now need are therefore 0.2504" (6.360mm), 0.2582" (6.558mm), 0.2626" (6.670mm), and 0.2492" (6.330mm) … and of course, as sods law dictates, only one of the current shims is big enough to use to polish down to use as one of the new’uns (i’ve got a 0.2562" I can use to make the 0.2504")… so, it looks like I need three new closers - one at 6.5mm and two at 6.75mm, and some wonderful time with the oilstone … :smiley:

Openers have been nowhere near as big a problem - two are not worth changing as gaps are between 0.0035" and 0.004" - on the others I will need to go up to a 0.160" and a 0.145" to get optimum 0.003" gaps.

You’re comment on old shims does sort of point to the obvious in terms of club members - between us we must have every size we’ll ever need tucked away somewhere - now, how are we going to set up an exchange? Measuring’s the easy bit - if we could then send our oldies in with a request for “three thou thicker than that please…” it’d make DIY valve shimming so much easier…

Now then , come on - how many got bored before getting to the end of that little self-indulgent techie piece? :stuck_out_tongue:

Hi again Wilbert,
Years ago Tony Brancato ran a system whereby you sent him your old shim telling him the gap that you had and the gap that you needed he then supplied the correct shim for your needs.
(He probably would still do this).
As I’ve said these days it’s easier to just hit the Internet and order the ones you need after doing your sums.
Again as I’ve said I have a large selection of shims collected over the years, this includes buying a complete set of 4 Valve shims from V Two, these were 1/2 the price of buying original items!
The EMS shims are cheaper still!
Down 'ere in the West Country there was a few of us with a collection each and we would swap and borrow each others shim collections.
Over the years lads have retired from biking, moved away etc, so this has now gone by the board.
The last time I lent out my shim kit, (To a club member who despite being much more well off than me hadn’t bought any himself) I lent it on the deal that whatever shims were used the lad borrowing them would replace them…
See if you can guess what happened?
I’m sure you could see this coming, I waited over 18 months to get the replacements and then I had to source them myself…
He later paid me my out of pocket expences, the result being that I don’t lend my kit out anymore.
Unless I can stand over it, which usually means that I do the job for whoever needs to do their shimming.
The idea that you’ve put forward is OK, but in practice it only takes one lad to take the Pi*s for it all to fall apart as I found out!

Steve R (South)

How is the 900 project going I see you sorted out those heads mine is coming along am now running an ignitech ignition which is really good not been on a dyno yet tho steve

Hi Steve,

Only got one 'bike at the moment and too busy riding the thing to strip it down… current contract ends in a couple of weeks and new work not expected until mid August so should have a couple of weeks in which to do a service and a piston / head change - I took the chance of a ‘clearance sale’ in the States to get hold of some 92mm and 94mm 11.5:1 comp forged pistons…

I’ll be fitting the 92’s together first with the modded heads, then probably go to the 94’s with some FCR’s next year (I got a set of 4 off a 'blade, so not a straight bolt-on, but fairly simple) …