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Choosing the correct valve shim size

wasang

wasang

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Oct 7, 2025
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Location
Southampton
Bike
M900ie
Hi fellow Monster owners.
I am about to order some replacement 8mm closure shims for my 900ie S2R.
According to the manual, the closure gap should be between 0.03 - 0.05mm.
The gap on one of the valves measures 0.07mm. Shims are supplied in 0.05 increments.
If this is the case, I can only reduce the gap to 0.02mm which is again outside of the range.
There must be a reason why a minimum of 0.03 was selected probably due to heat expansion
of the metal so 0.02mm would be too tight when the engine was hot.
What would be the best thing to do in this case. Leave the gap at 0.07 or reduce it to less than the required minimum?
Your advice would be much appreciated.
Thanks
Wayne
 
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From my experience: when you fit a shim, it doesn't always fit exactly as you'd hope it might. Now that maybe down to measurement tolerances/accuracy but if it's too loose it will always be too loose. You can, if necessary 'lap' a slightly oversized shim to fit. On this basis and assuming your measurements (and the shims) are exact, I'd go with the tighter fit because if it's marginally too tight it can be 'adjusted'.

Ideally a shim 'kit' is the best way to go so that you can fit, test and refit until you find the right size (I have seen two, seemingly identical shims but found one to be tighter than the other once fitted) not cheap but likely cheaper than a one-time valve service at a Ducati dealer and you've got them for the future.

As for how tight a closer should be, I work to 0.05mm maximum gap, with the minimum as small as possible but important that there's no drag (can be felt rotating camshaft by hand) but if there's a clear 0.02mm all the way round the cam cycle then it'll be fine and as it wears it'll increase anyway.
 
It's been a while since i done shims on the Monster but I'd be happy with 0.02 mm on the closers. i think i may have went slightly tighter even. Be sure the half rings go in the right way, they can affect the clearance and measurements.
 
IMO much of the movement in valve clearances is down to the half-rings which basically look like bits of bent wire, they also break frequently especially if clearances are allowed to get too loose (though they will still work even when broken), when I got my Monster there were several broken half rings in it.

As I had already done so on the 916, I fitted MBP retainers - these are a precision machined collet to replace the half rings, they are a much more solid fit, can only go in one way and pretty much eliminate needing to change shims.

For example, last year I checked the valve clearances in my 916 having previously checked in 2020 and only one valve was showing a marginal difference and this was likely down to how I measured them (it is subjective and access is tricky, especially on rear exhaust valves on 4v engines) but even so it was still within my tolerance and, well within those specified by Ducati.

Similarly my Monster has rarely needed any adjustment though I had the engine apart in 2021 due to a broken gearbox and whilst in there I noticed the exhaust valve guides were sloppy so had them all replaced and the seats re-cut, meaning all clearances needed to be reset.

I didn't check them again until 2024 and, as expected on new seats, they had settled in a little though still within tolerance. I adjusted them accordingly and checked them again last year for peace of mind and they were still spot-on the previous settings, I won't even bother checking them this year.

I would highly recommend MBP collets/EMS shim kit, a fairly big outlay but if you're DIYing the servicing it'll pay you in the long run.
 
Brilliant! Thanks you all for your in depth knowlege and advice, very much appreciated.
I have purchased new wire collets from Ducati which have taken up most of the slack
but I am not impressed with their finish. Bits of bent sprung steel with a poor cut at the ends
(looks like they've been cut with a pair of blunt wire snippers). I'll take your advice and purchase
the MBP retainers and order myself an EMS shim kit.
As for lapping the closure shims, I was advised not to lap them to size because they were hardened
after machining. Think this was rubbish now you mention it as you can see the original machining marks
on the base of the shim.
Again, Thanks for your advice,
Wayne
 
Shims should be through hardened so isn't a problem, just be careful to get an even lap if you're doing it.

I've lapped many without a problem and so, consequently have several shims that are slightly odd sized (which is why dealers generally don't do it) but mine are just for my use so no problem as I just use what works best.

Some info re. hardening here;


Since EMS finished trading, Desmotimes is probably the best shim kit/MBP supplier, sells a kit with everything you'll need. Not cheap and you'll get hit with VAT/import fees unless there's a UK supplier?
 
I go on the basis of a 6000 mile service interval for valve clearances.
From 20,000 miles to about 38,000 my half rings nearly all broke up every time they were checked, but they have settled now and seem to survive.
Also the clearances settle and less of them need doing as the mileage increases.
I sometime get away with just a lap on the odd tight one.
Lapping a shim down is perfectly okay. I just use a bit of 1200 wet n dry on a flat plate with a bit of thin oil. (3 in 1 is my favourite.)
Don't get carried away, it will soon cut down.

If you want to justify a shim kit; I was charged £216 for a valve service last time a couple of years ago. Mind you that was the nail in that particular "mechanic's" coffin and he won't be getting any more work from me, nor any recommendations! I mean what on earth has turning round the filler cap and adjusting the time on the clock got to do with a valve service?
But still, Carl is just a 4 letter word beginning with C..... No names mentioned.. :ROFLMAO:
 
Mr Gazza said:
I go on the basis of a 6000 mile service interval for valve clearances.
From 20,000 miles to about 38,000 my half rings nearly all broke up every time they were checked, but they have settled now and seem to survive.
Also the clearances settle and less of them need doing as the mileage increases.
I sometime get away with just a lap on the odd tight one.
Lapping a shim down is perfectly okay. I just use a bit of 1200 wet n dry on a flat plate with a bit of thin oil. (3 in 1 is my favourite.)
Don't get carried away, it will soon cut down.

If you want to justify a shim kit; I was charged £216 for a valve service last time a couple of years ago. Mind you that was the nail in that particular "mechanic's" coffin and he won't be getting any more work from me, nor any recommendations! I mean what on earth has turning round the filler cap and adjusting the time on the clock got to do with a valve service?
But still, Carl is just a 4 letter word beginning with C..... No names mentioned.. :ROFLMAO:
Click to expand...
He did a great service on my old 900 Dark quite a few years ago,don't know what they're like now
 
if you're lapping shims get your fine emery/wet&dry on a flat surface and move the shim in a 'figure 8' pattern (not back and forward) giving it a quarter turn every now and then, this should help ensure an even lap.
 
Hi. I have now finished lapping my closing shims so that the horizontal and vertical cams have no drag as suggested. This has left a gap around 0.01mm or less so I can now work on the opening shims.
I have shimmed many different engines including British (BSA tappets) and Japanese (Honda, Yamaha) and with each there is a minimum gap to allow for heat expansion of the metal since the work is carried out cold.
If this is correct then surely a minimum gap must be left to allow for heat expansion on the Monster as well? The cam is going to slightly expand and the shim will very slightly increase in size as the engine gets hotter.
What is your experience with this as I seen even professional Ducati engineers use the "cam drag" principle?
Would be interesting to get everyone's opinion about this,
Cheers
 
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Just checked old set of scribbles from my last shim check/ adjustment and see that i set my closers to negligible gap, i.e. just able to turn the cam with no resistance but unable to get a feeler guage into the gap. Last time i checked since that, all still turning smooth and the cam lobes etc all sweet and shiny.
I'm not an expert, and very happy to be corrected by wiser ones on here but - the closer gap doesn't tighten with heat. As the head expands, the valve/stem expands too and the closing shim will move away from the rocker fork, unlike the opening gap which closes as the valve stem and other gear expands. Similarly, as the valve seats more into the head with wear, the valve stem will protrude further back, loosening the closing shim and tightening the opener.
 
the above sounds correct, except 'zero free to turn' means when you can't get your smallest feeler guage in, the SHIM should spin without reststance, not the cam.
 
Valve clearances from the 'old' M900 workshop manual (before they widened the tolerances for easier/cheaper maintenance) are (mm);

Opener, Intake: 0.10 - 0.12
Opener, Exhaust: 0.12 - 0.15
Closer, Intake & Exhaust: 0.03 - 0.05

Which seem sensible and what I work to.

As for 0.01, maybe OK but how are you measuring it, how easy does the feeler slide, one man's tight is another's just right.

Also, once you have the openers set then check the closers again because whilst, in theory it shouldn't affect them, you may find they feel different once you have the openers correct - you are measuring combined loaded/unloaded clearances after all so there is some degree of subjectivity and, at those small numbers the tiniest change makes a big change.

Whilst I said 'as small as possible' not sure I'd be happy with 0.01 but, I think it would be difficult to establish that it was correct and if it doesn't drag then I'll wager it's more than that anyway.
 
Great advice thanks. I will probably work to the same measurements as the M900 manual and recheck when the openers
are in place as advised. Back into my man cave again. Yipee
 
I've just been looking at the (Italian Language) Ducati service manual for S2R and with regards to valve clearances, it states;

Valore Montaggio;

Opener, Intake: 0.10 - 0.15
Opener, Exhaust: 0.10 - 0.15
Closer, Intake & Exhaust: 0.00 - 0.05

Valore Controllo;

Opener, Intake: 0.10 - 0.20
Opener, Exhaust: 0.10 - 0.20
Closer, Intake & Exhaust: 0.05 - 0.10

From which, I take the first as the optimal and the second as permitted/service limit because, let's face it if you find an opener clearance of 0.16 and a closer of 0.06, it's not going to cause any problems so hardly worth trying to bring it back to optimal.

No surprise either that the service limits are +/- 0.05 as that is the difference in shim sizes so, unless you're going to lap them those are the available 'steps' plus, from the first numbers Ducati are obviously happy with 0.00 closer clearance.

IMO, a loose closer is less critical than a tight opener as despite the Desmo system, the valve have springs anyway so will still close.

As the valvetrain wears then generally the openers close up whilst the closers open up accordingly.
 
Looking at that information it seems ok to use the "cam drag" principle and have the measurement near to 0.00
The opening measurement as you say is more critical and to ensure that the value is within tolerances.
Thanks again for this invaluable info.
 
As a confirmation of exactly how much clearance you have, use a feeler gauge in the gap whilst turning the cam. e.g. if you have a 0.1mm gap then stick your 0.1mm feeler in the gap and rotate the cam, you'll see whether or not the 0.1mm is truly accurate depending on how much drag it creates. Especially so if you stick a 0.15mm in (assuming you have 0.05mm closer gap), it will obviously be tight but exactly how tight is very informative.
 
Great info. Thanks for that advice. Will check the gaps today using your proceedure. This is a really good way of
checking the clearance. Cheers
 
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