Derek's Tech Info- Valve Clearance Limits

A useful technical article from the UpNorth Tech Guru, Derek. This info is taken from a Ducati Mail list post.

There have been a few questions regarding the valve adjustment limits on 2V engines and I think its time to re-post our notes on the subject so here they are:


These notes pertain to the 2V belt driven cam 900 series engines found on late model Supersports and Monsters.  What we are doing here is intended to supplement the information found in the owners/shop manuals and through other sources. It’s a good idea to keep the shop manual handy during the process for reference.  We list some of these sources later in the page.  This process is actually very simple and can be tackled by anyone who is inclined to do their own maintenance with a minimal investment in tools and about a day’s worth of time.


The first step involves removing the seat, tank, battery and fairing sides to gain access to the engine.  On the Supersports the rear shock must be removed.  We use a short adjustable link between the swingarm and the rear cylinder.  This supports the rear end and allows both the shock and the exhaust valve cover to be removed.


After cleaning the area around each valve cover carefully remove them.  Use some care here and you can save the gaskets.  On our bike the oil cooler must be detached from the front exhaust valve cover and swung down out of the way.  Remove the spark plugs and the cam belt covers.  Set the front cylinder to TDC compression (intake and exhaust valves closed) by rotating the rear tire with the transmission in 6th gear.  Check the cam belt pulleys.  The drive pulley should have a dot that lines up with the cast-in marker on the engine side cover while the cam pulley dots line up with tiny tits on the rubber belt cover mount at the cylinder head.  We remove the cam belts to allow easy rotation of the cams when checking for binding during adjustment. It also makes it much easier to slide the rocker over when removing shims.  Owners of newer vintage engines have a bit of an advantage in this step as some of the previous years’ machines had an outer flange on the cam pulleys making belt removal/installation considerably more difficult.


And now to check the clearances on the opening rockers.  Start with the front cylinder and set the cam to line up the timing dots.  This sets both valves to the closed position.
We use a General® feeler gauge to measure the clearance between the rocker and the opener shim.  This should be between 0.004” and 0.006”.  The General® gauge will allow you to measure this in steps of 0.0005”.  Record the measurement at each valve in a table for easy reference.  The rear cylinder is similar except the cam pulley dots don’t line up at TDC compression.  The cam dot will be at about the 4 o’clock position when the valves are in the middle of their closed period.  There is no need to move the crank at this point, just turn the cam by hand for these measurements.


To check the closer clearances is a little more difficult.  John and I usually work together when doing this.  One of us applies pressure to the closing rocker using a soft brass rod while at the same time rotating the cam back and forth past the TDC position in order to feel how much pressure is being applied to the rocker.  You only want to overcome the closer spring pressure here, not force the rocker against the cam.  You rotate the cam slightly to feel how much ‘bind’ you are getting while you push against the rocker.  The other one of us is now busy checking the clearance between the closing rocker and the closer shim.  I start with the 0.0015” feeler and if it doesn’t go in I feel for binding between the shim and rocker by rotating the shim on the valve stem with my fingers.  If the shim rotates smoothly I know the clearance is between 0.0000” and 0.0015” which is within the range we are looking for.  If the 0.0015” feeler is a loose fit I try the next sizes up in 0.0005” steps until I determine the actual gap.  This procedure is repeated for each valve in turn and the data is entered in our table.


Once we have determined which shims need to be changed, we remove them.  Get hold of four plastic 35 mm film containers and label each one to correspond to each of the four valves on the engine.  All of the shims, clips, and retainers from a valve will be kept in its corresponding container as they are removed.  Only remove the shims from the valves you are going to change, but you will have to remove the opener shim on any valve you are going to change the closer shim on.


The opener shims are easy to remove if the belts are off the engine.  Use a small hook to pull the spring steel clip off of the opening rocker pivot. While rotating the cam a little near the point at which the valve is about to open, slide the rocker across the pivot pin exposing the opening shim.  It can now simply be lifted off the end of the valve stem.
If you plan to remove the closer shim, you must do two things at this point.  First, rotate the crank so that the piston of the cylinder that you are working on is at TDC.  This will limit how far the valve can slide into the cylinder and prevent you from having to remove the head to retrieve it!  Second, check the side surface of the valve stem where the bottom of the opener shim ends for a ridge.  The closer shim is a sliding fit on the stem and in order to remove it this ridge must be cleaned-up.  We use a very small stone intended for sharpening pen knives etc. and lightly rub away the ridge while turning the valve by hand.  Don’t get grit in the valve train while doing this.


To remove the shim we return to our brass rod technique to push the closer rocker away from the shim.  The cam must be rotated (you can see now why we remove the belts), to the position where the valve would be in the open position in order to do this.  While John is holding down the rocker I slide the shim down toward the rocker exposing the two half rings that are lying in the groove on the valve stem.  I then pluck the rings from the groove using a small magnet and slide the shim back up the valve stem and off into my waiting hands. .  John then gently releases the pressure on the rocker allowing it to return to its rest position.  Be careful not to loose the rings and watch out for broken ones.  If you do have a broken ring, replace them in pairs only.  We can now tie the valve up using a piece of copper or aluminum wire between the groove in the stem and a valve cover screw temporarily installed in the head casting.  This little dance is performed on each valve where we intend to change a closer shim.


At this point we are ready to take a break and figure out what shims we have and which ones we need to buy.  You may get lucky and find you can swap or re-use some of your shims.


In order to select a new shim, we need to know what shim we have, and how much thicker or thinner it needs to be to give us the clearance we want.  On the opener shims we simply measure the thickness of the shim between the surface that contacts the rocker, and the inside surface where it rests on the valve stem.  A 0 - 1” micrometer is used to measure this (but a 0 - 25 mm metric one is even better).  Ducati shims come in steps of 0.05 mm (or about 0.002”).  We have found the shims themselves tend to measure a bit larger than the listings in the parts catalogue, so we work using the actual measurement that we get from our installed shims.  Its best to convert your measured shim sizes to metric by multiplying your inch measurements by 2.54 to get mm.  As the engine breaks-in, the opener gaps tend to shrink while the closer gaps tend to widen.
This is not a rule, just a trend.  For each valve we select the size of shim that will bring the clearance back within the specified range.  Remember that the new shims will come in steps of 0.05 mm (or 0.002”) and can be a little on the big side.  So if you have a 2.61 mm opener and a gap of say 0.007”, you could select the next largest size in the list at 2.65 mm (actual 2.66 mm approx.) to reduce the gap by 0.002” to an acceptable clearance of 0.005”.  We always bring our micrometer to the shop and measure the new shims ourselves to verify the size (and select the ideal thickness from the range).
The closer shim is a little more involved as it requires the use of a Ducati ‘tool’ to measure the actual thickness of the shim.  The tool is just a pair of spacers you use with your micrometer and if you don’t want to buy it you could always bring your closer shims to the dealer and let the highly trained Ducati Technician measure them for you.  Be careful when selecting the closing shim.  Don’t be too finicky about getting the closing gap as close to zero as possible.  The range between 0 and 0.002” is tricky enough to achieve especially for the first time desmotech.  That range describes a single size step in the stock shim sizes.  If your clearance was 0.002”, then leave it there and check it again next year.  If you buy a shim that is going to put you at a theoretical 0.0000” clearance, count on spending considerable time hand lapping that shim on a piece of glass and wet/dry paper and installing/uninstalling it trying to get a fit that doesn’t bind against the cam.  This may be necessary in any case, even with careful planning.  The shims are hard and material comes off pretty slowly.


Once you have the shims that you need, its time to put everything back together, almost.
Before you start sprinkling shims into your beloved engine, there is one trick that makes enduring this lengthy discussion worthwhile.  Go back to those half-rings that hold the closing shims in place on the valve stem.  Grab a magnifying glass and take a real close look at the wear pattern on the top and bottom surface of the ring.  You will notice that on the side that faces away from the shim, the groove in the valve stem made a slight impression.  That impression tends to lie closer to the inside of the circular ring.  Flip the ring over and you will notice that the shim left its own telltale marks but they favor the outside of the ring.


The identification of these impressions and the correct orientation of the rings in the valve will help ensure the clearances you get after putting everything back together are what you expected when you made your calculations.  A significant portion of the change in clearances in the valve system during break-in can be attributed to these little impressions.  Putting the rings back in upside-down or replacing them with new ones will mean the system will have to make a new set of indentations with a corresponding change in clearances.  This can’t always be avoided however if your rings are badly worn or broken and need to be replaced.  We have found that once the bike’s break-in process is over and the clearances have been adjusted, Ducati valves tend to keep in excellent adjustment for a long time.  In fact, unless there is a problem, its best not to adjust them until after the break-in period is over, just check them.


Putting the shims back in is pretty much just a reversal of the removal process.  Check each cam after installing the closer shims for binding by rotating the cam by hand.  Also check your clearances again to see how close you came to your expected result.  The hardest part is getting the rings to stay in the grooves.  A little oil helps them to stick while you insert them.
We hope you find this information useful and stress its not the only method in town, but it works well for us.  If you don’t do your own valves then this may give some insight into the process.  You can see it takes some time even for an experienced mechanic.
Thankfully, in street engines at least, once the valves are adjusted correctly, they tend to stay that way for quite a while. 


Lloyd MacLean & John Papes

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