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
Please note that Ducati-UpNorth.com cannot accept any liability for the accuracy or content of this section. Visitors who rely on this information do so at their own risk. If you are unsure it's worth contacting your local Ducati dealer who will be able to help. Do not attempt a repair or modification if you do not have the correct tools or knowledge to do so.