While this page is nested in the 2V side of my website (the 900 came first), the same principles apply to both the 2V and 4V valve adjustments.
Here's some information to help the beginning Ducati mechanic relate to some theory about adjusting the valves on our eccentric machines.
If you're not a mechanic, then maybe you'll appreciate what your mechanic goes through in determining how to adjust your valves.
Also see the desmo page for a better picture of the valve gear.
- Make sure that the cylinder that you're adjusting valves on is at TDC.
- Measure the unloaded and loaded gaps.
Please recheck your work once you're done with a cylinder...
rotate the engine and simply double check.
- In my notes for installing MBP collets are pics of the valve gear during a valve adjustment.
The steps shown there are identical to this valve adjustment.
- The difference we'll call delta (D). This difference is also the closer shim clearance.
- Now you subtract 0.02mm from D to figure out how much thicker the new closer shim should be, which I'll call dc, for delta close.
- The next step is to figure out the adjustment for the opener shim.
The unloaded gap is the opening clearance... now you want to subtract .076mm (.003") or .10mm (.004") to figure out how much thicker the new opener shim should be.
Let this quantity be do, for delta opener.
- Remove the shims that you need to adjust, measure them, then get new ones to replace them.
A real life example:
Desired clearances: opener = .003" = .075mm, closer = .02mm (unmeasurable in inches).
Unloaded gap = .004" = .101mm
Loaded gap = .006" = .152mm
D (delta) = .152mm - .101mm = .051mm
This is the clearance under the closing shim.
dc = .051mm - .02mm = .031mm
This is the difference in closing shim sizes we will seek.
Pay attention to "direction" as we want a closing shim that's
Opener gap = Unloaded gap = .004" = .101mm
do = .101 - .075 = .026
Remove shims then measure with micrometer:
Closing shim = 6.52mm
Opening shim = 3.45mm
New Closing shim = 6.52mm + dc = 6.52mm + .031mm = 6.551mm or 6.55mm
New Opening shim = 3.45mm + do = 3.45mm + .026mm = 3.476mm or 3.47~3.48mm
- If you don't need to adjust your closer shim, there will be practically no difference between the loaded and unloaded gaps that you measured above. BUT, also, you'll be able to just turn the closer shim when you're loading the closer rocker arm with the screwdriver. This condition of where you can turn it but not actually fit a feeler gauge to either measure a wider gap or in between the closer shim and the closing rocker arm is when the closer shim is properly adjusted.
Be sure to take a micrometer with you to buy your new shims.
Ensure that they are not thinner than your computed thicknesses.
Too thick is OK, as you can shave them down on sandpaper.
See the note below on checking the closer shim clearances.
The other reason for bringing yor own measuring device is an issue with accuracy.
Most instruments you buy today have great precision, but their accuracy can drift enough to affect the closing shim size.
Note that precision would compare to differentiating between steps in a long stairway, while accuracy is knowing that you're on the 122nd step vs the 123rd.
Now, see I use a piece of cylinder stock to help me check the shim size. I put the 3/8" x 3/8" roller bearing piece in on top of where the valve's rings sit, then measure the total clearance, then subtract the height of the stock when doing the calculations. Of course, this always adds some confusion, but that's part of the mystery in desmo valves. People with 4V motors will want to run down and buy a Kawasaki small valve shim for their stock, and get a 3.00 mm one to make the measurements easier. The 4V motors have different diameter (smaller) valves than the 2V motors.
- More on checking the closer shim clearance
Some guy emailed me to remind everyone how about the dents that the half rings get from wear.
The half rings that hold the valve and closer shim together tend to get dents in them, and if (when) you put them in upside down, the closing shim clearance readings may get tighter.
You actually can tell which side was up if you look closely at them, as one side of the half ring will be worn on the bottom and the other on the inside a bit.
You probably should replace these at any signs of wear, I do when the wear is real bad, or if they manage to break.
The 4V people will notice that the half rings are a real tight fit between the valve and closer shim.
- The closer shims may be uneven. I check all around with the micrometer before installing them. I consider 0.01mm tolerable, but will reject any with more wear. When checking your clearance, you could rotate the closer shim around a bit to make sure that you're on the highest part of the shim.
- Always double check your measurements before pulling shims and adjusting valves!
- If you have to force a feeler gauge in, it is too big. Put a feeler in a phone book and push it in and out. That's about how it should feel for measuring the proper gap.
- Obviously, I can't be held responsible for anything that you do to your bike, so if you totally follow what I say and screw up your bike then try to sue me or something dumb, I'll tell the court that you're the fool that believed what you saw on the internet. :)