Valve Adjustment

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.

Of course, there are many ways to adjust your valves, the way that I illustrate below is one that I find easy. I also confirm my measurements by sliding feeler gauges between the closing rocker and the shim, which is simply another (more obvious) method.

Be sure to go to your local dealer (or ) and get the new HAYNES manual for the 600/750/900 2V bikes from 1991 to 1996. This manual includes the SS’s and the Monster’s and while not exactly correct for the FI Monsters and SSs, will still be relevant as the engine and valves are the same. I got one in 1997 and am very impressed with it and wish I’d have had it for the 2 years prior!

Instead, I’ve pretty much learned everything in there on my own.

Four valve owners can get a manual from Ducati (people call these factory manuals) – or Haynes just came out with a 4V manual. This new Haynes 4V manual should be available at around Feb 2002.

As far as 2V clearances, I talked to a dealer in 1997/8, and they said that the factory’s new valve adjustments are retroactive to include all 2V desmo’s. They also said that the new valves are very much the same as the old ones as far as wear goes even though they are allegedly bimetallic. While the new specification of 6000 miles and up to .007 on the closers are extreme, they said that up to 3 thou is OK.

And always run the openers at .004.

I recommend 3500-4000 mile intervals and adjust the closers if they’re greater than .002. But if you spend a lot of time at or above redline, you really should adjust it down to the no clearance spec of at or below .001.

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:

Some Notes:

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.

Ducati 350 S Desmo

See the note below on checking the closer shim clearances.

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.