2004 Ducati ST3 Valve Clearance

[Ken]

When I purchased my ST3, I also purchased the $200 Ducati Service manual. Under valve clearance, the following specified limits are listed:

Opening Rocker Arm
Intake
Nominal .020mm
In Operation .013 -0.18mm
Check 0.05 - .18mm

Opening Rocker Arm
Exhaust
Nominal .020mm
In Operation .013 -0.18mm
Check 0.13 - .25mm

Closing Rocker Arm
Intake
Nominal .015 mm
In Operation .013 -0.18mm
Check 0.05 - .23mm

Closing Rocker Arm
Exhaust
Nominal .015 mm
In Operation .008 -0.13mm
Check 0.08 - .20mm

The check setting are straight forward enough. However, why did they list the in operation settings? In addition, why is the nominal setting for the Opening Rocker Intake (.20mm) outside the check limits of .05mm - .18mm?

I have the Desmotimes manual that lists values that are different from these. It states:

Intake
Opener .10 - .15mm
Closer .10 - .15 mm

Exhaust
Opener .10 -.15mm
Closer .5 - .10mm

It recommends .10mm for the intake opener, closer and exhaust opener and .05 for exhaust closer.

Which one is correct or neither correct?

[stryder]

I can't check any manuals but I use LT's recommendations of .002 for the closers and .004 for the openers IIRC. (inches)

[ducatimike]

I confirm what Stryder said. I used those clearances in all the desmoquattro motors I have owned. I first started hearing about using tighter clearances from racers years ago and tried it with no problems. My bikes definitely run smoother with the tighter clearances. Also, larger closer clearances beget even larger clearances as the half rings get hammered and deform.

I think Ducati used the larger clearances to give the service guys a break, where they check the clearances but dont actually change out any shims. I always set the the clearances to the nominal. If the clearance is out one shim size I change the shim. But I am kinda anal about it and I have unlimited shims to work with.

Mike

[mlukason]

I use LT's clearances too. No problems!

[StuST3]

I also used LT clearances as well and it runs better. My exhaust were out but the intakes were perfect. I did the inspection at 9k miles.

[Ken]

Several valve adjustment sources state, "The perfect closer clearance can be felt. You should NOT be able to rotate the closer shim when the engine is at top dead center compression on the cylinder."

If Ducati recommends a closer shim clearance of .05 -.23mm, there shouldn't be any pressure from the spring loaded closing rocker. If the closer shim doesn't rotate, wouldn't your shim gap be 0?

[ducsbill]

Originally Posted by Ken

Several valve adjustment sources state, "The perfect closer clearance can be felt. You should NOT be able to rotate the closer shim when the engine is at top dead center compression on the cylinder."

If Ducati recommends a closer shim clearance of .05 -.23mm, there shouldn't be any pressure from the spring loaded closing rocker. If the closer shim doesn't rotate, wouldn't your shim gap be 0?

I think that measuring is the best way. I suppose there might be enough pressure by the closer helper spring to make it difficult to rotate the shim, but I can't think of any reason why a zero gap would be good. There needs to be some allowance for expansion due to heat. I try to get as close to the minimum gap as possible when I check the valves on my bikes. They seem to run more smoothly (a "feel" thing I know, but what can I say ).

Bill W.

[stryder]

Originally Posted by Ken

Several valve adjustment sources state, "The perfect closer clearance can be felt. You should NOT be able to rotate the closer shim when the engine is at top dead center compression on the cylinder."

If Ducati recommends a closer shim clearance of .05 -.23mm, there shouldn't be any pressure from the spring loaded closing rocker. If the closer shim doesn't rotate, wouldn't your shim gap be 0?

The closer clearance is measured with the rocker arm loaded, ie pushed down by a tool, taking the closer spring pressure off the closer rocker arm/closer shim. It's the difference between the original previously measured opener gap when the closer rocker was unloaded/full closer spring pressure on the rocker arm-closer shim, and the new, widened gap after the closer rocker arm is pushed down/loaded, no spring pressure. When the closer rocker is loaded, the closer shim should/will easily spin on the valve because there is clearance. The closer spring is there to help shut the valve fully at lower cylinder pressures, due to that clearance.

[Ken]

Originally Posted by stryder

The closer clearance is measured with the rocker arm loaded, ie pushed down by a tool, taking the closer spring pressure off the closer rocker arm/closer shim. It's the difference between the original previously measured opener gap when the closer rocker was unloaded/full closer spring pressure on the rocker arm-closer shim, and the new, widened gap after the closer rocker arm is pushed down/loaded, no spring pressure. When the closer rocker is loaded, the closer shim should/will easily spin on the valve because there is clearance. The closer spring is there to help shut the valve fully at lower cylinder pressures, due to that clearance.

Then the original statement from the LT Synder Desmo Mainteance and Modification Guide is not correct. Even with the tighter valves setting recommend in this guide, a .05 closer shim setting should allow you to rotate the closer shim at TDC.

On the original post, the Desmo Times manaul recommends for the exhaust closer, .05 - .10, not .5 - .10.

[stryder]

Originally Posted by Ken

Then the original statement from the LT Synder Desmo Mainteance and Modification Guide is not correct. Even with the tighter valves setting recommend in this guide, a .05 closer shim setting should allow you to rotate the closer shim at TDC.

On the original post, the Desmo Times manaul recommends for the exhaust closer, .05 - .10, not .5 - .10.

I don't have any my manual close to me so I can't comment further, and the one I have at home is the original edition of the ST3 included ST manual. If you haven't already posted at the Desmo Times bulletin board in the ST section I suggest you do. LT is aways answering question on his board and he may be able to clarify yours.

http://ssnyder.proboards.com/index.cgi?board=ST