ST2 shim sizes. Valve clearance.etc - Ducati.ms - The Ultimate Ducati Forum
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post #1 of 23 (permalink) Old Dec 8th, 2009, 7:51 am Thread Starter
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ST2 shim sizes. Valve clearance.etc

ST2 shim sizes. Valve clearance.

--------------------------------------------------------------------------------

Recently bought a 1998 ST2 with 20k Imperial miles on it.
Thought I would start with a full service as it has no recent history.

Checked valve clearances and 3 have closer clearances of around 0.10mm
one has a closer clearance of 0.20mm

I have referred to the Ducati workshop manual and am confused by what it has to say about clearance specifications.

OPENING ROCKER ARM
Inlet:
0.05 - 0.12mm/0.0019 - 0.0047in.
Exhaust:
0.05 - 0.15mm/0.0019 - 0.0059in.
A clearance (A) of up to 0.05mm/ 0.0019in
is permitted: above this clearances
must be reset.

CLOSING ROCKER ARM
Inlet and exhaust:
0.03 - 0.20mm/0.0012-0.0078 in
A clearance (B) of up to 0.20 is permitted; above this
clearances must be reset.

Is there something being lost in translation from the Italian here?

with regards to the opener clearance it states
0.05 - 0.15 mm(exhaust)

but then mentions
"A clearance (A) of up to 0.05mm is permitted: above this clearances must be reset."

This appears to be telling me that up to 0.15mm is acceptable but then appears to say that clearances over 0.05mm must be reset.

Am I missing something here?


Regarding the closers it states
0.03 - 0.20mm and then mentions,
"A clearance (B) of up to 0.20mm is permitted; above this clearances must be reset.

This appears to reiterate that its o.k.to run up to 0.20mm clearances on the closers.

Later, the manual goes on to say that.

"It should be remembered that on Desmodromic valve timing systems any increase in opening clearances will automatically decrease the closing clearances and vice versa.
If you change the opening adjuster you must therefore also change the closing adjuster."

I do not understand how the one can effect the other.
They are opened and closed by different cams. When you check the opening clearance the valve is always going to be closed unless you have less than no closer clearance.
Surely if I reduce the opening clearance with a larger shim it wont effect the clearance clearance between closer rockker and closer cam lobe.

If anyone could shed any light on this issue I would be grateful.
I dont want to put it all back together and then read somewhere that I have done it wrong.
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post #2 of 23 (permalink) Old Dec 8th, 2009, 8:42 am
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Simplified version...if the clearances you measure are not inside the specifications then you need to change the shims. Referencing the closer clearances you provided they are all inside the specs. Most dealers would leave them alone, however I think the experienced folks on the lists would recommend that all clearances are better when on the tighter end of the range. And, generally the clearance specifications on exhaust valve closers are tighter than the intake valve closers. The openers use the same clearance specs across all valves, at least on my ST3.

There are multiple spreadsheets around that can help with getting everything all correct. I can send you a copy of the one I use for my ST3. It would be easy to ignore the the extra intake valve. You plug in the measured clearances and the shims in place and it will show you what shims to acquire.

Bill Wagner

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post #3 of 23 (permalink) Old Dec 8th, 2009, 9:14 am
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Quote:
Originally Posted by sadolfart View Post
"It should be remembered that on Desmodromic valve timing systems any increase in opening clearances will automatically decrease the closing clearances and vice versa.
If you change the opening adjuster you must therefore also change the closing adjuster."

I do not understand how the one can effect the other.
They are opened and closed by different cams. When you check the opening clearance the valve is always going to be closed unless you have less than no closer clearance.
Surely if I reduce the opening clearance with a larger shim it wont effect the clearance clearance between closer rockker and closer cam lobe.

If anyone could shed any light on this issue I would be grateful.
I dont want to put it all back together and then read somewhere that I have done it wrong.
For any given valve (either intake or exhaust), even though they are opened/closed by different cams and different rocker arms, the shims are on the same valve stem. So putting a thicker opening shim (at the top of the valve stem) pushes the whole valve stem downward. This will reduce the clearance on the closing shim (mounted part of the way down the valve stem) by the difference between the thickness of the old opening shim and the new opening shim. If the closing clearance was correct before changing the opening shim, it will now be wrong. The fact that they are actuated by different cams and different rocker arms is immaterial.

In practice, you should start by measuring the closing shim clearance, and adjusting that to the correct value (I use zero, which is tricky to achieve, check out the Pro Italia video, the Ducatitech.com video, or LT Snyder's 2V maintenance manual for more details). Then replace the opening shim to compensate for the closing shim change and the original error (if any) in the opener clearance (I use 0.1mm as my target here).

It sounds complicated but really isn't, if you're careful and think about the mechanical design of the valvetrain!

'98 ST2, '87 750 F1, '00 Honda CBR929RR, and a Ural
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post #4 of 23 (permalink) Old Dec 8th, 2009, 9:20 am
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Quote:
Originally Posted by shasta mcnasty View Post
putting a thicker opening shim (at the top of the valve stem) pushes the whole valve stem downward.
No, it reduces the clearance. It would only push it down if there was less than 0 clearance!

The opener only has an effect on closer clearance if you are using the loaded/unloaded method of determining closer clearance. If you directly measure closer clearance, it has no effect at all.

The closer has no effect on the opener clearance.

Tom

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post #5 of 23 (permalink) Old Dec 8th, 2009, 10:24 am
 
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Tom is correct concerning the independence of the opening and closer clearances. The clearances are measured when the valve is shut. By adding a larger or smaller opening shim, you are only changing the clearance of the opening rocker to the shim. The valve itself has not changed position so the closer clearance is not affected. Same goes with changing the closer shim clearance. The valve has not moved, just the clearance with the closer shim and the closing rocker has changed.

This of course assumes clearance exists when the valve is completely shut.

Mike
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post #6 of 23 (permalink) Old Dec 8th, 2009, 12:12 pm
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I should have phrased my explanation in terms of the effect changing the closer clearance has on the opener, not the other way around...the way I wrote it is misleading at best, wrong at worst. Sorry for the bad exposition, and thanks for the clarification.

What I meant to convey was that if you have correct unloaded opener clearance (i.e. you're pushing down on the closing rocker arm while measuring opener clearance...maybe that's called loaded opener clearance, I never remember which is which!) but incorrect (too large) closer clearance, then putting a thicker closing shim in to set the proper closer clearance will require putting a thinner opening shim in to maintain correct opener clearance. If you put a .1mm thicker closing shim in, you will need to put a .1mm thinner opening shim in to maintain the same unloaded (or loaded if I've got the terminology backward) clearance.

Admittedly, that's not what I said, and thanks again for pointing out my sloppy explanation...

'98 ST2, '87 750 F1, '00 Honda CBR929RR, and a Ural
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post #7 of 23 (permalink) Old Dec 8th, 2009, 12:57 pm Thread Starter
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Hi Ducsbill. I should be very grateful to receive a copy of the relevant spreadsheet.
I am new to these forums. How would you send them or could you post them on this thread somehow?
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post #8 of 23 (permalink) Old Dec 9th, 2009, 2:33 am
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Quote:
Originally Posted by shasta mcnasty View Post
What I meant to convey was that if you have correct unloaded opener clearance (i.e. you're pushing down on the closing rocker arm while measuring opener clearance...maybe that's called loaded opener clearance, I never remember which is which!) but incorrect (too large) closer clearance, then putting a thicker closing shim in to set the proper closer clearance will require putting a thinner opening shim in to maintain correct opener clearance.
No, it doesn't, the unloaded clearance will be the same, regardless of what you do to the closer.

To clarify,

unloaded gap = opener clearance

loaded gap = opener + closer clearance

loaded - unloaded gap = closer clearance

So, as you can see, the unloaded gap depends only on opener clearance, whereas the loaded gap is the sum of the opener and closer clearances, and therefore the closer ONLY affects the loaded gap!

Tom

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1992 XV250
1998 ST2
2003 SS1000DS
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post #9 of 23 (permalink) Old Dec 9th, 2009, 5:07 pm
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Quote:
Originally Posted by sadolfart View Post
Hi Ducsbill. I should be very grateful to receive a copy of the relevant spreadsheet.
I am new to these forums. How would you send them or could you post them on this thread somehow?
You should find it attached just below. This is MS Excel 2003 in zip format. Hope it helps. I've forgotten who created this originally so I can't give proper authorship credit.
Bill W.
Attached Files
File Type: zip DesmoCalc_v3_BillW-20090405.zip (25.9 KB, 246 views)

2005 Ducati ST3, Black
2007 Ducati MTS 1100S, Black
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post #10 of 23 (permalink) Old Dec 12th, 2009, 11:08 am Thread Starter
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shim calculator

Many thanks to Ducsbill for posting the shim calculator on this thread.
Unfortuately my pewter doesn't have excel ,so I will have to try and find a friend that does

Incidently, you know how hard it can be to accurately measure the unloaded gap beacause it is so easy to inadvertently compress the spring.

I discovered that a small jemmy/pry bar can be used to lightly lever the end of the closing rocker shut, allowing you to accurately measure the opener clearance without wondering if you are opening the valve against the spring.

Thanks to everyone for their help and advice.

Regards Pete
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