910S replacement Valve shims formula - MVAgusta.net
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post #1 of 4 (permalink) Old Yesterday, 07:11 AM Thread Starter
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Question 910S replacement Valve shims formula

Hi, I'm doing a valve clearance check at 53,000kms and have the cams, buckets and shims out. The Engine Manual formula at Section B p. 43 reads:
C) Calculate the D difference between the compared play and optimal play shown on the chart [see valve play specs];
D) Read the value of S thickness on the tablet;
E) Choose new tablet/shim with an S+D thickness

Inlet upper spec: 0.24mm
Measured Valve play/clearance: 0.13mm
Measured present shim thickness is 2.42mm

MV Formula:
Calculated difference between valve clearance and upper value of spec D =0.11mm
Value of thickness marked on the shim S =2.45mm
New shim thickness S+D =2.56mm

This doesn't seem right since my clearance is already below the minimum spec of 0.15mm with the 2.42mm shim and requires a thinner shim in order to widen the valve clearance gap up to the top of the spec.

I've checked my Honda CBR100RR manual and it gives the formula:
Calculate the new shim thickness using the equation
below.
A= (B-C)+D
A: New shim thickness
B: Recorded valve clearance
C: Specified valve clearance
D: Old shim thickness

Using this formula, I get a new shim thickness of 2.31mm.

Many other sources on the net corroborate the Honda formula.

What am I missing with the MV formula?

cheers, Claudio

Brutale 910S 2006, KTM SMT 990 2010, Suzuki V-Strom DL650A ABS (ex BMW R1150RT 2002)
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Last edited by claudiop; Yesterday at 07:14 AM.
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post #2 of 4 (permalink) Old Yesterday, 09:15 AM
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You subtract the variance from spec from the existing shim thickness.... you want to install a thinner shim to increase clearance. It's just the way you read/interpreted the Italian translation in the manual.

Yes...you need a 2.30 shim (they come in increments of .05) or a 2.35.

OR you can machine the shims to be precise. Go for a clearance that is in between minimum and maximum. Near impossible to get exactly on or the other.
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post #3 of 4 (permalink) Old Yesterday, 05:12 PM Thread Starter
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Thanks for that confirmation.... BTW I'm Italian and native speaker so I checked with the Italian engine manual also. It states...

C) Leggere sulla pastiglia il valore dello spessore S;

Literally, this translates,
C) Read on the tablet [shim] the value of the thickness S

I don't know how else it could be interpreted.

Still, thanks for the confirmation, cheers Claudio

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Brutale 910S 2006, KTM SMT 990 2010, Suzuki V-Strom DL650A ABS (ex BMW R1150RT 2002)
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post #4 of 4 (permalink) Old Today, 07:29 AM
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You are not plugging in your numbers correctly.

Calculated difference between valve clearance and upper value of spec D:

.13mm (clearance) - .24mm (upper spec) = -.11mm

Value of thickness marked on the shim S =2.45mm

New shim thickness S+D:

2.45mm + (-.11mm) = 2.34mm

Or for your measured value:

2.42mm + (-.11mm) = 2.31mm

2007 910R and 9 other bikes
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