Desmo Shim Calculator

Both the opening (over the valve, under the opening rocker) and the closing shim (the half-ring under the closing rocker) behave the same way in the arithmetic:

new shim = current shim + (measured clearance − target clearance)

resulting clearance = measured clearance − (new shim − current shim)

A thicker shim always gives a smaller clearance, on both sides. The calculator snaps the ideal thickness to the shim sizes you listed above and picks the one that lands closest to the middle of your target range, then shows the clearance you will actually end up with.

Openers tend to tighten with use and closers tend to loosen, which is why setting openers near the low end and closers very tight leaves room for wear between services and keeps the valvetrain quieter.

Presets are a convenience, not gospel. Anything marked "verify" is an approximation — check your own workshop manual and edit the numbers; whatever you type is what gets used and saved.