Camshafts and valves - say it quickly and it just trips off the tongue - it also is precisely what delivers the (considerable) power and torque to the simply superb engine this component suits.
Ensure all the components that contribute to the aforementioned performance are in perfect functional condition, valve opening and closing rocker arms, valve guides, the valves themselves and of course this Closing Rocker Adjuster (shim) to ensure the valves fully close to the correct clearance from operating rocker.
Other sizes of shims you may wish to consider: