if memory serves me right, they're the sort of tappets where you have the tappet screwed into the rocker and then a locking nut on top?

If so, a couple of good pieces of advice I would have to give is, for a start make sure the piston is in the correct part of the cycle before taking measurements, so that the rockers are at their most loose i.e. checking for TDC.

Another, when tightening the lock nuts after making your adjustments, be sure to hold another spanner on the top of the tappet itself because as you tighten the locknut, its likely the tappet will want to turn with it loosing your adjustment.

Currently, they're main ones I can think of, I'm sure Kev will improve on this further though.

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09 XT660X:

CCC Stainless Rounds, Stage 1 DNA, Stage 2 DNA, PCV With Custom Autotune Map, PCV AutoTune, Home made O2 eliminator, Self machined Fork Spacers, DIY Autotune Switch.