The engines were built with stock tolerances by "relay". The only thing non-stock in them are the valve springs, oil pan baffling, and full stud kit. (new factory oil pump). Add the white gloves and lots of Plasigauge.

Editorial Notes:
In my opinion, the reason for unreliable rebuilds currently is, that the V-tech heads and blocks have such difficult to match tolerances. The factory uses assembly jigs and robotics' for tolerance control and efficiency.

This is a hand built engine. Assembly tech had the value of being able to retrieve hard to establish or non-published tolerances from sister one (intact engine) during reassembly of sister two. (I call it relay re-building) This way you are assured to have the rebuilds match previous factory specs in all regards by hand. Very time consuming.

Bisimoto Engineering tunes forced air F20c and F22c and says replacing bolts with studs is the way to go if you want to retain reliability.
In testimony to reliability is the fact that I've enjoyed over 24 race weekends using the same engine with no loss of performance or signs of wear.