Flytest
A small % of lycomings cannot be balanced, but this depends on whether the aircraft has suffered a tip strike at any time and then had the same crankshaft re-fitted. The fact that said crank passes bench concentricity checks, or output flange trueness checks is irrelevant.
According to several engine shops I have discussed this with, the reason a few % of Lycos can't be balanced properly is because Lyco have rather wide margins when it comes to matching up their pistons, rods, etc, and also they don't dynamically balance the cranks well enough.
Would a crank bent enough to noticeably vibrate still pass the post-prop-strike NDT and the concentricity test?