Why would you ultrasonic test the block/crank/rods. ultrasonic is for subsurface defects ie manufacturing problems/inclusions or for problems on the far surface (not for near surface or on surface defects - ultrasonic wave is still forming in the near zone). My recommendation would be for Liquid penetrant testing (LPT), LPT should detect defects open to the surface (ie cracks), the orientation of the defect is irrelevant. However, if you know the orientation of the defect and the material is a ferromagnetic (which the block, rods and crank are) you could also use Magnetic particle (detect smaller defects). I would stay away from Radiographic testing though, as this requires a density change in the material and is less sensitive then the other methods for the type of defects you would be looking for.

Anyway I digress sorry to hijack the post.