Hey Glort,
Had that a few times before, mostly on hydro-locked outboard motors.... The land based ones almost always came down to being caused by removal/refitting of the flywheel on the crank with a bit of grit thrown in for extra fun on the taper by the local "engine doctors" 99% of the time, remove, clean up scarring, if any with fine emery cloth and refit after washing ALL crap off with "petroleum acid" (RUG) or benzine, torque to spec and Bob's your auntie!!
All good after that.... Never had to lap a taper in as yet (Excepting of course, newly made and not so well fitting replacement parts, but CI, not Al ones....)
Cheers
Ed