|———————————— Flywheels, Rods and Crank ————————————|

You have to have the heads off to perform this procedure and it is conclusive. If you hold the rod just under the piston with one hand (like choking a chicken) and pull up on it, then use your other hand in a fist to hit the top of piston like a hammer action, a bad crank will make a very loud knocking sound as you do it. I do that with pistons removed, but if you don't want to pull them what I just explained should work just fine. It could even show knocking at the wrist pin although the lower rod bearing will fail first usually. You will hear it in the front rod first because the rear rod holds up a little longer when the crank starts to fail.

Video is from XLF member, onadraw. ¹⁾