TKG has it right. If the crank is multipiece pressed together, any sudden stops twist the flywheel around the crank pin. This could be a problem on any multi-cylinder engine. All of the ZDZ (and DA) singles use a cantilevered (one piece) crank.

On the motorcycle engines with ball bearing cranks, before they would take 'em racing, they would weld the crank to prevent it from twisting.