Is it required to pull or move the 3.8 liter engine to replace the Harmonic Balancer on a 1995 Buick Lesabre?

definitely NOT

but you need to block movement or rotation of engine, best done by removing flywheel cover and clamp flywheel with vice grips-that will prevent the rotation after slight rotation and lockup. Nut on front is tight and will take 1/2@ breaker bar and a cheater pipe. Haven't seen a impact that will break those nuts