I change the balance on one or two flywheels a month for both ford and chev guys---where they ve changed a clutch/flywheel and got the wrong one ---and about once every 3 months I'll get one where some engine shop changed weight on the flywheel instead of the crank so the standard weighted flywheel will shake--then I got to change the old wheel to neutral, index and transfer that weight to the new wheel and then balance it which takes us back to where we have a balanced assy without taking the engine apart---