The Simple Facts

• Prop balancing does not correct or mask other engine problems.
• Prop balancing is not engine balancing, rather it is a finely tuned marriage of the prop to the engine under normal operating conditions.   
• Pilots will grow accustomed to almost any vibration level over time.
• 4 out of 5 pilots believe their engines are running smoothly immediately after overhaul. This is normally only a 'perceptual' improvement as new 'Lord' mounts function exceptionally well, isolating prop unbalance vibration to the engine where it can nonetheless undermine reliability.
• 4 out of 5 props require 20-40 grams to reduce unbalance and vibration to zero after overhaul.
• A 30 gram static unbalance becomes a 75 pound oscillating side-load at the front engine bearing at 2400 rpm.
• A one mil 'installation error' between the centerline/interface of a perfectly balanced prop and the engine crank flange results in ~.3 ips/50 lb side-load at the front engine bearing.
• 90% of prop/engine installations are off centerline by at least 1 Mil. The weight/gravity alone of the prop hanging on the prop bolts as they are torqued guarantees at least some interface/centerline error.            
• Vibration causes work hardening/metal fatigue which leads to cracks over time.
• Instruments and avionics are sensitive to vibration damage which is often expensive to repair.
• Prop unbalance and the resulting vibration amounts to wasted energy.
• Vibration exacerbates pilot fatigue and can cause passenger concerns.
• Years of experience, skill and digital equipment are prerequisite to spin balancing a prop to within ± 1/10th gram.