Air carrier Inspector reported; during a fan blade retaining pin torque check on an ERJ 170 aircraft; blade #16 missing its bumper. The bumper was found jammed between the blade and hub. A new bumper was installed and all fan blades; bumpers and pins reinstalled.

Narrative

During fan blade retaining pin torque check (follow-on to Fan Blade Pin Restoration); heard the sound of a loose bumper inside the fan hub. Found blade #16 to be missing it's bumper. (Blade was exceptionally loose compared to others). Three other blades had to be removed to locate the missing bumper; since it was jammed between a blade and the hub. Thorough visual inspection of hub; blades; pins and bumpers was performed; with no defects noted to any component. Missing bumper was retrieved; but was heavily damaged from tumbling around inside the hub. New #2 bumper was installed per GE Maintenance Manual. All fan blades; bumpers; and pins were reinstalled; along with the aft and forward fan spinners. Engine operational check performed. No defects noted. Fan blade #16 bumper was apparently never installed correctly. Suggestions:Reiterate the importance of an inspector being present during any and all engine fan maintenance; and assure that they are actively involved; and not just standing around. The bumper that was incorrectly installed should have been caught by either the mechanic performing the work; or the inspector monitoring the maintenance activity.