SIR: there's some seriously flawed info on this thread.
1- DO NOT EVER use ANYTHING to lock up the primary drive CHAIN on any H-D powered motorcycle. i don't care if it's a leather belt or extremely stale Pop-Tarts. terrible idea.
2-everytime a thread surfaces on here with "front end knocking" involved, the stock-in-trade answer is "loose/faulty steering neck bearings". it seldom is and was clearly not the case in your situation. there is an exacting and specific simple method any home-brewed wrench can perform to decipher between "fork chatter" and faulty steering head bearing set.
3-steering head bearings are simply checked for longitudinal movement....lateral movement....lock-to-lock turning feel. that's it. done with complete front end "as delivered" and wheel a few inches off the ground. there is NO other method that works.
4-you have what i call "cartridge fork chatter". in some instances a simple oil drain...flush...and refill will resolve it IF done correctly. other times they'll need removed, disassembled and inspected by someone familiar with them to determine the guilty culprit. it's always either a loose cartridge...worn slider bushings...or both.
