How to Replace the Bump Knob on a Bolens String Trimmer

Having a hard time removing your trimmer spool? You might need a new bump head knob assembly. The bump head knob assembly consists of a plastic knob with a captive bolt. The bolt holds the spool to the trimmer head and the knob gives you an easy grip to tighten the bolt, as well as a surface to tap on the ground to feed more line. After years of use, the knob will wear down so the bolt is exposed. Maybe the knob has stripped out around the bolt and no longer turns the bolt when you rotate the knob. Or the bolt has rusted or seized to the spindle, and you need to break the plastic knob off in order to put a wrench on the bolt.

Let's get started.

REMOVING THE BUMP KNOB   1. Remove the bump knob.

a. Unscrew and remove the bump knob from the trimmer head.

INSTALLING THE NEW BUMP KNOB

  2. Install the bump knob.

a. Thread the new bump knob onto the trimmer head.

b. Hand-tighten the bump knob to secure the inner reel.