Troybilt TB22 String Trimmer and the Flying Bump Knobs

[unit91]

Here's mine.

 

[ILENGINE]

Outer housing looks like it is in good shape. String spool looks like it is getting chewed up,

 

[unit91]

Ordered a new spool. We'll see what happens. Thanks.

 

[unit91]

Outer housing looks like it is in good shape. String spool looks like it is getting chewed up,

Installed new string spool with string, and new bump knob. Bump knob flew off after about 10 seconds, just like before. Is the bolt in the bump knob supposed to turn freely inside the knob or remain fixed?

 

[ILENGINE]

It should be a square headed bolt inside the bump knob, and if it turned you couldn't screw it on.

 

[unit91]

It's as you described it. Bolt doesn't turn. Any chance it could be the string?

 

[ILENGINE]

I don't think it is the string. The only other thing I could think is could be is the threads in the shaft where the bump knob screws into is worn, and loosing friction preventing the knob from properly tightening down. Something else to look at is make sure the internal thread cavity is clean. Maybe grass built up or something else causing a bottoming out effect.

 

[unit91]

Thanks, I'll check.

 

[unit91]

If I take the string spool off and run it with just the bump knob installed, the knob stays on at all speeds.

 

[unit91]

Backside of stri g spool