It is a little while since I worked on Echo products but think this should be correct.
When you look behind the strimmer head there should be a metal boss. In the side of the boss there should be a hole. In the tool kit for the strimmer there should be a metal bar (if not available find a strong solid bar the aproximate size of the hole. This hole should align with another in the drive casing. When aligned isert bar to lock the drive. Grip the strimmer head assembly and unscrew (this may be lefthand thread).
Robin S, August 2008
