At the top of the sleeve part of the boom is a gear and that is supposed to turn against a rack of teeth all along the inner slide part of the boom extension, to make the boom longer or shorter.

However, it just spins but does not grab the rack. The inner boom piece slides back in under its weight without resistence. If I push down on the thing that holds the axle, I can get it to work as long as I'm holding it.

In the photo you can see I slip a piece of paper along the line where they should be meshing.


How can I tighten up the clearance/tolerance on this part in a normal Lego manner, rather than briging in other materials or modifying the standard shape?

  • 1
    I had no such issue with that model, so likely something went wrong during the build. I recommend checking the instructions carefully, perhaps rebuild partially. Commented Apr 14, 2022 at 16:42
  • As I explained in my answer the 8 tooth gear should be replaced a 12 tooth gear, but can you explain why there is an older type 8 tooth gear in your set rather than the newer dual face one ? Non dual face light bluish gray was last in a set in 2007, the 42082 set is a 2016 set Commented Apr 14, 2022 at 21:29

1 Answer 1


According to the instructions the 8 tooth light gray gear you have now should be a black 12 tooth bevel gear:

enter image description here

I.e. replace this one:

enter image description here

by this one:

enter image description here

  • Luckily, this is a very easy fix!
    – Alex
    Commented Apr 15, 2022 at 5:31

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