I created this using Fusion 360.

This is the Forbidden Lower chain guide DIY.

I believe with this mod you can increase pedal efficiency by lowering drag created by the bad undersized lower chain guide pulley.

MRP recently released the MXg SL, this mod adapts the E13 guide to function like the MRP.

Print using 80% or greater infill for durability laying flat on build plate.
I printed with PETG for strength.

1. Materials needed:

   • M4 Nyloc nut
   • Shimano or Sram derailleur jockey wheel (with bearing shims, if applicable)
   • M4 washers 4-5 of these to use as spacers
   • 2 printed chain re-tension sides (attached)

2. Preparation:

   • Flip the bike so it's resting on the saddle and handlebars.
   • Remove the rear wheel.

3. Modify the lower chain guide:

   • Loosen the torx bolt in the center of the E13 LG1 chainguide a few turns.
   • Push on the bolt so the rectangle logo on the back side of the chainguide pops out.
   • Remove the torx bolt from the guide (you'll reuse this).
   • Slide off the lower guide section, leaving the bare E13 LG1 armature.

4. Assembly:

   • Install the torx bolt with the head facing the non-drive side of the armature.
   • Add one 3D printed side, the jockey wheel, and the other 3D printed side to create a sandwich.
   • Add on the nyloc nut. Test fit the chain.

5. Adjustment:

   • Use M4 washers on the bolt between the armature and the printed piece to achieve the perfect chain-line between the jockey wheel and the chainring. I found this was very easy to see with the bike upside down.
   • Reinstall your rear wheel. Inspect the chain line once more and adjust if necessary.
6. Congratulations!
   • Once you achieve the right chain-line, tighten everything up and you're ready to hit the trails. Go enjoy your ride!