Canon imagePRESS C850 Series Troubleshooting Manual page 65

12) Pull the operation tray cover [1] in the arrow direction to remove.
13) Remove the clip [1] and the E-ring [2] from the back end assist unit, and replace the timing belt [3] with the new type.
[Attention] Be careful not to lose the torsion spring [4].
14) Put each shaft through the back end assist unit, and attach the clip [1] and a new E-ring (XD2-1100-402) [2].
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