The adjustment distances are crucial.
In this case, the top of motor pulley - 116, should be adjusted to 14.2 mm above the top plate. If this is too high on the motor shaft, you may not have enough down movement to allow nut - 110 to catch. Also, the tooth belt pulley - 112, drives a cam up and down, move the cam to the lowest / position and you again can get 110 to catch.
The crucial adjustment dimension is 14.2 of the top of motor pulley above the top plate which should give the pitch assembly enough travel.
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