Remove the old spring by unlatching the outer leg of the spring from its groove on the cutter head casting.
Rotate the spring coil on its plastic mandrel until the other shorter leg of the spring comes free.
Pull the coil free from its mandrel.
Insert the short leg of the spring into the gap between the black casting and the carriage and feed the coil onto its plastic boss so that the long leg of the spring is pointing vertically up.
Rotate the leg leg clockwise when viewed from the left and latch it under the groove in the casting on the edge of the raised circular upstand.