First remove the central top bolt using coins or a screwdriver. The two elbowed connection arms can now be detached from each other.
1. Lay the ROK on a bench/table and knock out the metal pin that connects the main arm to the elbowed connection arm. (Sometimes a spray of WD40 or equivalent is needed to loosen the pins if they are too tight.)
2. With the pin removed, the connection arm is free from the main arm. Take care not to discard the two bushes.
3. Undo the bolts securing the main arm to the ROK body with an allan key.
4. Replace with the new arm and tighten the bolts ensuring the teeth on the cogs are aligned.
5. Insert the bushes into the connection arm, place in the correct position on the main arm and reinsert the steel pin by tapping with a hammer. Ensure that the pin is sub-flush by tapping it in carefully with a masonry nail.
6. Align both arms over the central hole in the plastic piston/plunger, push through the stud and retain with the threaded stud.