To repair a casement window crank, take out the extension and operator arms of the window; check if the handle of the crank, the arms and the gears are worn out; and clean the gears, frame, sash and track of the window. Then, lubricate the sash, crank and hinges and reassemble the parts.
Begin repairing a casement window crank by opening the window so that the extension arm's knob, made of vinyl, can be taken apart. Then, undo the wooden stopper to detach the arm. Also, take out the window's operator arm by detaching a C-clip, pushing the arm into an access slot or unscrewing it from fittings that are hinged.
Check if the gears, handle of the crank and window arms are damaged or clogged. Using a wire brush, remove accumulated rust from the gears. Apply cleaning solvent over the gears with a toothbrush to clean them, and then apply some multipurpose lubricant.
With the same wire brush, remove accumulated grime from the window's sash, track and frame. Lubricate the underside of the sash with petroleum jelly or auto lubricant. Do this with gloved hands, and remove extra lubricant with a rag.
Then, replace the crank of the window. Apply some multipurpose lubricant on the handle of the crank and the hinges. Open and shut the window a few times to distribute the lubricant uniformly in the gears.
If this fails to repair the crank, install a replacement piece.