You will need to have the 4mm Valve Chuck Disassembly / Assembly Tool
[This tool is required to perform the following operations]
STEP 1: Remove the chuck cover from the Chuck Bearing Assembly, being careful not to pull any wires from the cover.. Rotate the Chuck so that the Grind Mark on the front collar and the Yellow Mark on the Spring is Vertical as shown in the photo below.
STEP 2: Remove the (3) three 8 x 32 x 5/16 slot head screws from the Chuck End Cap (Black) shown below.
(Note: your end cap may look slightly different. The design has been
improved since these photos were taken.)
STEP 3: Use the Disassembly Tool (picture at the top of this document) which is standard equipment with your machine, put the 8 x 32 screws (3) into the chuck shaft in a 1/4 of an inch. Put the 1/4 x 20 Hex Head Bolt finger tight against the End Plate.
STEP 4: Remove the Chuck Yoke.
STEP 5: Loosen the 1/4 x 20 Hex head bolt counterclockwise. As you release the 1/4 x 20 bolt, the spring pressure should begin to release... NOTE: You may need to soak the chuck in Automatic Transmission Fluid to remove grit and make the collars slide easier.
STEP 6: Remove the Chuck Disassembly Tool.
STEP 7: Begin to remove the outer collar from the chuck shaft. Next, remove the Loading Cup with the four (4) springs. The large spring and inner collar will be removed along with the Thrust Step Washer. As you take the Inner collar off the steel chuck balls (9.16) may fall out of the chuck shaft.
STEP 8: Remove the Chuck Handwheel and belt from the chuck shaft. Remove the chuck from the chuck bearing assembly. Clean all parts with denatured alcohol. (and for lubrication nothing other than ATF)
STEP 9: (1) put the shaft back in the chuck bearing slide. Use Automatic Transmission Fluid (ATF) only and coat the chuck shaft. Make sure the keys are vertical.
(2) Put the thrust washer, spring, and  three rear balls back on the chuck shaft, making sure that the yellow mark is lined up with the keys. Hold on to the bottom balls so they don't fall out of the shaft.
(3) Slide on the Inner Collar, so all three rear balls are inside of the collar.
(4) Put the front set of balls in the shaft. install the loading cup with four  springs facing out.
(5) install the outer collar, making sure the ground mark is lined up with the keyways.
(6) Reinstall the Disassembly tool. Put the three screws (8 x 32) in one quarter (1/4) of an inch. Begin to tighten the 1/2 x 20 bolt, making sure that the collars are still lined up with the keys. Run the 1/4 x 20 bolt in until it is tight.
(7) Reinstall the Chuck Yoke.
(8) Remove the Disassembly Tool and reinstall the chuck end cap with the three 8 x 32 screws.
(9) Reinstall the chuck handwheel and belt, making sure the chuck and chuck handwheel are snug to the chuck bearing slide. (there should be no
lateral movement of the chuck in the bearing saddles and the belt should
be as loose as possible without slipping to absorb motor vibration.)
(10) Reinstall the chuck cover. Make sure there are no wires touching the chuck.