A Small V-Conic
The TIMEX Model 78 is an 8‴ x 9½‴ movement featuring the “V-conic” bearings system and rugged two plate design. Whereas most watches utilize bridges, Timex has constructed the Model 78 movement with full plates to take advantage of the accuracy inherent in this type of design. This accuracy insures complete interchangeability for the escapement and gear train without the need for selective fitting and adjustments which complicate the repair of most watches.
To clean the Model 78 it is necessary to remove only the sweep second hand, dial, ratchet wheel, stem and balance.
Exploded View
Note the tubular pillar, 168, and its own screw at 5168, which the Model 80 does not carry.
Disassembly for Cleaning
Removing the Dial and Hands
Remove the sweep second hand. Do not remove the minute or hour hand.
The dial is clamped to the movement by means of two tabs which are bent through dial holes located on the dial plate.
Once the dial is off there is no need for further disassembly of the dial assembly for cleaning unless severe contamination is present on the friction and cannon pinions. Should further disassembly be necessary, removal of the minute hand will free the friction and cannon pinion assembly. The friction pinion is held in the cannon pinion by a snap fit.
The Dial Tab
Cross section through the dial, tab and dial plate. Only two tabs are used, against four on the Model 80.
Removing the Ratchet Wheel
Grasp the crown in the fingers of one hand and release the click by holding the click away from the ratchet wheel. Let the crown revolve slowly in the fingers, being careful not to let the crown slip.
When the mainspring has been fully let down, remove the ratchet wheel washer and ratchet wheel.
Removing the Crown and Stem
To remove the crown and stem assembly, invert the movement so that the movement plate is facing you, then turn the set lever screw and lift the tail of the set lever out of engagement with the stem.
The Set Lever
The set lever and set lever screw seen on the movement plate.
Removing the Balance Wheel
Two “V-conic” jewels are used as bearings for the balance staff. The bearing on the dial plate is mounted in a screw so that fine endshake adjustment is possible.
Remove the hairspring wedge pin, being careful not to distort either the pin or the hairspring.
Rotate the balance wheel slowly until the hairspring tail is free of the hairspring wedge pin bracket and the regulator.
Loosen the balance screw assembly counter-clockwise using a suitable screwdriver, until the end of the balance staff is free of the “V-conic” bearing, then carefully remove the balance assembly.
The V-Conic Bearing
Cross section through the balance, showing the V-conic bearing carried in the balance screw assembly on the dial plate.
Cleaning & Lubrication
After removal of the balance wheel and the other parts mentioned on pages 78.3 through 78.5, the movement is ready to be cleaned. If a cleaning machine is used, place the movement in the basket with the dial plate down to insure proper drainage of the fluid from the mainspring barrel. It should be well swirled in the cleaning fluid, after which two sets of rinsing fluid should be used. The final cleaning fluid must be absolutely clean. After cleaning, the movement should be thoroughly dried.
If a cleaning machine is not available, the same procedure should be followed manually, by grasping the movement firmly around the stem and shaking it in the cleaning and rinsing fluids to insure that the fluid will pass through the entire mechanism. The balance assembly should be cleaned separately in a small jar to prevent damage to the hairspring. Only standard watch cleaning solutions should be used throughout.
Reassembly
Replacing the Balance
Replace the balance wheel carefully into the movement by tilting the wheel and inserting first the dial side pivot, the hairspring side, then the movement side pivot into the “V-conic” bearing. Adjust the balance screw enough to hold the balance in place.
By rotating the balance wheel, insert the hairspring into the regulator slot and hairspring wedge pin bracket. Before repinning the hairspring, make certain the impulse pin is within the slot in the fork of the pallet lever.
Repin the hairspring making sure that the wedge pin is straight and true, as any distortion to the pin could interfere with the normal breathing of the hairspring. The endshake is now finally adjusted.
The Hairspring and Regulator Slot
The hairspring should be in light permanent contact with the inside edge of the regulator slot.
The Sweep Second Hand
Replace the sweep second hand by driving it just below the end of the sweep second staff. Be certain the sweep hand is set below the chamfer on the top of the staff.
