Tech Tips:
Repair of Smiths Pin Clock
CE 3120/3123 series
Commentary by the late Graham Robinson,
Hillman Owners Club of Australia

Failures of these clocks as used in Humber Snipes, Hawks, Alpines and maybe Hillmans are many and causes are varied.  Refer to Fig. 6 (exploded parts view) below.

Main cause is the carbonising of the offset pin on the balance wheel (48) and the corresponding contact pin (14) that sits on a fulcrum post.

Second cause is incorrect polarity applied when installing causing the rectifier bridge (17) and other items to be burnt out, rendering the clock inoperative.  White rectifier assembly (17) is negative ground where Green rectifier assembly (17) is positive earth.

Third is that any loose posts (15/10 & 19/21) within the clock itself will cause shorting to ground and cause carbonising in other areas.  Balance wheel hairspring (48) is one.

Fourth is when the earthing pin (16) to start the clock is used too often and particularly if any loose posts (15 & 10) are prevalent will cause secondary burning or carbonising throughout the clock mechanism.

Minor adjustments to the circuit can circumvent a lot of these problems.

One is to install a separate switch to disable the clock when not in use or when standing for long periods.  The second is to fit a small power diode (EM401) across the rectifier assembly (17) protecting it and the clock from spurious voltage sparks that causes carbonising.  Lastly a suitable capacitor 10uf 25V also fitted to ground from the rectifier assembly will reduce sparking and noise if a radio is fitted.

It is prudent to have the offset balance wheel cleaned every couple of years to stop carbonising, where possible.

Or one could fit a Kienzle or other quartz movement into the housing.  I believe some Rover clocks are also compatible.

      Page S 32   Fig. 6   Front Reset Clock General Arrangement of Movement
  1. Back Plate
  2. Pole Piece Securing Screw
  3. Setting Support Plate
  4. Pole Piece
  5. Spacer
  6. Coil
  7. Balance Support Nut
  8. Balance Support Assembly
  9. Centre Spindle and Wheel Assembly
  10. Connecting Bracket
  11. Rectifier Screw
  12. Insulating Sleeve
  13. Setting Spindle Return Spring
  14. Contact Hairspring Assembly
  15. Contact Hairspring Pillar
  16. Setting Spindle
  17. Rectifier
  18. Rectifier Bridge
  19. Upper Insulating Plate
  20. Screw (for contact hairspring pillar)
  21. Lower Insulating Plate
  22. Setting Pinion
  23. Setting Spindle Washer
  24. Setting Wheel
  25. Setting Pinion Spring
  26. Setting Spindle Collar
  27. Minute Wheel
  28. Insulating Tube
  29. Rectifier Pillar
  30. Retaining Plate
  31. Retaining Plate Screw
  32. Dial Washer
  33. Regulation disc
  34. Hour Wheel
  35. Spring (for regulaton disc)
  36. Locating Plate Screw
  37. Bottom Bearing Locating Plate & Adjustable Bearing
  38. Cannon Pinion
  39. Balance Platform Assembly
  40. Friction Spring
  41. Insulating Ring
  42. Regulating Spindle
  44. Double Support Plate
  45. Double Support Plate Securing Screw
  46. Transverse Wheel Assembly
  47. Escape Wheel Assembly
  48. Balance Wheel Assembly
  49. Regulator Disc Spindle Assembly
  50. Anchor Post
  51. Anchor Post Screw
  52. Hairspring Taper Pin
  53. Top Bearing Assembly
  54. Regulator Lever Assembly
  55. Regulator Lever Washer
  56. Top Bearing Screw
  57. Regulator Wheel
  58. Setting Spindle Washer (Brass)

     Page S 16 the Balance Wheel :

The balance wheel should now rest as shown in the illustration above.  If this is not the case, steady the balance wheel, insert the into-beat tool SR/D. 170 into the slot in the hairspring collet and adjust the hairspring tension until the correct position is obtained.
The bottom bearing should now be screwed in until there is just sufficient enshake in the balance to ensure free running.  The reset wheel should now be fitted using a hollow punch or a similar suitable tool.
     Page S 8 Circuit Diagram :

Technical Description:
Current flows from the supply terminal to the wiper contact via the rectifier, rectifier bridge, contact hairspring and the coil which is connected in parallel with the rectifier.  The earth return for completing the circuit occurs through the hairspring when the wiper contact touches the impulse pin.

When the starting spring is brought into contact with the rectifier bridge it completes the circuit and energises the pole pieces causing the balance to deflect.

When the spring is released current ceases to flow in the coil allowing the hairspring to return the balance.

The wiper contact and impulse pin now take over the function of supplying the current pulses to the coil as the balance oscillates.

Grant Rodman of the Jaguar Car Club of Tasmania read this article, and kindly submitted his own commentary on Changing the Polarity of a Smiths Pin Clock.

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