1. Lift front of machine and place a suitable block under crankcase so that fork can extend fully with the wheel just clear of the ground.
  2. Remove inflation valve dust cap and slightly depress valve stem, allowing all air pressure to release. (Do not depress the valve stem too far, as this may damage the spring and impair the sealing qualities of the valve.)
  3. Disconnect brake cable, remove wheel and mudguard with stays complete.
  4. Slacken off 5/16-in. B.S.F. bolts on fork crown fitting.
  5. Grasp outer tube PD 1701-4A or PD 1701-4B with both hands, and by careful twisting and pulling slide down off the top static seal PP 17-22. This operation is to be performed carefully, otherwise the seal may stick to the tube and tend to jump out of its groove. If this does occur, the ring should be carefully replaced, making sure that it is not twisted.
  6. At this stage, it is advisable to place a piece of stout, greased paper around the top portion of the outer tube, to prevent the paint from being scratched on withdrawal of the outer tube through the holes in the fork crown fitting PD 1701-19.
  7. With a special spanner engaged in piston PD 1676, unscrew same by holding spanner and twisting axle fitting (right-hand thread). Inner and outer tubes may now be lowered and removed. The inner tube should not be withdrawn from the outer tube unless it is intended to examine the shroud and scraper ring as it is impossible to re-insert the scraper ring over the inner tube without damage unless the former together with the shroud is dismantled from the outer tube. If this is the case, slide the outer tube off the inner and remove the greaser P. 6B and screws PD 1811. The shroud PD 1682 will now slide off, together with the packing seal PP 16-15 and scraper PP 16-14, leaving the bearing exposed.
  8. Unscrew nut from centre tube and remove flat washer and buffer PD 1701-30. The piston complete may now be withdrawn.
  9. Remove split bearing PD 1677, spacer ring PD 1685 and gland ring PP 12-23M.

To Reassemble Forks reverse the above procedure.

It will be noted that all the above operations may be carried out without disturbing the fork crown fitting PD 1701-19 or the handlebar clip lug PC 1701-5. If it is necessary to remove these items, proceed as follows :-

  1. Remove handlebars, speedometer, and drive, etc.
  2. Unscrew steering damper knob PD 1502-10, and withdraw complete with rod.
  3. Remove damper nut PD 1701-26.
  4. Unscrew nut and slacken off cotter bolt PD 1701-23. The handlebar clip lug may now be lifted off and the fork crown fitting withdrawn through the headstem of the machine. Care is to be taken not to lose the balls from the steering races.

When re-assembling the fork, precautions should be taken so that all parts are scrupulously clean. It is advisable to smear glands and sealing rings with a little high-grade lubricating grease before reassembly.

To avoid the lengthy process of pouring oil through filler plug holes, the forks may be refilled in the following manner :-

After the piston has been assembled to inner tube, extend inner tube until there is approximately one inch gap between bottom of piston and lower buffer. Then, with outer tube about one and a half inches below the bottom of the top internal fitting, attached to the handlebar clip lug, pour in oil until full. Push outer tube up over static seal and tighten the clamp bolts on the fork crown, taking care that the small air vents on the outer tube are in their correct relative positions. Assemble mudguard, wheel and brake cable and lower machine to the ground.

With a suitable can held beneath the inflation valve, unscrew the valve core by means of the Schrader cap and allow the fork to close fully, surplus oil being collected in the can. Use only one of the following recommended grades of oil: Mobiloil "Arctic," Single Shell or " Castrolite." Replace valve core and inflate with tyre pump. The fork is correctly inflated when, with the rider mounted and balancing against some convenient support, the red marking dots on the inner sliding tubes are in line with the bottom edges of the shrouds PD 1682. A fork which has been completely dismantled is prone to " settle " slightly in the first few miles. It should be re-inflated to the correct position. Thereafter, the fork should require even less attention than that given to the tyres. Apply six shots from the grease gun to the greaser on each leg before road test.

When Fitting a New Fork Complete, as Supplied by the Makers, it is not necessary to disturb any of the air seals, if the following procedure is adopted :—

Remove damper knob and nut, and slacken off cotter bolt PD 1701-23 Unscrew filler plugs PD 1678. The handlebar clip lug may now be withdrawn from the fork. Place balls (nineteen balls) in the lower race of steering head on machine, using grease to make them adhere. Push steering tube of fork up through centre of steering head and hold in position whilst the top ball bearings, ball race and dust cover are mounted. Replace handlebar clip lug in position, and screw damper nut PD 1701-26 up finger tight.

Slacken off clamp bolts on fork crown fitting. Replace filler plugs and screw up tight. Tighten damper nut PD 1701-26 until correct adjustment of ball races is obtained. Tighten cotter bolt PD 1701-23. Tighten clamp bolts on fork crown fitting. Replace damper knob and adjust.

Fault Finding.




Fork is stiff in action

Lack of lubricant on bearings.

Apply grease gun (six shots).


Wheel spindle incorrectly adjusted.

Slacken clamp on axle fitting. Bounce fork a few times, and re-tighten.


Fork crown clamp bolts so tight that outer tube becomes distorted, and presses on piston.

Slacken bolts until fork moves freely.


Split bearings PD1677 have been assembled with foreign matter beneath them, causing tightness in bore.

Dismantle split bearings, and remove high spots.


Mudguard stays distorted.

Reset stays. See page 29






See instructions on removing Front Wheel. (Re-aligning outer tubes). Pages 15 and 16.

Fork is stiff in action.

Outer or inner tubes damaged accidentally.


Insufficient damping

Lack of oil.

Top up.


Viscosity of oil too low in tropical climates.

Replace oil with Mobiloil BB or Castrol XL.

Damping too fierce.

Oil too viscous.

Replace oil with recommended grade. If this is already in use, excessively low temperatures  will have the same effect, but this is not usually serious, as the additional damping improves the steering characteristics under icy road conditions.

Fork " bottoms " readily.

Lack of air.

Inflate to correct position.


(fork correctly inflated with air)

Lack of oil.

Top up.

Fork hammers on full extension.

Over inflation.

Deflate to correct position.

Fork loses air pressure (oil traces on lower sliding tubes)

Leaking gland ring.

Replace. Examine bores for scores. If these are too deep to be polished out, replace outer tubes.


Leaking static seal on piston PP 17-1.

Replace faulty seal.


(oil traces around top of outer tube)

Leaking static seal PD 17-22 on top internal fitting.

Replace faulty seal.


(no oil leakage).

Leaking inflation valve core; or

Leaking inflation valve washer PD 1561-43, or Leaking static seal PP 17-22 ; or

Leaking static seal PP 17-17; or

Leaking balance pipe

Replace faulty part.