Although the taper roller bearings fitted to the pivot of the rear fork are unlikely to require attention other than greasing at 10,000 mile intervals, they can be adjusted to compensate for developed slack. The method is the same as for the wheel hubs. The fork is retained by a long 1/2-in. dia, bolt, with a B.S.F. thread at one end, passed through the primary chaincase-engine casting and the Duralumin gearbox end-plate. To the back of the casting is bolted a steel plate which also retains the battery carrier, etc. The fork bearing assembly should be of such width between nuts that it is just possible to slide it into place between the two supports.
The front forks require attention at 15,000 to 30,000 miles intervals, depending on type of usage. This is probably the effective life of the main thrust bearings of the 'Girdraulic' forks used on the 'C' and 'D' models. All bushes used on these, and on the 'B' are of the self-lubricating sintered-bronze type but, nevertheless, periodic attention with the oil-can does no harm. Oil nipples were, in fact, specified towards the end of production and new spares are fitted with these.
Wear at the bushes can be felt by push-pull motion on the fork ends and observing each pair of bushes in turn; placing a finger over the part where wear is expected is sometimes even better.
Worn bushes are tapped out with a suitable drift, or they may be threaded and extracted with the aid of a stud, a nut and a distance piece. New bushes must go home squarely. Careful sizing of the housing and bush avoids the need for reaming afterwards. Spindles also wear, though not so rapidly.
In 'Girdraulic' forks most wear occtirs at the thrust bearings, which are not too easy to service. With the fork dismantled, a correctly bushed and shimmed lower link will fall under its own weight when dropped after the retaining bolt is tightened. The four sintered-bronze bushes are trapped in pairs in the eyes of the link, one being inserted from each side of each eye. These work on steel eccentric motion blocks locked to the through-spindle and it is clear that the eccentrics must be shimmed at such a distance apart that their flanges restrain the end float of the link without imposing friction.
It is the shims that are difficult to deal with and making up a bullet-shaped nose to the spindle greatly assists offering up that component through the shims; the latter, of course, have figure-of-eight holes in them to permit trail variation and it is this hole shape that fouls the spindle during rebuilding.
When correctly assembled, all dust caps, or thrust washers used on the 'B' forks, must be free to turn without end-float.
Prior to stripping 'B' forks, the attitude of the links should be noted. They should be level when the machine is unladen and on the rear stand; if raised at the front then the spring is 'tired' and should be renewed. The test does not apply to the 'C', and ' D' fork as the fork-blade hole centres are differently disposed.
Some riders feel that the 'C' handles better without the inner coil springs in the front forks and accordingly discard them. Distance pieces up to 1-in. in height should be dropped into the lower spring boxes so as to jack up the front a shade. The tip also assists 'tired' springs. Another idea is to add a Norton clutch spring to each inner when the front end of the machine is carrying some additional weight not compensated for by reversing the eccentrics to the sidecar setting.
When reassembling the spring boxes, jack the front wheel clear of the ground and remove the front damper so that the forks may fall beyond their normal permitted extent. Pull up the lower box with a gloved hand while an assistant inserts the lower bolt. Using a tourniquet of stout sasheord is an alternative device. The method of levering the box over the lug with a screwdriver is a risky one and often damaging to the knuckles.
To fill Vincent dampers, solder a 1/8-in. B.S.P. union to the base of a can, screw this union into the damper-filling orifice and top up with SAE 20 mineral oil. Gently work the damper to expel the air. Remove the can when the damper is full, carefully looking for any bubbles that may still rise to the surface. Fully compress the damper and replace the filler plug.
Suspension damping on the 'B' machine is effected by a friction-plate assembly. Beware of the Ferodo material becoming glazed, and also of grease on it, or on the steel plates. Its resistance is controlled by an adjusting screw.
No adjustment is, of course, possible with the hydraulic type used in the 'Girdraulic' fork at the front on the 'C' and 'D' ranges or in the same damper at the rear of the 'C' or in the damper-cum-spring unit at the rear of the 'D'. The 'C' used a Vincent-designed-and-made damper while the 'D' specification called for Armstrong components pre-sealed, non-adjustable and non-maintainable. The 'D' damper fits the 'C' at the front or rear, though it may be necessary to ease away some richness of castings not intended originally to take the Armstrong front unit. Both types of front damper may cause metallic noises due to the nominal 5/16-in. hole of the attachment bolt becoming oval, or the bolt itself wearing. The damper hole can be bored out and rebushed to be a free fit on the bolt linking the two eye pieces.
If Armstrong units are fitted as replacements on the 'C', note that the side marked 'top' must be uppermost at the rear and face forwards (and therefore uppermost) at the front. By cutting a section out of the 'B' rear-spring upper-mounting tubes, a damper can be fitted. Leaking Vincent units should be returned to the factory for specialist attention, or replaced by the leakproof Armstrong type. Exercise great care over the assembly of the damper into the lower, rear-suspension anchorage for fear of bending the damper rod and so ruining the unit. This can be avoided by the use of suitable distance-pieces.
Series 'B' and 'C' rear springs settle with time and usage and this results in the attachment eye bolts twisting out of line. Slacken, reset and reassemble. The large Armstrong 'D' unit also settles a little with use; for most solo work, the tougher sidecar-strength spnng may be used.
On other machines one solo and one sidecar rear spring may improve roadholding, especially with really effective and heavy damping, say that offered by SAE 50 oil-provided the damper seals will retain it! With the singles, it is possible to use combinations of rear-spring resistance by incorporating one, or more, twin springs. A very heavy sidecar outfit may call for the abandoning of the damper and the substitution of a third spring and box. If heavier springs are fitted, the spring claws will have to be carefully opened out with a round file.
Do not attempt to judge the roadholding of a machine in cold weather until the dampers have warmed up slightly and the fluid has become less viscous.
Changing the trail and effective spring loading from solo to sidecar or back again is extremely simple. Jack up the front, slacken off the lower rear 'Girdraulic' spindle nut and twist the eccentrics through 180 degrees until the new stops contact the link. Retighten the nut. With the 'B' it is necessary to fit sidecar top links (shorter) and a stronger spring. Ride none of the models solo with the forks in the sidecar position; the trail is insufficient. Driving a sidecar outfit with solo forks is possible but very tiring.
Sidecars seem best fitted with the third wheel about 8 in. ahead of the rear wheel, with their centre of gravity as nearly as possible on a line drawn between the sidecar spindle and the steering head. A sprung chassis should be fitted so that the cross rail is horizontal when loaded ; an unsprung one requires a 1-1/2-in. rise at the rear corner next to the machine. Experiments with short top links, cutting down the trail, have been successful, the 4-in. hole centre-dimension 'Girdraulic' top link being reduced to 3-1/4 in. and the eccentrics used in the solo position with the springs packed up. With the trail reduced at the eccentrics, the steering damper is needed, the multi-plate one fitted from engine number 11937 being recommended.