Telescopic fork, Steering damper

Telescopic fork

The 1934 Nimbus was, together with “BMW” the first in series built motorcycle with telescopic forks.

The front fork is of a very simple design. The outer legs of the telescopic fork are made of 1” pipe which has an internal diameter of 25.4 mm. The inner legs of the telescopic fork have a dimension of Ø 25 mm x 2.5 mm and are 635 mm long. This length was changed to 650 mm, probably due to changes of the anchor plate with No 1526. The visible parts of the threaded plug of both inner tubes, and the open slots for the wheel nuts, are approximately 25.7 mm in diameter and 46 mm long.
Due to changes in the anchor plate with No 2551 (rim protection against water), the flat part of the anchor plate for attaching it to the front fork, was extended.  At the same time, the diameter of the threaded plug was changed to 25 mm and its visible part to 57 mm.

The bottom bearing of the head tube had a tendency to loosen. To prevent this from happening, in late 1934, a 6 mm wide section with coarse notches was applied to the head tube, at the position where the bearing was to be fitted. The head tube does not have the grooves for the circlip for the handlebar’s threaded plug. These circlip grooves were added later.
The telescopic tubes slide in each other without any form of bearing bushes. Although the tubes are lubricated, this leads to “friction” and severe wear. The wear can cause the telescopic fork to chatter when using the brakes. The ‘novel’ solution the factory found for solving this problem was to bend the inner fork tubes, which solved the problem in the short term, but in the long term this caused severe wear.

It is very difficult to find an inner front fork tube, in an acceptable condition, but fortunately the tubes are replaceable. An hydraulic pipe with the dimensions Ø 25 x 2.5, which is on the shelf at most hardware stores, can serve this purpose. 

The lower 15 cm or so of the inner telescopic tubes are nickel plated.

The spring system, which lies within the inner fork tubes, consists of thick, right-handed main springs with thin, left-handed additional springs inside. It is unclear whether or not the first telescopic forks had the inner springs fitted.

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Inner telescopic tube, spring and fork gaff.

The telescopic fork at the lower end is provided with a leather sleeve for sealing the inner and outer fork tubes. The leather sleeve is attached to the outer fork tube with simple 5 mm wide nickel plated brass clips.
The legs of the telescopic fork are lubricated with grease by means of two nickel plated nipples in each leg, type AM 6 x 0.75 DIN 3402.

Steering damper

The steering damper, which is fitted below the head tube, consists of friction plates on the front fork and frame respectively, together with two fibre friction discs.  The steering damper is adjusted with the aid of an 8 mm tension bolt, running through the head tube.

The tension bolt is made of chrome plated steel and provided with a cylindrical head with a cross bar.

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