First published in 1990 by Notabene, Copenhagen DK
Danish edition 2008: Nimbus – vedligeholdelse by Motorploven, Hadsten DK
A shortened English edition 2012 was published in 2012 by Books on Demand GmbH,
København, Danmark
This new size edition is published in 2018
Cover photo: Finn Nielsen
Print: Books on Demand GmbH, Norderstedt, Germany
ISBN: 9 788 743 019 213
© Knud Jørgensen and Books on Demand GmbH
All rights reserved. With exception of quoting brief passages for the purpose of review, no part of this publication may be recorded, reproduced or transmitted by any means, including photocopying without permission of the author (exceptions are given in the book).
The first edition of ´NIMBUS – vedligeholdelse’ (NIMBUS - Maintenance) was published in spring 1990 and at that time titled: ´NIMBUS - og kunsten at vedligeholde den´. (NIMBUS: The Art of Maintenance).
A second Danish edition was published in 2008, and many have asked for an English edition, hence the publication of this edition in 2012. This new size edition was published 2018
There were 4,500 Nimbus-C motorcycles registered in Denmark in spring 2015. If we take account of the 1,000 in use abroad, almost half of the total production of 12,715 motorcycles survive to this day. All require maintenance and repair, and from time to time renovation and restoration. This book is about the first three of these subjects, and together with ´Nimbus -Technical Development’, it may also be useful in restoration. The content of this book is by large limited to those operations which a skilled owner can do or can have done. Many repairs nowadays have to be left to a professional workshop, as mistakes can become very expensive and irreplaceable original parts may be damaged.
Many thanks to Ben Geutskens and to Charles Duffill for their work on the English edition. Errors or shortcomings remain the author’s responsibility.
Højbjerg, October 2018
Knud Jørgensen
This book is intended as a guide to the maintenance and repair of Nimbus type C motorcycles built between 1935 and 1959. The first Nimbus-C series, built during 1934 and 1935 and with serial numbers 1301-1551, differ somewhat from later models. See Andersen, J. B. (1996): ´Nimbus model C 1934´. An English translation of this book is available on www.geutskens.eu
The 1934 rear wheel to which this book refers was in fact fitted up to 1937, and the 1934-2 carburettor model was used up to 1938.
The earlier Nimbus type A/B 1918-1928, widely but unofficially known as the ´Kakkelovnsrør´ or ’Stovepipe’, is described in Andersen og Jørgensen (2007). ´Nimbus 1918-28 “Kakkelovnsrøret”
The many changes to Nimbus-C between 1934 and 1959 are described in Jørgensen, K. (2016): ´Nimbus – Technical Development 1934 - 1959´, This book explains the ‘early’ versus the ‘later’ design, the ‘low’ telescopic fork as opposed to the ‘high’ version, etc.
In the description of the various dismantling, repair and reassembly procedures, spare part numbers are given in brackets. The spare parts catalogue issued by A/S Fisker & Nielsen in 1951 and corrected in 1958: (´Værkstedshåndbog – originale reservedele´) has been reprinted many times by Denmark’s Nimbus Touring Club (DNT) and others.
Every illustrated part in the catalogue is numbered. This part number will be found in the list on the opposite page. An underscored illustration number indicates that the numbers of any earlier versions of the part are also listed. The serial numbers applicable to different versions are given in the column to the left of the part numbers.
Reference is also made to Weidinger, S. (2007): Nimbus – Ord-bog – Dictionary - Wörterbuch.
| Number of cylinders: | 4 in line |
| Bore: | 60mm (available oversize’s: 60.6mm, 61.2mm or 61.8mm) |
| Stroke: | 66mm |
| Cubic capacity: | 746 cm3(761 cm3, 776 cm3or 792 cm3). Figures in brackets are for 1st, 2nd and 3rd oversize. |
| Compression ratio: | 5.7:1 (domed pistons) or 5.4:1 (flat-top pistons) |
| Power output: | 22 bhp / 16.2 kw @ 4500 rpm. (5.7:1 compression) 18 bhp / 13.2 kw @ 4500 rpm. (5.4:1 compression) |
| Max. speed: | Solo: 120 km/h.; with sidecar: 95 km/h. |
| Cruising speed: | Solo: 90 km/h.; with sidecar: 75 km/h. |
| Gear ratios: | 1st: 2.43:1, 2nd: 1.53:1 (or 1.57:1), 3rd: 1.00:1 (or 1.04:1) |
| Final drive ratio: | Sidecar gearing: 4.92:1 (59/12) Solo vehicle: 4.07: 1 (57/14) or 4.00 (56/14) |
| Brakes: | 150mm or 180 mm drums, front and rear |
| Wheel base: | 1301 – 7500: 1410mm 7501 – 14015: 1435mm |
| Rake: | 65 ° |
| Trail: Overall lenght: Overall width: Overall height: |
Frames1301 – 7500 60mm 2160mm 780mm 1050mm |
Frames 7501 – 14015 65mm 2200mm 720mm 1100mm |
| Seat height: | 710mm |
| Dry weight: | 185kg (with passenger seat) |
| Petrol tank: | 12,5 1itre, of which approximately 1 litre reserve |
| Tyres: | 3.50” x 19” (possible front wheel »Sport« 3,25” x 19”) |
| Wheel base: | 1301-7500: 1410mm; 7501-14 015: 1435mm |
| Front fork offset: | 1301-7500: 60mm; 7501-14 015: 65mm |
| Valve clearance: Contact breaker |
Inlet: 0.3 mm, exhaust: 0.7 mm (cold engine) |
| gap setting: | 0.7mm |
| Plug gap setting: | 0.7mm |
| Ignition sequence: | 1 - 3 - 4 - 2 |
| Ignition timing: | 1650 rpm: 37° before top dead centre (TDC) |
| Valve timing: | Inlet valve opens: 7° before TDC closes: 39° after bottom dead centre (BDC) |
| Exhaust valve opens: 42° before BDC closes: 4° after TDC |
|
| Battery: | 6 V/ 12 Ah |
| Dynamo: | 8V/70W |
| Lighting: | Low beam / high beam: 35/35 W Parking light: 4 W (possible 5 W) Tail light and licence plate light: 5 W Brake light: 15W Instrument light: 1,2W Ignition/charge warning light (Bosch): 4W Ignition/charge warning light (lighting switch): 2W |
Fasteners and locking methods:
Thread types
All threads on the Nimbus-C are right hand, with the exception of that on the speedometer drive worm (7572 or 8361), which is a left-hand thread. With few exceptions, threads are standard metric or metric fine.
Fasteners
Bolts, screws, washers and nuts for Nimbus-C are standard engineering hardware items. Their precise sizes can generally be read from the spare parts list. For example: Plan 9C in the spare parts list calls for: 7651 Screw 6 – 0,75 x 13mm, that is, an M6 screw with an under- head length of 13mm and a thread pitch of 0.75mm (metric fine).
Bolts
On the Nimbus-C all bolts are hexagon head, and the following sizes are used:
* 6mm (10mm across flats)
* 8mm (originally 14mm across flats, replacements 13mm)
* 10mm (17mm across flats)
* 12mm (19mm across flats)
Screws
All screws are slot head type.
Studs
All studs are 6mm, 8mm or 12mm, either plain or shouldered
Nuts
All nuts are hexagonal, either plain, castellated (locked by split pin) or domed (as on wheel spindles). (Dynamo bevel gear retaining nuts are an exception, being round castellated pattern requiring a special spanner).
Washers
Fibre washers are used in some places to prevent damage to surfaces. Flat washers of galvanised or stainless steel are used for the same purpose. Spring washers are locking washers (see below).
Locking methods
* Spring washers are used when connecting parts. Spring washers must be in direct contact with the screw head or nut. A flat washer should be placed under a spring washer if the fastening to a light- alloy metal surface,
* Locking washers / locking tabs prevent fasteners from loosening, typically by means of a section of the washer or tab being folded against a flat of a bolt head or nut, while the washer or tab is itself secured against turning.
* Locking wire can be used if the bolt head or nut is drilled.
* Split pins are used to lock castellated nuts to drilled bolts.
* Special purpose adhesives such as 'Loctite' are now available and are very effective when applied to thoroughly cleaned and dry fasteners. There are various grades of these 'anaerobic expansive' products. Some are suitable for locking bearings into place.
Torque settings
In some cases, applying the correct torque setting to a fastener is essential. (Page 210) The head of the bolt may bear a code indicating the grade of material and therefore the maximum allowable torque. Recommended torque settings assume clean, dry, undamaged threads. Torque figures are usually specified in foot-pounds (ft/lbs) or New- ton-metres (Nm).
Hammers
* Engineer's ball-peen hammer
* Soft-faced hammer (rubber, plastic, or fibre faced)
Spanners
* Adjustable spanners
* Ring spanners
* Open-end spanners
* Combination spanners (one ring end and one open end of the same size)
* Sockets - used with square-drive ratchet handles
* Box spanner / tubular spanner
* Torque wrench
Pliers
* Combination pliers
* Circlip pliers
* Multigrip pliers
Screwdrivers
Make sure you have a selection of flat-blade screwdrivers to fit the varied sizes of slot-head screws found on the Nimbus. The blade of each screwdriver should be ground so that the flat sides are slightly hollowed and parallel at the tip, reducing the risk of damaging the screw head. Right-angled screw drivers can be useful where access is difficult (for example when removing the Nimbus dynamo’s brush holder screws).
Special-purpose tools
For the Nimbus-C motorcycle the factory developed a set of 'Service Tools' for certain specific repair operations. General-purpose tools can be used, but with care and less conveniently for some, but not all of these operations. In such cases, repairs have to be carried out in a specialised workshop. Factory service tools marked * appear in the DNT Drawing Archive.
Where service tools are mentioned or illustrated in this book, tool numbers and the Archive drawing numbers are given.
| Drawing | Tool | Tool description |
| 8999 | N10 | Puller for dynamo gear wheel |
| 8999 | N14 | Puller for dynamo gear wheel |
| 9000* | N11 | Puller for flywheel |
| 9000-2* | Puller for flywheel | |
| 9001* | N12 | Puller for crankshaft bevel gear wheel and main bearing |
| 9002* | N15 | Holding bracket for dynamo |
| 9003* | N16 | T-bar socket for upper dynamo bevel gear retaining nut |
| 9004* | N17 | T-bar socket 27mm for flywheel and fork stem top nut |
| 9005* | N18 | Offset 14mm spanner for cylinder head fasteners |
| 9006 | N22 | Circlip fitting tool |
| 9007 | Reamer, connecting rod small end bush | |
| 9007 | Puller for camshaft bevel gear wheel | |
| 9008 | N25 | Valve facing set, complete in box |
| 9009 | N26 | Engine stand |
| 9010 | Workshop stand | |
| 9011* | N27 | Drive shaft tool |
| 9011-2 | Puller for drive shaft hub | |
| 9012* | N28 | Adjustment gauge for final drive pinion |
| 9013* | N29 | Puller for wheel bearing outer race |
| 9014* | N32 | Distance piece, rear hub assembly |
| 9015* | N33 | Fork bush extractor for bush |
| 9016* | N35 | Test mandrel for fork tubes |
| 9017* | N36A | Test gauge for fork tubes |
| 9018* | N36B | Test gauge for fork tubes |
| 9019* | N40 | Spanner 46mm steering head bearing nut |
| 9020* | N41 | Alignment tool for clutch plate |
| 9020-2* | Alignment tool for clutch plate | |
| 9021* | N42 | Retainer for connecting rod bolt |
| 9022* | N43 | Drift for gudgeon pin |
| 9023* | N44 | Clutch compression tool |
| 9024* | N45 | Drift for main bearing |
| 9025* | N46 | Drift for bevel gear wheel |
| 9026* | N47 | Valve spring compressor |
| 9027* | N48 | Drift for valve guide |
| 9028* | N49 | Drift for small end bush and bevel gear bush |
| 9029* | N50 | Drift for small end bush |
| 9030* | Frame alignment gauge | |
| 9031* | N52 | 'C' spanner for speedometer worm gear |
| 9032* | N53 | Drift for front wheel bearing and telescopic fork bushes |
| G-9033* | N29 | Extractor for front wheel bearing |
| 9034* | Rear frame alignment tool | |
| 9035* | N56 | Drift for fork stem bearing cone |
| 9036 | Drilling template for cylinder head (Valve enclosure) | |
| 9037* | N58 | Drift for removing sidecar axle |
| 9038* | N59 | Drift for fitting sidecar axle |
| 9040* | Tool board with profiles | |
| 9041* | Tool holders for tool board | |
| 9042* | Tool board | |
| 9043* | Installation tool for dynamo upper bevel gear 7115 | |
| 9044* | Installation tool for dynamo upper bevel gear 7147 | |
| 9046* | N54 | Hand reamer 16mm for connecting rod small end bush |
| 9047* | Drilling template for saddle suspension brackets | |
| 9048 | T- bar socket 14mm | |
| 9049 | T-bar socket 19mm |
Improvised tools
If factory service tools are not available, consult the Drawing Archive. In many cases it may be possible to make a substitute, as exact dimensions are given. Right: In absence of tool number 9003/N16 T-bar socket.
Measuring equipment
In order to be able to take dimensions in case of engine overhaul, a vernier, dial, or digital calliper and a micrometer will be needed. Dial gauges are particularly useful for measuring specified tolerances (as in trueing wheels) or backlash (when fitting gears).
Drawing Archive
The Nimbus-C factory engineering drawings available in the Drawing Archive were produced 40 to 70 years ago to the standards of that time, and are certainly very useful today. Some more recent drawings lack precise spare part dimensions and do not comply with the requirements for technical drawings. Some spare parts do not have original factory part numbers but have been assigned an identifying number. That is the case with helical . timing gears for example.
In 2006 the Danish Nimbus Touring Club (DNT) produced two compact discs with original Nimbus construction drawings and drawings of prototypes and new developments.
The opening text on the CD reads:
Drawings from A/S Fisker and Nielsen’s drawing archive were registered and photocopied by Danmarks Nimbus Touring in 1982 and as many missing drawings as possible have been re-created by measuring spare parts. All drawings were scanned by Danmarks Nimbus Touring between 2002 and 2005.
The Nimbus-C drawings are organized according to A/S Fisker and Nielsen's Parts Catalogue published in 1951 and updated in February 1958. Drawings for the Nimbus A/B are organised according to component categories. Drawing numbers with a preceding G are combined drawings which illustrate multiple parts. The meaning of a preceding E is unclear, but might indicate a repeat order. Trailing characters to a drawing number indicate the following:
S (Smede) - the drawing is of forged parts
P (Plade) - the drawing is of sheet metal parts
A (Arbejde) - a working or production drawing
K (Kalkule) - a drawing including calculations or other documentation.
Nimbus-C archive drawings
Whereas there is a limited collection of drawings for the Nimbus- A/B, an almost complete set of drawings for the Nimbus-C survives. The drawings are on CD and arranged in folders corresponding to the organisation of the Nimbus-C Parts Catalogue. Each folder contains all drawings
Each file contains a sub file with drawing in PDF-format (to be opened with Adobe Reader) and a file with drawings in TIF-format. Besides, all files open up automatically in JPG-format. Most of the scanned drawings are very large and besides that, very dirty. That means that a certain computer capacity is required for opening and printing the drawings, where required, especially those which are in TIF-format.
Archive searching
Use the computer search function, specifying the drawing number (part number).
Removing the engine from the frame
Disconnect all wires from the battery. Disconnect the earth/fuse holder (8032) from the engine (where applicable).
Remove the screws (5400) from the brush-holder cover (7872) on the right side of the dynamo. Label the 'D' and 'F' wires before disconnecting them to avoid any mistake when reconnecting them. Disconnect the wire to the 'D' carbon brush and remove the brush. Disconnect the 'F' wire.
Disconnect the 'I' wire from the ignition coil (7706) (see wiring diagram).
Remove the ignition coil by detaching the H.T. leads, swinging down the retaining clip (7690 or 8185), and easing the ignition coil forward. If the coil does not readily separate from the distributor (7392 or 8175), remove the screw (5350) from the distributor adjustment plate and remove the ignition coil and distributor together. This will remove the rotor (7432) at the same time.
For hand-change machines:
For foot-change and later version gearbox machines:
- Pull in the clutch until a wooden block can be wedged between the clutch release arm (9218) and the mudguard.
Remove the split pin (3867) from the release arm and remove the clutch cable (8944). Wire the release arm in place and then remove the block.
Remove the centre stand (7300 or 8328). The motorcycle will need to be supported by blocks under the footrests.
There are alternative ways to continue:
Either:
Or:
Leave the rear wheel in place.
- The centre stand can now be refitted to the frame.
Replacing the engine in the frame
- Place the engine and gearbox assembly on blocks, so that the four engine mounting holes will be at the same height as the mounting holes in the lower frame when both wheels are fitted to the motorcycle. For an engine with the later gearbox, the clutch release arm (9218) has to be wired in the fully-in position so as to clear the mudguard.