Fisker & Nielsen and the Nimbus
The Nimbus motorcycle must surely be one of the most over-looked two-wheeled transport gems of today. Certainly quirky looking, and definitely interesting, I have always loved them, admiring their advanced design, and high quality manufacture since I saw my first one while camping in the Isle of Man back in 1972.
"Why advanced design?", I hear you say, perhaps coughing slightly. Well, to answer that question you have to take a few steps back in time.
In the very beginning, there was a company called Fisker & Nielsen Ltd. Started in 1906 by Hans M Nielsen and Peders A Fisker, it was formed to make quality electric motors, switchgear, and related items of their own design. The company was very good at this work, and quickly built good reputation for quality products. In 1910, Peder A Fisker thought it would be a good idea to take their expertise with electrical items into into making vacuum cleaners. Unfortunately, Nielsen did not agree with this suggestion, and the partners decided to go their separate ways. The company name 'Fisker & Nielsen Ltd' remained with Pedar A Fisker. So the vacuum cleaners he dreamed of were designed, manufactured, and sold. They were an excellent product and made the company good money. (in fact Nilfisk was the brand name - and they are still made today).
It is claimed that Pedar A Fisker once saw a motorcycle parked-up by the side of the road. Although fascinated by the concept, he was quite disappointed in its poor design and construction. Sensing the growing market for personal transport, he vowed he could and would make one better.
His first motorcycle (nicknamed 'the stovepipe') was an Inlet-over-exhaust configuration produced around 1918, and was a very modern design (for the time) incorporating many of the features found on motor cars. 4 cylinder in-line engine, a 3-speed gearbox and single-plate clutch, with shaft drive to the rear wheel. It was called 'Nimbus' - which means halo (the sort of glow you would find around a saint).
When the Nimbus first appeared, competitors mocked its strange look (a round-tank in a sea of flat-tank motorcycles). However, it was a good reliable performer and was quite popular. Pedar A Fisker promoted the model by riding one himself in various trials and races with notable successes. The design went through an improved 'B' version, before production stopped around 1928, by then 1252 motorcycles had been manufactured. Although a very good motorcycle, it was just too expensive to sell in enough quantity for the recessionary market conditions at the time.
Fast-forward to 1930s for the next motorcycle.
During 1930 Pedar A Fisker thought the markets were recovering, and the time was right for another motorcycle. He and his son Anders Fisker put their minds to designing a new model, using what had been learned from the older models. Anders had gained a degree in engineering in 1932, and would have been well equipped with knowledge of new techniques and materials for this job.
By 1934, the old 'B' stovepipe had been completely re-designed into the new 'Model C', and this is where more of the 'advanced engineering' bit comes in. When British motorcyclists were married to single cylinder machines - usually side valve engines - chain drive - heavy girder forks and frames - usually no electric lights, and needing to wear oil-proof boots - Fisker & Nielsen Ltd produced the 'Model C' - bristling with innovative features - a motorcycle truly way ahead of its time.
Model C - way ahead of its time
Its specification included a 4-cylinder over-head valve engine with split Babbitt big-end bearings, and massive abuse-tolerant ball journals for the mains. The block was mounted in-line with the frame, horizontal crankcase joint with one-piece sump pan, shaft-driven overhead cam, shaft drive to the rear wheel, telescopic forks (by the way - Nimbus invented telescopic forks). The fuel tank sat down between the frame rails to keep centre of gravity low, and also served to stiffen and strengthen the strip steel frame in that area. The carburettor incorporated a fuel 'pumper' mechanism for easy starting and better acceleration - and it also had a built-in efficient air cleaner. More subtle engineering features included pressure-fed lubrication feed to the gears in the gearbox, crankcase venting to the carburettor (which also served to lubricate the inlet valves), a twist-grip lighting switch (which feels exquisite in operation), coil ignition with distributor - and an ignition key. The dynamo fitted was of their own design and manufacture - so powerful, you didn't really need a battery to produce ignition sparks. You could always get home with a dead battery (just like a magneto unit). Couple all this with the a dedication to keep manufacturing costs low, and maintenance simple - it should have been a winner - and it pretty much was in Denmark. The model C became affectionately known as 'Humlebi' - which is Danish for 'Bumblebee' - mainly because it buzzes along like one.
The Danish army and police bought many 1000s of them, as did the postal service - usually fitted with a sidecar - Nimbus making about 12,000 machines in all up until production was stopped in the late 1950s. They were never sold in the UK, and not many outside of Denmark for that matter as far as I can tell. Judging by the various articles I've read, the Nimbus motorcycle was more a labour of love for the company. It never reached its projected annual sales figures of 1000 per month, probably didn't make much money in real terms, and it would have been a constant distraction from the making of vacuum cleaners. So I guess we have the accountants to thank (or blame, depending on which view you take) for the demise of the Nimbus motorcycle.
Getting back to the engineering aspects, there has been some considerable discussion and passing negative comments on the failure to fully enclose the valves and springs in early-on in the design as was the trend with every other engine manufacturer. Such was the genius of the Model C, I think there could have been a deliberate reason not to do that in 1934, and continue to do it almost until production finished in the late 50s.
Being non-enclosed, the valves and springs ran in a constant flow of cooling air. This enabled them to act as superior heat sinks for the valve seats, stems, etc, and thus they performed much better and had a longer life. Continuous lubrication of the valve stems wasn't necessary because the valve guides were of the right material (cast iron) in the first place. In any case, the inlet valve is lubricated by crankcase oil vapour as it is sucked through the carburettor.
Fully enclosed valves on a very late
production Nimbus - disastrous
Valve-gear changes in tried by Nimbus in 1959 could prove this theory. In an effort to 'modernise', the last few Nimbus made were fitted with purposeful looking alloy castings that fully enclosed the valve gear. The results were pretty close to disastrous. Cylinder heads overheated, and warped, and burnt valves became a frequent problem in no time at all.
Performance-wise, the Model C was never designed to win any speed races, although it was used extensively for racing and trials within Denmark - notably by Josef Koch. There are just two rear drive bevel gear sets - ratios 1:4 (solo) and 1:49 (sidecar) - insufficient for proper racing anyway, and the cast-in inlet manifold limits the breathing of the engine to one small carburettor. The Model C was a good reliable workhorse however, covering very large mileages with little trouble, and several have been on successful historic round-the-World overland trips. The 'Bumblebee' was so ahead of its time in design, it hardly needed to be changed at all in all the years it was made, and this was part of its downfall. By the late 1950s people were buying cars, and young motorcyclists were being lured away by glitzy multi-cylinder motorcycles from Japan - with horizontally split crankcases, electric lighting that worked, oil-fed gearboxes, and telescopic forks …
By the way, Nilfisk are still in business making vacuum cleaners and other things, highly revered for performance and quality even now.
Today you can stand a 1930s Nimbus next to almost any motorcycle from the 1980s - and from a distance (with eyes screwed-up) you wouldn't easily be able to tell which was the first motorcycle to be made.
© 2013 - R T Reich - all rights reserved
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