Nimbus 750-Four

Fours are nothing new. Sin ce th e ea rly years of th e ce ntu ry, a host of manufact urers have shoe-horn ed four-cylinder engines int o road­going motorc ycles; FN in Belgium , H ender so n in th e USA, count less oth ers aro und th e wo rld , and eve n, bri efly, Brough in th e UK. And th e mo st en d u rin g of th ese wa s a s m a ll co m pa n y from Copenhagen , Denmark РNim b us.

In 1918 the company’s founder, Peder Fisker , launched his first production machine, the ‘Stovepipe’ Nimbus. Loosely based on the FN, it was exquisitely made, with swing arm rear suspension only one of several innovative features. Although the years brought a few diversions, the basic layout was to remain until the very last Nimbus; four cylinders longitudinally in-line, with shaft final drive.

Specifications

Engine

Horsepower

transmission

Frame

Brakes

top Speed

Years in Production

air-cooled 746cc SOHC longitudinal four

22 bhp @ 4500 rpm

3-speed

riveted steel strip construction

drum / drum

60 mph

1919 – 1960

The early Nimbus was very expensive to produce, and the onset of the Depression demanded that economies be made. The Mk II , introduced in 1934, was much more utilitarian . Gone was the rear suspension , and the brazed tubular backbone frame gave way to a curious affair of riveted steel strip. The Mk II had Fisker’s own telescopic forks, however, several months ahead of BMW’s and probably the first on any motorcycle .

The new 750cc engine , too, was advanced: a SOHC four, with inclined valves and hemispherical combustion chambers. The camshaft was bevel driven, whilst the crankshaft ran in just two huge ball bearings. The big-ends were shell-type. A three¬≠ speed gearbox transmitted the Nimbus’ modest power by shaft to the rear wheel.

This was never likely to amount to a performance machine. Cooling , with four close-set cast-iron cylinders each heating the other’s air, was always poor. The valve-gear is open to the elements. The two-bearing crank would flex if revved hard. And the single 26mm Nimbus carburettor is probably the smallest ever fitted to a four. Power in standard trim (and the Nimbus was never much tuned) was 22bhp at a leisurely 4500 rpm . Whilst this was good for brief bursts up to 60mph, sustained flat-out cruising evidently warped the cylinder head ‘like a banana’.

But 1934? Yes, and not really. Fisker was, as a matter of policy and temperament, opposed to change for change’s sake. So the Mk II continued in production, in much its original form, until 1958. Any part from a 1956 Nimbus will almost certainly fit one 20 years older, and vice versa. Such changes as were made were minor, mainly to instruments, brakes and other ancillaries .

To the end of its life, the Mk II retained its rigid rear end. In solo use the ride, like almost everything about the machine, was deeply idiosyncratic. This was a machine for riding with dignity , never panache.

Yet it was, in Denmark at least, a moderately successful motorcycle. In all, something like 12,000 Mk II’s were produced. It was rugged, economical (60-plus mpg), maintenance was simple, and it hauled a sidecar with ease. The MkII became popular with Danish tradesmen and military alike.

Even after motorcycle production ceased in 1958, the factory continued to manufacture spares. Although this was mainly to honour its obligations to the military, even in the late sixties it was possible to have a Nimbus built from new parts to special order.

But was it a superbike? Not really. Sure, it was a four, which might otherwise mark it as special. But everything about the Nimbus, far from looking forward to the days of high-revving sports bikes, harked back to an age of motorised gentlemen’s carriages. It was an utter anachronism, surviving into the Space Age but almost Edwardian in character. Yet, if nothing else, it shows that there is nothing innately sophisticated about multi s. As such, it is a useful book-end to an era that ended with fours of an altogether different ilk.

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