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Vincent Firefly

by Peter Green

In 1952 the hallowed halls of the Vincent-HRD Owners' Club were trembling with anticipation.  The Stevenage factory had intimated that a new model was about to be announced to the motor cycling press.  Prospective purchasers waited impatiently, cheque books at the ready.  Prospective record-breakers postponed their attempts with their current machines.

In 1953 the same hallowed halls were trembling with shock.  The manufacturers of "The World's Fastest Standard motorcycle - This is a Fact, not a Slogan!" had announced a clip-on engine of 45cc - the Firefly! Indignation filled the pages of 'MPH', the esteemed journal of the VOC.  It is certain that, if a Firefly owner attempted to join the Club in 1953, he would have received a very frosty welcome indeed!

Nowadays, a Firefly is regarded as a most desirable asset amongst the Vincent fraternity.  Epics such as the efforts of 'Team Firefly' in the 1991 FIM Rally in Eindhoven have added their own little bit of glory to the marque.  But how did the Firefly come about?

For many years, Phil Vincent had had a very good relationship with Miller, the electrical people.  Hence, while most other motor cyclist's batteries were kept happy with the superb Lucas AVC unit, the Vincenteer's battery either boiled with rage or faded through lack of nourishment with the Miller cartridge trying to supply its needs.  Be that as it may, in 1952 the motor cycling press announced a new clip-on engine: the Miller Firefly.  A road test and technical description appeared but the exact date and in which of the two main British motor cycle magazines eludes me for the moment [It was The Motor Cycle on 31/1/1952 and there was also a photograph of the Brussels Show model in the previous week's edition - Ed].  The machine seemed much the same as the Firefly that went into production, except that the sliding back of the engine to engage the rear wheel was accomplished by a lever below the saddle on the left hand side of the cycle.  For some reason Miller didn't continue with the production run; this passed to Vincent Engineers instead.

The engine unit went on sale in 1953.  The only significant change was that the rear wheel engagement was effected by a handlebar lever, rather like a clutch lever in reverse.  Pull in to engage.  A ratchet holds the lever in.  Release the ratchet to disengage.  The only other handlebar control to the engine is the combined decompressor and throttle lever.  Forward shuts the throttle and opens the decompressor; back shuts the decompressor and opens the throttle.  The engine fits on rails under the bottom bracket of the cycle and slides back to engage the rear wheel with a toothed roller.  This location gives a nice low centre of gravity and does not upset the trim of the cycle.  The long thin tank fits to the down tube of the cycle frame.

There are a few interesting technical features.  The engine unit has to be very slim to fit where it does but a spacer is normally used to make the gap between the pedals about an inch wider.  There is only one size of bearing; this is part number VF41 and is a ball bearing of dimensions 3/4" × 1 5/8" × 5/16".  The RHP number is KLNJ3/4 but the equivalent by any other manufacturer of bearings will suffice.  An alternator is fitted; surely one of the first cyclemotor units to be so equipped; the vast majority of larger motor cycles in 1953 still relied on dynamo and DC electrics.  Ignition is by a coil fitted in a recess at the base of the fuel tank.

Few problems were experienced with the engine unit.  The only major one that I know of concerned the rear drive roller, part number VF131AS.  The outer toothed rim is rubber bonded to the inner sleeve.  The bonding was prone to failure on some early models but this was quickly rectified.  The only problem that I have with my Firefly is a reluctance to start on petroil from cold but a few squirts of lighter fuel down the carb does the trick!

Production life of the Firefly was only three years.  In 1953 only the engine unit was available; in 1954 and 1955 it came fitted in a specially designed Sun cycle.  [The complete machine was known as the Vincent Power Cycle. Sun frames were used at first, later ones were made by Phillips. - Ed]  In 1955 Vincent Engineers ceased production of their big motor cycles, although they continued for some more years with industrial engines, Amanda water scooters and the like.  Demise of the Firefly, however, is usually blamed on the NSU Quickly.

It is widely known that a liaison between Vincent and NSU led to the ill-fated NSU-Vincent Fox production run.  What is not generally realised is that Vincent took on the marketing of the Quickly in the UK.  This they did at the expense of the Firefly and to their own eventual cost, as they were so successful at selling the little German machine that NSU decided to cash in on it and handle sales of the Quickly themselves in Britain.


Engine 47.6cc, 2-stroke, bore 38mm, stroke 42mm
Power 1bhp @ 4,200rpm
Weight 24lbs
Electrical equipment Alternator output 6V, 9W; recommended head lamp bulb 6V, 6W; tail light 6V, 0.04A
Ignition Original spark plug KLG F20.  For maximum performance or long-distance runs KLG F50 can be substituted.  Alternatives: Champion L10 or Lodge C14.
Fuel Tank capacity 5 pints.  Petroil mixture 20:1

First published - February 1996

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