AJS 7R 3A Boy Racer
AJS 7R 3A Boy Racer | |
Manufacturer | |
---|---|
Production | 1952 |
Engine | Single cylinder, 4-stroke, OHC Triple-Camshaft |
Compression ratio | 12.2:1 |
Top Speed | 193 km/h / 120 mph |
Ignition | Lucas magneto |
Spark Plug | B6ES |
Transmission | 4-Speed |
Frame | Tubular double cradle |
Suspension | Front: Telescopic fork Rear: Dual shocks |
Brakes | Front: Drum Rear: Drum |
Weight | 129 kg / 285 lbs (dry), |
Oil Capacity | 4.0 L / 8.4 US pints |
Fuel Capacity | 22.7 L / 6.0 US gal |
Manuals | Service Manual |
It could reach a top speed of 193 km/h / 120 mph.
Engine[edit | edit source]
The engine was a Air/oil cooled cooled Single cylinder, 4-stroke, OHC Triple-Camshaft. The engine featured a 12.2:1 compression ratio.
Drive[edit | edit source]
Power was moderated via the Dry, multiplate Ferodo.
Chassis[edit | edit source]
Stopping was achieved via Drum in the front and a Drum in the rear. The front suspension was a Telescopic fork while the rear was equipped with a Dual shocks. The 7R 3A Boy Racer was fitted with a 22.7 L / 6.0 US gal fuel tank. The bike weighed just 129 kg / 285 lbs.
Photos[edit | edit source]
Overview[edit | edit source]
AJS 7R
Built by Associated Motor Cycles? Very good indeed: It was in production and winning trophies from 1948 to 1963. Known as the Boy Racer, the 7R won three successive Junior Isle of Man TT races, from 1961 to 63. It was powered (occasionally underpowered, if truth be known) by a 350cc four stroke single, and designed to combat the all-conquering multi-cylinder Italian motorcycles. Which it did, very effectively, in the hands of racers like Ted Havens.
Cycle World Road Test
From time to time we like to show you an exercise
in style and grace which stands out from lesser breeds as a Chanel original does
from discount house muu muus. (Voice from the parts room, "how many cylinders
does a Chanel have?") Style is not easily acquired nor is it generally the
result of a conscious effort in design: one has to look only at some of the
chrome-tank English Twins of the Fifties or bloated Japanese multis to see the
truth in that although everybody knows a nice girl who is as homely as the back
of a bus. Still. The subject of our Salon is the AJS 7R, one of those happy
marriages of circles, curves and lines that produces a harmonious whole and the
daring genius who thought of gold paint (not anodized) for the mag crankcases
and cam-drive tower wrought better than he knew. I am sure that the 7R riders
went just a little faster because they looked nice. Perhaps that is why KTT
Velocettes were so successful. At any rate the cobby lines, large tank,
businesslike engine and subtle curve of the exhaust pipe give the 7R one of
those unmistakeable silhouettes that bring enthusiasts on the run from the other
end of the paddock. Isn't that handsome?
The 350-cc ohc "Boy's Racer" so called because
it was produced as a reasonably priced customer's machine, was brought out in
1948 at a difficult period in AJS racing fortunes and although not outstandingly
rapid at first, proved to be both reliable and competitive over its 14 year
production run and as such, served as a nursery for many riders of international
repute. In common with most English bikes, its design roots lay way in the past,
in this case the celebrated "cammy" AJS introduced in 1927. The parent firm,
known then as Stevens Brothers, started out in the usual way in the late 1890s
fiddling with various proprietary engines but in 1909 the company decided to
market what amounted to a 29cc flathead-powered motorized bicycle under the name
of AJS, for Albert John Stevens (the, only brother with a middle initial) and
furthermore to run it in the TT. Results were not all that remarkable but the
company persevered, in 1914 bringing out an ohv 350 with an add-on gearbox
giving four speeds in all. With this AJS cleaned up the 350 class, taking the
1st four places plus 6th and the company was on its way.
Development on the sly during the war ensured
that Ajays were ready for the TTs immediately afterwards with an inclined-valve,
hemispherical chamber 350 which, after the usual teething troubles and a bit of
strategic pushing, managed to take the Junior three times on the trot. This last
win, in 1922, saw the introduction of the so-called "big port" Ajay which had
undergone a fairly thorough redesign with not only cams as big as their
gearwheels but an exhaust port of something like 2 5/8 in., a sort of odd
modification when looking at some of today's bikes but at that time fuels,
compression ratios (5.75:1), cam timing etc. may have dictated different ideas
about scavenging. At any rate these early models are still recherche
among vintage freaks. The following years showed that inventive minds were
working at the factory, what with the introduction of aluminum heads with
cast-in bronze seats, foot pedals for both internal expanding brakes to leave
the driver's hands free for his multitude of hand levers (including throttle!),
dry sump lubrication, and even going modern to the inlet valve becoming larger
than the exhaust. At the same time, the racers still featured a foot-operated
oil pump most of the time as well as the cylinder head being held down by a sort
of strap or stirrup. At any rate, Ajays were still racing energetically and
placing but not coming up with wins in the TT, a significant barometer of
success to the buying public in those palmy days. Following an OHC Velocette's
win in 1926 a new machine was brought out in '27 with chain-operated ohc (three
rockers for two valves at 900), dry sump, and proper four-speed gearbox still
controlled by a hand change. This was the first of the "7" series which, after a
slowish start, won many laurels up through the years in 250, 350 and slightly
overbored even in the Senior. Numerous modifications were made including getting
rid of the extra rocker and their success even might have been greater but for
failures of accessory components. Isn't it always the way.
Racing is expensive, however, as a number of
manufacturers have found out and in a marked period of short money (1931) the
Stevens brothers went bust and the factory was sold to Matchless. Development
went on, including production of a recordbreaking (would-be) Twin and a Four
which could be supercharged and in fact was raced in that form, one of that type
doing a 100 mph lap (Walter Rusk up) in Ulster. Emphasis thus swung over to
bigger bikes, though without much luck in racing due to a rather limited
development budget. In fact the famous but unlucky Porcupine Twin was originally
designed as a "blown" bike but was forced to run with carburetors due to the
usual FIM policy change after the 1941 war. In this form it did win some races
but mostly showed a lot more weight than was really needed. With all the real
hotshots from Europe now appearing on the scene, AJS then thought that it was
time to resurrect the cammy 350 and as noted, brought it out in 1948.
Considerably more modern than its predecessor, if you can say that about any
English hike, the 7R was raced, fairly successfully by works riders of the
caliber of Les Graham, Bill Doran, Reg Armstrong ad infinitum against the likes
of Foster and Frith (Velocettes) plus Bell and Lockett (Nortons) with equivocal
results for what amounted to a new design
mostly. As the years wore on
development began to give rewards and positive successes were notched both by
the works and the myriad private owners, especially as Velocettes were now on
the verge of becoming "orphans". In an effort to drag more power out of the 7R,
in 1952 AJS brought out a triple knocker version with three valves, two of them
exhaust (back to the Big Port syndrome!) which were worked by a geared layshaft
running off the inlet camshaft, that lucky object taking the drive direct from
the cam chain. This version was quite rapid and took some 13 world's records at
Montlhery in 1952, including the Hour at 115.66 mph. Furthermore, New Zealander
Rod .Coleman finally won the Junior TT on one, teammates finishing second and
fourth, and hopes began to be expressed that the 7R 3A would also be put into
limited production along side its single cam brother. But this was not to be,
Matchless's directors showing the same far-sightedness that led to the collapse
of most of England's motorcycle factories. To be sure, the Matchless G45 and
G50, both derived from Ajays, made one small attack more upon the scene but the
foreign multis were upon them and in 1962, manufacture of the beloved 7R ceased,
to be followed four years later by the collapse of AMC (the parent firm) and its
swallowing up by Dennis Poore's Manganese Bronze Holdings, for all the good that
did.
A lack of signal success in the TTs did not
necessarily mean that a bike was no good. Both Norton and Velocette had been
doing the Island for years, having the requirements absolutely taped as Harley
does the dirt tracks over here, and also took care to retain Island specialists
who could and did go around at 100 mph (like the legendary Harold Daniell) when
you couldn't see your hand before the face. The 7R was put out as a customer's
racer primarily, which meant that the ultimate Nth wasn't dragged out of it; in
a company where development costs were somewhat limited, most of the money
allotted went to the turkey Porcupine. However 7Rs were quite often found among
the works runners at the TT in a good place and in the hundreds of small
Continental and English contests where the owner-driver-mechanic had to live out
of his van, the robust qualities and good handling resulted in many victories.
Fastest lap is all very well but the checkered flag counts.
This particular example is a 1956 model updated
to 1961 specs, owned by William A. Bass III, a consulting engineer of Long
Beach, Calif. The machine was imported from England some time in 1956, possibly
bought new, and after some racing and passing through several sets of kind hands
(the bike is unrestored except for the tank) was snatched up by Bill to join the
other goodies in his garage. Fundamentally the 7R engine is a Single (!) with an
almost square bore and stroke ratio (75.5 x 78 mm) giving something like 42 bhp
at 7800 rpm. The bottom end is rather sturdy with smallish flywheels to cut oil
drag and a caged roller bearing on the big-end of the forged steel rod although
a titanium one was used occasionally. Piston is a full-skirted four, ring
Specialloid model with cutouts in the slightly domed top and the crankpin
drives two oil pumps plus a Weller-tensioned chain up to the camshaft. The
light-alloy cylinder has an austenitic iron liner shrunk into it but the head,
the heart of any racing engine, shows most of the trick 'work. Of the same light
alloy with shrunk-in aluminum bronze or austenitic iron valve seats (inlet and
exhaust respectively) the camboxes have pits for the mousetrap valve springs,
Terry usually. By 1953 roller tappets were fitted on the two rockers and a lot
of concentrated work by engineer and former TT rider C.J. Williams on the head
before the 1956 series improved it tremendously. The engine was originally meant
to run on postwar "Pool" petrol which was about like Mexican regular gas and
thus C.R came out something like 8:1. With the advent of better fuels or even
alky (Bill's 7R likes either Avgas or methanol) Mr. Williams airflowed the head
by one of those primitive test-rigs that the Poms seem to specialize in and came
to the conclusion that a slightly down-swept port shape gave better mixing, a 13
1/8 in. long inlet tract reduced megaphonitis, a 13/8 Amal was just the ticket
and a squish pattern head enabled CR to be raised to 12.2:1. Power all through
the range as well as improved fuel consumption was the result.
Externally the 7R doesn't look too much different
from its predecessors but in fact the "new" frame holds the mag crankcases more
firmly, the vibration-producing alloy brace from the engine to the top of the
gearbox has been replaced with a decent steel one, the giant early megaphone
which resulted in about a 500 rpm power band was replaced with a smaller reverse
cone mega, and the fade-prone "jampot" rear shocks went to wherever old shocks
go and Girlings took their place. The lovely tank with cutouts for knees is held
by an adjustable strap across the top (to allow for fitting sprint tanks) and
holds a useful 5 gallons while the similarly contoured dry-sump oil tank takes 7
pints; these are probably Imperial measurements and in the US we can squeeze a
bit more in. Front suspension is looked after by AJS Teledraulic forks which
seemed to work all right. I asked a Knowledgeable Person whether Norton forks
were ever fitted as they were on many of the Triumph GPs and he said that the
Norton ones were too heavy; one of the main advantages of the 7R was its
comparatively light weight of 285 lb. and no wonder with mag crankcases, cam
boxes, timing cover, chain cover and hubs at both ends. Gearbox of course was a
four-speed Burman with final drive of 4.87, it is no good going into sprockets
as they have probably been modified endless times, and the dry clutch, exposed
on the left side, is a multiplate Ferodo-faced unit familiar to all by the
fish-factory smell it makes when slipped. Also in the English tradition are the
difficult to find 19 in. wheels fitted with Goodyears front (3.0019 although
2.75 is recommended) and rear (3.50-19 although 3.25 ditto).
I wasn't about to ride the 7R in the teeming
spaces around the Queen Mary, especially with a rather loud megaphone fitted, so
we have to rely on the impressions of owner Bass. He states that the bike is
absolutely delightful and handles "like a Ducati" which must make both Italians
and English feel happy. Under way the Ajay is smooth, light and agile, being
able to be flicked about, and the brakes in moment of stress are v good for non
discs. Like all small-capacity racing engines, the Single is extremely peaky and
at low rpm will hardly pull its own weight, necessitating a lot of clutch slip
(perhaps that's why the IOM start is downhill) but commences coming on the pipe
to give some useful power at around 5800, pulling strongly from then on to
redline at 7400. His top speed at the present gearing he has calculated at
around 120 mph well tucked in and the Lucas rotating armature mag manages to
keep up with that
or has in the past although he confides that at the last
Vintage meeting at Laguna Seca he had a feeling that the Prince of Darkness
better have his brushes changed. Starting drill is also normal practice; tickle
the hell out of it, retard the spark, bump back onto compression, snick into low
gear, pull in the clutch and run like anything, preferably with the aid of a few
friends, and leap aboard. A hot plug (usually a B6ES) is usually fitted for
warmup and something rather colder, one of Champion's Gold Palladium range,
fitted for serious work.
Model. | AJS 7R |
---|---|
Year | 1952 |
Engine Type | Single cylinder, 4-stroke, OHC Triple-Camshaft |
Displacement | 349.2 cc / 21.3 cub in |
Bore X Stroke | 75.5 x 78 mm |
Cooling System | Air/oil cooled |
Compression | 12.2:1 |
Oil Capacity | 4.0 L / 8.4 US pints |
Exhaust | 1-into-1 |
Induction | Carburetor, 1 3/16 Amal |
Ignition | Lucas magneto |
Spark Plug | B6ES |
Starting | Kick |
Max Power | 29.8 kW / 40 hp @ 8000 rpm |
Clutch | Dry, multiplate Ferodo |
Transmission | 4-Speed |
Final Drive | Chain |
Final Drive Ratio | 4.87:1 |
Frame | Tubular double cradle |
Front Suspension | Telescopic fork |
Rear Suspension | Dual shocks |
Front Brakes | Drum |
Rear Brakes | Drum |
Wheels | Steel, wire spokes |
Front Rim | 2.75 x 19 |
Rear Rim | 3.50 x 19 |
Dry Weight | 129 kg / 285 lbs |
Fuel Capacity | 22.7 L / 6.0 US gal |
Top Speed | 193 km/h / 120 mph |
Review | Cycle World |