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In the early fifties the most popular British four-strokes were still pushrod singles. 500cc machines typical of this era were the Matchless G80 and the AJS Model 18, both manufactured by Associated Motor Cycles (AMC) in London. The two aforementioned models were made in the same factory, the only difference in the two being the position of their chain-driven magnetos.

The magneto in the AJS was in front of the cylinder, where the Matchless was behind. The position of the magneto on the AJS allowed access to the separate dynamo. The Model 18S was a little heavy but it offered much better performance and fuel economy than the fast cars of the same era.

A design from the 1930s, being manufactured 30 years on, the AJS was updated when a spring frame rear suspension was included (hence the 'S'). The suspension was a vast improvement on the bouncy rear end but the wheel travel was only 75mm.

The Engine

A modest performance from the low compression engine in 1950 was brought about by conditions in Britain at the ime. Petrol rationing was abolished in 1950 but branded fuels did not return to the High Street until 1953. If you couldn't get your hands on high-octane aircraft fuel you were limited to standard low-octane 'Pool' petrol. A compression ratio of 6:1 would have caused the engine to overheat and damage the piston and valves.

The good thing about low compression was that it was easy to kickstart and had more flexibility at low revs. The AJS wouldn't reach 80mph but it would go along at less than 20mph in top gear. This meant that a small amount of petrol went a long way.


Shocking Development
AMC designed its own telescopic front fork for the 1941 Matchless G3/L, but they chose to copy Velocette's twin-shock swingarm rear suspension for it's top of the range AJS and Matchless singles and twins. Shorter vertical units were introduced in 1949. The 'Candlestick' shocks had only 50cc of SAE 20 oil in each damper. They were prone to bottom-out and leak and had drain and filler plugs which encouraged the owners to overfill the dampers, meaning further leakage. 'Jampot' shock replaced these on the 1951 version.

Technical
Production : 1949-1963
Engine type : Single cylinder, pushrod 2 valve, 4 stroke
Capacity : 498cc
Bore and Stroke : 82.5 x 93mm
Compression Ratio : 5.9:1
Fuel System : 27mm Amal Carburettor
Power : 23PS @ 5,400rpm
Dry weight : 177kg
Top Speed : 78mph

Comments

Sedrick   5th March 01

Just a quick note to say what a suberb write up on the AJS. Good job tiger.

Naz   22nd October 01

I own a 1949-51 Ajs 350. I dont really know which year!!! Its got shocks that look like candlesticks....but a restorer told me that the shocks aren't part of the original config, and that my bike was built rigid!!! Your article was brilliant but I was hoping maybe if you could tell me if all Ajs's built in and after 1949 were fitted with candlesticks? Also what do the jampots look like and what're their specs? Thanx and keep up the exemplary work!!!

Spannerman   24th October 01

Naz, your model was build rigid. As for the jampots, you should probably contact the AJS Matchless Owners Club with your engine and frame number so that they can sort out the origin of your bike. Thanks for your comments.

Helder Genesio da Silva Ferreira   18th February 02

My BIKE is AJS Model 18S 1952

Ray Gigg   21st March 03

I owned a 1949 AJS 350 Have often wondered what AJS stood for. Was it ARTHUR JAMES SMITH or SPENCER?

alygunawan   29th March 03

ajs is the best motorcycle,i haved 1957,i feel in heaven if i ride my AJS.
i'm very-very satisfied. Ajs is the best bike i ever had and i love him more than ever!!!!!.

IAN WOOLGER   2nd April 03

HELP HELP, i am looking at the back wheel of an 1957/58 AJS single, was 350 but the cylinder has been changed to 500cc, lights powered by alternator ignition by mag. Has anyone out there had their wheel bearings "lock up", Its not my bike, but the old boy who owns it needs it sorted. I was a modern jap bike mechanic, so brit stuff is a bit out of my league. Any info on the rear wheel assembly and diagrams etc would be a great help.Rear wheel has speedo drive on it and rear sprocket brake assy is what i would call "quick release" any ideas???

randy montgomery   18th April 03

Some of your info is wrong. The early 1950's matchless G-80 had its magneto in front. I think the AJS 500 single did too. Just a different style cover. See your own illustration at the top of this page! Having the mag in front allowed access to the generator in the back. Bikes with magdynos did not, by definition, have magneto and generator in different places.
My 1952 G-80S had 9.5 - 1 piston and racing exhaust cam and was hard to start but could beat a Bonneville off the line (for a couple hundred feet). The G-80CS was even faster. The standard spec models were slugs.

Nikolaus J. Benz   8th May 03

Hi,
I used to own a new AJS 350cc bike in the 1950th. The bike was purchase from Mead & Thompkinsons in Glooucester and it was registered under ODD 898.
Is it possible that you are able to tell me if this bike is still in existence and if so who the owner is.
Your reply would be appreciated. Many thanks.
Nikolaus


John   26th May 03

Hi

Nikolaus J Benz

That sounds a good old Gloucestershire name Nik :-)

I think you meant Mead and Tompkinson's in London Road Gloucester. Their shop was adjacent to a railway bridge and they also had a teasure trove of old bikes taken in as part exchanges and stored under one of the railway line arches next to the bridge. For a short time around about 1960 they were using a 1930s V twin BSA with a sidecar for deliveries. I wonder what happened to that!

Christian   13th June 03

As owner of a charming slug:
The mag moved in front of the cylinder on the G80 for 1952. The earlier G80 did not have a magdyno, but a mag placed directly above the dynamo behind the cylinder. Much fun for the army service departments dealing with the G3L, having to dismatle and retime the mag and its drive each time the dynamo was up for a check.

AJS stood for Albert John (or Jack) Stevens, the oldest of the Steven brothers.

Robert Taylor   19th June 03

Help I recently purschased a
Matchless 500cc 1957
Engine number 57/16m s 32104

looking for information on bike
Regards Rob

John Filbee   16th July 03

Hello,
Currently own and run a 1947 matchless G80 that appears to be a mixture of parts. I am seeking advice on a problem of the plug fouling at lower speeds. I think the fault may be with the carb which is a monobloc 389/1 rather than the original 276, does anyone have info on the jets, needle position and type, and slide used as it appears too rich at lower revs

Andy   3rd August 03

Nice read I have my eye on a 1957 trials Ajs 500 twin, out here in Australia, its all been restored but missing the clock any clues on value or where I could pick up the missing bits


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