The Prototypes : Roarer and Model O




The ROARER : (1939)


A supercharged twin cylinder racing bike aimed at winning against
the supercharged contemporary BMW.
One single prototype was manufactured.


2 vertical cylinders, 4 stroke, OHV, 2 carburators

2 parallel contra-rotating crankshafts, geared together
(a technical layout which will inspire the Model O)

Cylinder : 497,7 cc

(Bore : 68 mm ; Stroke : 68.25 mm)

Compression rate : 8.78/1 then 7.5/1

Boost pressure : 4 psi

Measured engine power : 54 bhp

3 plate clutch

4 ratio gearbox

shaft driven


This bike was raced at the 1939 Senior Tourist Trophy, where it
experienced overheating and plug issues, leading to the decrease
of the compression rate down to 7.5/1.
Supercharged bikes being banned after WWII, it's never been raced
again. It's been rebuilt rather than restored by its new owner
Ivan Rhodes and his son Graham, starting in 1983. They needed to
manufacture all internal engine elements from an exploded artist's
drawing since no original drawings were available. Its official debut
was the Historic Parade on the Isle of Man in 1989.


Click here to see the details of the engine





The Model "O" : (1939)


This is the prototype of a commercial bike which never went into
production probably because of WWII.

2 vertical cylinders, 4 stroke, OHV, 2 carburators

2 parallel contra-rotating crankshafts geared together
(a technical layout inspired from the Roarer)

Cylinder : 688 cc

Bore : 74 mm ; Stroke : 68.25 mm

3 plate clutch

3 ratio gearbox

Shaft driven


It's been fully restored during the 70's by Michael Postlethwaite and
now belongs to Titch Allen. It is usually on display at the Stanford Hall








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