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| J Type Profile |
Work on a replacement for the two-seat M type probably started along with the development of the C and D types. Almost certainly, the development for the cross-flow cylinder head for the later Cs could not be justified unless linked to an engine with a much longer production period in mind. The final design decisions were taken in early 1932 and by the London Motor Show that year the replacement was finally ready for public inspection. The J series cars were to replace the M, C and D types utilising one basic chassis design. Inevitably the chassis was another development from EX120/C type with the same ladder frame, cross tube bracing, underslung at the rear and utilising the sliding trunnions for supporting the springs. The engine also had similarities with the M type being four cylinder with two main bearings, the front bearing retaining its large diameter ball race. The cylinder head was quite different though, being the same as fitted to the later racing C types; cross flow with separate inlet and exhaust ports for each cylinder, of quite generous proportions. A plenum type inlet manifold was used for the two carburettors on the ‘off-side’ of the head and a well designed exhaust manifold was fitted on the ‘near-side’. No inlet ‘hot spot’, for economic running, was provided and valve timing retained the standard MG design, first seen on the C types. Engine power was now transmitted through a new four-speed gearbox of Wolseley design, which was much lighter than the old ENV box and topped with a neat, cast aluminium, remote gear change mechanism giving the unit a very sporty look. The two-seat car, designated J2, had simple and stylish bodywork with rear hinged, sharply cut-away doors, two scuttle humps housing an engine turned aluminium dashboard with plain instrumentation. At the rear, was a 12 gallon petrol tank, shaped to the back of the body but held down to the chassis by a simple inverted Y shaped spare wheel carrier. With its cycle wings, and absence of running boards, the J2 looked every bit a sports car and was an immediate success. The four-seat version, known as the J1, had the same body as the D type but with a much more powerful engine and four-speed gearbox, giving the car a completely different character.
The J4 was designated the race car of the series and had the same engine and ENV gearbox of the C type but fitted with a fully counterbalanced crankshaft, a front mounted supercharger and a door-less version of the J2 body. The J3 retained the standard two-seat body but had a supercharged 750cc engine, similar to the J4 but without a fully counterbalanced crankshaft. There appears to be a ‘J5’ on some of the design drawings that still exist, representing an un-supercharged version of the J4, but this car never went into production.
Unfortunately, like all new designs, the J was not without its problems. When the J2 was offered to the motoring press for testing, they were full of praise with its performance and while on speed test at Brooklands, managed to get the car officially timed at over 80 mph. This was a phenomenal performance for any standard production car at the time and for the speed to be achieved by a car with an unblown 847cc engine was almost unbelievable. Unfortunately, when the cars were delivered to customers, the 80 mph speed proved to be elusive and the test J2 got the reputation of having been specially prepared for the press. There is no doubt that a standard J2, with the windscreen down, can do 80 mph given a long enough, flat piece of road but the engine has to be set up accurately to specification and well balanced. An engine with inaccurate valve or ignition timing, even if only very slight out, will prevent the magic numbers appearing. Also, the J1 and J2 engines retained the same basic crankshaft as fitted to an M type, but now required to transmit nearly twice as much power as that unit and inevitably some of them broke. Clearly the two bearing crankshaft had come to the end of its development line and something much bigger and stronger was required but this had to wait until 1934. In spite of all this, the J series were very popular cars.
J type specification
Wheelbase
Track
Steering
Brakes – J1 & J2
Brakes – J3 & J4
Wheels
Tyres
Chassis weight
Weight of complete car:-
open two-seat
open four-seat
Salonette
J3 & J4 open two-seat |
7' 2" (2.18m)
3' 6" (1.06m)
Marles Weller
8" drums, cable operated
12" drums, cable operated
2.50" x 19" side laced wire, Rudge type
4.00" x 19"
10 cwt (508 kg)
12 cwt 84 lbs (647.7 kg)
[swept-wing cars 28 lbs heavier]
13 cwt 28 lbs (673 kg)
14 cwt 56 lbs (736.6 kg)
13 cwt 28 lbs (673 kg) |
Bore
Stroke
Stroke
Capacity
Capacity
Power output
Power output |
57mm
J1 & J2 - 83mm
J3 & J4 - 73mm
J1 & J2 - 847cc
J3 & J4 - 746cc
J1 & J2 - 36 bhp
J3 & J4 - approx 70bhp, depending on tune |
J1 27th July 1932
J2 27th July 1932
J3 3rd November 1932
J4 10th March 1933
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to 7th July 1933
to 10th January 1934
to 27th July 1933
to 28th July 1933
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| Cars produced: |
Total 2494 |
J1 open four-seat
J1 Salonette
J2 open two-seat
J3 open two-seat
J4 racing
Chassis only |
262
117
2061
22
9
23 |
J type pictures:
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