Yorkshire may not be renowned for automotive engineering,
but in its West Riding on the outskirts of Bradford there was a hive of such
activity. This article focuses on the Jowett car company who ended up with
their factory at Idle just north of Bradford.
The Jowett name goes back to 1901 when Benjamin and William
Jowett along with Arthur Lamb set up a cycle business that went on to
manufacture V-twin engines for driving machinery. I do not intend to describe
the whole Jowett history, but instead will focus the developments of their most
famous engine; the flat-four fitted to the Javelin and Jupiter cars.
Following the Second World War, many vehicle manufacturers
were conservative design-wise as they re-started production for civilian
products. This was not the case with Jowett. Their Javelin saloon introduced in
1945 was inspired to some degree by the popularity in England of the Lancia
Aprilia. Gerald Palmer had joined Jowett as Chief Engineer during the War at
the mere age of 30. The Javelin was his first vehicle. This advanced car
utilised a flat-four cylinder engine which offered many benefits such as:
- Compact engine allowed spacious seating (up to 6) within a given wheelbase
- Notably vibration free
- Low centre of gravity
- Excellent visibility due to the low engine height
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| Jowett flat-four |
The new engine had overhead valves and was initially
available in two forms, a 1200cc unit of 69.5 by 78mm bore and stroke, and a
1500cc version of 72.5 by 90mm bore and stroke. The smaller unit was intended
for the home market, whilst the bigger engine was destined for export. Both
engines had a compression ratio of 7.25:1. Subsequently there was a change in
Jowett policy which caused Palmer to concentrate on the larger 1500cc engine.
In its early form the engine had a two-bearing crankshaft
running in white-metal bushes carried on the crankcase, a circular spigotted
cover at one end eliminated the need for a split crankcase. The crankcase was
cast in aluminium alloy to D.T.D. 424 specification. And wet cylinder liners
sat on a joint washer at the base and were clamped down by the detachable
cylinder heads.
Cast iron cylinder heads were utilised which incorporated a
vertical inlet port leading to siamesed valve ports which allowed the use of
one carburettor per pair of cylinders. The exhaust ports were at the bottom of
the cylinder head, with the exhaust gas being taken away by an integral
manifold under each head. A metal duct directed cooling water to each valve
seat. The combustion chamber was a stepped type; the inlet platform providing a
squish area to promote charge turbulence over the exhaust valves, from which
side the mixture was ignited.
The valves were push-rod actuated with hydraulic tappets
also being incorporated into the mechanism to account for thermal expansion of
the aluminium crankcases. These tappets were lubricated from one of the main
oil galleries, with lubricant filtered by the full flow method.
The new engines, in both sizes, were extensively tested both
on the bench and roads. The prototypes had 10mm spark plugs, but subsequently
14mm plugs were used. The 1496cc version produced 40 BHP, but this was soon
increased to 50 BHP due to improved engine breathing.
To be continued.
To be continued.