Keep Mediocrity at Bay
Throughout the 20th century, Britain produced many remarkable – in some cases world-changing – internal combustion piston engines. Unfortunately for the everyday motorist on the street, most of them were to be found in aircraft, ships, railway locomotives, motorcycles and even a few racing or luxury cars.
Even in the post-WW2 era, all-iron in-line engines were the staple offering for the British Big Six, side valves were still commonplace, and the RAC horsepower rating system cast a long (stroke) shadow over cylinder proportions even after Britain introduced a flat tax rate. Such engines were not particularly powerful, nor even efficient, but were trusted by the motor trade and buying public, and were forgiving of unsophisticated and imprecise casting, machining and assembly methods.
Into this cautious, conservative, yet somewhat confused land came Palmer’s flat-four, designed and developed in wartime.
The Javelin engine was not revolutionary in its design, but it was far more exotic and eclectic in its influences than anything found in comparable British cars. The aluminium block was formed in two parts, vertically split at the crankshaft centre line. Cast iron wet cylinder liners were used, with an open deck arrangement. The cylinder heads were symmetrical, a clever trick which mean that there was no need for different left and right heads. Aluminium alloy was tried for the heads of some early experimental engines, but cast iron was adopted for production.
The overheard valves are in an in-line configuration, operated through rockers by pushrods and a centrally mounted camshaft on the top side of the engine. Zero-lash hydraulic tappets were specified. Crossflow porting was used, with the exhaust manifolds on the underside of the engine. In all applications each cylinder bank was fed by its own Zenith downdraught carburettor in order to avoid long inlet tracts.
The ‘clean sheet’ design allowed ancillaries to be positioned for easy accessibility in the Javelin – and later Jupiter – engine compartment, and notwithstanding the engine’s complexity, it could be removed and replaced within an hour.
Before he departed from Jowett in July 1949, Gerald Palmer had sounded concerns about the company’s promotion of the Javelin through motor sport. The cars’ successes were the result of the rightness of Palmer’s design; advanced suspension and steering, a low centre of gravity, and a light, low-drag body. Nevertheless he agonised that the engine was still at an early stage of development, and was being stretched beyond the limitations set for its purpose of powering a “utility saloon”.
So were the parent’s anxieties justified? Racing and rallying Javelins and Jupiters were no more blighted by breakdowns and retirements than their peers, but engine failures in service were sufficient to warrant at least eighteen significant engineering improvements to the engine from the start to the end of series production. Crankshaft breakages and cylinder head gasket failures were the best-known issues. The head gasket issue usually resulted from wet-liner shrinkage or sinkage. A copper-asbestos-steel gasket and a re-specified bottom liner seal largely addressed the problem, with greater security provided by the stiffer mid 1952-onwards Series III cylinder block / crankcase castings.
As early as 1950, the hydraulic tappets were replaced with solid pushrods and conventional adjusters. Component supply problems and failures of the adjustment-free tappet mechanism as a result of lubricant contamination were stated as the reasons for the change. Armstrong-Siddeley adopted hydraulic tappets around the same time as Jowett, and reverted to the solid type with even greater haste.
A 1949 change to the hardening process for crankshafts seemed to address problems in early production, but following later failures, a more rigorous investigation by Keighley Laboratories, an external consultancy, identified weakness of the two piece cylinder block / crankcase castings as the primary cause of crankshaft failures. This problem had not manifested itself in development and early production as the first 2000 engine blocks were sand-cast, rather than gravity die-cast, and were stronger as a result.
The improvement process gained pace with the appointment of Donald Bastow as Chief Engineer in mid-1952, effectively eclipsing Charles Grandfield, who left Jowett the following year.
The mid-1952 on Series III engines had additional cast-in ribs in the block sections to increase strength, and broadened oilways. The Series III engine was at that time work in progress insofar as a gruelling testing programme was instigated as soon as the new block was put into production. 40,000 miles of intensive testing at the MIRA test track near Nuneaton on each of three Javelins was completed without any engine failures.
The improvement process continued with further refinement of liner to block sealing in 1953, and in 1954 the forged black-sided crankshaft was introduced with unmachined webs and a new post-forging processing method. Cylinder liner and seal design refinements continued, to address the problems with differential thermal expansion and liner sinkage relative to the block deck resulting from internal forces.
The Holy Grail of Jowett crankshafts was the drop-forged oval web produced by Laystall. This was developed by Dr. Ker Wilson, an engine specialist at De Havilland. His design incorporated refinements to the balance weights to counterbalance rotational oscillation and end-to-end movement.
To their great credit, Jowett’s management and engineers were unrelenting in their work to exorcise the alloy block flat four’s weaknesses and refine it into a reliable and durable engine with above-average durability and reliability. Regrettably the best engines arrived too late, with only the end-of-days Jupiters benefiting from the black-sided crankshaft.
The Jowett flat-four was Gerald Palmer’s only engine design to reach production. Much later in his life he expressed regrets that the pre-1947 taxation system had denied him the freedom to design the engine best suited to Jowett’s purposes:
“I’m not awfully proud of that engine. The unit was designed with the current car taxation in mind, which was based on the cylinder diameter. Had I known this was going to be replaced by a flat rate of tax, I would have designed a short-stroke large-bore engine, which would have been much more compact and lighter, with better combustion and a larger power output”.
Popular Classics – March 1990
The pre-1947 tax system was in essence a tax on cylinder bore, which resulted in engine designs with very undersquare cylinder proportions, and often contrived valve operation and combustion chamber designs which maximised valve area over all other considerations.
As an imperfect principle, long-stroke engines are good for hauling heavy loads from low speeds, as found in light commercial vehicles or overweight saloons. However their high piston speeds are problematic in sustained high-speed use. In pre-motorway Britain this was not a major concern, but in the export or die era, with sights firmly on nation-continents with long-distance highway systems, small capacity long-stroke engines struggled to operate calmly or reliably.
The Javelin’s engine was not absurdly undersquare, and had conventional in-line overhead valves, but the 72.5mm x 90mm proportions compromised future expansion.
The unit was just a little too tightly dimensioned. At a policy review meeting on 20 March 1950 Jowett’s management contemplated stretching Palmer’s engine longitudinally by around two inches to accommodate a 90mm x 90mm cylinder size which would have provided a 2.3 litre capacity, and even the possibility of a very oversquare 1.5 litre engine. I have also been advised that Jowett built an experimental engine with unchanged cylinder centres, and a 3.0″ (76.2mm) bore, giving a 1641cc capacity. Neither idea came anywhere near to production.
Much more recently, a Javelin engine was successfully bored out to accommodate 3.1″ (78.74mm) pistons in overbored standard liners giving a 1755cc capacity.
All talk of expandability is of little consequence. Palmer’s greatest failure was to recognise the limitations of the British engine production infrastructure, and the amount of development effort required to de-bug a “new-right-through” engine. To the credit of his successors at valiant little Jowett, the company rose to the challenge and addressed the problems one by one in a rigorous and methodical manner, and by 1954 had the makings of an outstandingly good engine.
Over the half-century which followed, the British automotive industry produced far too many troublesome engines, and also ruined some good ones. Some were produced in vast numbers, with complete denial of points of failure far more egregious than the Javelin engine’s.
We should regret that Jowett’s conscientious efforts never brought their just reward.
My thanks are due to JCC members John Cash and Geoff McAuley for their valued assistance in providing historical information, and the specialised knowledge of present-day Jowetteers.