Thursday, 6 October 2016

Jowett flat-four engines: Developments for sports cars and racing

In 1949 the Javelin engine was developed for completion motoring and class victories were obtained in events such as the Spa 24 hours race and the Rheineck-Walzenhausen Hill-Climb. The Spa Javelin produced approximately 57 BHP and was fitted with the oil cooler and copper-lead bearings etc. Flywheel weight was also halved from 28lb to 14lb. These Javelins also raced at Silverstone.
Class winning Javelin saloon at Spa in 1949

Jowett had also decided to put into production the two-seater sports Jupiter, the chassis of which was based on a tubular-frame design evolved by Leslie Johnson in association with the German engineer Eberan von Eberhorst.

The Javelin engine was required to be developed to give 60 BHP at 4750rpm for use in the new car. The compression ratio raised from 7.25:1 to 8:1 by reducing the volume of the combustion chamber and by changing the shape of the piston crown. Javelin port sizes, bearings and camshaft were used unaltered, but heads and ports were polished. A Delaney Gallay oil cooler was fitted, initially located behind the fan. Later a Bowman block cooler was mounted on the front of the off-side cylinder block. Instead of 23mm carburettors, 26mm Zenith 30 VIG carburettors were used. Later these were replaced by the easier-to-tune Zenith 30VM units. The oil sump capacity stayed at 9 pints. As there was more room under the car, the off-side exhaust pipe joined the main pipe at the rear of the near-side manifold and not in the manifold as on the Javelin. The shape of the Jupiter body called for air-extractor louvers which were not used on the Javelin and when overheating was experienced in Continental driving and Alpine work, the radiator was increased in size. Louvers were also added in the bonnet top. Intake noise was less of a concern with the Jupiter, so no air silencers were used for the carburettors and eventually the Vokes air filters were replaced by AC units.

Jowett issued “Competition Tuning notes” to Javelin who sought an increase in performance. Port-polishing and relieving was covered and stronger outer valve springs were recommended. Special pistons were declared available that increasing the compression ratio from 7.2:1 to 7.6 and 8.0:1, a reduction in combustion chamber volume of 2cc and further 3 cc respectively. The standard Zenith VM4 and 5 carburettors could be replaced by 30 VM Zeniths and it was assumed the hardened crankshaft, copper-lead bearings, larger water and oil pumps, later oil filter assembly and oil cooler would be employed.

Subsequently similar tuning of the Jupiter was permitted with a compression ratio increase from 8.0:1 to 8.5:1 for 80-octane fuels, this being attained by the use of thinner gaskets. Stronger inner valve springs were recommended and the flywheel could be lightened. It was assumed that correct fitting and assembly would be ensured and that modified h.t. cylinder-head studs, Lucas DVX4A distributor and Champion L 11S or LA11 spark plugs would be fitted.

Then next step was to prepare the Jupiter for racing. For Le Mans in 1950 a compression ratio of 8.5:1 was employed by using the thinner head gasket and with the stronger inner valve springs, high-duty ignition distributor and lightened flywheel, the output was 64 BHP. To obviate gasket trouble the strength of the cylinder-head studs was increased from 45 to 60-65 tons tensile, but the number and position of the studs were unchanged. The spark plugs were up from L 11S to LA11. The car was a great success; winning the 1500cc class at 75.84 mph.

For 1951 the porting and valve timing were improved and after further experimenting with compression ratios of 8:1, 8.5:1, 9:1 and 9.25:1, the latter ratio was employed. Just over 100 mph was obtained from the R1 Jupiter, but after six hours at Le Mans the C.A. gasket collapsed. A composite copper, asbestos and steel gasket was found satisfactory, after experiments with solid copper, laminated aluminium and corrugated cupro-nickel gaskets etc. This gasket went on to be used on all production engines but, eventually, for racing, a gas-filled metallic sealing ring at 600 lb/ pressure in a circumferential recess on the liner top flange stood up to the highest compression ratios. A Plexseal gasket was used as a water joint. The gasket failures were finally traced to sinking of the cylinder liners and this was cured be redesigning the liner bottom seal; a rubber ring trapped between the liner bottom flange and the crankcase permitting metal-to-metal contact between liner and crankcase, obviating liner sinking and enabling the initial liner interface on the gasket to be maintained.
R1 Jowett Jupiter competition version of the Jupiter sports car in 1951 guise

The 1.5 litre class was won again at Le Mans in 1952. A 9.25:1 compression ratio was utilised with flat-top pistons. The serrated-face big-ends were used and the top piston-ring lands were increased from 3/32 to 1/8in. To reduce the tendency of piston-ring flutter and increased oil fling, pressure loading of the scraper ring was increased to 70 lb/ 2 BHP was gained by using solid-skirt pistons due to lower friction. Trailing oilway drillings were used on the crankpins to feed oil at a point of minimum pressure.

The pistons were now solid-skirted and of die-cast silicon alloy, with the top gas ring chromium plated. Stronger valve springs allowed the engine to rev to 5500 rpm. KE965 (EN 54) exhaust valves combated a neck temperature of 700-800 degC which had caused an XB valve to break during the Silverstone Production Car race. The stems were chromium plated, 0.001 in extra clearance given in the guides, and the valve tip at the rocker end was stellited. With 0.5 ml per litre of lead in the fuel, valve life was approximately 200 hours at 4500-5000rpm.

An external carburettor balance pipe with an internal diameter of 5/8in was now required. Lodge spark plugs in waterproof covers were also used. The crankcase was stiffened by ribs radiating from the main bearing regions and the walls were also stiffened. The Marston Excelsior oil cooler, radiator and reserve fuel tank were fabricated in aluminium, with a weight saving of 45lbs. An axle ratio of 4:1 was employed instead of the former 4.56:1. The engine now had a fuel consumption of 0.51 to 0.57 pint/BHP/hour, equal to a race fuel consumption of 18 mpg. All this resulted in a third consecutive 1.5 litre class win at Le Mans.  

The standard crankshaft broke on test after only 50 hours on a dynamometer running at 4200rpm with compression ratios above 8:1. A crankshaft failed which had run approximately 200 hours during the 1950 TT race when an 8.75:1 compression ratio was used. These failures led to a mathematical investigation into crankshaft dynamics and the most probable cause of the crankweb bending fatigue was thought to be axial and torsional vibrations of the crankshaft in conjunction with the presence of an adverse residual stress in the crankpin fillet adjacent to the fracture. This residual stress was due to induction hardening of the bearing surfaces especially if followed by a cold straightening operation allied with stress rises in the form of sharp fillet radii abd tool marks on the webs. A new crankshaft was developed incorporating fillet radii on all bearings of not less than 0.1in. The crankpins were also drilled in order to reduce the off-centre weight and the magnitude of the bending loads. Great care was also required when induction hardening the crankpins to ensure that the hard zones did not extend into the webs. Experiments showed that shot peening the fillets could increase the fatigue resistance considerably.

A polar load diagram was drawn up for the big-end bearings for running above 4750rpm. Sufficiently high inertia loadings were discovered to warrant drilling the racing crankshaft with oilways at 60 degrees trailing on each crankpin. The oil temperature under racing conditions was held to a maximum of 75degC.
R1 Jupiter in which won its class in 1952 at Le Mans

Besides the 1.5 litre class victories at Le Mans, further wins were obtained at Watkins Glenn and in the 1951 1.5 litre class of the TT race.

The Jowett Javelin and Jupiter engines really were race developed, as almost all the modifications found through racing were incorporated into the mark 3 engines:

  • Crankshaft - The crankshaft was redesigned to increase its fatigue strength. Modifications included increasing crankpin and main bearing fillet from 0.05in to 0.1in. The hardening methodology was also altered to ensure hardness did not run into the crank webs. The crank-pins weight was reduced by drilling them with a 7/8in hole through them; the object to reduce the bending load on the shaft
  • Oilways – The oilways in both the crankshaft and crankcase were modified; in the the case of the crankshaft these were repositioned so that they emerge on the crankpins at the point of minimum load. In the case of the crankcase the oilways have were increased in size to prevent the potential of restriction, especially under cold starting conditions.
  • Bearings – These, with the exception of the rear main bearing, were of Vandervell manufacture and of tri-metal construction which consist of a steel backing strip onto which is cast a layer of copper-lead alloy; this layer of copper-lead is plated with an 0.003in thick coating of lead indium alloy which acts as a bearing medium
  • Crankcase –This was stiffened by the addition of radial webs on the front, centre and rear panels. This also helps to minimise noise.
  • Cylinder heads – The combustion chambers and ports are polished and the ports are aligned with the manifold ports. This was done to improve the gas flow characteristics.
  • Camshaft – An adjustable end location was provided so that individual adjustment can be carried out to reduce noise from excessive end float.
  • Cylinder liner bottom seal – This was redesigned to consist of an oil and heat resisting rubber ring trapped between the liner bottom flange and the crankcase. There is thus metal-to-metal contact between the liner bottom flange and the crankcase, which obviates any tendency to liner shrinkage due to collapse of the bottom joint. This ensured that the initial liner interference on the gasket is maintained and results in greater gasket reliability
  •   Oil pump –This is of a submerged design which ensures instant priming under all starting conditions, and the relief was by-passed to the suction side of the pump to reduce oil churning and frothing in the sump.
  • Pistons – The size of the piston ring top land was increased to improve fatigue resistance.
  • Spark plug covers – The original design of Bakelite covers with a bayonet fixing was replaced by a rubber design from Lodge.

Thursday, 1 September 2016

Jowett flat-four engines: Early development

During early prototype testing of the Javelin it became apparent that the engine was mechanically noisy in a harsh resonating manner. This was deemed to be a major problem given that the Javelin was to be a luxury small family car and as such a remedy was required. Two types of crankcase had been manufactured, one in cast-iron, the other in aluminium. Experimental testing on these early designs made it clear that there was considerable whirl of the crankshaft and a certain amount of flexing on the crankcase was evident from edge marking on the bearings.

The next stage of development was to manufacture a cast-iron crankcase and a three bearing crankshaft, the bearing-cap joint faces now being horizontal, so the crankshaft could be dropped out of the bottom of the engine. The first engine tested of this type was a 1200cc unit, but when experiments were carried out with larger diameter liners, increasing the capacity to 1500cc, considerable crankcase ‘thump’ was experienced. To overcome this for testing purposes a boiler plate was bolted across the bottom of the bearing-caps, however this only highlighted the inherent weakness of this crankcase design. Subsequent development led to the adoption of light-alloy crankcases split vertically, which permitted the use of tie-bolts, making the whole assembly much stiffer.
Alloy crankcase of the production Jowett flat-four

Jowett had noted that cast-iron crankcases resulted in a quieter engine, but it was decided that the alloy crankcase should be proceeded with as it had been designed for die-casting. The cast-iron version was approximately 10% quieter than the alloy one, but was naturally heavier. In view of this and the difficulty at that time of obtaining iron castings, the spilt alloy crankcase was decided upon. It was also at this stage that the 1200cc project was dropped, as there was a large performance difference between it and the 1500cc engine.

When the revised engine was power tested, a considerable drop in performance was seen above 4250rpm. This was attributed to inadequate breathing and poor turbulence in the stepped head. The valve lift was increased from 0.275in to 0.315in and the ports ‘cleaned up’. Weslake was called in to inspect the combustion chamber and he evolved a semi-pancake head with 14mm plugs easier to produce and increasing top-end power by 15%, while providing smoother running. The exhaust system was changed from streamlined exhaust ports brought out to the bottom face of the head, to a manifold bolted to the underside of the head, the off-side manifold feeding into a pipe running round the front of the engine to enter the near-side manifold and take benefit thereby of extractor action. The main exhaust pipe led from the back of the near-side manifold. It had 1 3/8in inside diameter and the power drop with silencers was only 3 BHP compared with an open pipe. This new exhaust arrangement gave a power increase of 1.5% and resulted in the cylinder heads no longer being handed, a production and servicing advantage.

Jowett engine sectioned

Snatchy running below 20mph lead to an increase of flywheel diameter to the limits of the bell-housing. Another alteration required following testing, was to change the main bearing clearance due to rapid crankcase expansion. A steel housing giving 0.0003in to 0.0018in clearance at assembly temperature was adopted.

The Javelin emerged as the first really new British post-war car. It was a comfortable, brisk 5/6 seater saloon giving 75/80 mph and 28/32 mpg with advanced aspects such as the flat four engine, torsion-bar suspension and wind-defeating body form

The prototype engines, developing 40-45 BHP had been satisfactory in respect of bearings, but long-distance driving on the Continent with the early production versions showed up a tendency to run big-end and main bearings.

With the previously mentioned improved breathing 50-52 BHP was developed at 4500rpm, and it was decided that white-metal bearings must be replaced by copper-lead bearings, if possible in conjunction with the existing EN 12 steel crankshaft. The flat-four layout led to higher oil temperatures than are experienced in in-line designs, which contributed to the bearing failures.

Initially sintered copper-lead bearings with a white metal flash of 0.00125in were utilised with the un-hardened steel crankshaft. These bearings showed no signs of fatigue, but were extremely sensitive to dirt and scuffing on the crankshaft. A hardened crankshaft was therefore adopted with special care being paid to assembly and running-in. It was also found that the stepped location on the big-end led to distortion on tightening, so a new con-rod was devised, the big-end having an offset serrated face and clamp bolts increased to 0.375in and 400lb/in tightening torque. A dirt trap hole of 1/16in diameter had a negligible effect on oil pressure and consumption. The crankshaft was induction hardened on the journals and pins to a hardness of 512-530 Brinell, and the bearing surfaces were lapped to a finish of 8-12 micro-inches against the former 12-24 micro-inches. A softer bearing material of 30% lead, 1.2% tin and 68.8% copper with a 0.00025 in plated white-metal layer for running-in was used with the new rods and crankshaft and the bearings now stood up to 50 BHP and 4750 rpm in spite of the higher oil temperatures and compact bearings of the flat-four layout.

The lubrication system was thoroughly tested in the initial stages of development, an engine being rigged for measurement of oil spillage from bearings, relief valve, ancillary services etc. As a result, the feed to the main bearings was increased and the size of the oilways increased to 7/16in diameter to obviate a possible danger of bearing starvation under cold-start conditions with the full-flow filter system adopted to ensure clean oil for the hydraulic tappets. The pressure relief valve exhausted beneath the sump oil level to avoid aeration and later the discharge was by-passed to the pump suction side, within the cover.

Initially the three-bearing crankshaft engine suffered with oil swirl due to air transferring from one side of the crankcase to the other. To prevent this, a surface baffle was fitted which allowed the free passage of air only. Originally the oil pump had been mounted on a bearing cap, but the vertically split cases obviated this location, so it was moved to the timing-case wall and driven by spiral gears from the crankshaft. The distributor was also repositioned to allow it to be mounted vertically and use a common drive-shaft as the oil pump from the spiral bevel gear on the crankshaft. The oil pump capacity was also increased which meant oil pressure rose from 50lb/ to 65lb/ Following use on Jowett’s competition cars, an oil-cooler built to Jowett’s specification was incorporated on production engines in 1952. Initially this was placed rewards for accessibility, but later was moved to a location between the fan and radiator. With the oil-cooler in circuit, pressure pulsations occurred at audible frequencies until the previously mentioned dirt-trap holes in the big-end caps were deleted.

In vehicle testing it was shown that louvers in the bonnet became ineffective in terms of extracting air from behind the radiator above 50mph. Pressure areas were checked and it was found possible to take air from behind the radiator via apertures in the front wheel arches.

An issue with early production engines was noisy valve gear, even with the zero lash hydraulic tappets. Improved manufacturing tolerances were introduced, but the noise was still deemed unacceptable. Jowett then went on to investigate the effect of valve opening/closing ramp sizes and also velocity profiles. After much experimentation Jowett settled on cams with a 0.008in opening ramp and 0.020in closing ramp (from the fierce initial 0.002in and 0.006in ramps on the inlet and exhaust respectively). Unfortunately hydraulic tappets became unobtainable during 1950 and the noise level rose somewhat with the enforced use of conventional tappets.

Experiments were made with the material for camshafts and tappets. Excellent results were found with a high duty 1% chromium cast iron camshaft with a tip hardness of 40-45 Rockwell C and chilled iron tappets of a similar hardness and a finish of 7-10 micro inches. A phosphate process on cam and tappet faces to retain oil during running-in was found to be beneficial, but not necessary.

Five different types of liner/piston combinations were used in the course of development. Vacrit high-duty manganese chromium iron liners with a 280-270 Brinell surface hardness were originally used, in conjunction with split-skirt pistons in LO-EX or LM13 alloys withtwo D/26 radial thickness pressure rings and a slotted oil-control ring.

A taper-faced Vacrome chromium-plated top piston ring was adopted to cut oil consumption, without complete success. Liner distortion was suspected and investigation showed that whilst 0.008-0.010in gasket nip at 38/40 lb/ft cylinder head tightening torque was satisfactory to retain gas and water seals, this was highly critical; any degree of higher torque loading or excessive nip caused local liner collapse and consequently distortion. To counteract this, the liner section was stiffened and an internally-stepped second ring fitted to facilitate quick bedding-in of the chromium-plated piston ring. Following this a Javelin ran 80,000 miles in the course of testing by Avon India Rubber Co. Ltd., gave an average of 3,700 mpg of oil at 37.39 mph average speed, and maximum bore wear averaged 0.002in, equal to 40,000 miles per thou.

Due to the Javelin’s unusual firing order of 1-3-2-4 carburation was paid special attention. Cylinder 1 and 3 are fed from one carburettor via siamesed ports, and 2 and 4 from the other carburettor. To prevent a weak mixture in the front two cylinders of each bank caused by inlet tract surge, a 0.55in diameter balance pipe was added between the two carburettors. Intake noise was a problem on the Javelin and Jowett went on to test many different types of air filter and silencer, but no satisfactory solution was found. Instead Jowett evolved their own baffle box which was located in the alligator-bonnet, tuned to length to suit the induction system, and connected to a resonance chamber which was coupled to the air intakes by vertical pipes having squash rubber connections which broke as the bonnet was lifted. A non-spill oil-bath air filter was incorporated.

In addition to the early bearing failures and excessive oil consumption, gasket blowing was an issue on some Javelins. It was subsequently found that this was due to a too small an asbestos content at the fold of the gasket, however it was only with the increased output for competition purposes that this cause was identified.

Sunday, 7 August 2016

A product from Yorkshire: The Jowett Javelin and Jupiter flat-four engines

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

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.

Wednesday, 20 July 2016

Paul Dunstall: Genuine Domiracer Equipment

In 1958 Paul Dunstall went somewhat against the grain and started to race a Norton Dominator motorcycle. This was quite unusual at the time, as generally they were not considered to be a machine fit for this purpose and Norton already produced a very able racing motorcycle in shape of the Manx. Through his racing exploits Paul developed the Norton Twin with considerable success and following his retirement in 1960, was able to offer a range of special and tuning equipment for the various models. In 1961 he became an official Norton dealer.
In 1963 Dunstall purchased the works Norton Domiracer that had been ridden by Tom Phillis to 3rd place in the 1961 Senior TT. He also purchased all remaining spares and stock relating to Doug Hele’s experimental  lowboy project.

Tom Phillis 1961 Senior TT

This is a short blog on his catalogue from the early 1960’s listing the parts available for these models.

Dunstall provided race bikes for many riders over the years, the following are listed in his catalogue:-
Chris Conn
Dave Degens
Dave Downer
Joe Dunphy
Dereck Minter
Sid Mizen
Fred Neville
Tom Phillips
Colin Seeley

He continued to develop the Norton Twin throughout the 1960’s and in 1969 started the season with a radically different spine-framed machine designed by Eddie Robinson. This frame was manufactured for Dunstall by Jim Lee at his Birstall premises in Yorkshire and was considerably lower and lighter than the previous lowboy design. Jim went on to produce some very successful spine-framed machines of his own, the most successful being the TR2B Yamaha raced by Mick Grant.

Dunstall Drainpipe

And so to the catalogue.

By 1966 Dunstall was building complete machines, based on the Norton, BSA and Triumph twin cylinder models available at the time. As well as offering various light-alloy and tuning modifications, options included seats, tanks and fairings, all of which gave the machine a distinct Dunstall look. In 1970 he became a Honda dealer and parts were included in his later catalogues for these machines. He also put his name to a 3 cylinder Kawasaki racing motorcycle designed and built by Alan Baker. Again the frame and tanks of this machine were built by Jim Lee in Yorkshire and it used a double disc front brake designed by Eddie Robinson which had previously been used on the ‘drainpipe’ Norton bike.

Dunstall continued to sell customising parts for Honda, Kawasaki, Suzuki and BMW machines until he sold the company name in 1982.