Four Cylinder 2 Litre XK Engine – 1948
On display in the Collections Centre at Gaydon we have one of only 4 remaining, four-cylinder XJ/XK engines that were built during the development of the XK engine. It has the same overall configuration as the six-cylinder XK engine: chain driven twin overhead camshafts; two valves per cylinder; hemispherical combustion chambers and twin SU carburettors.
During the 1930s William Lyons had developed the Swallow Coachbuilding Company to become a mainstream motorcar manufacturer. From the Standard Motor Company came purpose-built chassis and engines for the range of SS and SS Jaguar models. World War Two put a stop to private vehicle production in Britain and all manufacturers turned to war work. SS Cars was no exception and they repaired aircraft as well as supplying various sidecars and trailers to the armed forces. Lyons started planning a 100 mph saloon that would be available post-war which would need a new, more powerful engine. One that would set a new standard in power plants and he also understood the importance of it looking attractive.
Lyons was fortunate to have three very talented engineers working for him: William Heynes, Walter Hassan and Claude Baily. They spent the hours during fire-watching duties discussing the requirements and planning a series of engines. In the pre-war years the small four-cylinder 1½ litre saloon sold in larger numbers than the six-cylinder 2½ litre and 3½ litre models. Lyons foresaw a period of austerity after the war when there would be a greater demand for a smaller engine. Consequently, both four and six cylinder versions were envisaged.
Two four-cylinder engines were developed side-by-side, coded XF and XG. The latter appears to have been bench run first in 1943 and was a four-cylinder unit with a bore and stroke of 76 x 106 mm giving 1,776 cc. Heynes wrote that it was ‘really a conversion of the existing Jaguar four cylinder push rod engine; the head and valve gear, and also the inlet ports were based on the BMW 328 cylinder head. In the Jaguar design the push-rods and the rockers were found to be difficult to silence to the standard necessary for a touring saloon engine.’ The XG consisted of a newly-designed aluminium alloy cylinder head with hemispherical combustion chambers mated to the Standard 1½ litre block, which had been stretched from 1,608 cc (69 x 106 mm) to 1,776 cc for the 1938 model range. All the valves of the XG were operated from the existing single camshaft, tappets and modified pushrods, up to rockers situated in the near-side rocker box. Hassan described the inlet ports as being ‘almost vertical, formed in pairs and connected by a large balanced passage and fed by two 1½ inch bore SU carburettors.’
The XF twin-cam engine was first run on 27 November 1944 and as Heynes later wrote: ‘This engine was the first example of a double overhead cam (DOHC) engine made. It was designed primarily to prove the type of head and valve gear, which it did very adequately. We found the crankshaft design was inadequate for the very high speed at which the engine would otherwise operate. Nevertheless, the engine fulfilled its function and gave a lot of sound practical data’. The XF was run on ‘Pool’ petrol – a mix of various brands, blends and octane ratings mixed or ‘pooled’ for use in the rationed private sector. Running at 2,000 rpm it gave 23.3 bhp and 56.3 bhp at 5,000 rpm on twin SU carburettors, but no fan or gearbox was attached. This engine was not without its problems as Hassan reports: ‘After a few minutes, oil was trapped under the valve tappets causing a loud hammering noise. The valve gear was taken down and 3/16” was removed from the bottom of the tappets so that the breather ports in the tappet guides were uncovered at full valve lift.’ Some damage to the camshaft and cam followers was noted and repaired in time for trials to continue. However, it failed on 8 December, when ‘The flywheel securing bolts sheared before the test could be completed and the engine was removed to the experimental shop for strip and examination.’
When the XF engine was rebuilt and returned to the test bench it was rated at 1,732 cc. Tests had established that the DOHC arrangement of the XF was the best. Both XF and XG were side-lined in favour of another four-cylinder engine design with a bore and stroke of 80 x 98mm and 1,996 cc. Given the code XJ, this is generally regarded as the real forerunner to the XK engine. Most of the experiments with port and head design were carried out on the XJ, as were trials with valve gear and camshaft drives, resulting in its final configuration of: a pair of chain driven, overhead cams, two valves per cylinder and hemi-spherical combustion chambers.
The first XK engine was not run until October 1945. This was ‘XK Engine No. 1’ – a four-cylinder unit with a three-bearing crankshaft, a bore and stroke of 76 x 98 mm and a capacity of 1,790 cc. The engine was still a small capacity unit similar to the XF, XG and even the pre-war Standard-SS Jaguar units.
However, at this stage, even though Heynes mentions a six-cylinder version, tests appear to have been carried out on the four-cylinder XK which gave 76 bhp during early trials and later 83 bhp.
Heynes wrote that the XJ was changed so many times that no accurate drawing could be produced to represent the engine at any stage when it was in a settled state.
The design was quickly moved on through to a six-cylinder version with a bore and stroke of 83 x 106 mm with a capacity of 3,182 cc and then on to the production XK engine.
A six cylinder XK was run for the first time on 15 September 1947 recording a power output of 142 bhp at 5,000 rpm. It was apparent that the six-cylinder layout was a much better and much smoother configuration than the four cylinder. Jaguar did not have the resources to develop both engines and work concentrated on the six-cylinder.
One of the four-cylinder XJ engines (80 x 98 mm 1,996 cc) was fitted with modified pistons giving a 12:1 compression ratio and this was loaned to Major A.T.G. Goldie Gardner for use in his MG Special. Gardner drove this to over 176 mph (109 km/hr) at Jabbeke, near Ostend, in Belgium to set a new speed record in the 2-litre class. He broke the flying mile, kilometre and five-kilometre Class E records. At the time it was considered remarkable that his engine was unsupercharged. The new records were: mile 173.678 mph, kilometre 177.112 mph and five kilometres 170.523 mph.
Gardner’s record breaking run was in September 1948 – just before Jaguar announced the XK120 Super Sports with the six-cylinder XK engine at the Earls Court Motor Show.
The brochure for the XK did offer an XK100 version of the car fitted with the 4 cylinder engine, but none were ever made.
Gardner’s MG Special is now on display in the ‘Record Breakers’ section of the British Motor Museum but fitted with an MG engine.