The A-Series may have been almost immortal by the early 1970s, but it did not stop the company developing alternatives. Here we describe the H and K-Series prototypes which were designed for the ill-fated ADO74 supermini.
Transmission-in-sump could have had a future
Any AROnline readers who have read the Metro development story might recall that, back in the mid-1970s, the decision was made to build a car around a developed version of the A-Series engine and transmission. This was instead of designing a new power unit.
Both the ill-fated BMC 9X and ADO74 had been destined to have an all-new engine. Eminent Engineer Roy Brocklehurst described how the company were, ‘tickled pink with its NVH performance’, once the upgrades had been made which turned it into the A-Plus.
A new decade, a new engine
However, what about the engine that had been passed over when the ADO74 was scrapped? Obviously, at the time of the Metro launch in 1980, the company’s Directors tended to describe the K-Series engine as not being a great enough step over the A-Series to justify the cost (and, in essence, they were correct to do so, as Bill Appleby and his team knew what they were doing when they designed the A-Series), but that is to undermine what Austin-Morris engineers achieved with the H and K-Series engines.
In 1972, when the ADO74 programme began, the engine which was then intended to be used was called the H-Series and that employed the transmission-in-sump layout. As the ADO74 was initially devised as a straight replacement for the Mini, the capacity was limited to a maximum of 1000cc.
Transmission-in-sump, like its predecessor
The integrated engine/gearbox was designed for ease of servicing, and access was achieved by removing the single sump – the clutch was also similarly easily accessible through its cover. In one fell swoop, this clever design overcame the criticism of the A, B and E-Series engines that they were difficult to service. This design also did not sacrifice the undeniable packaging advantage of the transmission-in-sump system.
Ray Battersby, who was one of the H and K-Series designers, said: ‘Harry Webster was the engineering dictator and control freak of all we did in the engineering block. His design strictures were designed to prevent any future boring and stroking of the cylinder block.
‘The very narrow cylinder bridge width would also cause much anguish by Coopers and Klingers, who were each tasked with producing a cylinder head gasket design able to withstand the heat, the fretting and general hostility in this bridge area without leaking between adjacent cylinders.’
So, what did the H-Series engine look like?
According to Battersby, ‘the first H-Series engine ran on schedule on the test bed in December 1971.’ It was a 1000cc ‘dedicated’ engine that had been laid-out by Harry Webster in a planning document, released on 24 September 1970. It was an extremely compact unit which featured Siamesed bores (just like the E-Series engine) and an OHC cylinder head with bucket tappets (see Battersby’s comments, above). The distributor was mounted directly on the end of the belt-driven camshaft and the water pump and alternator were driven from the crankshaft.
The oil-pump was also crankshaft mounted. A two-shaft transmission layout was designed, and this was driven by helical spur gearing. This was carried in a housing integral with the rear transverse face of the cylinder block. The clutch was of conventional design, and this had a separate cover.
According to Battersby, it was ready to go. ‘One engine, after running in, was subjected to a 400-hour Endurance Test, which started on 11 January 1972 and was completed on 11 February 1972,’ he said. ‘This gruelling test was the equivalent of running on the road for 26,000 miles with the engine running at full throttle and full load for over half of the time. The full test comprised of 69 cycles (each of 5:50 hours).’
Why was the H-Series dropped?
In total, four or five H-Series prototypes were built, and were run for between 200 and 800 hours on the test bed and 25,000 miles on the road in ADO16 mules. But the H evolved into the K-Series engine, when the ADO74 grew, and the limitations of the 1000cc upper limit became too much for the larger car.
In essence, the K-Series differed from the H in three areas: it had a larger engine capacity, the gearbox featured five ratios and more of it was inclined steeply to the rear to improve packaging.
The new two-shaft, five-speed gearbox was carried in a hefty housing, cast integrally with the rear face of the cylinder block (see diagram above) and, like its predecessor, the engine and gearbox were closed off underneath with a single pressed steel oil pan. As before, servicing was made relatively easy by this layout – since the gearbox internals and crankshaft could be released by the removal of simple half-bearing caps.
So, what did the K-Series engine look like?
The K-Series evolution was to have been the definitive ADO74 power unit, and was designed in two forms: the 900/1100 version, and later 1100/1300. This change in policy was down to Harry Webster deciding to hedge his bets about the new supermini’s engine range make-up. It was laid down in late 1972.
Like the H-Series, the 900/1100cc K-Series was canted back, but according to Battersby, ‘its cylinder bank was also canted back relative to the sump joint-face. Its doubly laid back cylinders allowed the unit to fit beneath the very low bonnet-line of ADO74.’
However, as Battersby put it, ‘something gave Harry Webster the jitters, because no sooner had we started designing the K-Series 900/1100 than he issued another edict, changing the capacity range yet again. This led to the birth of the K-Series 1100/1300cc project. Due to the continuing stipulation in Webster’s ‘Design Considerations’, neither the bore nor the stroke of the K-Series 1300cc engine could be increased.’
The H and K-Series prototypes are canned
The ADO74 project was then dropped and its engine died with it. The legacy of these engines was their inspiration within the design of the A-Series OHC and O-Series OHC engines, whose cylinder heads and valvegear bear the hallmarks of their ancestry.
According to Battersby, good progress was made on the H-Series before it grew up to become the K. ‘I believe that within this ‘family’ of engines (H-1000, K-900/1100, K-1100/1300), only the H-Series was ever built and only the H-Series was ever run on a testbed and fitted to a vehicle for road testing. I seem to recall that many of the K-1100/1300 parts were manufactured, but not assembled by the time the project was scrapped in 1974.’
Would the story of the Metro have been any different with this engine in place? Probably not, as the car was a success, and a long-lived one at that, with its A-Series engine.
Is the Editor of the Parkers website and price guide, formerly editor of Classic Car Weekly, and launch editor/creator of Modern Classics magazine. Has contributed to various motoring titles including Octane, Practical Classics, Evo, Honest John, CAR magazine, Autocar, Pistonheads, Diesel Car, Practical Performance Car, Performance French Car, Car Mechanics, Jaguar World Monthly, MG Enthusiast, Modern MINI, Practical Classics, Fifth Gear Website, Radio 4, and the the Motoring Independent...
Likes 'conditionally challenged' motors and taking them on unfeasible adventures all across Europe.