Engines : H and K-Series prototypes
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 engines that were designed for the ill-fated ADO74.
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, instead of designing a new power unit – both the 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.
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 – an extrememly compact unit, it featured Siamesed bores (just like the E-Series engine) and an ohc cylinder head with bucket tappets. 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, which 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.
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.
In total, four H-Series prototypes were built and were run for 200 hours on the test bed and 25,000 miles on the road.
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: the capacity was now 1300cc, the gearbox featured five ratios and the block 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.
Five prototypes were built and run on the road in ADO16 mules and completed 800 hours on the test bench, but the project was part of the ADO74, and so was shelved when the new supermini was canned in 1973. 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…