Engines : O-Series
The O-Series was designed to act as the company’s mid-range engine mainstay for the late 1970s and beyond.
If at first you don’t succeed…
The formation of Austin-Morris from the ashes of BMC in 1969 allowed BLMC’s product planners to focus on the demands of the middle market, without worrying too much about the more specialised demands of Rover-Triumph. One thing was clear – lots of new car development may have taken place under the old regime, but none of it was very close to seeing the light of day following the Leyland takeover. Designing new cars was one thing, but what about engines? After all, the A- and B-Series engines were both well over ten years old, by this time and yet, were proving difficult to replace.
In the case of the B-Series, it was not as if it were a bad engine; in fact, in twin carburettor form it proved more than adequate of propelling the Morris Marina and MGB with some degree of verve. The B-Series engine’s troubles lay its inability to pass the upcoming US emission laws, proposed for 1975, and given that the MGB was sold in such huge numbers over there, it was essential for BLMC to develop a “clean” engine.
It was in 1971, that the need was formalised, and a project to develop a B-Series replacement was instigated. At the time, it was Geoffrey Johnson’s responsibility, as Chief Design and Development Engineer, to oversee this plan. Reporting directly to Harry Webster, Johnson (who himself was probably still in some way finding his way around the Longbridge “system” as a new recruit to the company) wrote to his boss, laying out what the best plan of attack would be. He stated that an OHC version of the B-Series, sporting an aluminium cylinder head and displacing 2-litres would deliver more than enough power and torque to outgun the B-Series, even in “anti-smog” guise.
Engine development was carried out on an earlier 2-litre B-Series prototype, produced by BMC engine-man Stan Johnson. This engine dated back to 1964-65, but was not considered a clever enough update of the original B-Series engine to warrant serious consideration. This particular unit displaced 1998cc and featured siamesed cylinder bores and off-set conrods in order to use the existing 1.2-/1.5-litre cylinder block.
According to Lyndsay Porter’s AUTOCAR O-Series article, it was in the summer of 1972, that this plan was dealt something of a shattering blow.
“In the summer of 1972 a bombshell report landed on Webster’s desk. The B-OHC engine had been developed to the point where the block had been revised to take advantage of the absence of pushrods, although the camshaft was retained as a jackshaft to drive the distributor and oil pump. The problem was that the engine could not be built!”
Essentially, B-Series tooling was past its prime. Porter again: “The plattens which guided the cutting tools into position had been re-drilled so many times that they were like ‘paper doyleys’ in the words of one Longbridge engineer. ‘If it hadn’t been for the good grace of the blokes on the shopfloor, who would pack the machines into line daily using shims or even bits of cigarette paper, the whole thing would have been packed up years before,’ another engineer has told me.
So that was it – BLMC’s ambitions for the Austin Marina allied with continuing MGB success in the USA meant that increased output was required – and that would require an entirely new facility in order to meet demand.
However, this set-back did not completely arrest B-OHC’s development, even though it should have. Throughout 1972, work continued, and projected (gross) power figures were reported back to management: 112-115bhp for B-OHC, compared with 106bhp for the 2-litre B-OHV and 96bhp for the existing standard MGB unit. By September 1972, the design for the prototype engines was pretty much finalised, and although anticipated production volumes were still fluctuating, it was still to be produced in serious numbers, given that it was planned to be used in the MGB, Marina (ADO73 facelift version) and the ADO71. As can be seen from this list of cars, B-OHC would need to be capable of being used in in-line as well as transverse installations – as well as being compatible with the ADO71’s T-I-S gearbox, as well as the Marina/MGB’s end-on unit.
Because of the tremendous need to get the new engine into production at the earliest opportunity, Geoffrey Johnson was required to order new tooling for the engine’s production line, even though it was yet to be formally signed off! This led to all sorts of problems with the final development phase of the engine – after all, it severely compromised the design process… Porter’s article relates that Geoffrey Johnson really was hamstrung: (We needed to put a breather modification in place), “…but it couldn’t be done because there was already a particularly crucial piece of transfer line machinery where we wanted to put it. Getting round that problem was the biggest difficulty we had with the whole engine.”
By the autumn of 1972, the O-Series name was formally applied to the B-OHC, and it marked the point in time when the final link with the original engine was removed (…”the deletion of the “camshaft”/jackshaft so that the whole B-Series tappet chest could be pared away”). The B-Series’ design had acted as a starting point, but no parts were shared – and this is demonstrated by the cylinder block’s light weight (due to the walls being thinned), meaning that the strength of block could be braced in to the exact tolerance required. This weight management would underpin the O-Series’ transformation into the M-Series during the 1980s.
However, it was not all sweetness and light. Although the engine casting could now be considered an all-new unit, Harry Webster decreed that the B-Series powered Marina’s cast crankshaft could be used in the O-Series, in order to amortise that item’s costs to the company…
The closing months of 1972: It was stated that it was critical to get the O-Series in production by April 1974, so that the US-Spec Marina and MGBs would be ready for the tighter emmissions imposed for the 1975 model year. This plan was changed when it was decided that the MGB would be killed-off in favour of the TR7 – although the O-Series would still be a requirement for US Marinas. Shortly after this, the MGB was given a reprieve…
February 1973: Marketing decided that the MGB would be replaced by the TR7, but it would remain in production as an insurance against the late introduction of the new Triumph.
May 1973: The decision was taken to use the O-Series in the MGB after all – and that it was possible to sell 1000 ‘Bs per week.
Summer 1974: The O-Series was proclaimed as an essential addition to the MGB for the 1977 model year… until the following month, when this was put back until 1978.
Mid-1975: North American Austin Marina cancelled…
If this list looks bad, remember that the company was going through a degree of turmoil at the time, as model plans were revised, or cancelled at an alarming rate. Throughout this period, two things were constant – the MGB’s O-Series conversion had become a running issue within the company, especially when viewed alongside long-term TR7 plans. The second factor was that the O-Series would be used in the front wheel drive Princess and the rear wheel drive Marina. The only question was – when.
O-Series finally launched
The first production car to use the O-Series arrived in 1978 – and that was the Marina. Sadly, Harry Webster’s preferred plan of offering the O-Series in 1.6- and 2-litre form was scuppered by the cost advantages of using 2-litre version’s head casting on the smaller unit, raising the capacity to the unusual size of 1.7-litres. Advantages over the B-Series unit were a lower all-up weight, but in terms of refinement and performance, the motoring press found little to get excited about.
Shortly afterwards, the O-Series Princess 2 appeared – and this was the first showing of the larger 2-litre version. The 1994cc unit produced a less than sparkling 93bhp at 4900rpm in single carburettor form, and did nothing to improve the Princess reputation with buyers for being a slow car.
That is not to say that the O-Series was without its merits; only that it was a bit of a “rough diamond” in the early years, offering little advantage over the outgoing B-Series – certainly in terms of performance and refinement. As stated though, it was a good 20kgs lighter than the B-Series engine, and the block was shorter and therefore easier to package. Also, the aluminium cylinder head allowed for unleaded fuel usage… (it is a shame that the O-Series powered MGB never made it).
It was also usefully reliable.
It also figured in Austin-Rover’s 1980s plan for prosperity.
In 1980, the first rear wheel drive 2-litre O-Series powered car appeared: the Ital 2.0 Automatic. In 1982, a 2-litre twin carb version was installed under the Rover SD1’s sleek bonnet, and then in transverse form in the Ambassador. In 1984, it appeared in the Montego and Maestro with an end-on Honda designed gearbox (and very effective it was, too) – so there was no doubt that the O-Series was an adaptable engine.
Of course, the O-Series story did not finish with the Maestro and Montego – and after an intensive development programme during the mid-1980s, it was transformed into the twin-cam 16V M-Series…
Fundamentally, the O-Series was a good engine, and if nothing else, demonstrates that when asked, BL could get the job done in the most trying of circumstances. Perhaps, it was launched when in need of final development, but given the lack of resources available to BL at the time, it is a miracle that it appeared at all.
Is the Editor of the Parkers website and price guide, formerly editor of Classic Car Weekly, and launch editor/creator of Modern Clsssics 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 unfeasable adventures all across Europe.
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