BMC C-Series engine

Austin C-Series engine in an Austin-Healey 3000 Mark II

The BMC C-Series was a straight-6 automobile engine produced from 1954 to 1971. Unlike the Austin-designed A-Series and B-Series engines, it came from the Morris Engines drawing office in Coventry and therefore differed significantly in its layout and design from the two other designs which were closely related. Displacement was 2.6 to 2.9 L (2,912 cc) with an undersquare stroke of approximately 89 mm, bored out to increase capacity.

Mission

The new engine was required to replace BMC's inherited diverse collection of 2½-litre engines made to prewar designs and Austin's wartime designed four-cylinder BS1. A long-stroke engine, though closer to square than BMC contemporaries, with a cast iron block and cylinder head using Weslake patents, its overhead valves were operated by pushrods. Previously, Rileys used high-mounted twin camshafts with short pushrods, and Wolseleys used single overhead camshafts. There appear to have been plans for a twin-camshaft version for the new Rileys and Wolseleys corresponding with the (unreliable) MGA Twin Cam, but these plans were dropped in 1955. It was given a crankshaft with four main bearings (instead of seven) which later proved to put a restriction on power output and engine speed.

The C-Series has always been considered an engine that was both large and heavy for its capacity and power output, initially proving to have little benefit, aside from the greater refinement of six-cylinders, over the Austin-designed four-cylinder 2.6-litre BS1 engine installed in the Austin A90 Atlantic and Austin-Healey 100. Austin's engineers attributed this to poor cylinder head design. In 1957 the Healey was given a twelve-port head, increasing output by 15 bhp or fifteen percent. In 1959 carburetters were revised and replaced. In 1961 the inlet tract was improved, exhaust timing was adjusted, and twin exhausts added. Later in 1961 the saloon engines were slightly detuned and the Healey version's performance upgraded, probably by Weslake. Then the Austin Healey Mark III was announced.

Riley Big Four 1937-1938

The C-Series was also less efficient than, and in engineering terms was a retrograde step from Nuffield's engines: the Riley-designed Riley 2½-litre Big Four twin-cam four-cylinder unit fitted in the Riley RM series, and Riley's prewar cars, and the Wolseley designed Wolseley 2.2-litre straight six with a single overhead camshaft used in the Morris Six MS version of the Wolseley 6/80 which dated back to the early 1920s.

The Austin BS1 had begun as a late wartime Rix and Bareham design, two-thirds of a Bedford-based wartime truck engine, for a 2.2-litre ohv unit intended for a British jeep which became the civilian Austin Champ. Its use spread to Austin's Sixteen, their light commercial vehicles and the FX3 taxi.^[1]

However the C-Series was much more reliable than these units and cheaper to manufacture.

Version 1

Applications 1

• 2.6 L (2,639 cc) 77 x 89 mm
  • 1954-1959 26A Austin A90 Six Westminster /A95/A105 announced 18 October 1954—85 bhp @4300rpm^[2]
  • 1954-1959 26W Wolseley 6/90 announced 19 October 1954—95 bhp @4500rpm^[3]
  • 1955-1958 C26M Morris Isis
  • 1958-1959 26R Riley Two-Point-Six

1967 Austin Healey 3000

• • 1956-1959 26A Austin-Healey 100-6

Applications 2

• 2.9 L (2,912 cc) 83.36 x 88.9 mm. Four bearing crankshaft.
  • 1959-1968 29WA & 29WB Wolseley 6/99 and 6/110 announced 8 July 1959—112 bhp^[4]
  • 1959-1968 29A Austin Westminster A99/A110 announced 17 July 1959^[5] —108 bhp @4750rpm^[6]
  • 1959-1964 29VA & 29VB Vanden Plas Princess 3-Litre
  • 1959-1967 29A Austin-Healey 3000

Revision

With the car market demanding ever-increasing power and performance in the 1960s, especially from sports cars such as the Austin-Healeys BMC engineers concluded that the existing C-Series with four main bearings could not reliably withstand more than 150 horsepower in road use and 170 horsepower for short periods in competition. The four-bearing engine was also limited as to its maximum rotational speed due to the relative lack of crankshaft support.

With demand for the Austin-Healey 3000 still strong and development of what would become the Austin 3-Litre underway BMC carried out a thorough redesign of the C-Series with the aim of improving the power output and reducing both the engine's weight and its overall size. The engine was reworked to carry seven main bearings, steel ancillary castings were swapped for aluminium alloy ones where possible and the main block and cylinder head castings were redesigned to have slightly smaller external dimensions while retaining the same cylinder capacity of 2,912cc. The manifolds were altered for more efficient 'breathing', especially at high engine speeds.

BMC aimed for a 30 per cent weight reduction (175 lbs or 80 kg) and a maximum reliable power output in competition tune of around 200 horsepower. In the event a minimal weight saving was returned - the revised engine was only 45 lbs (20 kg) lighter than the old version. The main identifying feature of the 'mark 2' C-Series engine is the much narrower Rocker cover, which is only around half the width of the cylinder head, whereas the original engine has nearly full-width cover.

By the time the new engine was available the Austin-Healey 3000 had been dropped and was replaced by the MGC. No real use was made of the revised engine's greater strength and the power outputs were broadly similar to the original 2.9-litre engine at 145 horsepower.

1968 MGC GT

Applications 3

• 2.9 L (2,912 cc) 83.36 x 88.9 mm. Seven bearing crankshaft.
  • 1967-1971 29AA Austin 3-Litre
  • 1968-1970 29GA MGC

Racing engines

Much of the potential in the revised C-Series was demonstrated by the six specialised racing versions of the MGC built for 12 Hours of Sebring races in 1968 and 1969. These cars, dubbed the MGC GTS, used special versions of the C-Series engine. The first car was built with an engine where both the head and the block were cast in aluminium alloy but this proved troublesome and all the cars eventually used the standard iron block with an alloy head. The head had a higher compression ratio, larger valves (from the Ford Essex V6), revised porting and redesigned exhaust system as well as using triple twin-choke Weber carburetors. These specialised versions of the C-Series made an easy and reliable 200 horsepower with a weight loss similar that hoped for in the redesign process. However the inherent cost of these engines and the commercial failure of both the MGC and the Austin 3-Litre meant that none of these alterations were considered for the production units.

End of run

The C-Series was increasingly outdated in terms of its construction (as an all-iron overhead-valve engine), power output and power-to-weight ratio, which was a significant factor in the poor sales performance of both the cars it was installed in. It was effectively replaced, after a short hiatus, by the 2.2-litre straight six version of the E-Series engine, introduced in 1972. The E-series provided larger capacity six-cylinder engines made on the same tooling as the four-cylinder. Only the Australian market was offered the 2.6-litre replacement known as the Blue Streak.

Japan

In the 1950s, Nissan of Japan licence-built the Austin A40 and A50 with their B-Series engines.^[7] In later years, this engine was fitted to Nissan's own designs of light trucks. The B-series engine was developed further in Japan, particularly to redesign the perennially leaking rear crankshaft seal. This improved engine was known as the 'C Series' or eponymously as the 'Stone engine' after its designer. This overlapping name has led to a persistent myth that the six cylinder C-Series engine was also licence-built in Japan; it was not.

Nissan would later become known for their own design of inline six, used in the Nissan Z-car. Although this sports car concept traced its heritage from the big Austin-Healeys, the new SOHC engine had no inheritance from the Austin C-series engine.

References