The Rover Six Cylinder SD1 Story

The 6 cylinder story.

When British Leyland (BL) was formed in 1968 it found itself with no less than 8 different 6 cylinder engines for its car ranges.
Make Model Capacity BHP(Net)
Austin/Austin Healey/Wolseley A110 / 3000 / 6/110 + 2912 123-150
Austin/Wolseley 2200 / Six ++ 2227 108
Jaguar All models 2483-4235 120-245
Austin/MG Three Litre / MGC ++ 2912 145
Rover P5 + 2995 121
Triumph Vitesse / GT6 / 2000 / 2.5PI / TR5 1998-2498 90-142**
Vanden Plas* Princess R + 3909 173
Vanden Plas Princess + 3993 120
*Designed & made by Rolls-Royce **150BHP sometimes quoted is gross figure
Although some were about to be discontinued +, others were newly introduced engines++. The company knew it had to rationalise its engine production.
The Grand Plan
BL decided for the 1970's & 1980's that the front wheel drive cars would continue with the E series 2227cc engine, Jaguar would continue to use it's XK engine but develop a replacement for possible introduction at the end of the 70's. Rover & Triumph were to develop a new 6 cylinder engine which could also be use in other rear wheel drive cars in the BL empire.
Luckily the new 'Rover' engine was not to be developed by the ex-BMC division based at Longbridge, so might have had a chance of being a modern design, but BL decided that the unit would basically be based on the existing Triumph OHV engine. (Although introduced in 1960 it was really a 6 cylinder version of the Standard 8 (1952) with a long stroke and small bore). Triumph (not Rover) engineers would be responsible for the design.
The engine was developed to take an overhead camshaft, but by 1972 so many of the components were unique, it was decided to start on the design again, not use any existing components & base the engine on the experience gained from the Dolomite Sprint engine and the years spent on the OHC conversion. All they had to do was make sure the engine fitted the Triumph 2000/2500 engine bay and be machined on the existing Triumph engine production line (thus limiting the differences in size of the new engine).
Next it was decided the engine did not need to be machined on an existing production line, but still had to fit in the Triumph engine bay. So could be made a bit bigger.
At the end of 1972 a further decision was made shorten the height of the block so that the connecting rods from the Triumph Dolomite Sprint could be used. A great deal of experimental development of the valve sizes was done at this stage
At the beginning of 1973 it was decided that the new Rover SD1 was to replace the Triumph 2000/2500 range as well as the P6 which meant the new engine did not have to fit the Triumph engine bay and could be made wider as the new Rover was designed with a V8 in mind and had a wide square engine bay. This also meant the block could be made longer allowing the engineers to dispense with the siamesing of the cylinder bores which would allow water to surround each individual cylinder. It also meant the crankshaft bearings could be widened. The engine block casters asked for the engine to have a short water jacket so that production could be made easier, but it was found the pistons could not cope with the varying temperature this created. A solution was found by squirting oil from an outlet on the conrod up to the underside of the piston. But this then meant the engine did not use the Dolomite Spint conrods and was now unique and shared no components with other BL engines.
The engine which up to now had had small exhaust valves and much larger inlet valves was found to be restricted by the breathing caused by the vast difference in the valve sizes. The exhaust valves were now increased in size to 35.6mm and the inlet valves reduced to 42mm. No problem was found regarding excessive heat build up on larger exhaust valves because of the alloy cylinder head and the breathing improved dramatically.
Rover engineer Spen King insisted that the new engine should have an extremely strong bottom end so the crankshaft journals were induction hardened and were to be fitted with soft bearings to allow a long life. Instead of the 7 main bearing as found in the majority of other 6 cylinder engines, 4 main bearings were to be fitted to cut down on friction (It was now May 1973)
Now the block casters now found they could cast the block with a standard full length water jacket so all the work done on finding a solution to the short water jacket problems were now a waste of time but the solutions were still incorporated in the engine design.
It was now 1974 and the World was now effected by the fuel crisis and fuel economy was now a priority. The 2600 engine designed to replace the Triumph 2.5PI engine was reliably producing around 150 bhp net so it was felt that toning down the valve timing by using the same camshaft in both the 2300 and 2600 fuel economy would be improved as well as the saving from using a shared component. Also 150 bhp was uncomfortably close to the flagships 3500 V8s' 155 bhp.
The valve gear although of a similar design to that used on the Triumph Dolomite Sprint had cast iron rockers instead of the steel ones on the Sprint engine. This modification was done to reduce the need for extra lubrication.
The 2350cc & 2598cc engines only differed length of stroke & in the carburetter tune.
The new engine reach production in 1977 and was fitted to the Rover 2600. The smaller 2300 model was made available 6 months later.

The engine was supposed to be built at a rate of up to 1,600 a week at the Canley plant & although supposed to be fitted to other cars was only ever fitted to the Rover SD1 2300/2600 and ceased production during May, 1986.

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