The Triumph ConnectionThe Six Cilinder Engine.
The early origins.
The origins of the 2300 and 2600 six cylinder engines go back a long way to the 803 cc 4 cyl of the 1952 Standard Eight. This very sturdy unit was gradually enlarged, as with many good concepts, to 948 cc. When more capacity was needed for the Triumph Herald range the cylinders were placed out of centre wich cleared the studs so that a bigger bore could be used. This move gave a capacity of 1147 cc and it became a very popular engine in the Triumph Herald and Spitfire range. With 67 bhp at 6000 rpm it gave the little Spit very lively performance for its day.There was even more life left in the design and it was bored up from 69.3 mm to 73.7 mm together with the same stroke of 76 mm this gave 1296 cc and pushed power up to 75 bhp. Then it was about time for another increase. The stroke went up from 76 to 87.5mm and with the original bore diameter of 73.7mm this stretched the capacity up to 1493 cc.
In the mean time another project was started at Triumph. The four cylinder was taken and with two cylinders added this gave a 1596 cc six cylinder. One of the smallest six cylinders available that day, long before Mazda made a selling point of it!. The stroke remained at the old 76 mm.
The story for the six looks like the old little four. Soon another rebore brought capacity up to 2-litre with a bore of 74.7mm. The Triumph 2000 (A competitor to the Rover 2000) was sold standard with this sweet and silky running engine.
The new TR sportscar line of Triumph could do with some additional refinement and power. The old big four Standard engine was reliable but just did not deliver the power needed. There was no more room for a bigger bore in the small six cylinder so the stroke was drastically enlarged to 95 mm. This gave 2498 cc. A really massive increase from the original 803 cc unit!
The long stroke 2.5-litre gave a healthy 150 bhp in the TR5 and was equipped in Europe with the mechanical Lucas injection system. In the US the car was called TR250 and was specified for 105 bhp equipped with Stromberg CD carburettors. Originally the injection system was developed for the US cars but it turned out the injection system also needed additional environmental control systems which reduced power. A much cheaper carefully setup Stromberg setup did the job be it at the cost of much lower power.
Development for the SD1
A new power unit is a significant landmark in the progress of any vehicle manufacturer. Because of the enormous capital investments involved, an, engine design has to envisage decades rather than years of service. Hence the design thinking behind the brand new Rover 2300 and 2600 engines is of particular interest. They are the first completely new engines to result from Leyland's long term planning since the 1968 merger. There are no carry-over components whatsoever from previous designs.
Reliability, simplicity and longevity
The design brief for these engines naturally called for refinement and zestful performance expected in cars which were to succeed the much-loved Rover 2200 and Triumph 2000/2500 ranges. Thoroughly up to date efficiency, particularly in the vital cylinder head area, where the power is actually developed, was therefore high on the list of priorities. But also, in the light of the economic and environmental pressures becoming apparent by the beginning of the 1970s, other factors also loomed large in the proposed specification. Spen King, now Director of Product Engineering for Leyland Cars, was directly involved in the early groundwork for this new design as Director of what was then the newly integrated Rover Triumph Engineering division. Describing the philosophy behind the design, he says "As with the overall Rover SDI vehicle concept, we were conscious of the need to minimise the number of components, while still achieving high standards of performance.
"If you reduce the parts list significantly, the benefits multiply all along the line - you cut the investment bill and you improve reliability. The drain of the world's finite resources, materials and fuel is minimised and everyone from the production line to the service bay and the spare parts counter is able to do a better job. Starting from a clean sheet of paper, after rejecting early proposals to adapt existing components, we were able to make really radical improvements on every aspect of the engine design, from good foundry practice to easy service accessibility in the car."
This is how the design team were encouraged to think. They worked to such good effect that the 2300 engine, known internally as the PE 146 (petrol engine, approximately 140 cubic inches displacement, 6 cylinders) and the 2600 engine, (similarly titled PE 166) differ only in their crankshaft stroke, piston specification and carburettor tune. All other components are common.
In line with the requirement for first rate reliability, daring innovations and unknown frontiers of technology were deliberately avoided. Instead, the design involves a distillation of all that is known to be sound practice, drawing on considerable production and service experience with previous Rover and Triumph engines, and a study of recent competitive developments.
The end result for the owners of the new Rover 2300 and 2600 is a refined, reliable power unit that is enjoyable to drive behind; it has the responsiveness to please a sporting driver and the tractability for traffic use or gentle touring. Economy, both in terms of fuel consumption and easy servicing is enhanced by the inherent durability which has been painstakingly designed into every working part of the engine.
High performance head
The cylinder head, gravity die-cast in aluminium alloy, has a classic high efficiency cross flow configuration. Using the ingenious overhead camshaft layout now so well known in the Design Award-winning Triumph Sprint cylinder head, the two valves in each cylinder are operated by the same overhead cam. The inlet valve is operated directly by the cam, via an inverted bucket tappet, while the exhaust valve is actuated by a cast iron rocker from the same cam. Hence it has been possible to use optimum valve inclination (40° included angle) while keeping the compact simplicity of a single camshaft design. The camshaft, rocker shafts and tappet slides are all located in a single high pressure aluminium alloy precision die casting to facilitate assembly and servicing. This full-width casting mounts directly to the cylinder head.
The inlet valve has a head diameter of 42 mm (1. 6 in.), the exhaust valve a head diameter of 35. 6 mm (1.4 in.) and both valves have chromium-plated stems for durability. They run in pressed-in cast iron guides, and seat on shrink-fit sintered iron inserts. A single valve spring is used for the inlet valve, while the exhaust valve uses a common spring supplemented by a smaller inner coil to account for the extra inertia of the rocker.
Compact combustion chamber
Formed partly in a pentroof shape cast into the cylinder head, and partly in the piston crown, the combustion chamber has the compactness necessary to meet modern requirements in emission control while providing good performance and economy.
First belt-driven camshaft from Leyland
The camshaft is made of cast iron, runs in seven direct bearings in the cam carrier, of
Full advantage has been taken of the advantages of aluminium die casting in this head design. The twelve inlet and exhaust ports are all smoothly profiled and of generous section, for good breathing. Good cooling, especially of the exhaust valve, is ensured by well-controlled water passage shapes, while the combustion chambers have good uniformity of size and surface finish.
Rugged bottom end
Cylinder head design is the key to the power output of an engine; where durability and reliability are concerned, attention is turned to the 'bottom end' - the cylinder block, crankcase and crankshaft. Here the 'clean sheet of paper' was enthusiastically exploited by the engine designers. The cylinder block is cast in chrome iron, and the bores are equally spaced with water cooling jackets all around each bore. Because the ancillary drives are all 'tidied out of the way', the block is classically symmetrical, with no heat distortion problems. Also symmetrical is the bolt pattern for the cylinder head - ensuring even clamping. Fourteen, equal-length high tensile 12 mm set bolts allow a high tightening torque on first assembly of 122 to 130 Nm (90 - 95 lbf. ft) which obviates the need for further retightening after assembly. A steel cored, composite faced cylinder head gasket is used.
Manufacturing and quality control are both eased considerably by the simplicity of the block casting. A very rigid crankcase is achieved by generously ribbed scantlings, and a crankcase skirt which extends well below the crankshaft centre line.
With a view to minimising friction and thus enhancing economy, a four main bearing crankshaft was specified in the original design brief. The crankshaft is an extremely strong and rigid steel forging, with large journal diameters (main 70.38 mm / 2.77 in., crank-pin 50.5 mm / l.98 ins.) ensuring overlap even with the longer stroke 2600 engine. Single hole, oblique oilway drillings are used to avoid dirt or swarf traps. Induction hardened bearing journals contribute to the inherent durability of these engines, as demonstrated by a recently stripped 50.000 mile test engine which had unmarked journal surfaces. A torsional vibration damper is incorporated in the front crankshaft pulley. Steel-backed, leaded-bronze bearings with a lead indium overlay are used for main and big end bearings. The symmetrical forged alloy steel connecting rods have fully floating gudgeon pins, while the piston specifications vary to suit the two engines. The 2300 has Hepworth and Grandage solid skirt 'W' slot pistons, each with two compression rings and one scraper ring; on the more powerful 2600 unit, there are high-duty Mahle solid skirt pistons, similar to those used in the Dolomite Sprint engine, with a different compression height and an integral steel band in the skirt to` control temperature expansion. These also have three piston rings as on the 2300 pistons, the number being deliberately limited to three to minimise fuel-wasting friction. Lubrication of the bores and cooling of the piston undercrown is effected by a 1.2 mm (0.045 in.) oil squirt hole in the connecting rod.
Integrated lubrication system
Following the theme of simplicity and easy servicing, the eccentric, multilobe rotor oil pump is driven directly off the front of the crankshaft, and is neatly housed, along with the filter mount and relief valve in a single high-pressure die casting bolted to the front of the crankcase. The oil filter is a full flow, disposable cartridge type. In common with the V8, 3500 model, the oil pressure switch on 2300 and 2600 models has an additional safety function in that it isolates the electric pump in the fuel tank when oil pressure falls below 0. 21 kgf / cm2 (3 lbf / in.2) to avoid fire hazard in an accident.
A Ram induction and free flow exhaust
Both engines have common inlet and exhaust arrangements. The cast aluminium inlet manifold carries twin SU HS6 carburettors, and has long inlet tracts, researched to enhance torque by ram effect. Carefully graded water heating is provided by a steel gallery pipe cast in situ into the under-sides of these inlet tracts. The carburettors incorporate the latest SU emission control features, with ball-bearing dashpot slides and capstat (wax thermostat) compensation for fuel viscosity variation with temperature. The pressed steel air filter encloses twin replacement paper elements, and is fed from a remote-mounted ATC (Air Temperature Control) unit of the familiar Design Award-winning Leyland bi-metal flap valve type. This mixes cool, ambient air from the front of the car, and hot air from a stove shroud on the exhaust manifold.
Careful design of the exhaust manifold clamping arrangements, with twin bolts on each port, has made it possible to dispense with any form of gasket. The cast iron of the manifold forms a gas-tight seal directly against the aluminium head's exhaust port flanges, hence avoiding one of the most commonly troublesome gasket joints. There are twin exhaust outlets to long separate down pipes for free exhaust flow.
Ideally placed for servicing, horizontally mounted on the front offside of the cylinder head, the conventional Lucas 54 D6 distributor is driven off the camshaft by a skew gear and a very short drive shaft. A Lucas 16C6 ballasted coil provides the high tension feed. Starting is by a Lucas 2M100 pre-engaged starter motor, while the alternator is 23ACE 55 amp unit in common with the 3500.
The high efficiency design of these engines yields excellent power outputs without stress. Developing 123 bhp (DIN) at 5000 rpm, the 2300 unit offers an extra 25 bhp over the previous Rover 2200 four cylinder engine, and 31 bhp more than the Triumph 2000 TC unit.
Similarly, the 2600 engine, with 136 bhp at 5000 rpm, offers a considerable increase over the 106 bhp of the Triumph 2500 TC/ 2500 S engine. This means that despite the extra accommodation provided by the new Rover body design, worthwhile performance gains are also achieved, while retaining similar levels of fuel economy.
The efficiency of the engines is demonstrated by the specific fuel consumption curves, with both engines returning under 0.5 pints per bhp hour in the commonly used 3000-4000 rpm speed band. ends