The Standard-Triumph 6 cylinder engine was originally developed for the Standard Vanguard Luxury Six, which came out in 1960, see below:
Beginnings: The SC four
The story of this engine starts with the Standard Eight of 1953 for which an entirely new 4-cylinder engine, known as the SC (small car) was designed by David Eley. Although new, the engine block had to be machined with tooling purchased for the Triumph Mayflower engine so the cylinder centre dimensions of the new 803cc engine were shared with the Mayflower's side valve 1247cc unit. This new in-line engine had overhead valves operated by push rods with the camshaft in the block, with both the cylinder block and head made of cast iron. It is notable for having both manifolds (exhaust and inlet) on the right hand side, and the distributor, camshaft, spark plugs and oil filter on the left-hand side, differentiating it from the similar capacity "A" series engine with which it is sometimes compared; they share the same bore and stroke (58 x 76mm) giving 803cc. The SC engine can be seen below:
The Six or 20S
Although the 6 cylinder engine was based on the 4 cylinder, David Eley, who was responsible for both, says that it "wasn't just a six-cylinder version of the SC" and talk of finding the seam where the additional 2 cylinders were added is wrong! It was not even manufactured in the same factory, being cast at Bean Industries (pictured below) which Standard-Triumph had just acquired (it's history goes back to the 'Bean' motor-car, click here to find out more). However it did share the location of the ports, distributor and camshaft, and had similar front and rear block faces. Below is a cut-away of the 2 litre engine, showing the position of the main components. Also the cylinders were siamesed i.e. cast with no water jacket between them, this was done so the engine would be short enough to fit into the Standard Vanguard 6. This also later helped when fitting the unit to small cars like the GT6 and Vitesse. However this also meant that there wasn't room to increase the capacity by enlarging the bores, the only way to do this was by increasing the stroke (see table below).
Although the cylinder head of the original 20S engine had individual inlet and exhaust ports from the start (unlike the SC engine), the breathing was not as efficient as it could be, this came with the inproved head design which came out in the mid to late 1960s as fitted to the GT6 Mk2 and TR5.
The original carburettors fitted were a Solex, which were not entirely successful (cold starting problems). Although SU carburettors were better, as they were made by competitor BMC, they couldn't be used. A similar variable choke carburettor had to be developed, and this was successfully done by Dennis Barbet of Alford & Alder (a wholly owned subsidiary of S-T). This new carburettor, which had rubber diaphragms, eventually became the Zenith Stromberg CD which was fitted to all the subsequent versions of the six-cylinder engine (until BMC became part of British Leyland, owners of Triumph). Strombergs can be seen in the picture below of the RHS of the engine. Another picture below shows the LHS of the engine showing from left to right the alternator, coil, distributor, mechanical petrol pump and below that the oil filter.
Beans below, where the 20S engine and cylinder head were cast:
|Various incarnations of the Standard-Triumph 6 cylinder engine|
|Year||Bore & Stroke||Capacity||Power||Car model|
|1962||66.8 x 76mm||1596cc||70bhp||Triumph Vitesse 6|
|1960||74.7 x 76mm||1998cc||80bhp||Standard Vanguard 6|
|1966||74.7 x 76mm||1998cc||95bhp||Triumph Vitesse 2 Litre|
|1966||74.7 x 76mm||1998cc||95bhp||Triumph GT6|
|1963||74.7 x 76mm||1998cc||90bhp||Triumph 2000 Mk1|
|1969||74.7 x 76mm||1998cc||-||Triumph 2000 Mk2|
|1967||74.7 x 95mm||2498cc||150bhp||Triumph TR5|
|1968||74.7 x 95mm||2498cc||80bhp||Triumph TR6|
|1968||74.7 x 95mm||2498cc||80bhp||Triumph 2.5PI Mk1|
|1969||74.7 x 95mm||2498cc||80bhp||Triumph 2.5PI Mk2|
|1976||74.7 x 95mm||2498cc||80bhp||Triumph 2500 Mk2|
The Legacy - The new SD1 Six of 1977
When Triumph engineer Mike Loasby designed the successor to David Eley's Six, elements of the original Triumph block were retained to allow continued use of existing casting and machining equipment, just as had previously been done with the original SC engine. Also cast by Bean Industries, the block was lengthened by 20mm, the bore and stroke dimensions of 81mm and 76mm/84mm were retained, and water passages were introduced between the cylinders.
See a Standard-Triumph - 6 cylinder Engine Animation by Williams Illustration
Click on the image above to see in youtube (the animation is fantastic!)