When the Triumph marketing department set about promoting the Dolomite, certain liberties were taken that, at best, could be described as misleading. The offending advertisement appeared in the UK on June 7th, 1974 and was headed "The Design Council Award has gone to our head".
It was issued to proclaim the good news that a Design Council Award had been made in respect of the Dolomite Sprint's ingenious valve gear for its sixteen-valve
cylinder head. It was excellent that this neat piece of design work, led by Spen King, had been officially recognised. But unfortunately in underlining this the copy-writers went badly off the rails.
In saying that 16-valve engines (for four-cylinder power units) "have been around the racing circuits for years and are fine for power" they implied that these were all twin-cam engines which they labelled as "noisy, fussy and temperamental".
They embellished this by remarking that these problems "still show themselves in many expensive twin-camshaft high performmance saloon cars .... " Apart from this remarkable mis-statement in a full-page Times advertisement being rather unkind to another Coventry-built car, the XJ6 Jaguar, it became nonsensical by saying that "the complicated twin-camshaft configuration" was "hitherto essential to sixteen-valve engines".
The Triumph copy-writers had conveniently overlooked such classic single-cam multi-valve engines as the Bentleys of W. O. Bentley, the Brescia Bugatti of Ettore Bugatti, the sports
Sunbeam of Louis Coatalen, not to mention the 2-litre and 3-litre Bignan prooduction power units.
In stating that 16-valve racing engines invariably had twin-cam valve-gear the Triumph publicity department conveniently overlooked one of the most successful single-o.h.c. multi-valve racing cars of all time, namely the Mercedes that finished first, second and third in the 1914 French GP.
They had also forgotten about the single-cam 16-valve racing engines by Nazzaro, Opel, Fiat, Rolland-Pilain, Sizaire, and AC. What Triumph had done in the Sprint engine was to actuate the eight inlet valves efficiently by prodding them directly from the single 8-lobe o.h. camshaft, at the cost of using eight rather long rockers to actuate the eight
exhaust valves.
Is this such a simple solution as it sounds?
Some of the early sixteen-valve single-o.h.c. 4-cylinder engines had 16-lobe camshafts and 16 rockers, examples being the sports
Sunbeam which employed 16 short bell-crank rockers, and the Brescia Bugatti in which 16 non-pivoted lightweight sliding "banana"
tappets replaced the conventional rockers. But the original 3-litre Bentley engine had just an 8-lobe camshaft and eight forked rockers, like the Dolomite Sprint, but with shorter rocker gear. In production form it and the 4½-litre Bentley used a 12-lobe camshaft, with separate rockers for the
exhaust valves and shorter double-arm rockers for the inlet valve's, or a total of 12 rockers, the layout adopted for the all-conquering 1914 GP Mercedes.
The truth was the Dolomite Sprint could really only claim to have eliminated four or eight of the rockers normally found in a four-cylinder sixteen-valve single o.h.c. power unit by the substitution of abnormally long
exhaust rockers. It could hardly claim many marks for its direct actuation of eight of the valves, a la Hispano-Suiza, when this classic layout was not used for its remaining eight valves!
Misleading as the advertisement was on technical grounds, the Triumph Dolomite Sprint remained an excellent car. It is worth recalling that in their beautiful catalogues the old Bentley Company used to claim that the use of four valves per cylinder not only improved the breathing of their engine bur increased its reliability, "The seating area is increased by 50% and in consequence the cooling surface is greater, and a greater volume of water can be circulated through the space surrounding the seatings.
Further, the hammering effect on the seating of a single large valve with a strong spring is greatly diminished by using two light valves with light springs," they claimed. Realising that there were twice as many valves to grind-in, they hastily added that this chore should not be required until the car had done 20,000 miles!
Of course in 1974 you didn't grind-in your valves, so Spen King had all the advantages on his side. It is probable that when Henry (or Birkigt?) designed the 1912 GP Peugeot engine with four valves per cylinder and is reported as saying he did this, not to improve gas flow or to reduce valve inertia, but simply to have a standby in case of failure of one of the valves, he may have been misquoted and that what he was aiming at was reducing the likelihood of valve trouble, for the reasons given in the old Bentley catalogues.
However, gas flow is improved, as Bentley knew, by doubling-up the number of valves, unless a wide-angle, hemi-head arrangement is employed, and this the Sprint engine does not have, as its unique layout would then require even longer rockers! The offending ad is shown below...
