Design and styling
Envisioned as a luxury sports car, the Triumph Stag was designed to compete directly with the Mercedes-Benz SL class models. All Stags were four-seater convertible coupés, but for structural rigidity – and to meet new American rollover standards at the time – the Stag required a B-pillar "roll bar" hoop connected to the windscreen frame by a T-bar. A removable hardtop was a popular factory option for the early Stags, and was later supplied as a standard fitment.
The car started as a styling experiment cut and shaped from a 1963–4 Triumph 2000 pre-production saloon, which had also been styled by Michelotti, and loaned to him by Harry Webster, Director of Engineering at Triumph from the early to late 1960s. Their agreement was that if Webster liked the design, Triumph could use the prototype as the basis of a new Triumph model. Harry Webster, who was a long time friend of Giovanni Michelotti, whom he called "Micho", absolutely loved the design and spirited the prototype back to England. The end result, a two-door drop head (convertible), had little in common with the styling of its progenitor 2000, but retained the suspension and drive line. Triumph liked the Michelotti design so much that they propagated the styling lines of the Stag into the new T2000/T2500 saloon and estate model lines of the 1970s.
It has been alleged that internal politics meant that Triumph intended, but were unable, to use the proven but old technology Buick designed all aluminium Rover V8. The no-fit story is probably a myth as Rover, also owned by British Leyland, simply could not supply the numbers of V8 engines to match the anticipated production of the Stag. "Brand loyalty" between Triumph and Rover was high as they were former rivals. Triumph engineers preferred their new design, despite being heavier than the Rover V8, because of its superior overhead cam design.
Harry Webster had also already started development and testing of a new unique, all Triumph designed overhead cam (OHC) 2.5 litre fuel injected (PI) V8 to be used in the Stag, large saloons and estate cars. The vision was to allow Triumph to compete in the V8 marketplace. Under the direction of Harry Webster's replacement, Spen King in 1968, the new Triumph OHC 2.5 PI V8 was enlarged to 2997 cc (3.0 litre) to increase torque and the troublesome fuel injection dropped in favour of dual Zenith-Stromberg 175 CDSE carburettors to meet emission standards in one of the target markets the USA.
The Triumph Slant-4 engine shared the same basic design as the Triumph V8, consisting of a single overhead cam cast iron block with aluminium heads. However the cylinder heads of the two engines do not share the same footprint on their respective engine blocks. This same engine manufactured by StanPart was initially used in the Saab 99. Using a gear driven water pump, the Slant 4 could be easily installed in a front wheel drive car. This same water pump design was used in the Stag V8.
As in the Triumph 2000 model line, monocoque construction was employed, as was fully independent suspension – MacPherson struts in front, semi-trailing arms at the rear. Braking was by front disc and rear drum brakes, while steering was power-assisted rack and pinion.
The car was launched one year late in 1970, to a warm welcome at the various international auto shows, which soon turned sour after delivery to the market with reports of engine problems. Some of these were due to the perennial problem of poor build quality, endemic to the British motor industry of the time, while others related to design problems in the engine. These included:
- long simplex roller link chains combined with inadequate engine maintenance and factory specified 7,500-mile (12,070 km) oil change intervals. The chains could last less than 25,000 miles (40,200 km) resulting in expensive damage when they failed;
- inadequately sized main bearings in the early OHC 2.5 litre V8 design with short lives, changed in the 3.0 litre design;
- aluminium head warpage due to poor castings, head gaskets which restricted coolant flow, leading to overheating;
- water pump failures relating to poor drive gear hardening, prematurely wearing out the gear and stopping the water pump.
- In some cases, overheating was caused by clogged waterways in the cylinder block which were found to be filled with casting sand left over from manufacture.
British Leyland never provided sufficient budget to correct the few design issues of the Triumph 3.0 litre OHC V8. Many owners adopted a popular conversion of the car fitting a Rover V8, Ford Essex V6, Buick 231 V6, or Triumph 6-cylinder engine but now such conversions fetch lower prices than a genuine Stag V8-engined car.
However, renovators over the years did iron out the V8 problems, rather than Triumph engineers.
- Cooling Problems:
- A larger radiator.
- Annual coolant flushing.
- A high dose of modern anti-freeze to overcome the overheating problems.
- Modern fully synthetic engine oil clearly assisted in cooling the cylinder heads – fully synthetic oils can cope with far higher temperatures and resist degradation.
- Appropriate fully synthetic oils to give superior lubrication and keep the engine interior clean.
- Improved metal finishes:
- Hardened crankshafts.
- Hardened metals on other components.
- Ignition System:
- Superior electronic ignition systems.
- Modern rubbers:
- Modern rubbers used on radiator hoses, heater hoses, fan belts and the likes are technically superior and more reliable than those installed in the 1970s.
These add up to an engine that now runs very well. If these glitches had been eliminated by Triumph, the engine could have been used in many other models in addition to the Stag.
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