Triumph Stag - Production

Production

The car was launched one year late in 1970, to a warm welcome at the various international auto shows. The Stag rapidly acquired a reputation for mechanical unreliability, usually in the form of overheating. These problems arose from a variety of causes.

First, the late changes to the engine gave rise to design features that were questionable from an engineering perspective. For example, the water pump was set above the engine. If the engine became hot in traffic, coolant escaped from system via the expansion bottle and the overall fluid level then fell below the level of the pump. As well as preventing coolant from circulating, this also caused rapid failure of the pump. Even when the system was topped up again, the failed water pump would not circulate coolant and further overheating ensued. Water pump failures also occurred due to poorly-hardened drive gears, which wore out prematurely and stopped the water pump.

A second cause of engine trouble was the choice of materials. The block was made from iron and the heads from aluminium, a novel mixture that required the use of corrosion-inhibiting antifreeze all year round. This point was not widely appreciated either by owners or by the dealer network supporting them. Consequently the engines were affected by electrolytic corrosion, so that corroded alloy debris came loose and was distributed around inside the engine.

A third cause of trouble was the engine's use of long, simplex roller link chains, which would first stretch and then often fail inside fewer than 25,000 miles (40,200 km), resulting in expensive damage. Even before failing, a stretched timing chain would skip links and cause valves to lift and fall in the wrong sequence, so that valves hit pistons and damaged both.

Another problem with the cylinder heads was the arrangement of cylinder head fixing studs, half of which were vertical and the other half at an angle. The angled studs when heated and cooled, expanded and contracted at a different rate to the alloy heads, causing sideways forces which caused premature failure of the cylinder head gaskets. Anecdotally this arrangement was to reduce production costs as the cylinder head mounting studs and bolt were all accessible with the rocker covers fitted. This allowed the factory to completely assemble the cylinder head assembly before fitting to the engine. However this was not possible in the end due to the cam chain fitting and setting of the cam timing requiring the removal or the rocket covers.

Finally, although pre-production engines cast by an outside foundry performed well, those fitted to production cars were made very poorly in house by a plant troubled with industrial unrest and poor quality control. To this day, restorers continue to find quantities of casting sand inside stripped engines. Poor manufacturing standards also gave rise to head warpage, and head gaskets that restricted coolant flow, which also led to overheating.

This combination of design, manufacturing and maintenance flaws caused a large number of engine failures. Time magazine rated the Triumph Stag as one of the 50 worst cars ever made.

At the time, British Leyland never provided sufficient budget to correct the few design issues of the Triumph 3.0 litre OHC V8. The Stag, also, was always a relatively rare car. British Leyland had around 2,500 UK dealers when the Stag was on sale and a total of around 18,000 were sold in the UK. Thus the average dealer sold only seven Stags during the car's whole production run, or roughly one car per year. This meant that few dealers saw defective Stags often enough to recognise and diagnose the root cause of the various problems. Many owners simply replaced the engine altogether, often with the Rover V8, Ford Essex V6, Buick 231 V6, or with the Triumph 6-cylinder engine around which the car was originally designed. Such conversions fetch lower prices today than a genuine Stag V8-engined car.

Surviving Stag engines can be made to run reliably by attention to these points. However, renovators over the years did iron out the V8's problems, rather than Triumph engineers.

Cooling system problems are typically addressed by:

• A larger radiator
• Fitting a switchable, electrically-powered fan
• All-year-round use of a 50:50 water:modern anti-freeze mix to overcome the corrosion problems.

Other improvements widely adopted by owners include:

• Hardened crankshafts
• Hardened metals on other components
• Electronic ignition systems
• Polyurethane suspension bushes
• Modern rubbers used on radiator hoses, heater hoses, fan belts etc, which are technically superior and more reliable than those installed in the 1970s.

These add up to an engine that now runs reliably. If these glitches had been eliminated by Triumph, the engine could have been used in many other models in addition to the Stag.

The last production Stag (BOL88V) is kept at the Heritage Motor Centre