Theme : Engines – The 1970 Triumph Stag V8

Ah, the Triumph Stag V8, the stuff of classic car legends.

1970 Triumph Stag V8
1970 Triumph Stag V8

It’s all there for a long chat at the pub: dashed hopes, shoddy Midlands workmanship, the dark days of British Leyland’s decline. There’s even a bit of Italian in there, as Giovanni Michelotti styled the car. The bit we’re interested in is the V8 though.

This unit was conceived in the middle of the 60s in response to the growing demands of the UK market for more powerful engines as the motorway system expanded. Triumph had some sixes and jolly nice they were too but they were not enough. They also needed more swept volume for a planned push into the US market and, no doubt, to compete with the Germans who were about to offer V8s in their Mercedes-Benz R107 (SL) and C107 (SLC) vehicles.

What was the Triumph V8? It was 3.0 litre unit designed by Triumph themselves, being more or less two Triumph slant-4 engines placed together. It had one OHC per cylinder bank and had a cast iron block with – crucially – aluminium heads. It had a single crankshaft which is partly responsible for the engine’s rather pleasant noise (if it runs).

In order to meet expectations at the time, the original plan for a nice 2.5 litre unit was changed, rather late in the day it would seem. Spen King, the chief engineer, insisted the Stag’s ought to be a 3.0 litre unit, to be run with carburettors. Increasing the diameter of the cylinders to increase the volume meant the walls were thinner and less able to conduct heat. The aluminium cylinder heads were designed to close tolerances as well. As a result of poor management and a lack of experience on the part of the workforce, the heads were often not produced to a high-enough standard.

The other problem was that the losses Triumph were running lead to cost cutting. The purchasing department found a cheaper supplier for the head-gasket which often failed. There was not enough time spent on engineering the problem of water-circulation either. The results of this meant the engine was liable to overheating when used hard.

1970 Triumph Stag
1970 Triumph Stag

If all had gone well, the Triumph Stag V8 would have made a convincing alternative to similar GTs from Mercedes and BMW but was much less costly (about half the price). It got good reviews and rather had the field to itself. There were not very many alternatives to its formula of V8 power and open-top style. But the problem of over-heating engines ruined its chances. And had all gone well, Triumph might just have avoided the ghastly decline that followed from 1970 to 1980, ending in the bathos of the Triumph Acclaim, a four-cylinder family saloon, a re-badged Honda.

Post-script: there is some debate as to whether the Rover V8 might have been a better engine for this car. Allegedly the engineers lied when asked if the Rover V8 might fit. When this option was mooted a lot of time had already been spent on the Triumph V8 so understandably the engineers did not want to see their work discarded. Since engines matter, it would have been preferable to have V8 expertise in BL rather than to have to buy-in the know-how by using the GM-derived Rover unit. Additionally, even if the Rover V8 did fit, it may not have had the required characteristics of the Triumph design.

Author: richard herriott

I like anchovies. I dislike post-war town planning.

11 thoughts on “Theme : Engines – The 1970 Triumph Stag V8”

  1. Anyone who has heard a Stag working properly will probably say that, if only BL hadn’t shot itself in the foot (yet again) by skimping on development, the Triumph V8 was undoubtedly a good thing. The other thing it skimped on was bodywork. Agreed, it looks good enough now but, at a time when a Mercedes SL looked completely different from a saloon, there was obviously too much carried over from the Triumph 2000/2500 to fully justify the ‘Alfa and Merc Look Out’ advertising. However good the concept, or clever the engineering, the British industry always seemed incapable of hiding its underlying meanness.

    1. Whether one likes it or not, there’s little doubt that the R107 SL looked about a decade more modern than the Stag. This may add to its charms nowadays, but back then, it would mainly reinforce the public’s preconception of British automobiles, subliminally or directly. One could see the Triumph TR7 as a belated attempt at overcompensation.

  2. Further proof that the malaise was not bad luck but bad management is that the V8’s cousin, the Slant 4, was also beset by problems. This didn’t stop Spen King developing the ingenious Sprint engine – the first mass production 4 valve – but, impressive though its performance was at the time, production was so poor that it couldn’t achieve its original intended power figures. But over the North Sea (or possibly at Ricardo in Sussex) Saab started with the same engine and quickly turned it into the unit that, with ongoing development, continued in their cars until 2009.

    1. On the one hand Saab isn’t my idea of a V8 marque. On the other, a lack of larger engines was used as a stick to beat them. I’d probably split the difference and say there were some models asking for a six that made do with splurgy turbos and this cost Saab customers. Ideally they’d have had fours, turboed fours and sixes and kept everyone happy. An eight? Can anyone argue Saab made a body that called for one?

    2. Was thinking that Triumph was have benefited from somehow continuing its collaboration with Saab with the Slant-4 and V8 engines, especially in fixing the Triumph V8 engine though that would entail avoiding the formation of BL to begin with and Leyland Motors eventually owning Saab which is than subsequently positioned beneath Triumph.

  3. I’ll controversially suggest that the Triumph V8 would never have been a good engine. It was part of Lewis Dawtrey’s family of engines intended to replace the SC four, 20S “light six”, and the TR/Vanguard detachable liner four.

    The family originally comprised a 1200-1500cc slant four and a 2.5 litre fuel injected V8. The trouble was development was concentrated on the fours, leaving the V8 with narrower crankshaft bearings than was ideal. The 3.0’s 64.5mm stroke was probably as long as practicable to give an adequately strong crankshaft. The Stag engine had the smallest bore of any of the Slant 4 / V8 engines produced, at 86mm. The Dolomite Sprint’s 90.3mm bore would have given 3.3 litres with a the 64.5mm stroke, but Triumph probably avoided that with good reason.

    It does seem that they experimented with a 32 valve V8 – to my shame I can’t remember where I found this:

    British component suppliers’ inability to produce complex iron V8 blocks didn’t help. Sand-choked waterways exacerbated overheating problems. The Americans had many years of experience and it showed. The iron block / alloy head Stag engine weighed 446lbs, around the same as a 5 litre all-iron Ford Windsor.

    It gets worse. The tooling set-up dictated that a V8 needed four times the line time of a slant four. As Saab, Dolomite, and TR7 demand built up, the bell tolled for the V8, and the only car it ever powered.

    That’s enough misery. Here’s another fastback Stag:

    1. Apparently the displacement range of the Slant-4 and V8 engines were 1200-2000cc and 2000-4000cc respectively.

  4. One of the issues you are not mentioning is people in the 70’s filling these system with water or incorrect anti-freeze mix. They were use to British engines with cast iron heads and blocks. With that sort of engine you can get away with incorrect coolant mix.

    Do that with an alloy head and you’re asking for a world of trouble. The head will corrode, silt up all the water passages and it overheats. The head gasket is replaced, but the system isn’t flushed, so still fill of silt, so it blows another gasket.

    1. And I have it on good authority that this was an even bigger problem in the US whose mechanics were unprepared and treated it like a tough, cast iron US V8! Makes sense?
      Having worked for many years in a Japanese auto company, I also understand the failure of not providing sufficient support/tech training for dealer service departments when new & different models are introduced. I’ve no evidence, but it would seem to beg the question: did Leyland ignore the workshop in the UK & US (and Australia – where bye the way, the survival rate of Stags is extremely high) when they had an engine which they must have know required more TLC than its rivals?

  5. I have heard about this thing, but I had no idea just how bad the Stag engine was until I looked at some of the servicing videos.

    For example, the water pump goes in the top of the block underneath the intake manifold. The intake manifold must be removed to change the water pump ! In the video they show how the water pump gasket has to be shimmed to get the right clearances so it doesn’t leak (!).

    The water pump is driven by a vertical (!) shaft driven by a bevel gear from a timing chain driven jack shaft. This jack shaft also powers the oil pump and the distributer.

    That is quite a significant load on that jack shaft drive. At peak power, both water and oil pump likely consume at least 5 hp.

    So you would think that Spen King would have specified a robust jack shaft, sprocket and timing chain, but no, the chains and sprockets on this car looks like a child’s bicycle.

    Chains and sprockets have a mileage to failure of approx 25,000 miles, which is much worse than timing belt engines, even in the 1970s. Needless to say, the chains were not designed to be frequently changed, so they are much more difficult to do than a belt. The high side loads on the jack shaft bearing in the block caused rapid wear, which lead to a large oil leak and low oil pressure.

    The block, crank and rods look robust, comparable to other manufacturers. Although the main bearings are undersized, and have a history of early failure.

    It’s amazing that they invested a large amount of money to create this crap engine, when they already had the Rover V8 available. Spen King and co. tried to be “clever” in a whole bunch of ways on this engine, and ended up being the exact opposite.

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