Essay : Not their finest hour – AEC-Leyland 740/800 series V8 diesel

Mike Humble

The AEC V8 - Looked great and sounded amazing but dismally failed in practice
The AEC V8: Looked great and sounded amazing but dismally failed in practice

They say that jealousy is never the best policy for politics, a point proven when a well known former Labour Chancellor of the Exchequer was quoted as saying ‘we will tax the rich until the pips squeak‘. The internal politics within British Leyland have always been well documented. The Longbridge management loathed their opposite numbers at Cowley and the Triumph staff at Coventry looked upon Abingdon with envious eyes – it was all pointless bitter jealousy that played its small part in bringing BL quite literally onto its knees.

Who knows what could have been achieved if all parties actually worked in one direction instead of their ongoing and destructive localised inferiority complexes once BL had been formed. At the heavy end of the group Leyland and AEC had been bitter rivals for so many years with its collective ranges of bus and truck chassis. Both makers had staunch loyalty from their customers and both parties being known the world over for their solid and reliable vehicles, even to this day, think of a London bus and a Routemaster comes into mind – built of course by AEC.

Go back 40 years or more and very few hauliers would have ever considered purchasing a Foreign built truck, despite Volvo and Scania – Vabis already having a tiny presence in the UK market. Southall-based AEC had been quietly working on a new range of engines as far back as 1962 to cope with increasing weights and the expanding motorway network in Britain. Their largest power in the truck range was from the 12.5-litre 760 series diesel producing power between 180 and 260bhp but AEC could see that further power extraction required a whole new engine range for future trucks.

Work had started in 1962 on a compact V8 diesel engine of 12 litre capacity with a standard power rating of 250bhp in naturally aspirated form developed at an unusually high 2600rpm. Owing to the large bore short stroke, the V8 was not blessed with huge amounts of low end torque but AEC envisaged that with turbocharging the engine could address this shortcoming. It was also hoped that it could go on to develop 350bhp and beyond once proven. This new engine was proving to be problematic and AEC had held back from signing off the engine for full scale production as they battled to cure some serious shortcomings.

The Mandator V8 was the first recipient of the engine. Drivers loved them, operators less so!
The Mandator V8 was the first recipient of the engine. Drivers loved them, operators less so!

Once British Leyland had formed, the Leyland men visited all the plants to see what new ideas were in the cupboard and once the 800 series engine was public knowledge within the Leyland hierarchy, AEC were pressurized to get the engine into full scale production. The bigger picture of being part of British Leyland meant all divisions were under the cosh to highlight and showcase new ideas – irrespective of the fact if they were simply no good.  Test V8 engines had little more than 300 hours running experience and serious shortcomings were noted on the test bench way before any vehicle proving had taken place.

Some very strong opinions and outcries came from the Southall engine designers but British Leyland were having none of it. The engine was pressed into production and was destined to be fitted into the AEC Mandator tractor unit, even more worrying was the fact AEC had just a few months to further develop and prepare the new truck for sale. BL had noticed with the 800 it seemed to have a solution to high power diesel engines yet the engineering quality led approach to manufacturing Leyland were once known was replaced by an inferiority complex. Leyland still viewed AEC as some kind of arch enemy that had to be defeated.

Into production it went and faults appeared right away. Overheating was common and if not spotted quickly enough by the driver, the top piston ring would fail causing the piston to eventually deform and pick up on the cylinder liner rendering all the aforementioned components as scrap. A larger bore engine of 13-litres introduced soon after fared better owing to thinner liners that dissipated heat better. Because of the smooth nature of this engine, drivers would often over rev without knowing and the splitter system of the semi auto gearbox had no interlock to prevent over-speeding in the ratios.

The splitter switch was also very sensitive to the touch and as a result, some drivers blew engines to bits by merely a glancing movement of this switch thus sending rods and pistons though the engine block casting by a result of over revving beyond its capabilities. But drivers loved them and tales of legend were soon banded about recalling stories of fully laden Mandator V8 units passing cars on hilly sections of the A1 – fully freighted. On full song, the Mandator V8 had an engine note almost like a racing car which led some operators to restrict the fuel pump not only to save the engine, but to save the drivers licence too!

British Leyland also launched the AEC Sabre coach chassis with the smaller 740 V8. It flopped badly and never really got beyond the prototype stage.
British Leyland also launched the AEC Sabre coach chassis with the smaller 740 V8. It flopped badly and never really got beyond the prototype stage.

Engine strength was compromised too. Because the engine was compact and short in length, the crankshaft bearing journals were much narrower than on traditional in line engines. Many operators found the big end shells were falling between 50 to 60,000 miles which caused customers to bitterly complain. While all this was going on around them, European rivals simply set up their stalls to disgruntled hauliers who simply walked away hand in hand with former AEC and Leyland customers – most of which never returned to a British product.

Even further misery came when Commercial Motor Magazine took delivery of a Mandator V8 tractor from Southall for road test purposes. After collection the vehicle barely travelled a few miles away from the AEC plant when disaster struck. The test vehicle pulled a cylinder liner downwards in the engine block thus grenading the bottom end of the engine. Once a replacement vehicle was sourced, the test went ahead and they commented on the ultra smooth nature of the engine but complained about the lack of torque unless the engine was being worked hard.

Southall engineers worked and sweated to cure the ails of the 800 V8 sadly to no avail and at best gained just tolerable levels of reliability. To get the engine to work properly a redesign of the engine block to extend the crank and bearing surface area would be required. By the early ’70s British Leyland was an open wound hemorrhaging liquid assets – there was simply no money or time to do so. Leyland had by now taken a turn in direction by developing their maximum capacity for minimum cost truck – Marathon and the V8 800 series diesel was quietly and quickly scrapped.

Top AEC engineers had pleaded with Leyland earlier to hold back on production of the engine and certain notable figures within the customer base remained loyal despite this tragic engine but now the solid engineering reputation of AEC was in tatters on a global scale. The 760 in line six engine was subsequently developed into a turbocharged power unit known as TL12 which became a dependable engine of up to 280bhp. Following the closure of AEC and the Southall plant in 1979, engine production of the TL12 moved to Leyland with engineers working on a 350bhp version, but by now all max capacity engines would be bought in and not produced in house.

The 800 series diesel marked a low point in British Leyland and was nothing other than a fatal disaster costing way more than just hard cash. AEC’s public reputation of a once trusted and respected company was destroyed by nothing more than a British Leyland ego trip. A lovely sounding engine that also looked impressive which quite possibly could have been a shining star if allowed to develop. A senior AEC manager once quoted some years later that British Leyland turned AEC from an engineering led company into a Guinea Pig for every hopeless idea that British Leyland could think of.

Mike Humble


  1. Sad story Mike. I would make one point though – AEC was absorbed into the Leyland Motor Corporation BEFORE the formation of the British Leyland Motor Corporation (as indeed was the Rover Company).
    I stress this because there is a tendency to somehow blame BMC for everything that went wrong after 1968. It could be argued that BMC/Austin-Morris suffered just as much grief from Leyland’s misjudgements as any other part of the group.

  2. I used to share a house with a big-time bus and train spotter (he’d actually spend his weekends trying to ride behind every example of every locomotive- I don’t mean each class, I mean every possible member of every class). He mentioned the AEC V8 as a project ordered by Leyland without being told what the V8 engine was supposed to be used for!

    Reading the above, I guess AEC did have a purpose for it, but not the time to develop it properly. Shame Leyland didn’t streamline their operations more efficiently so that the best of their products could be used to build world-class vehicles.

    Great video, that truck seems to go very well. Not sure of the legality of driving without the passenger door, even if it was a private trading estate. Sounded good- imagine that engine (properly fettled) in a decent coach!

  3. Makes you weep. Another story of management incompetence. AEC made some pretty fine train engines too, mainly used under late 50’s & early 60’s DMUs which had very long service lives. Of course these were 6 in line mainly rated at 150 bhp.

  4. Ian – yep, Leyland took over ACV the parent company but only really took a firm grip in the mid 60s.

    Chris – The V8 was first thought of in 1962 and was given Leyland’s thumbs up as you say, with no initial specific application until a panic request to get it into full scale production from Leyland in 1968.

    The 0.500 fixed head OHC range of diesels seems to be the well known ultimate fail of large diesels from BL, yet the L60 and the 740/800 were much much more of a complete arse of events.

  5. Another great read Mike, I vaguely remember this engine being a nightmare but always thought AEC were the brains behind Leyland as the Ergomantic Cabs were an AEC design? that Leyland also used…

    It is amazing (if that’s the right word) that Leyland almost had the World in their hands and yet so quickly the Mighty had Fallen, With all the money that was pumped in and chances they had, you cant help thinking that they were somehow Cursed.

  6. A damn shame, rather like the car part of the business, but inevitable given the envy and rivalries inside British Leyland. However, the Routemaster is one thing AEC will be famous for, rather than a little known lorry, and these buses still survive in large numbers.

    • ………..but sadly the AEC engines in the Routemaster have mainly been replaced by other engines, the originals being worn out. Another tragedy was that the front entrance, rear-engined FRM never went into production. Again, Leyland had taken over and had no enthusiasm to promote the vehicle. The prototype, 80% made from standard Routemaster parts, is still in existence, having led a full and uneventful working life.

  7. A very sad but common British story, remember the British dominated the world motor cycle industry as well and this fell apart at about the same time !!

    • Hi, very interesting article, I used to drive a Scania V8 in the 80’s and was told that engine was the old AEC failed project which Scania bought, can you confirm if this is the case. Thanks Richard.

  8. On the way back from the Mini Rally in Brighton on Sunday, I drove past the site of the factory in Windmill Lane. Sadly, there is no sign that it was ever there.

  9. Such a shame that a promising engine design was not allowed the gestation period necessary for reliable service. It clearly had some power, judging by the acceleration of the rebuilt lorry in the video clip!

  10. It really is a shame that the v8 was not allowed the funds or time for full testing and development. But, one thing that puzzles me is the fact that this v8 which was designed for higher power was designed with narrower bearings on the crank than a conventional straight 6! I would have thought this was a disaster waiting to happen on that fact alone? Why did they design it this way? I would think the developers and design team shot themselves in the foot from the outset. If with their experience it had a stronger bottom end from the word go, maybe the initial tweaking and ironing out of early problems would have been easier to sort out. I cant help but thinking they have to carry some of the blame.

  11. Mike seems to have talked to AEC sources only in this article.

    I’d certainly agree with Robbie that the bearings seem under specified for the job. It has to be borne in mind that shortly after the share-exchange that created AEC the only qualified engineers in the senior management team Sir Henry Spurrier and Stanley Markland died and resigned respectively, leaving a Salesman as Chief Executive and a coachbuilder as Chairman. It seems AEC had between 1962 and 1968 to develop the unit but only did so between its 1966 announcemnt and 1968 launch.

    Leyland Motor Corporation did eventually recruit an Engineering Director, in 1964, he was Albert Fogg, who had previously headed the Motor Industry Research Organisation.

    He gave the go-ahead to the AEC V8, the fixed-head engine and the Gas-Turbine, seeing them as units for up 250-350bhp, 150-250bhp and over 350bhp respectively. He also sold DAF the rights to produce the O:680 and O:400 who got a clause allowing them to develop them independently of Leyland.

    I think it was his age and the expansion of the role after the forced purchase of BMH which caused him to retire from post rather than the shortcomings of this, the 500 series or the gas-turbine.

    For a time Alec Issigonis, creator of the Mini, who was his counterpart at BMC, reported to him…

  12. Of course this engine was built on machinery installed in 1926. Leyland had no commercial vehicle production in wartime so could re-equip in 1945.

    The R-R eagle became the favoured lorry engine in the 1970s and that was built on 1950s machinery.

  13. I ran two marathons lots of years ago, one was left hand
    drive imported from Holland, which I bought from Malcolm
    Harrison Stoke on Trent.
    I changed the oil gave it a grease round and went too Muscat
    Oman.But later I was having head gasket troubles.
    and it died in Austria.

    • I know Astrans, the company that used to operate lorries from Britain to the Middle East, gave up on Leyland Marathons as they couldn’t cope with the desert heat and spares were hard to find. Scania became their lorry of choice in the eighties as it could huge mileages and heat without any problems, the cabs were more luxurious and they had dealers all over the Middle East.

  14. Lack of development time was not the sole reason for home and overseas users to change their purchasing from British to foreign made trucks. I was working for a an interstate trucking company in Australia in the sixties whose fleet consisted of all British made vehicles, mainly Albions, Leylands and Bedfords wih some larger Macks and a Diamond T. These all worked hard and seemed to keep the bosses happy until the dockers strike of 1967/8 when parts became impossible to obtain, so much so that the fleet became a shadow. Within a week of phoning CAV in Acton London to get told that they would not strike break and mail fuel pump parts to Australia so the foreign trucks started to roll in the yard and good by UK made gear. But then they were the dark ages of manufacturing in Britain and bosses had to cut corners to get anything into the show rooms if they wished to beat the opposition with new models.

  15. The article is a very true description of what happened between AEC and Leyland management teams, Lord Stokes did not help, he was very much a Leyland man, and was openly biased against AEC, some people in the know say that he first applied for an apprenticeship at AEC, was turned down and then went to Leyland…
    AEC were known as the engineering led manufacturer, and Leyland the sales led manufacturer… I am sure that a majority of the V8 problems could have been rectified, given the engineering experience at Southall. The V8s I knew in service were run by Marston Bros Ludlow and ETC at Ellesmere both shropshire based companies.
    My interest stems from learning to drive a HGV 1 on a V8 and then passed my test on this fine machine, our local RTITB group training association had one the 3 seats available in the V8 cab….Many good memories…

  16. AEC, another name that was killed in in the madness of British Leyland , and whose Southall and Park Royal factories closed in 1980 with the loss of 4000 jobs. Not forgetting a few miles up the road, the once famous Vanden Plas works in Kingsbury, which became infamous for producing a Vanden Plas Allegro ( although it did build the Daimler Limousine as well), which was culled at the same time as AEC. It makes you weep to see how the incompetence, petty rivalries, rushed product development and internal politics in British Leyland destroyed great automotive names in the seventies and early eighties, think also of MG, left to wither away, likewise Triumph, Wolseley, Morris and Bristol.

  17. In 1970 the truck market was dominated by British trucks and foreign names were almost unknown. Ten years later, trucks from Sweden, Germany and Holland had taken a large chunk of the market, with more reliable, pleasanter to drive and more luxurious vehicles, while some Bedford and Leyland trucks were crude antiques that drivers hated.

  18. All the takeovers, mergers and subsequent shutdowns and bankruptcies were mostly due to the fact that by the 60’s tax fiddling was seen as more important than actually producing anything.
    Whenone company buys another they can deduct the cost from profits and taxes and then claimdepreciation an dtax loss on closings and shutdowns.
    Look through some financial papers fo teh time toi read how Hanson,Slater-Walker and others were praised for imaginary profits as they ‘rationalised’ and ‘maximised return on investment’ when taking over and closing down old British companies.
    Hanson said that any of teh companies in his group could not spend over £500 without his express permission and giving a very strong reason for the purchase!

    • @ Rose White, you tax successful people at punitive rates and have high levels of corporation tax, and it’s no surprises people make a career out of tax evasion. Remember in the seventies, when the top rate of income tax hit 83%, a large part of the entertainment industry went into tax exile and people and businesses who remained found ways round such a crippling tax rate. Also corporation tax was at 50%, which must have been a disincentive to invest in the UK.

Leave a Reply

Your email address will not be published.


This site uses Akismet to reduce spam. Learn how your comment data is processed.