The engine had no lid. That was the strangest thing about it, and for a decade and a half, it was the strangest and most consequential thing in British road transport. Built as a single casting, block and cylinder head fused into one piece of iron, it powered the buses that carried half of Britain to school and the lorries that stocked every trunk road in the country. The firm that made it was a giant, the fifth largest vehicle producer on Earth with 28,000 workers in its truck and bus division alone.

Leland had survived two world wars, the climb from a village smithy, and every upheaval the British motor trade could throw at it. Within a decade of launching this engine, it was quietly dropped, and the company was never quite the same again. The idea belonged to Dr. Albert Fog, the meticulous engineer who joined Leland in 1964 as director of research and became group director of engineering within a year.

He inherited a company built on a century of mechanical reputation. It began with James Sumner, a blacksmith’s son from Leland, who in 1896 found partners in the Spurrier family and formed the Lancaster Steam Motor Company with twenty men and a workshop on Herbert Street. From steam vans came lorries and buses, and by the Second World War, Leland engines were driving Britain’s tanks. Sir Henry Spurrier led it through its greatest years and retired in 1963.

His successor, Donald Stokes, was a salesman with global ambitions. To match them, he turned to Fog. Fog’s answer to the industry’s oldest weak point was radical. Every diesel engine in the world was built in two main pieces, a block and a bolted-on cylinder head joined by a gasket that sometimes failed.

Leland’s own laboratory figures showed the fixed-head design ran far cooler and more evenly, with bore distortion reduced from a variation of thirty or forty degrees around the piston crown to just three. The engine could stand higher turbocharger pressures and run longer between overhauls, with Leland claiming over 300,000 miles. On the 30th of August 1968, the 500 was launched. Eight point two liters, five hundred cubic inches, one hundred seventy horsepower naturally aspirated with a turbocharged version promised above two hundred.

It had an overhead camshaft, exotic technology for a workaday truck engine, and a dry weight of 753 kilograms. The trade press called it revolutionary. The factory built to make it had been built to make weapons. The Spurer Works at Farington opened in 1953 as a government tank factory and was handed to Leland three years later.

The firm that launched the 500 commanded fourteen companies and 28,000 employees by decade’s end. In 1972, Leland built the 500 system, one engine shared across nine truck models from the 16-ton Lynx to the 22-ton Bison, with the turbocharged Buffalo at 212 horsepower. The engine was also meant to power a bus unlike any other. In July 1969, Leland and the state-owned National Bus Company announced a joint venture, the Leland National.

The bus was conceived whole, body and running gear designed together in metric measure for a Britain going metric. It would be built on a flowing production line like a motorcar, not assembled the slow old way, at a new plant at Lilly Hall in Cumberland, chosen to bring work to a region that had lost its coal and steel. The 500 lay on its side beneath the floor in horizontal form, the 510. Lord Stokes called the National at least five years ahead of world competition.

The first bus entered passenger service in April 1972 on the streets of Whitehaven, a few miles from the plant that built it. This was the summit of everything Leland believed about itself. The trouble announced itself in black smoke. Every 510 smoked on start-up, a cloud rolling out from a turbocharger slow to wake and a fuel pump that ran rich.

Operators watched the fuel accounts with horror. Where a rival Bristol RE might return fifteen miles to the gallon on local work, a National was remembered as managing about seven. The deeper troubles came when fitters opened the engine doors. Exhaust valves burned and dropped.

Pistons split or melted at the crown. Oil wept from joints, water seeped from tiny blowholes in the castings. Because there was no head to lift, reaching a valve meant drawing out the crankshaft and pistons and working upwards from the bottom. The whole engine had to come out of the vehicle first and be turned over on a bench.

A job that might take an afternoon on an ordinary diesel could swallow days. The trade gave the engine a name by 1977, the Headless Wonder, not said with affection. The legend at the time blamed the design, but the deeper truth was quieter. The design was sound.

It was the making of it that had gone wrong. Somewhere in the works, a handful of 500s were allegedly built with extra care, blueprinted by hand, and handed to apprentices with orders to run them into the ground. They wouldn’t die. The ones coming off the line failed in the field.

The engine had been shrunk to meet a weight target and fit a cab, ending up smaller and far more highly stressed than it had begun. And Leland, stretched across a struggling car division, strikes, and a financial crisis, had no money to start again. Three decisions built the trap. Fog chose a clean sheet engine instead of refining the proven 680.

The boardroom chose to build the National around the 510 and nothing else, a captive market with no fallback option. And after the crisis of 1974 and nationalization in 1975, Leland had no cash to build the right engine, so it managed the decline of the one it had. Operators in Scotland, Ireland, and New Zealand walked away. Gardner, shut out of the bus, is said to have taken Leland to law.

On depot sheets across the country, a grim new column appeared: Nationals awaiting engines. At one garage, as many as three quarters of its Nationals stood idle at once, waiting for engines that hadn’t come. The consequences reached far beyond the bus. British hauliers, who had bought Leland out of habit and loyalty, began to try the Swedes.

Quieter cabs, engines that didn’t smoke or drink or have to be hauled out to change a valve. They found they liked them. The fixed-head 500 was among the things that held the door open for Scania and Volvo to walk into Britain. Once open, it never closed again.

A reputation built over eighty years did not come back. The hauliers who left did not return, and their sons bought Volvos too. By 1980, the 500 was gone, replaced by the conventional TL11 with a head that could be lifted off. Fires had been reported in the buses, eighteen of them, with a hundred million of fresh investment needed.

Whole businesses sprang up to take the 500 out. In 1985, Crossville began fitting Gardner engines into its Nationals and reported fuel savings of twelve to fifteen percent. By 1986, another firm set its sights on repowering two to three thousand more. Thousands of near-new buses queued for surgery to give them someone else’s heart.

The plants closed or changed hands. The old tank factory became a business park. Part of the Lilly Hall site became a logistics depot. The bus side went through a management buyout, then Volvo bought it, and Workington built its last National in the early nineties.

But Leland Trucks still builds lorries in Leland, wearing a DAF badge now, owned from America, built by local hands. More than a hundred Leland Nationals have been preserved by people who loved them. In 2022, they gathered at Lilly Hall to mark fifty years since the first one turned a wheel. The last operator to run Nationals in earnest kept theirs going until the 28th of April 2007, most of them still carrying their original 510 engines to the end.

The engine you couldn’t fix, that smoked and drank and helped hand the haulage trade to Sweden, still earned its keep more than thirty years on. Look at the clean logic of the 500 now, the slim block, the gear-driven overhead camshaft, and it reads not as a blunder but as a design that arrived too soon for a foundry that couldn’t yet cast it true. The idea was right.

The world just wasn’t quite ready to build it.