The Ursus C45, with its single-cylinder hot-bulb engine, was built in large numbers in Poland.

Production started in 1947 and Dave Bickers remembers seeing them when he visited the country in the 1960s to compete in motorcycle races – he was seven times British champion and European champion twice.

“We saw them on the roads,” he says.

“Few Polish people had cars in those days and farmers used tractors instead.

The C45 had a front axle suspension a long time before it was available on British tractors because it was more comfortable on poorly surfaced roads.”

Ursus based the 45hp C45 on a Lanz Bulldog built in Germany in the 1940s and early 1950s.

A special feature of the Bulldog and several other Continental makes was the hot bulb or semi-diesel engine.

They were never popular in Britain, but many farmers on the Continent preferred a single-cylinder engine with few wearing parts and the ability to run on any liquid fuel including diesel, paraffin or old sump oil.

Hot bulb engines do not normally have a spark plug and use a hot spot inside the combustion chamber to ignite the fuel, but starting them requires patience and a strong arm.

A blowlamp heats the cylinder head to bring the hot spot to the required temperature – a 20-minute job that allows time to remove the steering wheel and attach it to the flywheel.

When the cylinder head is hot the steering wheel is used to turn the engine backwards and forwards against compression until it fires – and it might go either way because these engines run backwards or forwards.

Dave Bickers bought his Ursus about five years ago for 3000.

It was in working order apart from a leaky radiator, but when he started the restoration work in his workshop at Ivy Farm, near Ipswich, in Suffolk, he found that the oil pump had not been working properly.

“At some stage in its working life the maintenance was very poor,” he says.

“There was a lot of engine wear because of the lubrication problem and the clutch was badly worn.

Nearly all the split pins on the tractor were replaced by nails, even within the engine.”

Finding parts was easier than expected.

Ursus and Lanz engines are so similar that components are interchangeable.

With Bulldog tractors popular on the Continent, spares are plentiful.

For Mr Bickers, who also restores old motorcycles with small engines and fine tolerances, the big Ursus engine was a new experience, with its 24cm (9.5in) diameter piston, a gudgeon pin measuring 5cm by 20cm (2in x 8in) and a 13cm wide, 10cm diameter (5in x 4in) big end.

The crankshaft was so big that it was difficult to find anyone who could regrind it.

As well as engine parts, the 1000 restoration bill included eight new brass radiator cores at about 60 each and 300 plus for replacement clutch parts including four of the 43cm (17in) diameter plates.

Instead of cranking the engine, Mr Bickers has converted it to electric starting using a spark plug, a trembler coil and petrol from a small auxiliary tank.

When the engine is hot enough the fuel is switched from petrol to diesel.

Similar equipment was available as an option on Lanz and other Ursus tractors.

Bickers Action, the family engineering business that makes stunt equipment for films and TV including many of the Bond films, has excellent workshops.

“Apart from the size of some of the parts, restoring the Ursus was not a difficult job,” says Mr Bickers.

“Most farm workshops would have the tools needed.

We’ve ended up with an unusual and interesting tractor.

It always attracts a lot of interest at rallies.”

fwmachinery@rbi.co.uk