A one-of-a-kind tractor considered something of a legend among enthusiasts is pulling crowds to rural trade shows, more than 40 years after rolling off the property of a family-owned NSW manufacturer.

Key points: Carl Upton wanted to design a two-wheel-drive tractor that could compete with American four-wheel-drive models

Carl Upton wanted to design a two-wheel-drive tractor that could compete with American four-wheel-drive models Only one was built and it has changed ownership several times

Only one was built and it has changed ownership several times It has gone on display at regional trade shows for the first time in more than 40 years

The Upton HT14/350 — considered to be the largest factory-built two-wheel-drive tractor in the world — was built by Corowa business Upton Engineering in 1978 and was the last tractor the business ever built.

It was designed by Carl Upton who, in his twenties, was determined to prove that a two-wheel-drive tractor could pull the same load as a four-wheel-drive model.

The last time it had been shown in public was at its launch at the AgQuip Field Days in 1978, but this month its current owner has taken it on the road and put it on display at trade shows.

People travelled from around the country to the recent Mundulla Show in South Australia to see the tractor's public appearance, including organic farmers Andrew and Danielle Taylor from Ardlethan in New South Wales.

"We've done a 1,500-kilometre round trip in three days," Mr Taylor said. "Well worth the trip."

The Upton HT14-350 is thought to be the largest factory-built two-wheel-drive tractor in the world. ( ABC Rural: Leonie Thorne )

To someone unfamiliar with agricultural machinery, the Upton HT14/350 might just look like any other big yellow tractor.

But to enthusiasts and its current owner, it represents an impressive feat of tractor design and a unique piece of Australian history.

Learning engineering at the 'school of hard knocks'

Mr Upton left school in 1966 when he was 16 and went straight into the workforce, helping with his father's business Upton Engineering.

He later went on to complete an apprenticeship as a fitter and machiner but learnt most of what he knows about design through experimentation.

"I often get asked where I got my design skills — my answer is the school of hard knocks," Mr Upton said.

Carl Upton worked for his father's company Upton Engineering in NSW. ( Supplied: Carl Upton )

He spent a lot of his early work life making repairs to tractors that broke down — sometimes in the middle of fields that were thousands of hectares in size — and eventually started making changes to the machines.

After years of fixing transmissions and making repairs, Mr Upton told his father he wanted to attempt something that was inconceivable in the late 1970s — build a two-wheel-drive model that could pull the same weight as larger four-wheel-drive machines.

The family business had collected military paraphernalia and had a two-acre yard full of army tanks, the designs of which would serve as inspiration for the Upton HT14/350.

"Because the Americans started importing the big four-wheel drives, we saw a need to go bigger with our two-wheel drives to give the Australian farmer a cheaper alternative," Mr Upton said.

"So I designed this really big one, and it was — and still is — the biggest factory-built two-wheel-drive tractor in the world."

'Big giant' unveiled in 1978

After a five-month build, the Upton HT14/350 lumbered "like a big giant" onto the agricultural machinery scene at the AgQuip Field Days and outperformed larger machines.

An early photo of the 23-tonne Upton HT14/350. ( Supplied: Upton Engineering )

"Everybody told me at the time you couldn't do it," Mr Upton said.

"But as you can see today [at the Mundulla Show], we are pulling against six-wheel-drive twin-engine tractors, of 450 horsepower, and we are pulling the sled exactly the same distance, with a two-wheel drive and 350 horsepower."

Despite its size and power, the Upton HT14/350 was the only one of its kind ever built and the last tractor built by the business, which today focuses on irrigation technology.

Upton Engineering built machinery on request, and in the 1970s found it difficult to compete against importers offering finance on tractors that were ready to take home from the shop.

But many Upton tractors built pre-1978 were still operational and highly sought after by collectors.

An incredible find

The Upton HT14/350's current owner, David Bowden from Currency Creek in South Australia, had been coveting the HT14/350 for years after seeing it for the first time on a wheat property in Deniliquin, NSW, in 2000.

Tractor enthusiast Dave Bowden purchased the tractor after admiring it from afar. ( ABC Rural: Leonie Thorne )

"We got there very late one night, and we did a few laps in it, and from that day onward I thought, 'I want to buy this tractor'," Mr Bowden said.

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Years later, after losing contact with the Deniliquin wheat farmer, Mr Bowden spotted a tiny newspaper advert that read 'Upton tractor for sale'.

But for Mr Bowden, it wasn't the usual buy-and-sell acquisition — the tractor had been seized by the Federal Police after a raid on a previous owner's property.

"So I rang it up, the bloke said, 'Yeah it's for sale', I said, 'Which model is it?' and he said, 'I don't know, it's just a big tractor'," Mr Bowden said.

"So he went and got the model number and it was the one I was looking for."

Luckily for Mr Bowden, the bank did not know the rarity or value of the Upton HT14/350 — and in 2004 he scored it for a bargain.

'They can't believe they missed it'

So, after changing owners a few times, being seized in an Australian Federal Police raid, and appearing in a DVD series about the world's largest tractors, the Upton HT14/350 became something of a legend among enthusiasts.

"Because of the internet today, there are huge fans following these Upton tractors," Mr Upton said.

"They've developed a cult following, you might say, and people are trying to collect them and restore them wherever they can."

Mr Bowden has done some work and made some repairs on the Upton HT14/350 and has been taking it to agricultural shows in regional Australia.

Other than private viewings, like the one that made Mr Bowden covet the tractor in 2000, this year marked the first time the tractor had been shown in public since its launch in 1978.

Danielle and Andrew Taylor from New South Wales viewing the Upton HT-14/350. ( ABC Rural: Leonie Thorne )

When the Upton HT 14/350's appearance in a tractor pull at the Mundulla Show and the Keith Diesel and Dirt Derby event in South Australia this month was confirmed, word spread among enthusiasts.

The Taylors, who are fans of Upton Engineering, already own a tractor from the company and were excited to see the HT14/350.

"There was only ever one HT built," Mr Taylor said.

"I've noticed on social media lot of people talking about [the Upton HT14/350 appearing at Mundulla] and they can't believe they missed it."

Mr Upton said it was amazing that something he built in his late twenties was still notable today.

"Not bad for a little guy in Corowa who left school at 16," he said.