Allpar Forums banner
1 - 1 of 1 Posts

Premium Member
2,290 Posts
Hillman Imp cars (also Sunbeam Stilleto, Singer Chamois, Husky Estate, Asp, and Commer Imp Van)

based on an article by Keith Adams

Land vehicle Vehicle Car Classic car Coupé
The Hillman Imp's beginnings date back to 1955, when the 1-litre class was gaining sales in the UK. Michael Parks, the project engineer (who later went on to work for the Ferrari F1 team) and Tim Fry, the co-ordinating engineer, were given a clean sheet of paper and responsibility for pushing the new car through. Fry and Parkes thought that the new car should:

  • Have room for two adults and two children.
  • Be capable of at least 60 mph maximum speed and 60 mpg fuel economy.
  • Be fun to drive.

The UK's first gas rationing since World War II, as a result of the 1956 Arab destruction of a Syrian oil pipeline, put more pressure on Rootes to move forward, especially as German "bubble cars" started to sell in quantity, despite poor driving dynamics and safety; they managed to get 40 miles per gallon.

The Slug: Hillman's Imp Concept

Land vehicle Vehicle Car Motor vehicle Classic car

According to Graham Robson, the team soon came up with a highly aerodynamically styled economy saloon named "the Slug," powered by an air-cooled Villiers flat-twin engine. The car's design objectives would have been met, but Rootes board members made it clear they were not allowing Rootes Group to produce a car so similar to the German "bubble cars,"
or to compromise the Rootes Group name by selling an austere car. Allegedly, Lord Rootes hated the sight of it so much, he refused to ride in it.

Motor vehicle Vehicle Car Classic car Automotive design

The board concluded that Rootes needed a small car, but it needed to maintain the quality and solidity of the rest of the Rootes range. It needed a four cylinder engine, and had to accommodate four adults. From this desire to create a bigger, better mini car, Project Apex was thus created; Technical Director Peter Ware saw it to maturity.

The Apex prototypes

Motor vehicle Line art Automotive design Drawing Vehicle
Rootes had no small car engine, and Tim Fry approached Coventry Climax, which made the FWMA aluminium racing engine. Coventry Climax was happy to co-operate, and Rootes developed the Coventry Climax engine was developed into something far more suitable for road use: it was expanded to 875cc, detuned to 39 bhp, and changed for longer life. Even in production form, the engine was more advanced than its immediate rivals, with an overhead camshaft and lightweight construction.

The "clean sheet" approach also extended to the gearbox: one of the problems encountered during Apex development had been gearbox failures, likely due to the "revvy" nature of the Coventry Climax engine, which demanded frequent gear changes.

The new car would needed a transaxle (gearbox and differential in the same housing), but because Rootes had never used this arrangement in any other cars, it hired Adrian West to design and build a transaxle that was strong enough to withstand enthusiastic use, yet be light enough to appeal to all buyers the car was aimed at.
West, who had experience in gearbox design at Simca, Renault, and Fiat, designed a transaxle with high change quality, largely attributable to the use of a baulk-ring synchromesh (something the Mini missed out on at its launch, and suffered from as a result). The combination of Coventry Climax engine and West transaxle was hard to beat; and it was years ahead of the opposition when the Imp was launched in 1963.

After Peter Ware ditched the aerodynamic styling of the original prototypes, Bob Saward's styling department looked to the USA. The Chevrolet Corvair was its model, since it was popular with the young at the time.

Land vehicle Vehicle Car Classic car Coupé
The decision to retain a rear-engined layout took a while. While continental companies tended to use it on small cars, UK companies tended to keep the classic front engine/rear drive layout.

In 1959, Alec Issigonis proved that front engine/front wheel drive was the future for small cars, with the original Mini. Engineers and designers knew that the rear engined family car had been rendered obsolete.

By that time, though, the Apex's rear engined layout was carved in stone.

After driving the Corvair, with its dangerous oversteering, Hillman engineers chose a costly semi-trailing arm independent rear suspension system rather than swing axles; swing axles were used up front, with reduced understeer by lower pivot points.

Production also became an issue with Rootes' cash-strapped status. The British government demanded that any loans be tied to a new factory in an enterprise area. Pressure led Rootes to Linwood, near Glasgow, far from Coventry.

The Apex engineering team was based in Ryton, and was treated as an entirely different entity to the main engineering office at Stoke. Making up for lost time, the Apex programme was hastened towards the end, which meant that several features the engineers wanted to hone (such as the pneumatic throttle, automatic choke, and marginal cooling) were never tested fully. Ware knew the dangers of launching a car without thorough development, and he was proved correct.
Graham Robson related that the Apex was committed to production far too early, probably because Rootes did not want a factory which would be standing idle when declared open in May 1963.

The Imp appears

The Imp was a long way below anything else in the Rootes range.
The motoring press were largely favourable about the Imp. The Imp's superb engine, gearbox, and handling were praised in equal measure. MOTOR magazine, in its road test of May 1963, was very enthusiastic:

Land vehicle Vehicle Car Classic car Coupé
The fact remains, however, that the Imp can be hurled into corners at speeds which would be suicidal with most saloons and with very little roll and no tyre squeal it just motors round them. It is so close to being a neutral steering car that different driving techniques can tip the balance one way or the other.

The gearchange, as we have said is quite certainly one of the best, if not the best we have ever handled.

For an 875cc car, the performance is astonishingly lively and bears comparison with many family saloons up to 1600cc.
Although it was rear engined, the addition of that lift-up rear screen meant that the Imp's practicality was also praised.
Motor was optimistic about the Imp's future: "If Rootes cannot sell 150,000 Imps a year, as they have planned, we shall eat our editorial hat."

However, problems that should have been picked up in late testing soon manifested themselves: defective water pumps and automatic chokes, overheating, water leaks, throttle problems, and lack of performance. A poor reputation for reliability would never be shaken off. Rootes dealers were ill-equipped to deal with such problems, and Linwood's industrial relations were poor from day one, so any running changes were drip-fed rather than rushed in.

Land vehicle Vehicle Car Classic car Coupé
John Simister's retrospective Motor article from 1986 noted some of the issues: "...the cylinder blocks for the die cast engine were cast in Linwood but had to be sent down to Coventry for machining and assembly and returned to Scotland for installation." It was madness, and was repeated with Avenger assembly.

The Hillman Imp's 1963 launch date was too late for another mini-car; the petrol crisis had passed and the economy was booming. The rear-engined layout was now seen as past its prime.

Helping to solve the reliability issues was a major revision at the end of 1965 which replaced the pneumatic throttle linkage and automatic choke, adjusted the front suspension, and made other changes. In 1968, the dashboard and steering wheel were changed; the large speedometer was replaced by a fashionable row of four round pods, putting the speedometer off to the right. The twin stalks were replaced by a single one; both moves were a regression.

The year after the Hillman Imp was launched, Rootes Group turned to Chrysler and exchanged a share of the company for cash.
Losses continued, and Chrysler's takeover of the Rootes Group followed in 1967.

Land vehicle Vehicle Car Classic car Coupé

Singer, Commer, and Sunbeam Imps; Husky Estate

May 1963Hillman Imp
Oct 1964Singer Chamois
Sep 1965Commer Imp Van
Oct 1966Sunbeam Imp Sport / Singer Chamois
Jan 1967Hillman Californian
Apr 1967Singer Chamois Coupe
Hillman Husky Estate
Oct 1967Sunbeam Stiletto
Oct 1968Commer Imp renamed to Hillman
Apr 1970Singer models phased out
Jul 1970Husky and van phased out
Mar 1976All Imps phased out

Even though the Imp was clearly defined as a Hillman at the time of its launch, it soon became apparent that badge engineering would be needed (possibly to avoid the bad reputation of the original). In short order coupé, van, estate car versions became available, and plusher Sunbeam- and Singer-badged versions were phased in. It was never going to be enough. By the time Chrysler was fully in charge of the company, it was clear that any further meaningful development of the Imp was never going to happen.

Facelifts were investigated and dropped, as were larger engined derivatives. The Chrysler née Hillman Imp was a dead-end in the company's history, even though it was eventually turned into a reliable car that handled and performed well. The rear engine layout played against it from day one.

Chrysler neither killed it or developed it; investing more into the small car, with its low price and high costs, was likely deemed a poor idea when there were so many other opportunities (including the Car of the Year Horizon).

The vastly simpler Avenger was also built at Linwood, but the little Imp remained in production until the new Sunbeam replaced it. This likeable small car did not owe anything at all to the Imp (or its front wheel drive design studies) apart from the 928cc slant-four version of the Coventry Climax engine.

In the end, just about half a million Imps were made over 13 years, a far cry from Motor's projections.

Ultimately, the Imp (like the Neon, Volare, and 1957 Chrysler Corporation lines) was a victim of the oft-repeated mistake of launching a car before it had been fully developed. Reputations are hard earned and easily lost...

Troy Winrich wrote that the Imp was imported into the United States; he read that only 40 were left in the U.S.

Sunbeam Imp racing success

To run in stock series, Rootes launched the Rally Imp in 1964, with a larger 998 cc engine; increased power came with ported heads, peformance carburetors, and exhaust changes. Factory-sponsored Imps took first and second place in the 1965 Tulip Rally, and George Bevan's team did well in the British Saloon Car Championship series; Bill McGovern took Sunbeam Imps to the championship in 1970, 1971, and 1972. The car competed in Asia and other parts of the world as well, and continues to run in vintage series.

An stroked Imp engine with twin Weber carburetors powered Andy Chesman's hydroplane, winning the 1972 world champtionship and setting an R1 speed record of 89 mph - a record that lasted over 20 years.

Line art Technical drawing Drawing Plan Diagram

Rootes' engineers knew that the Imp chassis was capable of handling more power; using the existing overhead-cam engine, tuned for performance, and using a body styled by Tim Fry, Bob Saward, and Ron Wisdom, the engineers stirred the pot to produce the Asp.

Land vehicle Vehicle Car Coupé Sedan

Rootes approached Jensen Motors and asked them to study the feasibility of producing the Asp for them, at the rate of 500 units per week. They planned a steel bodied car, with a fallback fiberglass design; it would use the standard 875cc engine, and the option of a more highly tuned 998cc variant.

The Asp project was dropped through lack of resources - Chrysler had yet to inject its cash into Rootes.

Land vehicle Vehicle Car Coupé Classic car

Chrysler 1904-2018

Spread the word via <!--Tweet or--> Facebook!

We make no guarantees regarding validity or accuracy of information, predictions, or advice - .
Copyright © VerticalScope Inc. All rights reserved. Dodge, Jeep, Chrysler, Ram, and Mopar are trademarks of Fiat Chrysler Automobiles.

1 - 1 of 1 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.