Hillman Imp
1963–1976 · Linwood · all-alloy overhead cam · and drums all round, first to last
The swing axles are at the front. The Imp is not a Corvair, and its engine is not a Coventry Climax.
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About the Hillman Imp
The Imp’s engine is the reason people still love it: an all-aluminium overhead-camshaft four, 875cc, water-cooled, canted at 45 degrees to keep the centre of gravity low and hung out the back over a transaxle. It was inspired by the Coventry Climax FWMA and then thoroughly redesigned for road use and detuned to 39bhp — so it is a Rootes engine, and no Climax part number applies. 440,032 were built at Linwood from 2 May 1963. Now the suspension, because this is the most repeated error about the car. The front is independent on U-shaped swinging semi-axles with coil springs and telescopic dampers. The rear is independent on semi-trailing arms — chosen deliberately because testing showed rear-engined cars on swing axles oversteered. The swing axles are at the front, not the back.
Brakes are drums all round for the entire 1963–76 run — two leading shoes at the front, 150 sq in of lining, and there was never a factory disc. Disc conversion is a common owner modification, so ask what is actually on the car. One genuine factory difference: the Sunbeam Imp Sport and the Stiletto came with a servo, along with twin Strombergs, a higher-lift camshaft, bigger valves, an oil cooler and a larger radiator. The other dates worth knowing are 1965, when the Mk II brought a water pump, a better head and conventional throttle and choke in place of the pneumatic throttle and automatic choke that gave the car its reputation, and 1968, when Chrysler redesigned the instrument panel and steering wheel. In New Zealand Todd Motors assembled 4,825 Imps between 1963 and 1965, and four-headlamp Sunbeam-badged cars in 1969–70.
Hillman Imp — specification & changes within the model
- Brakes
- Drums all round, 1963 to 1976, no exceptions and no factory disc option. Two leading shoes at the front, 150 sq in total lining area. Disc conversions are common — ask what is fitted. The Sunbeam Imp Sport and Stiletto had a servo; standard Imps did not.
- Suspension — and the error everyone makes
- Front: independent, U-shaped swinging semi-axles, coils, telescopic dampers. Rear: independent, semi-trailing arms, coils, telescopic dampers. The swing axles are at the FRONT. The “British Corvair” line has put the opposite into circulation and it is wrong. Front camber was later reduced by lowering the pivot points, and the Mk II had improved front geometry.
- The engine is not a Coventry Climax
- Inspired by the Climax FWMA, then redesigned — expanded to 875cc and detuned to 39bhp for road use. No Climax part number applies. All-aluminium, overhead cam, canted 45 degrees. 998cc also offered.
- 1965 — the Mk II fixes the reputation
- The launch car’s pneumatic throttle, automatic choke and marginal cooling were never fully tested, and the trade came to know it for water pumps, chokes, overheating and leaks. The Mk II added a water pump, a head with larger ports and valves, and replaced the pneumatic throttle and automatic choke with conventional items.
- Looking after an aluminium block
- Water pump at least every 25,000 miles. Neglected coolant corrodes the alloy and leaves flakes of metal floating in the radiator. The rubber doughnut drive couplings crack — check them.
- 1968 — the facia change
- Under Chrysler, the instrument panel and steering wheel were redesigned to a horizontal gauge layout. Facia and instrument parts split there.
- Same car, other badges
- Hillman Imp · Imp Californian · Hillman Husky (1967–70) · Singer Chamois · Chamois Coupé and Sport · Sunbeam Imp Sport · Sunbeam Sport · Sunbeam Stiletto · Commer Imp van. But the Californian, Chamois Coupé and Stiletto share a low coupé roof that is not the saloon’s — that roof, its glass and its seals are their own.
- New Zealand
- Todd Motors assembled 4,825 Imps here, 1963–65 — 125 in 1963, 2,500 in 1964, 2,200 in 1965 — plus four-headlamp Sunbeam-badged cars in 1969–70. (Enthusiast registry figures; the 1969–70 number is an estimate.)
- Where they rust
- Wheelarches, sills, door bottoms, bonnet, rear screen pillars (which in practice means a failed rear screen seal), floorpans and suspension mounts. King pins and bushes wear.
- Not claimed
- Earth polarity, and any chassis or VIN breakpoint for the Mk I to Mk II change. 12 volt with a dynamo is confirmed.