Jensen Interceptor

Magazine Subscription

Subscribe to Classic Motoring Magazine and save over 20%

Subscribe NOW

Available at all good newsagents including WHSmith

Do you drive this great classic or are thinking of buying one? Here’s how to ensure that you get the best out of your car for years to come

The Birmingham Ferrari, Jensen’s Interceptor, is perhaps the best supercar for the DIY enthusiast thanks to its old school American V8 engines and a chassis design that dates back to the 1950s. They are no longer the bargain buys they were just five years ago, but can be maintained relatively cheaply. Parts supply is very good, via an army of specialists, plus it used many parts from mainstream carmakers. Here’s how to keep your Jensen on the button!

1. Power output

Mod

Magnificent Mopar motor yielded 330bhp min and 385 in tremendous triple carb SP (Six Pack 7.2). If in good tune and you want more, there’s no shortage of tuning gear in the US – racier Crane cams, gas flowed heads, Edelbrock carbs etc, plus some have experimented with modern mapped fuel injection systems and claim 20mpg!

Mend

Famous Chrysler V8 is unstressed and so very durable. Chief concerns are broken exhaust manifolds which are pricey at on average £450- £500 to replace, and inherent high underbonnet temperatures that can take their toll on head gaskets and fuel lines along with making electrical wiring brittle. Car is a known overheater so ensure cooling system is top notch; consider fitting an uprated rad and fans.

2. Brakes

Mod

Jensen employed a Dunlop system on all models but then moved to Girling and used vented discs on the MkIII, albeit of a slightly smaller diameter. EBC pads are the logical first step before moving onto Fosseway Performance’s range of tailored upgrades including bigger discs although the most extreme conversions require moving up to 17inch wheels and tyres to enable fitment.

Mend

Most issues are caused by lack of regular use, allowing parts, such as calipers to seize up. Discs corrode too; £99.50 from Robey, pads £28.50. The twin master cylinder is expensive to replace (£240) but can cause some imbalance due to wear rates or fluid state; change first to see if it improves matters. Dunlop anti-lock parts rare (such as servo) plus requires specialists to repair and set up.

3. Bottom end

Mod

JIA cleverly fitted modern 5.7-litre Chevrolet engines and that vast engine bay can accept a variety of power plants, including ‘our’ own Rover V8 (along with a five-speed gearbox). There’s considerable stretch in these Chrysler engines by reboring – well in excess of 8-litres depending upon block size and if you use a standard crank of offset. See numerous ‘Mopar’ websites for more details.

Mend

It’s an old school V8 so simple, if heavy to repair at home. Oil pressure should be 40-60lb. Timing chain noise is common while irregular servicing leads to oil sludging so affecting the hydraulic tappets. A rebuild costs £5000ish. According to US experts, these engines ran with far too much ‘ignition retard’ and advancing it plus electronic ignition can see major gains without holding pistons.

4.Suspension

Mod

Conventional old Austin, design responds to orthodox uprating by way of better and adjustable damping (Spax, units typically averaging out at £110 a corner) before tackling the springs at £457 a pair (quality BCC ones) from SVC. Replacing worn bushes with poly substitutes available is a good move, such as as a leaf spring shackle kit (Superflex, £45) or full Superpro all-in kit at £182.

Mend

A big heavy supercar the suspension suffers so expect tired dampers and springs. Rear end settles; you should be able to insert two fingers easily between tyre and wheel arch gap. At the front, tired bushes plus worn wishbone and swivels need regular watching. Power steering is prone to leaks, invariably by the track rod ends and as an episode of ‘Wheeler Dealer’ showed, it’s a pig of a job even with the aid of a pit or lift.

5. body & chassis

Mod

Rebirth of the modern Interceptor gives potential scope to modifying the looks to fall in like (speak to JIA etc) although originality will count for most as years roll on, says experts Cropredy Bridge who is now making build to order new Interceptors. Martin Robey has details of the cars made and what options, etc were specified from new.

Mend

Panel supply, new and second-hand is pretty good thanks to experts like Martin Robey who purchased Jensen’s tooling as soon as the company closed. Bonnets (which differ depending on model) cost £1000 to fit, stainless side sill panels £195, side vents less than £50, sill assemblies around £2000 per side (fitted) but front wing part panel repair kits can be had for under £200.

6. Interior

Mod

Biggest change was the dash layout (some prefer original look) while dash top was changed to padded on later models. Tan was most popular trim colour (505) followed by black (393) and beige (392); only one chose biscuit, green and grey – some cars featured sheepskin trim. Wooden dash followed from 1974. Most popular mod is a nicer steering wheel over garish Jensen designs.

Mend

As posh as an Aston or Rolls, thus renovating a tired interior will cost equally as much! Rejen and Robey can supply new items but a retrim can cost £5000 and above depending upon model as later cars boasted walnut wood, although carpet sets generally cost a few hundred. Switchgear etc was sourced from a variety of carmakers, convertible top costs just under £700 from All Hoods Ltd.

7. Body & chassis

Mod

If you’re thinking of buying one, experts say that build quality dropped significantly when the MkIII was launched. Chassis is essentially the same as previous CV-8, part supply good but paints can be a problem as Jensen was in a habit of mixing up any colour to a customer’s choice but, officially, 241 were white, 77 yellow, 37 tangerine and 69 black. Robey has histories.

Mend

Rust along with cheapskate repairs are a worry. Wings, tube sections, floors (particularly at pedal box), sills, valance panels all dissolve with delight and if you’ve just bought the car, expect to see poor repairs due to historic lowly values. Box sections rot on the FF and sill condition is critical as they house vacuum tubes for braking so if they rot, no matter how minor, retardation efficiency is reduced.

8. Wheels & tyres

Mod

Best speak to Rejen, Robey etc on this. Interceptors started with 5inch items, 6in for FFs which can just about take a modern 205/70 tyre although can look ‘fat’; a 185 or 195 is probably best. Longstone can supply original 6.70 crossply tyre but recommends Pirelli Cinutrato or Michelin 185VR15 XVS but says if you’re on a budget then the Vredestein is the wisest choice with the 205/70VR15 Michelin XWX tops for a Jensen Interceptor III.

Mend

A variety of wheel designs were used and as a rule, the earlier the car the harder they are to source (ie Ro-Styles were pinched for Rover P5s!). As with all 4x4s, it’s important the wear rates are kept as uniform as possible or it can screw up the FF differentials. Speak to a tyre expert for the best type and size and have a four-wheel alignment check if it hasn’t been done for a while.

And another thing…

Leading Interceptor specialist Cropredy Bridge Garage has gone full circle by making its own built-to-order £100,000 Cropredy Interceptors. The Oxon-based specialist helped develop the Chevrolet-engined JIA models but now concentrates fully restored originals and allowing only modest improvements incorporated during the rebuild, such as better brakes and basic suspension modifications, if desired. If buying an early Interceptor, it may be that a later 7.2-litre unit has been fitted and you can ascertain this by noting the angle of the exhaust manifold bolts; they will point downwards on the later engine, say experts.