Big Healey guru John Chatham has put together the
ultimate 100/4 using high-tech engineering and a bullet-proof
engine. Mick Walsh prepares for some sideways action

It's difficult to imagine the hearty Healey guru John Chatham as a 12 year old pedalling down the Gloucester Road. But he still vividly remembers the day he fell in love with a Healey 100/4: "I was a regular fixture with my nose pressed against Henlys' showroom window, ogling a glorious red 100/4 revolving on a plinth. I'm sure its seductive curves induced my first orgasm," John recalls bursting into laughter.
Close to 40 years later, the bristol-based specialist is almost as enthusiastic about his first Healey love, having recently turned his attentions to a pretty 'four' after several decades of setting the pace on track and stage with his trusty 3000 racers DD 300 and GRX 884D: " My first Healey was a 100/4 and I won awards in just about every form of motor sport- rallies, driving tests, sprints, races and hill climbs, and then drove it to work again on monday morning. We'd shave lumps off the cylinder head to go quicker, but at the circuit it was simply aeroscreens and taped headlights. Its all-round capability always struck at the back of my mind."
That was back in 1962; it wasn't until last year that Chatham turned his attention again to the 100/4: " I knew it would never have the legs on the 3000 for the circuit, but for events like the Classic Marathon, I always considered it a more nimble car. The long stroke four has immense torque which provides effective punch when you really need it - particularly for hairpin bends. My goal was to prove the 100/4 could be quicker than the 3000."
Last year on the Marathon, John really proved his point. On the second timed stage in Belgium only the 'flying finn', Timo Makinen in a Mini Cooper was quicker. First time out of the box the 100/4's potential was proven, although the rest of the event turned out to be a disaster for Chatham's immaculate silver machine. On the first stage in England he holed the sump, and later in Germany a clutch hydraulic failure put him out of the running.
John's project - the development of the ultimate 100/4 - is essentially based around the 2.5 litre Austin diesel engine as used in the FX4 London taxi. Geoff Healey had considered this proposal many years ago when Austin Healeys were still in production.
The Austin diesel engine has a bullet-proof block and crankshaft to withstand the 22:1 compression ratio necessary to run a compression ignition engine and therefore overcome the inherent weakness of the original A90 petrol engine. Both Dave Jeffery of SC Austin Healey Parts and John Chatham were keen to see if Geoff's original proposals could be made to work. Design and development started seriously at the beginning of 1990.
It was decided to retain the shorter stroke of the diesel engine (101.5 mm compared to 111mm for the A90) in order to allow a higher revving engine and to avoid alterations to the substantial crankshaft. This is a nitrided EN40B forging with larger bearing sizes than the original. The block was over bored into the water passages, and then linered using specially made thick wall liners. These were then bored to virtually 91 mm for a capacity of 2615cc ( compared with 2670cc originally ). Ford Sierra Cosworth pistons were used and new con rods specially made ( the diesel rods being much too heavy for a high revving engine).
The top of the diesel block has a multitude of studs, non of which lined up with the holes for the petrol cylinder head. Two studs were very close and one of SC's new 100/4 alloy heads was machined specially to suit these. The rest of the studs in the block face were blanked off and the remainder of the studs required to fit the head specially drilled. All of the studs were specially made in EN24 heat treated to 80 tons to enable torquing up to 125 lb ft. Because of the engine family resemblance, the pushrod holes and combustion chambers lined up well enough.
SC had previously spent a considerable a considerable amount of time and resources with the Institute of Noise and Vibration at Southampton University. This work had been to overcome various mechanical failures caused primarily by crankshaft and camshaft torsional vibrations when the six-cylinder Austin Healey engine was producing large amounts of power at high revs. Now it was the turn of the four cylinder.
Research with the six-cylinder engines had shown that only static testing would be required with the four-cylinder diesel crank. Fortunately, the bullet-proof assembly passed with flying colours, with the comment that there could be a serious vibration period at 14,000 rpm! Not a problem.
SC now had a bullet-proof petrol engine but nowhere to put the distributor ( diesels don't use them ). The distributor probably could have been fitted under the inlet and exhaust manifold but this was not considered a viable option. Thus the problem was solved by fitting the distributor where the injection pump was fitted on the diesel engine. This meant using the diesel's timing chain layout but this was a heavy triple chain arrangement designed to run a maximum of about 3500 rpm. A completely new double chain layout was designed and made using modern dampers together with a specially designed oil-fed tensioner. A modified VW Golf distributor is used, pointing backwards from the timing cover under the dynamo.
Two 2 inch SU carburettors are used, together with a very special large bore exhaust manifold. The camshaft is ground to a profile similar to that used on the last of the works six cylinder competition cars. About 150 bhp has been recorded at the rear wheels, probably about 170 bhp at the flywheel, at around 6000 rpm. As the engine is quite happy running up to 7800 rpm there is obviously a lot more development possible. Larger carburettors ( Weber probably ) together with a much more extreme camshaft will release a lot more horsepower.
Once dave Jeffrey had completed development of the engine, John set about preparing a car to use the new levels of power. He had been saving just such a project for over 20 years, having previously acquired a well known alloy 100/4 once club raced by Mike Wakefield. Registered OYY 210 and fitted with a genuine 100S engine, John had made overtures that he'd be interested in acquiring it if it were ever sold.
Unfortunately he was on holiday when the owner made contact and by the time john returned the prized engine had been sold separately, but the rest of the car was soon back in Bristol. Over the years the car has been pillaged for other restorations but the alloy shroud, doors and boot were an ideal basis for the new project.
The suspension specification is simple: heavier front anti-roll bar and stiffer spring rates than standard, and heavy duty shocks all round. The bushing and locating points are all standard, while a touch of negative camber is employed at the front. Front discs are Girling MK1 spec with DS11 pads which have always proved effective enough hauling up the works 3000s. A twin plate competition clutch helps keep the massed weight down on the crank. Tulip straight cut gears and a competition 22 per cent overdrive provide an ideal set of six ratios to dial in the power, with the switch mounted on a standard BN2 gear lever.
A 20 gallon tank, 12-volt battery and spare wheel pack out the boot and leave next to no luggage space. The six point roll cage is cleverly disguised by a handsome alloy hard top, while the lower front cross bar proved ideal to mount Halda, navigator light and Speedpilot. The top also hides the non period high backed Kevlar rally seats but no sidescreens are fitted as John prefers to enjoy fresh air conditioning, and resents restricted vision - an important consideration as he tends to spend most of his driving time sideways. The instrumentation is as stark as a standard 100/4, but with the installation of a modern rev counter.
The exhaust is an inspired design by John, who was not keen on suffering a noisy under door exit or leaving the system on the road at the first stage. A slightly longer inlet manifold flows into a large diameter main pipe which is strapped up high to the chassis. The rear shroud and crossmember have been cut away to gain extra clearance and, combined with protective skids, the system survived intact after the demanding conditions of the Marathon. Quite an achievement for any full length Healey system.
The cars weighs in at 960 kgs compared to 987 kgs of the standard car, but that's still heavier than the 100S. As with most competition projects and event deadlines, the preparation of OYY 210 ran out of time for the Marathon. John would have preferred a longer shakedown but the finished car looked superb in Mercedes silver with red wires at Tower Bridge for the start. A holed sump on the first stage in England was gamefully patched with the help of the unipart service barge, but after setting a scorching pace through Belgium, those clutch hydraulics failed in Germany. In the pouring rail John and loyal co-driver Ken Bartram took the gearbox out at the side of the road, without the co-operation of a miserable German garage proprietor who refused to open up and allow the use of his ramp. Although by then well out of the running, the 100/4 continued to prove it's stamina and potential on the event. The run back with a pair of 3000s also provided an interesting mpg test. Using accurate mileage's measured on the speedpilots, the 100/4 returned a healthy 28 mpg compared to a 23 mpg best by the six.
True to the 100/4 experience, the interior leaked like a colander during downpours, soaking the driver and navigator. Under bonnet heat is still a continuing problem, particularly in traffic: the radiator is already extensively ducted by heat outlets are still not enough. Fuel vaporization is a big problem, particularly when waiting for the start of a special stage. The exhaust manifold is already wrapped in asbestos, but the car continues to stutter when the light goes green. A fuel return system could be the answer in an attempt to keep the gas cool.
John is determined to return and is also considering a team of 100/4s for next year's Mexican Carrera PanAmerican retrospective, but since the Marathon disaster OYY 210 has fulfilled all his ambitions on the circuits. At Mallory Park for a Healey Club Championship round John debuted the 'diesel', psyching up arch-rival Dave Hardy about his "secret development engine". Hardy has been campaigning 100/4s for many years, so holding him off to take second overall first time out was a proud achievement. The heated 10-lap tussle saw the two cars just 1.5 secs apart at the flag. Constant lap times of 48 secs were only 2 secs off Chathams Mallory best with DD 300.
Other highlights of 1991 were the Last Healey race of the season at Castle Combe when, in a father and son challenge against the Welch and Hardy clans, Joe Chatham in his first ever race came home sixth with OYY 210. Dad couldn't catch Dennis Welch but Joe headed the other sons to take overall glory for the Chathams. Next came a visit to the isle of white for the traditional Healey Club weekend which provided the opportunity for Geoff Healey to test the car. He returned after a brisk drive, and in his usual guarded manner just hummed and puffed on his pipe, without forwarding any definite judgement. However, about half an hour later he returned and complimented John that he thought "the engine was fantastic". He said it immediately reminded him of x224, the modified 100S chassis that the Cape works fitted with a Ferrari 2.5 litre, four cylinder F1 engine. High praise for the Austin diesel based unit.
As for John, well he'd still rather drive a 3000 on the circuit - namely his treasured evergreen racer DD 300: " I'm a sucker for its ultimate grunt, but the 100/4 is the best all round Healey. It's so easy to drive and the new engine has definitely cured the lazy response of the four without loosing that desirable low down torque. This one still really thumps from low revs. Everybody still considers them the pretty, no go Healey that could be licked by a TR, but we've certainly woken this one up. All the effort of the development has been worth it just to prove that. And I enjoy driving it more than GRX", John concluded. And for anyone who understands John's long affection for his 3000 rally warrior, that is quite a conversion.
Driving The Chatham Healey 100/4
To my mind the 10/4's cockpit lacked sporting charisma at the best of times. Gerry Coker's original styling sketches had a flashy American look, but the end result was basic and simple. Chatham's warrior is functional to the last with roughly cut carpets and black satin paint finnish on the dash and panels. Already the worn and scratched interior indicates the tough action this pretty car has already encountered.
Apart from the modern tacho, standard dials straddle the thick small leather rimmed wheel, while a large orange oil pressure warning light sits dead centre. Spread across the normally bare curve of the dash to the passenger's door are indicator knob, master switch and extra horn, while the Halda rally equipment is hung underneath on the rollover bar brace.
The gearstick is crooked well back to the driver's side and topped with a spun aluminium knob cleverly incorporating the overdrive switch. The plain door pockets are the only storage space, while inside is a cable door pull which aids rapid navigator exit to stop the clock at the end of a special stage.
The modern high backed rally seats are as tight fitting and as superbly supportive as you would expect. But in a fifties car, I can't forgive their unsuitable image, although thankfully the hard top hides them away. Strapped up in the harness, the driving position is still typically Healey - seated flat and low with legs straight and elbows bent for the close wheel. There's little to get nostalgic about in this gutted cabin as supreme function is the primary concern. So down to business: turn the centre ignition key, press the starter button and after a couple of churns the engine catches, sounding gruff and lumpy, more like a rally Escort than sporty Austin. Flex your right foot and the engines reformed response is instantly apparent, so much more revvy than the Agricultural fours I've previously encountered.
Out on the Road and opened up, the engine is little short of sensational, particularly in such responsive chassis. It takes a while to adjust to the extra revs in the 100/4 - changing up at 5500/6000 rpm rather than the standard 4000 rpm - but little of the engines low-down urge has been lost with the extra flexibility. But from 4000 rpm you really feel the power delivery as it spins to unheard of rev limits for such a humble truck engine. With close-cut ratios, the normally sluggish BN2 gear change is no handicap, and up to 60 mph, it could shave at least a second of a 100S. John reckons she's good for 7 secs, but the engines wide power spread is it's big appeal. The purists will decry its new performance as erroneous to the true character of the 100/4, but I bet Geoff Healey wished he'd pursued the development of the diesel after he'd sampled Chathams racer.
The combination of the direct steering, the bite of the improved brakes, the neutral chassis balance and the rapid six-speed with its trigger overdrive ratios inspires confidence. Even on the slippery, desolate roads down by the Severn estuary, this superbly sorted machine was irresistible. Dialling in the ratios with the engine singing at the top end, it feels and sounds proudly exotic. Later, watching John play to the photographer, powering through the turns and flicking the tail out on the damp roads, the exhaust rasp sounded more Moderna than Warwick. With John's enthusiasm for the project, it's a sound we shall hear regularly setting the pace on stage and track - when he can keep the wheels on the ground........
Mick Walsh

Article written by Mick Walsh and published in the March 1992 edition of Classic and Sportscar magazine