sidecar has been converted from rear-exit to front-exit layout to conform with CRMC rules
Pete Sutton (motoring journalist) stretches over the Imp engine, while Mark Camp tries to keep the rear wheel spinning
engine is angled backwards to gain downdraught effect via the two twin-choke Weber carburettors
leading link fork and twin disc brakes control the front wheel
with an estimated 120bhp on tap, the rear wheel can easily be persuaded to step out
not exactly a lightweight! Maze of coolant pipes makes the bike look complex
the machine has a healthy appetite for its 5 x 10in Dunlop Mini car racing tyres
sheer size of the machine is intimidating for the newcomer until its predictable handling becomes apparent
25 October 1972
Stamped on the drive casing are the letters 'KGB' with the date 25-10-72 - the only clues to the creators of this bulky masterpiece - Keith Blainey and sidecar racer Peter Williams, of Birmingham. Williams recalls how the outfit was born: "I got to know Keith Blainey when I raced BSAs - he was a neighbour of Peter Brown's you see - and we'd often meet there. Keith was a genius with engines, and had a lot to do with Formula-Four car racing, which was all Imp engines at that time. One day he said: 'You should stop messing about with twins and build an Imp outfit'. I said there were loads around but none of 'em had any go!"
Blainey guaranteed that the engine would be good, so the two built the first of the three 'KGB Imp' outfits they made. Williams did most of the chassis work, with Blainey concentrating on the engine and transmission. He claims that they were the first to use the drive system that Stuart Pearson, another Imp constructor, later gave his name to and remembers that the worst problem was the overstressed Norton gearbox.
"We had six boxes explode on us, and it got a bit dodgy flying into corners with the whole thing locked up. So what we did in the end was fit a rear sprocket almost as big as the back wheel and gear back from that to speed up the gearbox and reduce the torque loadings. That cured it completely: in fact we even had Norton's on to us to find out what we'd done, as they were having the same trouble on their John Player bikes!"
When they had finally sorted it, the outfit was indeed fast and Williams had many successes, including a 3rd place at the 1974 British GP behind Schwarzel and Boret on Königs, and the Ulster GP lap record at Dundrod the same year with a speed of 95.13mph using an 875cc motor, although they crashed later. That record stood for many years, but Williams soon moved to two-strokes as Königs, then Yamahas, had arrived. He thinks the Nelson/Camp machine was the second one they built, racing it for about six months before selling it to sidecar stalwart Bryan Rust some time in 1973.
Intelligently utilizing the engine as a stressed frame member, the chassis has survived the years relatively unchanged. The complete steering head sub-frame can be unbolted and wheeled away, leaving the engine free for major strips. The top rails covering the cam box are also detachable. Overall, the integral chassis is a thoughtful and functional, if heavy, construction typical of a 'progressive traditional' design of the early 1970s, when racing sidecar technology was in a turmoil of experiment and innovation, poised to leap into today's monocoque and space frame age. Twin eight inch discs brake the front wheel, one operated independently by the handlebar lever and the other by the footbrake, which also brakes the rear and sidecar wheels. Wheels and brakes were supplied by Terry Windle, and the outfit eats up the Dunlop 500L-1O CR65 Mini racing tyres at £75 a time.
In 1986 Richard Nelson (25) and passenger Mark Camp (26) were in their first year of chair racing, still wearing orange novice overalls. They were the surprise winners of the Classic Sidecar Race of the Year at the Donington Park Classicfest after early leader Pete Krukowski's BSA twin expired. With no prior knowledge of racing sidecars, and almost none of bikes of any sort, their victory over a lot of experienced crews was impressive. But they are not complete newcomers to racing, as Richard explains.
"We were doing all right in cars. Mark has more than 90 trophies for Destruction Derbies, and won the 1985 Saloon Stock Car Championship at Leicester in an Escort RS 2000 that I was preparing. In fact between us we were winning everything, and got fed up with it!"
Because they made a pretty good team, they looked around for a motor sport that would provide more challenge that could be shared. One evening in the garage Mark suggested sidecar racing, and soon they'd acquired a battered, well-used Imp-engined outfit from a club racer in Clitheroe, Lancs.
"When we found out that Imps were still in with a chance in the Classic club, we thought that would be our best bet, because I already knew a lot about them. Besides, they are dead cheap to run: you can get a set of pistons for £30!", said Richard.
They bought the outfit early in 1985, and in between stock car racing spent the year refurbishing it. The 12in. wheels needed changing to 10in. because 12in. treaded CRMC eligible tyres are unobtainable. The 'modern' rear exit position had to be altered to comply with club rules, and the chassis tubework was strengthened and tidied up.
A first outing at Brands Hatch in October 1985 was pretty disastrous. Mark remembers: "Neither of us had a clue what to do: I was watching the other passengers to see which way to hang out!" Even so, they came 10th in their first race. In the second, though, the big ends gave out. A previous owner had converted the engine to 'dry sump' with a Gardner diesel engine scavenge pump to return the oil to a tank in the sidecar nose. Surge on corners was causing momentary oil starvation.
The winter was spent studying videos of sidecar racing to brush up on technique, and tuning the engine. The oil tank was thrown away and an eight-pint sump fabricated. Neatly made, and crammed behind the front wheel to maintain ground clearance, it incorporates a level indicator and breather tower. Richard and Mark use Silkolene 'Pro 4' semisynthetic oil, changed frequently. At £104 for five gallons, though, any offers to buy it for them will be carefully considered, says Mark, the financial half of this efficient team.
A high-capacity adjustable competition Hillman Avenger oil pump feeds the tuftrided crankshaft. The steel con-rods are standard items, lightened and balanced, but with bigger diameter 3/8in. end-cap bolts. Richard, who does the engine preparation, spent a lot of time on the head, putting in larger valves, flowing the inlet ports and skimming it to give an 11:1 compression ratio with the Powermax high-compression pistons. The chain-driven overhead camshaft is a lumpy full race one, reputed to come from a twin Imp-engined road bike. Jammed in behind the steering head, two twin choke 30mm Dell'Orto carbs are fed four-star pump petrol from a 'Facet' electric pump through a paper filter and pressure regulator. Typically for outfits of this era, the fuel is carried in the sidecar wheel arch. Electronic 'Lumenition' 12 volt ignition is admissible under CRMC rules (they advise that it be concealed) so the 'black box', coils and a rev-limiter set to cut out at 1O,OOOrpm are carried underneath the kneeler tray moulding.
There are probably as many ways of mounting the engine and transmission as there are Imp outfits, but the Nelson/ Camp machine flouts the usual convention of laying the engine flat as in the car. Instead, it's angled backwards at about 45 degrees, giving the breathing a better downdraught effect and improved volumetric efficiency, according to Richard, and making access to the engine easier at the expense of a slightly higher centre of gravity. The hydraulically-operated Imp clutch is retained along with its bellhousing, onto which is welded a 'Pearson' type oil bath primary drive casing. Inside is a triplex chain, driven by a sprocket on the engine mainshaft to a gearbox chainwheel where the clutch would normally be. This is carried on a shaft supported by outrigger bearings which takes the power, via an Imp 'rubber doughnut' shock absorber, to a standard Norton gearbox hidden away beneath the engine, somehow managing to carry nearly three times more power than it was designed for.
Preamble over, the moment had arrived. Burbling up the pit lane to the Mallory Park track, the glass-fibre bodywork gently scraping on the bumps, I remembered Richard's instructions: "Mind the wheelspin; watch the oil pressure doesn't drop below 35lb as the pump body's scored; don't use the front brake hard as it'll lock the wheel; and don't rev it much over eight and a half." All counsels to caution, as if the prospect of unleashing 120bhp and a quarter of a ton whilst prostrated inches from the tarmac wasn't enough! Mark waved me into the traffic, I wound the feather-light quick-action twist grip, the motor's note instantly changed to scream with no hesitation or hiccups, and off we rocketed - pure power all the way from 3,500rpm.
If I'd had any doubts about driving this huge lump they were a waste of energy, because the KGB Imp is the most enjoyable three-wheeled experience I've had. Within a couple of laps I felt at home enough to start pushing it into the corners, and discovered that the harder you went the more it fed back. Into the endless curving right hander of Gerards, for example, you have to go in fast. Flat out in top on the straight, you dab the brakes and knock it down a gear, then hang on the power as the bend tightens. If you've got it right, the tail will step out and you'll enter the corner under power, drifting well, but with the front wheel tucked in and understeering. You can't see it, but the angle of the bars tells you, and you hang on tight: the steering and throttle need a firm grip. Underneath, the motor's bellow rises to a crescendo and the shaking tacho needle is near the red line, so you drop it into top somewhere half way round. The handling seems unaffected. You're going very fast, drifting less now, but the outfit is still understeering. The engine picks up in top like a steam train and I drive easily round a solo that comes diving by on the straight to get past before the exit where I aim to miss the bumps and new bits of tarmac that pass at space invader speed.
It all feels incredibly stable, in fact I find it difficult to gauge where the limits are. With so much power and weight being put through three mere Mini tyres, there obviously is a point where it will let go, and a couple of moderate controllable broadslides at the end of a session indicated we were perhaps approaching it. Richard thinks the weight actually assists the handling and enables him to stay on line where other, lighter Imps drift wide.
At the end of the back straight and into the Esses, you have to be careful not to overdo the first right hander and slide too deep to get a good line for the left, so you aim to get a steady drive through -again with the power hard on before you clip the apex of the right hander. Here the Imp was understeering quite noticeably, and perhaps Mark could have moved his weight further forward to counteract it. It's academic really though, as the whole plot slid through the corner smoothly and fast, Mark timing his move across perfectly as we clipped the markers on the left and screamed it in 3rd up to the hairpin. On hard with the anchors and changing down, the brakes are smooth and powerful and worked well at the one severe stop at Mallory - which is more than can be said for the gearchange. I found it awkward and imprecise, especially when changing down. The Quaife 5-speed box soon to be fitted should improve this and suit the engine better. Although it's torquey, it loves to be buzzed!
Mark's position along the straights was by the back wheel to prevent wheelspin. At hairpins this was even more of a problem - time spent melting rubber is time wasted - so we drove in on a gentle throttle. If this is done correctly, you slide it round neatly with the steering on full left-hand lock (which isn't much) lining up for the 'bus stop' chicane 20 yards away. There's no option but to follow the lOmph wiggles here, but at the left-hand exit, after a glance to see that Mark was in position, I poured on the power for Devil's Elbow. Round this left-hander, the outfit was superb! Wide and low enough to stay glued to the track, but with enough power to hang the back end out, it allowed me to just open up the throttle and find myself in a delicious lefthand drift, which a necessary gearchange (most probably suicide on more upright outfits) barely disturbed. All the time you are accompanied by the screaming bellow of the four-in to-one exhaust pipe at the front of the chair, the heat from that and the maze of coolant pipes and header tanks you're lying on, the blurred needles of the tacho and oil gauge, and the track flashing past two feet below. All the hand controls were light, but the sheer effort of hauling the thing round the demanding Mallory track had my hands trembling uncontrollably when we pulled in after eight laps or so.
It's not just fatigue that caused the quivers though. The Imp brew is a heady mixture of revs, noise, heat and speed, and its present owners admit to having more fun and excitement on it than they ever did with cars. With their blend of meticulous preparation, quiet determination and obvious commitment, Richard and Mark impress as a team heading for success in the increasingly tough classic sidecar world. With the KGB Imp, they've certainly picked up the right machine for it.
|Bore x stroke||72 x 60mm|
|Compression ratio||11: 1|
|Carburation||2 x 30mm twin choke Dell'Ortos|
|Output||120bhp @ 8,500rpm (est)|
|Clutch||single plate, dry|
|Brakes||(front)||2 x 8in discs|
|(rear)||1 x 9in disc|
|(sidecar)||1 x 8in disc|
|Tyres||5.00 x 10 Mini racing|
|Top speed||130mph (est)|
|Owners||Richard Nelson and Mark Camp, Derby|
Car of the year ! / by Pete Sutton; photography John Noble. - Classic Racer, winter 1986/87, No. 16. - pp.38-42. - [Track Analysis]
1,000cc KGB-Imp outfit - Hanging on to the rig that won the Classic Sidecar Race of the Year
The Imp Site
1000cc KGB Imp (Richard Nelson and passenger Mark Camp) (this file)
Nerus Impetus (Vic Phillips)
(The Teagle brothers)