The machine used to win a world championship always excites interest… must be something special after all, mustn’t it?
… a world championship-winning CZ. We look at a profile of the actual Ceezee Joel Robert won his world championship on in 1964.
The Sixties hadn’t quite got to the Summer of Love or even started swinging when 20-year-old Belgian Joel Robert made his first of many indelible marks in the history of motocross. In August 1964 Motor Cycling got hold of a feature about his championshipwinning machine, determined to unearth a few secrets these factory teams keep to themselves.
The press were to be disappointed, as they found out the machine was expertly maintained and if not built regardless of cost – this was the Eastern bloc after all. The team bikes were in tip-top condition and pretty standard fare as well as being basically what a racer could buy but with the aforementioned race-shop attention to detail, though that could also be achieved in a private environment.
It seems CZ had relied on simplicity rather than revolutionary concepts to produce their winning machines. The bike in this feature is Robert’s machine and shows the robustness of the engine which had been a CZ thing for some time and would aid restorers in the then future as these engines are virtually indestructible.
Relying on years of good engineering practice, coupled with the experiences gained in competition, CZ produced a motorcycle which was powerful, flexible and strong enough to outlast the rigours of a GP season. Motor Cycling learned the engine was a simple two-stroke in unit construction with a four-speed gearbox and the resultant unit has a peak power output of 26bhp at 5900rpm.
Surely there must be some trickery inside the engine masquerading as standard? No, sorry, and I quote: “…the engine employs a classic loop-scavenge system…” which basically means the fresh combustion charge is drawn into the crankcase as the piston rises and is pushed through transfer ports opened and closed by the piston as it travels up and down the bore creating pressure at either end of the scale. These transfer ports are formed in both the barrel and the crankcases.
In a move to provide engine rigidity and piston support, the barrel has an extended skirt or spigot extending deep into the crankcase mouth. Aha, the barrel and cases must be magnesium or other unobtainium mustn’t they? No, it is cast iron for the barrel and aluminium alloy for the cases and head, so hardly fancy. The head does have a twin plug arrangement and a squish band to promote a thorough mix of the combustion charge so the plugs can ignite it and produce the right amount of power from the mixture squeezed at 10.5:1 compression ratio.
The backbone of an engine is the crankshaft and CZ had made an extremely rigid unit with small diameter flywheels for snap acceleration as well as making the crankcase pumping much more efficient. To keep the crank turning easily, CZ used a double row bearing on the ignition side with two ball bearings on the drive side.
They also moved the clutch to the crankshaft which means it operates under much less torque than if it was on the gearbox mainshaft. A downside is this arrangement gives the gearbox itself a harder time because there’s less chance of the clutch slipping. CZ realised this, so did a lot of redesign work in the cluster. Because there had been issues with earlier models this redesign of the cluster included such things as using needle roller bearings rather than bronze bushes. Why? Because needle rollers don’t need a lubrication hole in the shaft, so instantly a weak point is eliminated. This robust 250 unit didn’t have a chain as primary drive, using instead spur gears deemed too noisy for a road bike but acceptable on a race machine.
Something Motor Cycling found interesting was the gear selection method, or rather it and it’s access. Accepting in the heat of the moment a scrambler is more concerned
with finding the next gear than the niceties of a smooth change, what was wanted was a robust and foolproof changing system. Even better, as far as a mechanic was concerned, the system could be inspected and repaired without splitting the engine. What was used was a large cam-track plate with a small connecting rod which ensured the gear selection was positive and with no chance of going past the stop into a false neutral, no matter how big the boots of the rider were. Inspection was through an access plate on the top of the engine.
This drive to simplicity wasn’t only restricted to the engine unit but the cycle parts too. A steel frame of tubular loop design with a strong but light swinging arm used a front fork constructed from light alloy sliders and steel stanchions with plenty of travel. At the rear were oil damped sealed units.
Helping the bike weigh in at a useful 218lb was the use of Elektron alloy for the wheel hubs – additionally lowering the unsprung weight too – and a fuel tank and seat pan laid up from glass fibre. It seems the factory had experimented with alloy sheet for the seat pan but found it difficult to manufacture the correct shape easily so used the glass fibre and were surprised to see a weight saving too.
In order to stop muck and dirt playing havoc with the engine internals as their riders blasted around the scrambles courses of the world, CZ fitted two air filters inside the induction chamber, thus ensuring maximum protection.
Along with the report, Motor Cycling had been supplied with some line drawings, clearly showing the championship engine and how it was laid out. The writer explained the main photo had the cylinder laid out at the front so as to show its relationship with the rest of the engine and begged the readers’ forgiveness if it seemed misleading.
But without the rider…
…a bike goes nowhere and in Joel Robert was someone who was taking the CZ to the top. Not that it had been a foregone conclusion, as in an interview with the young Belgian champion Motor Cycling learned prior to gaining a works CZ after a cheeky request to the factory, Robert had been completely off-form and thanks to machine failures had done more walking than riding. But, once on the Czechoslovakian machine he was on form again, and at 20 became the youngest ever world champion.
Roberts’ rise to superstardom was particularly rapid and from the 14-year-old who rode on private land before coming of age to compete, it only took six years to be world champion.
There were those who doubted the Belgian’s temperament and felt he was more likely to fall foul of the authorities looking after scrambling in Belgium. Indeed, his father had done just that and received a lifetime ban for an incident with officials. Luckily, young Joel was drafted into the Army for his national service and the enforced discipline of the military tempered his zest and allowed him to mature into a top racer.
Robert’s route to stardom involved a
series of small capacity field bikes, then at 16 a 250cc Zundapp which was replaced with a 250 Greeves for 1960. It was on this machine his talent began to show when he managed fourth in the Belgian lightweight championship. Great things were promised and Joel went to the 250cc British MX GP at Shrubland Park in 1961. It wasn’t a great debut as a flying stone left him concussed and he barely managed to get back to the paddock, detuned and out of the running. The next year however, he did the full season of GPS and managed excellent placings when the Greeves could stand the pace. When the Villiers Starmaker engine was introduced this seemed the answer to his prayers, yet still wasn’t up to the job and the costs of keeping it going were unfeasible.
It was at this point Robert cheekily suggested to the CZ factory they loan him one of their works machines. The factory did, it arrived in August 1963; by August 1964 Joel was world champion and no one was more surprised than him. Receiving his draft papers just before Christmas in 1963, he wasn’t even sure he would get leave to attend GPS. He did, went to Spain, was mediocre, managed to make the Belgian home round and… well… dominated the event to get his first win. The next three rounds saw his name at the top and even better it was with vastly different circuits from mud to bone dry, a great boost for his confidence. He lapsed a little after that but was back on form for three consecutive wins, including the British GP where our photos of him are from; the final saw the title go to Robert. He did a ‘just to be certain’ win in Russia but was unchallengeable at that point.
Of those wins in that season, it is possible the Czech GP showed his mettle, in the first leg he went from sixth to first; in the second leg he and Torsten Hallman shot away from the field and Robert was on the Swede’s rear wheel for 50 minutes until a balk by a backmarker made him stall his engine two laps from the end. Hallman vanished, Robert fired up and not only caught the Swede, but passed him to win the second leg.
Joel Robert was on his way... )
Youngest ever world champion... at that time at least. Joel Robert and his CZ. Don’t you just love exploded engine drawings? These show the CZ as Joel raced it.