In the history, the Czech technology has an excellent reputation in Europe for its industry of mechanical precision, much better than all its East-Europe neighbourgs. Without mentionning that
some Czech pilots were very good.The singles 2 strokes Jawa were excellent in regularity races, like the '6 days' and even unbeatable beginning of the 70's. Jawa made after speedway bikes, which became real milestones in that specialty. At that moment, the first 2 strokes CZ of motorcross were rival to the dominating 4 strokes.
In road racing, CZ and Jawa were present in all categories. CZ made 4 strokes engines while Jawa made first twin 4 strokes before developping 2 strokes, singles or multi-cylinders. In 1977, Jawa had developped a twin water cooled.
The mechanic
The 350 CZ 4 cylinders in V started the world championship in 1969 at Brno for the Czheckoslovakian Grand Prix. The machine was completely new, with this time a powerful multi-cylinder engine; it has so far used a single with double overhead camshaft developping 45 HP at 9,600 RPM, superior to the Norton Manx and other AJS 7R, but much less powerful than MV engines.
This project, the work of the engineer Frantisek Pudil, started in 1967. The developement of this complexe mechanic kept the engineers of the Czechoslovakian firm busy for a long time.
The bike has a 4 cylinders engine open at 90° and its overhead camshafts were driven by a gear cascade hidden by a huge case on the right side. The engine was placed in line with the bike, the two cylinders on the back at 10°.
CZ chose a bore and stroke classic super square: 50X44mm. Like this, the combustion chamber had a ideal form and the rotation could be higher thus the linear speed of the pistons was reduced.
The in-exhaust was assured by a 4 valves per cylinder architecture, and the 2 valves for the intake were in Titanium. The pistons, with a compression of 10.5:1 had only 2 rings. Carburetors were Dell'Orto SSI 28mm with 1 cuve per pair only. Ignition was classic ruptor. For the first version, the declared power was of 52HP. It was 62HP at 16,000 RPM on the last version.
For the lower engine part, the connecting rods were assembled by pairs, to permit the addition of a third support in the middle of the crankshaft, were sitted a big needle-bearing specially designed. The oil was contained in a big capacity tank, a pump sending oil to the engine as well as to the gearbox. Gearbox was a 8 speed driven by a dry clutch.
The frame structure, in tubes, made the engine as a part of the whole rigidity. This solution was later taken too by Ducati, for its bicylinders beginning of the 70's. The front fork was a Ceriani GP and the 4 cams brakes, again a Ceriani were what was found best on the market at that time.
On the track
In 1969, the main opponents of CZ were the MV Agusta 3 cylinders and the Jawa 4 cylinders 2 strokes. In the hands of Bill Ivy and a power of about 70HP, the Jawa was a real treat, even for the MVs.The developpements made during the following seasons permit to gain 10HP on the cz, making it more able to fight with the opponents at that time.
The best result was made in 1971, at the Czeckoslovakian Grand Prix when Bohumil Stasa arrived second in the wheels of Jarno Saarinen on his 350cc twin Yamaha. But mainly, the 4 cylinders got many success in national and international races and won the 350cc national title in 1971, again with Bohumil Stasa. The year after, it arrives second behind the Jawa twin of Frantisek Srna.
It is in 1972 that it misses the victory at the Austrian Grand Prix. Just few laps before the finish, the CZ was leading in front of Giacomo Agostini when it had to retire because of a lack of gas...
500cc
A 500cc version was made out of that 350 in 1971. The bore passed from 50 to 55mm, resulting in a total displacement of 420cc. The result was an engine even sharper, with estimated power of 72HP. At the end of the 1972's season, the racing departement of CZ had to concentrate on the production engines, in huge demand at that time; and abandon the road to concentrate on the off-road.
