Racing full cheek shaft 60 mm from Mazzucchelli for Vespa PX125/PX150
Sport crankshaft from Mazuchelli with 60 mm stroke (+3 mm compared to standard). It is an ideal addition to all sports and racing cylinders. The intake timing angle of this crankshaft is relatively long, making it more difficult to tune with the SI24/ SI26 carburettors than with a Stoffi or BGM crankshaft.
The long intake timing after top dead center ensures that a lot of the mixture already sucked in is pushed back through the carburettor in the lowest speed range (so-called blow back).
This causes the mixture to be heavily greased and the engine runs unevenly and stutters.
The ideal companion for this shaft is therefore a larger carburetor, which is inevitably accompanied by a longer intake path for this type of engine. This already dampens the spitting back into the carburetor relatively strongly, and an additional mounted resonance chamber (so-called boost bottle) makes it even easier to tune the engine. The larger carburetor cross-section fits well with the long control angles of the shaft and enables a significant increase in performance in the upper speed range compared to early closing crankshafts. Unfortunately, this is also accompanied by a loss of engine elasticity.
Unfortunately, the Mazuchelli shaft does not achieve the same width at the rotary valve timing cheek and at the shaft seal seat as the BGM shafts. As a result, the timing slot in the engine housing cannot be widened as much as with a BGM crankshaft.
The additional stroke must be compensated for in cylinders designed for the standard stroke of 57 mm. To do this, use either a 1.5 mm head OR a 1.5 mm base gasket. It is not necessary to work with a 3 mm gasket. The additional stroke of 3 mm is distributed over 1.5 mm towards bottom dead centre and 1.5 mm towards top dead centre.
A base gasket increases the control angle of the cylinder and thus creates the conditions for a sporty and speed-oriented power delivery. For full power, however, the exhaust angle often has to be increased in order to compensate for the disproportionately increased overflow angle compared to the exhaust angle. For everyday engines, it is usually advisable to compensate for the stroke with a 1.5 mm head gasket
. Cylinders designed for 60 mm stroke (Polini 221, Pinasco 225) do not require an additional compensating gasket.
- Stroke: 60 mm
- Connecting rod length: 110 mm
- Engines: PX200, Cosa200, Rally200 (Ducati ignition)
- Stroke journal: 20 mm (solid material)
- Required stroke compensation: 1.5 mm (base or head for cylinders with 57 mm stroke)
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