Racing crankshafts - rotary valve for classic Vespa
Racing shafts are a simple and effective tuning step for any rotary valve engine on a classic Vespa. A racing shaft enables higher revs. The engine becomes livelier and more agile. Better acceleration and higher top speed are the result. In contrast to the original crankshaft, a racing shaft almost always has a significantly longer intake time. The crank webs are streamlined and often polished. Racing shafts with a larger stroke are called long-stroke shafts. More stroke = more displacement = more torque. With racing crankshafts - rotary vane, the intake on the engine casing does not have to be adjusted.
As already mentioned Racing shafts higher engine speeds possible. The engine can offer more power and improves acceleration and top speed. Turbulence and stalls are reduced. The connecting rod is partly a forged connecting rod with additional lubrication holes or polished blade connecting rod. The lower connecting rod bearing is a silver bearing. All crankshafts are delivered with upper connecting rod bearings.
Racing shafts with a larger stroke are usually referred to as Long stroke shafts. More stroke = more cc = more torque. The extra stroke is compensated by thick seals, also called spacers, at the cylinder head and/or base. This allows you to play with the timing.
Racing lip shafts or Long stroke lip shafts are crankshafts in our range whose intake-side crank web has been machined to favour flow. On Vespa engines, the intake is usually located above the clutch-side crank web. The streamlined modification of this crank web often resembles the shape of a lip.
The next decision criterion is the choice of the right engine type.
Each engine type has its own racing shaft
For the Smallframes and Largeframes, the range is so large that we additionally offer these models with racing crankshafts inRotary shaftsandDiaphragm shaftsIn the case of Vespa scooters, we generally differentiate between the models according to their frame widths:
Smallframe - Vespa 50-125/PV/ET3/PK/XL
Largeframe - Vespa 125/150/Rally `57-
Largeframe - Vespa PX/T5/Cosa
Therefore, it is advisable to select the appropriate "vehicle type" in the field under "Classic Vespa" to see all crankshafts that are suitable for it.
More stroke = more cc = more power
Standard stroke: Originally the engine types differ not only in the cylinder diameters but also in the stroke as we have listed them in the engine classes.
Long stroke: If you want more torque, you go for long-stroke versions. In racing shafts, we refer to crankshafts with a longer stroke as long-stroke shafts to make them easier to distinguish.
Note: Stronger cylinder base or cylinder head gasket required. More stroke is usually compensated for by a head gasket half the thickness of the extra stroke. If a foot gasket is used to compensate, the exhaust should also be machined. This makes particular sense at higher tuning levels.
The subtle difference lies in the connecting rod
A longer connecting rod does not change the stroke, but the cylinder must still be raised accordingly. The advantage of the longer connecting rod is that it is less inclined at half stroke, so the piston exerts less lateral force on the cylinder wall, resulting in less friction. A longer connecting rod also lowers the maximum piston speed and thus also the change in speed of the piston during one revolution. This lowers vibrations.
The connecting rod is one of the most heavily loaded parts in an engine. It must transmit the force of the explosion, withstand extreme acceleration and withstand great heat. In addition, two bearings run in the connecting rod's raceways, one at engine speed, so a high quality connecting rod is suitable and important to prepare an engine for increased loads or to increase its durability.
There are a multitude of features and combinations of the implementation of features on a connecting rod. To make the selection a little clearer, we distinguish between three types of connecting rod:
Standard: A good connecting rod, but made to standard specifications.
Sport: An improved connecting rod
Race: A connecting rod that has been elaborately manufactured.
The better the crankshaft, the more effective the balancing and the smoother the engine.
Strong vibrations not only have a negative effect on riding comfort, they also affect the durability of the individual components on a scooter and, last but not least, the performance of an engine. A remedy is "finely balanced" crankshafts. "Finely balanced" is not actually a clear technical term. It is rather a colloquial expression for a particularly well-balanced crankshaft. Nevertheless, we have decided to use this term as information about a crankshaft.
Our top brands for racing crankshafts - rotary sliders for Vespa classics
SIP PERFORMANCE: As SIP Performance version with polished forged Conrod or in the Premium version with a high-quality bronze Conrod.
MAZZUCCHELLIthe classic Racing Crankshaft for Largeframe. Made in Italy. Good and favourable or as K2D version also suitable for stronger tuning.
SIP SPARE PARTS: Various Crankshafts for classic Vespas.
POLINI: For some years now, the Italians have also been offering Crankshafts for Vespa Models again.
PINASCO: Beautiful Shafts for Vespa Models.
SERIE PRO: Before the SIP PERFORMANCE Racing Crankshafts were available, worb5 updated us with the oldschool MAZZUCCHELLI Shafts. There are still a few types from this family in the range to fill any gaps.
Technology Tips
If you would like to delve deeper into crankshaft technology, we recommend our Technology blogs.
Customers ask - SIP answers
"What additional parts do I need for a crankshaft replacement?"
Often just penny items, but annoying if you don't swap them:
Wedges - don't put an old wedge in a new groove.
Engine gasket set - if you don't replace it, it will drip.
Crankshaft bearings - always replace both LIMA and KULU sides.
Oil seal crankshaft - here too, replace both sides.
Fuse basket - if you have a castle nut on the clutch, you need it.
