Racing crankshafts - Disc Valves
for Vespa 125/150/Rally from '57 onwards
Racing Crankshafts are a simple and effective tuning step for every rotary valve engine of a Largeframe Vespa from the 60s and 70s. A Racing Crankshaft enables higher engine speeds. The Engine becomes more lively and agile. The result is better acceleration and a higher top speed. In contrast to the original Crankshaft, a Racing Crankshaft almost always has a significantly longer intake time. The crank webs are aerodynamically optimised and often polished. Racing Crankshafts with a larger stroke are referred to as Long Stroke Crankshafts. More stroke = more cubic capacity = more torque. With racing crankshafts - Disc Valves, the intake on the Crankcase does not need to be adapted.
As already mentioned Racing Crankshafts make higher engine speeds possible. Engine can offer more power and improves acceleration and top speed. Turbulence and stalling are reduced. The Conrod is partly a forged connecting rod with additional lubrication holes or a polished knife-edge connecting rod. The lower connecting rod bearing is a silver bearing. All Crankshafts are supplied with upper connecting rod bearings.
Largeframe Racing Crankshafts with a larger stroke are generally referred to as Long Stroke Crankshafts. More stroke = more cc = more torque. The extra stroke is compensated for by thick gaskets, also known as spacers, on the Cylinder Head and/or cylinder base. This allows you to play with the timing.
Flowed Racing Crankshafts or Long Stroke Flowed Crankshafts are crankshafts in our range whose intake-side crank web has been machined to optimise flow. In the PX/T5/Cosa engines, the intake is located above the clutch-side crank web. The flow-optimised modification of this crank web often resembles a lip in shape.
The next decision criterion is the choice of the right engine type.
Each engine type of the Vespa 125/150/Rally '57 has its own Crankshaft
A distinction can be made between the following engine groups:
125/150 cc, 57 mm stroke, 105 mm Conrod: The first Vespa largeframes Vespa 125 VNB/GT/GTR 1°/Super/TS/150 VBA/VBB/T4/GL/Sprint/V 1°/Super 1° still come with a narrow Cone on the fan wheel side. It is only suitable for tuning to a limited extent, as the Cone is weak.
The thicker fan wheel stub of the later PX comes with the following models Vespa 125 GTR 2°/TS 2°/150 Sprint V 2°/Super 2°. All Crankshafts of the PX125/150 fit here. The range is large.
180 cc, 57 mm stroke, 110 mm Conrod: The Vespa 180-200 Rally with the first electronic Femsatronic Ignition gets a new Crankshaft.
200 cc, 57 mm stroke, 110 mm Conrod: the queen among the sports models of the 70s. The Vespa 200 Rally VSE1T 33997 ->. The Crankshaft of the later PX200 is used here for the first time. The tuning possibilities are enormous and popular. The range is therefore also very large and varied.
Note: Installing a PX Engine in the older models is also popular. Especially with a 200cc Engine, every vintage bike becomes a powerful and reliable touring bomber or racer.
More stroke = more cc = more power
Standard stroke: In addition to the cylinder diameters, the original engine types also differ in terms of stroke, as we have listed in the engine classes.
Long-stroke: If you want more torque, you can opt for long-stroke variants. For Racing Crankshafts, we refer to crankshafts with a longer stroke as Long Stroke Crankshafts to make them easier to distinguish. When looking for long-stroke variants of reed shafts, you need to pay attention to the stroke lengths. In the PX 125-200 cc class, the most common stroke variants are
60 mmvery popular for giving an Engine more stroke. These shafts usually fit into the original Crankcase without modification. If a high-quality Shaft is used, it is an upgrade without side effects.
62 mmfrom 62 mm stroke, the Crankcase must be adapted to the larger diameter of the Crankshaft.
Note: Stronger cylinder base gasket or cylinder head gasket required. More stroke is usually compensated for by a head gasket half the thickness of the additional stroke. If a base gasket is used for equalisation, the exhaust should also be machined. This makes particular sense for higher tuning levels.
The Conrod makes the difference
A longer Conrod does not change the stroke, but the Cylinder must still be raised accordingly. The longer Conrod has the advantage that it is less inclined at half the stroke and the piston therefore exerts less lateral force on the cylinder wall, resulting in less friction. A longer Conrod also reduces the maximum piston speed and therefore also the change in speed of the Piston during one revolution. The timing also changes with a long connecting rod. However, only slightly, because the piston elevation curve changes slightly. As the crank webs are held together by the Crankshaft Pin, it is desirable to have the highest possible pressing dimension to prevent the two webs from twisting. The connecting rod length is always measured from centre eye to centre eye.
The most common Conrods for PX/T5/Cosa:
105 mm: the standard Conrod for all models in this group except the PX 200.
110 mm: The standard Conrod for the PX 200. Often used as an upgrade for the Crankshafts of smaller engine blocks.
115 mm: Occasionally used for special crankshafts. E.g. for conversions with a particularly large stroke or our T5 60 mm stroke Shaft.
126/127 mm: QUATTRINI uses a 126 mm Conrod for its M232/M244 Cylinders. The Conrods of the SIP racing crankshafts for these Cylinders are 127mm to make it easier to compensate for timing differences. Other manufacturers such as BFA and VMC also offer large-diameter Cylinders for the connecting rod length.
The Conrod is one of the most highly stressed parts in an Engine. It has to transmit the force of the explosion, withstand extreme acceleration and endure great heat. In addition, two bearings run in the running surfaces of the connecting rod, one at engine speed, so a high-quality connecting rod is suitable and important to prepare an Engine for Elevation loads or to increase its stability. But how can you recognise a good Conrod and what are the structural differences that make it higher quality and more resilient?
The best-known features of high-quality Conrods:
Forged Conrods: compared to standard Conrods, they have a better strength-to-weight ratio. They are therefore more stable for the same weight or lighter for the same stability.
Silver bearings: The quality of the bearings used is of great importance for the service life of the Crankshaft. Bearing with a silver-plated cage are often used for connecting rod bearings. This is intended to improve emergency running properties and wear behaviour through better heat dissipation and adhesion of the oil film.
Additional lubrication holes/grooves: Additional holes or grooves allow more Oil to reach the bearings. This not only provides additional lubrication, it also helps with heat dissipation.
Polished connecting rod/blade connecting rod: A polished Conrod not only looks good, the smooth surface should also reduce turbulence. A surface treated in this way is also denser and more stable.
Blade connecting rod: A blade connecting rod is designed to minimise turbulence and the air resistance of the Conrod.
There are a large number of features and combinations of the implementation of the properties on a Conrod. To make the selection a little clearer, we distinguish between three types of Conrod:
Standard: A good Conrod that has been manufactured to standard specifications.
Sport: An improved Conrod that has at least two of the features listed above.
Race: An elaborately manufactured Conrod that has at least four of the features listed above.
This simplified division into three categories should help you to orientate yourself in the large selection of Crankshafts and Conrods.
A beautifully smooth-running Engine thanks to effective balancing of the Crankshaft
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. This can be remedied by "finely balanced" Crankshafts. "Finely balanced" is not actually a clear technical term. It is more of a colloquial term for a particularly well-balanced Crankshaft. Nevertheless, we have decided to use this term to provide information about a Crankshaft. We use the term "finely balanced" to describe Crankshafts that fulfil all three points mentioned above:
They are particularly precisely aligned.
They oscillate at 12 or 1 Clock.
The manufacturer has realised a certain balance factor in the design.
Unfortunately, this is no guarantee that the balancing of the respective Shaft is optimised for the intended Engine. But it is a clear sign of quality, which greatly Elevates the likelihood of a smooth-running Engine. More on the subject of balancing in our Technology blogs.
The special feature of rotary vane crankshafts: the timing
The timing of a rotary vane intake always results from the length of the cut-out in the Crankshaft and the length of the rotary vane sealing surface in the Crankcase. It is therefore difficult to specify the timing of a Crankshaft if the length of the inlet in the Crankcase is unknown. Even original casings are subject to fluctuations. If the Disc Valve is machined, every tuner designs their Engines differently and third-party casings (e.g. Malossi or Pinasco) also have different inlets.
For this reason, we only specify the cut-out of the Crankshaft in degrees, measured from the Crankpin. For example, a Crankshaft with 130°/6° timing opens at 6° measured from the Crankpin. The first, higher number indicates when the cut-out in the Crankshaft ends, i.e. when the Crankshaft locks the intake. In this case at 130°. Our designation "TDC" is technically not quite correct at this point. TDC here stands for the Crankpin and allows us to state the data as briefly as possible in the article designation, so it serves the purpose of clarity.
For some of the most common Long Stroke Crankshafts, we provide an estimate of the control times here:
115°/4°: quite close to the original timing. Particularly suitable for mild "road" tuning, e.g. Long Stroke Crankshaft SIP PERFORMANCE
125°/-5°: with intake timing extended by approx. 20°. The longer timing is very suitable for "sport" tuning, e.g. long-stroke shaft SIP PERFORMANCE. E.g. Long Stroke Crankshaft SIP PERFORMANCE
The times remain within a frame that is still very suitable for everyday use. The Engine does not lose power in the lower rev range and is easy to tune. The "sprayback" from the crankcase remains at a low level. At the same time, the contour of the control arm is designed in such a way that the gas can flow in as aerodynamically as possible.138°/6°: The MAZZUCCHELLI variant with a total intake timing of 132° is designed for very sporty or even "race" applications. The long cut-out after TDC ensures a lot of "sprayback" in the lower speed ranges, but also allows the Engine to draw in sufficient fresh gas in the higher speed ranges.
Sprayback refers to fresh gas that is thrown back out of the crankcase after the intake process. This effect is reinforced if the rotary valve inlet is open for a particularly long time after TDC. However, a small amount of spray-back always occurs at low engine speeds.
Our top brands for Crankshafts for Vespa 125/150/Rally models from '57 onwards
SIP PERFORMANCE: As SIP performance version with polished forged Conrod or in the premium version with a high-quality bronze Conrod. For "Road Tuning" with 115°/4° timing or for "Sport Tuning" with 125°/-5° timing.
MAZZUCCHELLIthe classic Racing Crankshaft for Largeframe. Made in Italy. Good and favourable or as K2D version also suitable for stronger tuning.
SIP SPARE PARTS: Small runs of very good Racing Crankshafts.
POLINI: For some years now, the Italians have also been offering Crankshafts for Largeframe Models again.
PINASCO: Beautiful Shafts for Largeframe Vespa Models.
SERIE PRO: Before the SIP PERFORMANCE Racing Crankshafts were available, worb5 updated the oldschool MAZZUCCHELLI Shafts. We still have a few types from this family in our range to fill any gaps.
Technology tips
If you want to delve even deeper into Crankshaft technology, we recommend our Technology blogs.
Customers ask - SIP answers
"What tools do I need to change a crankshaft?"
You absolutely need special tools:
Flywheel Puller - without this it will be difficult to loosen the Flywheel
Clutch Puller - (for smallframes and 150 GS/160 GS/180 SS)
Castle Nut Tool (the clutch on large and wideframes is originally fixed with a Castle Nut)
Holding Tool Flywheel - if you use the screwdriver, you risk breaking the blade
Clutch Holding Tool - this makes it easy to change the clutch
These tools make the service perfect:
Chuck for bearings and Oil Seals
