Crankshafts
for Vespa PX/T5/COSA
The Crankshaft is also the heart of the scooter in the Largeframe Models PX, T5 and Cosa. If you want to keep your Engine original, you can use the standard Crankshaft. A lot of power can be gained from the weak Vespa engine through targeted tuning. This depends on the choice of Crankshaft. Racing Crankshaft Disc Valves do not require any changes to the intake on the Crankcase. Fans of Reed Valve control and thus significantly more power will find what they are looking for in Racing Crankshaft diaphragms.
Standard or Racing Crankshaft? That is the question here
The different crankshaft types for the Vespa PX/T5/Cosa Vespa models:
Standard Crankshaft
We only refer to normal standard shafts as "Crankshaft" in the online shop. Perfect for a 1:1 replacement when overhauling the engine. 100 % legal. Standard Crankshafts are replicas of the originals. To avoid supply bottlenecks, we stock products from several manufacturers. In old Engines, the Crankshafts are often tight or the Disc Valve is rusted. Bearing and shaft seal seats are occasionally worn, connecting rod bearings are worn out or cones and keyways are defective. In such cases, the Crankshaft should also be replaced during an engine overhaul.
Racing crankshaft: Disc Valve
Racing Crankshafts usually have extended timing, polished crank webs and, in some cases, polished Conrods. Racing Crankshafts are a simple and effective tuning step for any rotary valve engine. A Racing Crankshaft enables higher engine speeds. The Engine becomes livelier and more 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. Turbulence and stalling are reduced. The Conrod is sometimes 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 referred to as Long Stroke Crankshafts. More stroke = more displacement = more torque. The extra stroke is compensated for by Spacers (thick gaskets) on the Cylinder Head and/or Gasket Cylinder Base. This gives you the option of simply playing with the timing.
Flowed Racing Crankshafts or Long Stroke Flowed Crankshafts are crankshafts whose intake-side crank web is machined to optimise flow. On PX/T5/Cosa Engines, the intake sits above the clutch-side crank web. A particularly flow-optimised machining of this crank web often resembles the shape of a lip.
Racing crankshaft: Reed Valve
Crankshafts whose design does not allow the use of the original rotary valve inlet are referred to as diaphragm crankshafts. A different type of intake control, usually a diaphragm, must be used. Diaphragm shafts are also available in different designs.
Full Circle Crankshafts have, as the name suggests, two completely closed cheeks. A large diaphragm inlet is required here. It only makes sense to use a Full Circle Crankshaft in conjunction with a direct inlet into the Cylinder. These shafts are also available with a long stroke. The basic idea behind the Full Circle Crankshaft is better pre-compression, which is achieved via the completely closed crank webs. However, in engines controlled via the Casing, even large milled diaphragm inlets with boost ports cannot prevent the mixture from being unfavourably obstructed by the cheek standing in the way.
Flowed Crankshafts are flow-optimised reed shafts that harmonise very well with reed intake manifolds. On PX/T5/Cosa Engines, the intake is located above the crank web on the clutch side. A particularly flow-optimised machining of this crank web often resembles the shape of a lip.
The Bell-Shaped Crankshaftor mushroom crankshaft, is a crankshaft whose shape resembles a bell or mushroom. It also offers the mixture as little resistance as possible. It is not quite as uncompromising as the Flowed Crankshaft, but the shape is symmetrical and the crankshaft is easier to balance.
Special racing crankshafts
The engine cases for special crankshafts are special because they do not fit into the original Crankcases. The SIP-BFA Crankcases are outstanding here. The massive Crankshafts are the key to the brute power of the 306 cc tuning.
The next decision criterion is the choice of the right engine type.
Each engine type of the PX/T5/Cosa has its own Crankshaft
A distinction can be made between the following engine groups:
80 cc: 48 mm stroke for Vespa P80X/PX80 E/Lusso/PX100 E.
125/150 cc: 57 mm stroke, 105 mm Conrod, for P125-150X/PX125-150 E/Lusso/MY/Cosa 125-150 and also the LML 125-150 Star/DLX/Stella/Via Toscana Models. If the Shaft is installed in the PX80, all 125-177 cc Cylinders can be ridden with the cylinder base turned down.
125 cc T5: 52 mm stroke, 105 mm Conrod, for Vespa T5. The cheeks and therefore also the rotary valve inlet are wider than on conventional PX Crankshafts.
200 cc: 57 mm stroke, 110 mm Conrod, for Vespa 200 Rally VSE1T 33997 ->/P200E/PX200 E/Lusso/MY/Cosa
Important: The PX/T5 engines fit in every largeframe and, with an engine adapter, also in every wideframe, making every classic car suitable for long distances or ready for more power.
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. In the case of 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: A thicker cylinder base gasket or cylinder head gasket is required. More stroke is usually compensated for by a head gasket with 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 subtle difference lies in the Conrod
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 the change in Piston speed during one revolution. This reduces vibrations.
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 in order 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 127 mm to make it easier to compensate for differences in the timing. Other manufacturers such as BFA and VMC also offer large-diameter Cylinders for the connecting rod length.
A distinction is made between standard Conrods and polished cutter Conrods , which are flow-optimised. High-quality Conrods also have lubrication holes or slots in the area of the bearings to better supply them with mixture. This is intended to prevent a Bearing from running "dry", becoming too hot and seizing on the Piston or connecting rod pin. The cage of high-quality silver bearings is silver-plated. This results in less friction, less wear and a longer service life.
Our top brands for Crankshafts for Vespa PX/T5/Cosa Models
MAZZUCCHELLI: Good and favourable standard and Racing Crankshaft for Largeframe. Made in Italy.
SIP SPARE PARTS: Special small series for Vespa Largeframe in top quality.
SIP PERFORMANCE: Developed by the brightest minds at SIP and produced in a high-tech tuning centre in Italy.
POLINI: For some years now, the Italians have also been offering Crankshafts for Largeframe Models again.
PINASCO: Beautiful Shafts for Largeframe Vespa Models.
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?"
The following special tools are essential
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
