Crankshafts for Vespa 50-125/PV/ET3/PK/XL
The Crankshaft is also the centrepiece of the Engine in Smallframe Models. We have been offering a wide variety of Crankshafts for Smallframe Models for many years and always ensure the highest quality. Depending on the cubic centimetre class of the Engine, we recommend special shafts for normal use or for use in tuning. The "Racing Crankshafts: Disc Valve" 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 the Racing Crankshaft: Diaphragm.
Standard or Racing Crankshaft? A question that not only smallframe riders ask themselves
The different crankshaft types for the Smallframe Vespa models:
Standard Crankshaft
We only refer to normal standard shafts as "Crankshaft". Perfect for a 1:1 replacement when overhauling the engine. 100 % legal. Standard crankshafts are replicas of the originals. To compensate for supply bottlenecks, we have several manufacturers in our programme.
Racing crankshaft: Disc Valves
Have a cut-out in the clutch-side crank web that allows the original rotary valve inlet to be retained. In most cases, the timing of the rotary valve inlet is longer than the original. This is intended to enable better filling, especially at higher engine speeds. On some types, the timing cheek is also optimised for better flow. Depending on the type and manufacturer, many of these Crankshafts have a Conrod with additional lubrication holes or higher-quality bearings or a forged connecting rod. A good Crankshaft is balanced to achieve smooth engine running. Particularly high-quality shafts use extra balancing weights that are inserted into the crank webs. All Crankshafts are supplied with upper connecting rod bearings. If you want to convert to electronic Ignition, you should go straight for the 20/20 mm Racing Crankshafts. The thicker and therefore more stable Cone is also recommended in combination with a Racing Cylinder.
Also Long Stroke Crankshafts are also available as Racing Crankshafts for smallframes.
Racing crankshaft: Reed Valve
These include full cheek, bell and Flowed Crankshafts.Full Circle Crankshaftshave two completely closed cheeks. A large diaphragm inlet is required here. This design is only recommended in combination with a direct inlet into the Cylinder. These shafts are also available with a long stroke. The 54 mm Shafts in particular have proven to be a guarantor of horsepower. In contrast to the original Crankshaft, a Full Circle Crankshaft has a closed crank web. Elevation of pre-compression and reduced air turbulence in the crankcase.
Flowed Crankshafts and Bell-Shaped Crankshaftsare special diaphragm shafts that harmonise very well in conjunction with a diaphragm intake in the crankcase. Here, a diaphragm intake is fitted in place of the original Disc Valve. The crank webs of the Flowed Crankshafts are specially reworked and flow-optimised. The mixture no longer hits the crank webs when it flows in. The pre-compression is reduced, more fresh gas can flow in and a higher filling level is achieved. Flowed Crankshafts are only suitable for diaphragm intake. Use as a rotary valve shaft is no longer possible. Bell-Shaped Crankshafts work in a similar way. The mixture is not given quite as much space, but they are symmetrical and easier to balance.
Some types have a polished knife-edge connecting rod and a lower connecting rod bearing as a silver bearing. All Crankshafts are supplied with upper connecting rod bearings.
Special racing crankshafts
These Crankshafts require special casings as they do not fit into the original Crankcases, e.g. Models from QUATTRINI or BFA.
The next decision criterion is choosing the right engine type.
Which Crankshaft is installed in my Smallframe?
As the Smallframe engines are compatible with each other, except for the automatic, we indicate the cubic centimetre class of the engine type here. A distinction can be made between the following engine types:
50 cc/43 mm: the small smallframes are short-stroke engines with 43 mm stroke and 87 mm Conrod. The Vespa 50/N/L/R/S/Special/SR/SS/PK50/S Models have a 19/20 mm Cone.
In the 80s, the Vespa PK50/S/SS/XL/XL2/FL/HP/N/Rush models were fitted with a thicker 20/20 mm fan wheel stub. All Racing Cylinders up to 115 ccm run with these shafts.
80-125 ccm/51 mm: the Crankshafts of the large smallframes have an original 51 mm stroke and a 97 mm Conrod. Here, too, there are differences in the cone dimensions: With 19/20 mm, the Vespa 90/R/SS/100/125/PV/ET3/PK80-100 S/PK125 are on the road.
On the Vespa 100/PK80-125 S/PK125, the stump grows to 20/20 mm and the PK 125 ETS/N/XL/XL2 Models have the most stable stump with 24/25 mm.
Racing Cylinders from 125 ccm require these shafts.
Important: With a suitable Cylinder and Bearing, all Shafts can be fitted to any Smallframe. Except for the PK automatic. These models have their own Crankshaft.
The stroke and the Conrod
As with the Cylinders, there are three Crankshaft classes for the Smallframe:
43 mm: All 50 cc Vespas with manual transmission have a standard stroke of 43 mm (short stroke) and a connecting rod length of 87 mm. They are suitable for all 50-112 cc Cylinders.
51 mm: All 80-125 cc Models have 51 mm stroke (long stroke) and a connecting rod length of 97 mm. These shafts are required for all 125 cc and larger Cylinders. A 51 mm is a Long Stroke Crankshaft for an original 50 ccm Vespa. Some hardcore shafts are also available with 105 mm Conrods.
54 mm and more: For performance fetishists! More stroke = even more power and torque for anyone with over 130 cc. The Crankcase must be adapted to the larger diameter of the crank webs.
Note: Stronger cylinder base gasket or cylinder head gasket required. Additional stroke should only be compensated for by a head gasket with half the thickness of the additional stroke; e.g. when converting from a 51 ccm engine. E.g. when converting from 51 mm to 54 mm, a head gasket 1.5 mm thick. If a base gasket is used for equalisation, the outlet should also be machined. This only makes sense for higher tuning levels.
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. A longer Conrod also reduces the maximum piston speed and therefore also the change in speed of the Piston during one revolution. This reduces vibrations. Popular connecting rod lengths for smallframes are:
- 87 mm: original for 50 cc models.
- 97 mm: original for 125 cc models.
- 105 mm: often used on Long Stroke Crankshafts. The original 97 mm Conrod is quite short. Especially in combination with more stroke, a longer Conrod ensures smoother running.
- 110 mm: is used for extreme conversions. Usually in combination with special Crankcases and Cylinders.
The different types of crankshaft - the Cone. This is where the Flywheel sits correctly
Another important distinction is the alternator cone on which the Flywheel/Polwheel sits. There are also three classes here. They differ in the dimensions of the alternator (LIMA) shaft seal seat and the bearing seat of the LIMA bearing:
19/20 mm:Oil seal seat 19 mm, bearing seat 20 mm, thin/pointed Cone with M10x1.5 mm pole nut, fitted as standard on classic smallframes and the PKs of the 1° series. Externally recognisable in most cases by the 2-hole mounting of the Intake Manifold.
20/20 mm: Shaft seal seat 20 mm, bearing seat 20 mm, thick/blunt Cone with M12x1.25 mm pole nut, fitted as standard on PK/S of the 2° series and the PK50XL Models. Intake Manifolds with 3-hole mounting were fitted almost exclusively on these.
24/25 mm: Shaft seal seat 24 mm, bearing seat 25 mm, thick/blunt Cone with M12x1.25 mm pole nut, standard on the PK125 ETS/N/XL/XL2.
Basically, the thicker the Cone, the more stable it is. This means that the 19/20 Cone is sufficient for simple tuning. If you want more, you should install at least the 20/20 Shaft. The more power and the higher the Engine revs, the greater the forces on the crankshaft stub and the greater the risk of it tearing off. The 20/20 Shafts can be installed in the 19/20 mm Casing with the appropriate Oil Seals. Conversion to an ETS Shaft with 24/25 mm Cone is easily possible on all gearshift models with the appropriate conversion shaft seal ring/bearing. This very stable Shaft can also withstand extreme loads. If you are converting from a thin/tapered to a thick/blunt Cone, you will also need the matching Flywheel/ Flywheel. It is then advisable to convert completely to an electronic Ignition, e.g. SIP PERFORMANCE VAPE, and save yourself the hassle of the old breaker ignitions. If you want to upgrade a 50cc to more than 125cc, you always need a 51-54 mm Shaft. This is also possible without any problems.
Our top brands for Crankshafts for Vespa 50-125/PV/ET3/PK/S/XL
MAZZUCCHELLI: Gute und günstige Standard- und Rennwellen für Smallframe. Made in Italy.
SIP SPARE PARTS: Spezielle Kleinserien für zuverlässiges Alltagstuning für Vespa Smallframe in Top-Qualität.
SIP PERFORMANCE: Entwickelt von den hellsten Köpfen bei SIP und produziert in einer Hightech Tuningschmiede in Italien. Im Smallframe Bereich werden bis zu 56 mm Hub im original Motorgehäuse ermöglicht.
POLINI: Seit einige Jahren bieten die Italiener auch wieder Kurbelwellen für Smallframe Modelle an, teils aufwendig gewuchtet und in ungewöhnlichen Größen
PINASCO: Schöne Wellen für Smallframe Vespa Modelle, egal ob Kurz- oder Langhub.
DRT: Hochwertige Kurbelwellen für Smallframe Modelle aus der italienischen Schmiede. DRT bietet sogar Langhubwellen für 50 ccm Motoren.
QUATTRINI: Im Vespa Smallframe Bereich bietet QUATTRINI nur Wellen für die hauseigenen Motorgehäuse an.
Technology tips
If you want to delve even deeper into Crankshaft technology, we recommend our Technology blogs.
Customers ask - SIP answers
"What does 19/20, 20/20, 24/25 mean?"
The numbers indicate the diameter of the seal ring seat and bearing seat of the crankshaft stub on the clutch side. Important when selecting the right components. Caution: The choice of the appropriate Flywheel (Flywheel) also depends on the type of stub. There are Flywheels with a 19mm Cone for 19/20 Shafts and Flywheels with a 20mm Cone for 20/20 and 24/25 Shafts.
