Crankshafts for Vespa Vintage Models
In old Engines, the Crankshafts are often tight or the Disc Valve is rusted. Bearing and shaft seal seats are often worn, the connecting rod bearings are worn or the cones and keyways are defective. The Crankshaft should therefore also be replaced during a major engine service. If the Engine is to be given a performance boost, then a Crankshaft with modern bearings should be fitted. If you want to keep your Engine original, use the standard Crankshaft. If you want to bring your Engine up to the latest state of the art, treat it to a Racing Crankshaft. A little more stroke, a high-quality Gudgeon Pin Bearing or a reinforced Conrod are not just for tuning fans. A crankshaft stub that can accommodate a modern Clutch or Ignition is also a benefit for everyday riders.
Should it be an original Crankshaft or a Racing Crankshaft?
The different crankshaft types for the Vespa 98/125/150/GS '57 and Vespa 160 GS/180 SS Vespa models:
Standard crankshaft
Standard crankshafts are replicas of the originals. We have made improvements to some models, e.g. a Gudgeon Pin Bearing for a lower frictional torque instead of a bronze bushing or a polished forged connecting rod. On some Shafts, we have replaced the original conical clutch stub with that of the late Vespa PX Models. This results in a large selection of possible clutches that were not originally available. The transition to Racing Crankshafts is fluid.
Racing crankshaft
By racing Crankshafts we generally mean all crankshafts that deviate from the pure standard specifications. These are
different crankcase shape
more stroke
longer or reinforced Conrod
Clutch/pole wheel stub not intended for the original parts
optimised intake geometry due to shape and cut-out
Special racing crankshafts
There are special engine casings for these Crankshafts because they do not fit into the original Crankcases. However, very few people install a BFA 306 cc Engine in a Wideframe or GS/SS, for example. But it does happen.
The next decision criterion is choosing the right engine type.
And it does turn - the Crankshafts of the first Vespa models
The Engines of the first Vespa models all have a direct intake into the Cylinder. The Crankshafts therefore do not require a cut-out for controlling the Disc Valve.
A distinction can be made between the following engine groups:
125 cc, 50 mm stroke, 110 mm Conrod: These delicate Crankshafts breathe life into the first Vespa models Vespa 125 V30-33T/U/Hoffmann HA/HB.
125 cc, 54 mm stroke, 110 mm Conrod: More stroke for the next generation of Vespa 125 VM1-2T/VN1-2T /ACMA 125 ACMA Paris, '51-'55 Vespas. The mushroom shaft becomes a full cheek.
150 cc, 57 mm stroke, 110 mm Conrod: The stroke for Vespa 150 VB1T/VGL1T/VL1-3T increases again with the number of cubic metres. These shafts can also be ridden on the VM/VN in conjunction with a 150 ccm Cylinder.
150 cc, 57 mm stroke, 105 mm Conrod: The top-of-the-range wideframes have a shorter Conrod and also a Cone on the clutch stub. They fit in all Vespa 150 GS and also in MOTOVESPA 150 S/Sprint/GS.
160-180 cc, 60 mm, 110 mm Conrod: The sports models of the 60cc Vespa 160 GS/180SS are long-stroke. Initially with bronze bushes, then with Gudgeon Pin Bearing.
Important: No PX Shafts fit into these Crankcases. However, if you ride a PX Engine in the Models, you must also look under PX/T5/Cosa.
More stroke = more cc = more power
Standard stroke: In addition to the cylinder diameters, the original engine types differ in terms of stroke, as we have listed in the engine classes.
Long strokeif 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. There is a small selection of Long Stroke Crankshafts with 60mm stroke for the Vespa Wideframe. For the GS160/SS180 Models, 60 mm is the standard stroke.
Note: Stronger cylinder base or cylinder head gasket required. Additional stroke should only ever be compensated for using a head gasket with half the thickness of the additional stroke. If a base gasket is used as compensation, the exhaust must also be machined. However, this only makes sense for higher tuning levels.
It all depends on the right 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 also the change in speed of the Piston during one revolution. This reduces the 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 to prevent the two webs from twisting. The connecting rod length is always measured from centre eye to centre eye.
The most popular Conrods
105 mm: The standard Conrod of the GS 150.
110 mm: Was used as standard on Lampe Unten Models and on GS 160/SS 180.
115 mmis used on a few high-end Crankshafts. The additional length must be compensated for with a foot seal.
A distinction is also made between standard Conrods and e.g. forged Conrods or polished cutter Conrods, which are flow-optimised. High-quality Conrods have additional lubrication holes or slots in the area of the bearings in order to better supply them with mixture. In older Vespa models, brass bushes were installed as Gudgeon Pin Bearing to minimise friction. Due to the high proportion of oil in the mixture and very low engine speeds, it used to be possible to ride reliably. However, as modern Engines reach higher speeds and less Oil is added, Needle Bearings are now generally used at the top and bottom of the Conrod. These can withstand higher speeds and, in the case of Racing Crankshafts, are also supplied with mixture through additional lubrication holes or slots. This reliably prevents a Bearing from running "dry", becoming too hot and seizing on the Gudgeon Pin or connecting rod pin. In high-quality silver bearings, the bearing cage is silver-plated, which leads to less friction and wear and therefore a longer service life.
Our top brands for Crankshafts for Vespa 98/125/150/GS/160 GS/180 SS
SIP SPARE PARTS: Special small series for Vespa Wideframe in top quality.
SIP PERFORMANCE: Developed by the brightest minds at SIP and produced in a high-tech tuning centre in Italy.
DRT: For a long time the only supplier for wideframes. Good quality "Made in Italy", also offers special solutions for wideframe models.
Technology tips
If you want to delve even deeper into Crankshaft technology, we recommend our Technology blogs.
Customers ask - SIP answers
"What other parts do I need for a crankshaft replacement?"
Often only cent items, but annoying if you don't replace them:
Woodruff Keys - don't put an old Woodruff Key in a new groove
Gasket Set Engine - if you don't change it, it will drip
Crankshaft bearings - always replace the LIMA and CULU sides as well
Oil Seal Crankshaft - replace both sides here too
NutLock Cap - if you have a Castle Nut on the clutch, you need it
