Racing crankshafts - Reed Valve
for Vespa 50-125/PV/ET3/PK/XL
Racing Crankshafts - Reed Valves are the ultimate in engine tuning for a Smallframe Vespa and a must-have if you want to achieve outputs of 15 hp and more. A reed shaft enables higher engine speeds. The Engine becomes more lively and agile. The result is better acceleration and a higher top speed. The crank webs are aerodynamically optimised and often polished. Depending on the design of the crank webs, we distinguish between Bell-Shaped Crankshafts, Flowed Crankshafts and Full Circle Crankshafts. The intake on the Crankcase must be adapted for all diaphragm shafts. There is no going back to the Disc Valve. But who wants to go back?
Crankshafts whose design does not allow the use of the original rotary valve inlet are referred to as diaphragm shafts. A different type of intake control, usually a Reed Valve, must be used. A Reed Valve controls the fresh gas supply according to demand and the operating situation. The negative pressure in the Crankcase opens the diaphragm; once the pressure difference is equalised, the diaphragm closes again. In this way, the Reed Valve automatically regulates the gas supply at the ideal control time. The control time of a rotary valve inlet, on the other hand, is rigid and cannot adapt to the respective engine speeds or operating situations. This means that the intake timing is either too long or too short in many speed ranges. In the case of the Vespa, the rotary valve intake is also relatively small. If a large Carburettor is installed for tuning purposes and the Engine speed is increased, the cross-section quickly reaches its limits and acts as a throttle.
Diaphragm shafts are available in different designs:
Full Circle Crankshafts have , as the name suggests, two completely closed cheeks. A large diaphragm inlet is required here. It really 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. The homogeneous shape also minimises turbulence in the Crankshaft casing. However, in engines controlled via the Casing, even large milled diaphragm inlets cannot prevent the mixture from being unfavourably obstructed by the cheek standing in the way.
Flowed Crankshafts are flow-optimised diaphragm shafts that harmonise very well with diaphragm intake manifolds. In most large-frame 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.
TheBell-Shaped Crankshaftis a Crankshaft whose shape resembles a bell or a mushroom. It also offers the mixture as little resistance as possible. It is not quite as uncompromising as the Flowed Crankshaft, as its symmetrical shape is not quite as ideally suited to the asymmetrical intake times of the Engine. However, a very large cross-section is available, especially in the phases with the greatest vacuum. As a result, the difference in performance compared to the Flowed Crankshaft is minimal. On the other hand, the symmetrical shape has the advantage that uniform balancing with an ideal balancing factor can be achieved more easily and effectively.
The next decision criterion is the choice of the right engine type.
Reed Valve crankshafts are even available for short-stroke engines
As the smallframe engines are compatible with each other, except for the automatic, we indicate the cubic centimetre class of the engine type here. The following engine types can be distinguished:
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.
More stroke - More torque - More fun
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. When looking for long-stroke variants, you need to pay attention to the stroke lengths of the diaphragm shafts. The most common stroke variants for small frames are
45 mm: A VMC speciality and particularly popular in Italy. The Long Stroke Crankshaft for the "small" 50cc Cylinders. This is interesting for all those who do not want to go over 125cc and still want to get the maximum out of the Engine.
54 mm:for those who want a reed valve but do not want to sacrifice maximum displacement, the 54 mm stroke Crankshaft is the right choice - for performance fetishists! More stroke = even more power and torque for all engines over 130 cc. The Crankcase must be adapted to the larger diameter of the crank webs.
56 mm:more is not possible in the original casing. The SIP Bell-Shaped Crankshaft goes the whole hog here, but the Casing must be spindled to such an extent that a new centring must be inserted and the Casing should be checked for openings after spindling. Or, more simply, the appropriateSIP Crankcase for this purpose.
Note: Stronger cylinder base gasket or cylinder head gasket required. Additional stroke should only be compensated for by a head gasket with a thickness equal to half the additional stroke; e.g. when converting 51 For example, when converting from 51 mm to 54 mm, use a head gasket 1.5 mm thick. If a foot gasket is used for equalisation, the exhaust 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 for Long Stroke Crankshafts. The original 97 mm Conrod is quite short. Especially in combination with a longer stroke, a longer Conrod ensures smoother running.
The subtle difference lies in the Conrod
The Conrod is one of the most heavily loaded parts in an Engine. It has to transmit the force of the explosion and withstand extreme acceleration and high heat. In addition, two bearings run in the running surfaces of the Conrod, one at engine speed. A high-quality Conrod is therefore 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, but 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 is intended to help you orientate yourself in the large selection of Crankshafts and Conrods.
The better the Crankshaft, the more effective the balancing and the smoother the Engine will run
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 will be optimally matched to the intended Engine. But it is a clear sign of quality, which greatly Elevates the probability of a smooth-running Engine. More on the subject of balancing in our Technology blogs.
And then there's the Cone
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. Bad choice for heavy tuning.
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 almost exclusively installed 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 speed, the greater the forces on the crankshaft stub and the greater the risk of it breaking 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/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 Reed Valve Crankshafts for Vespa 50-125/PV/ET3
SIP PERFORMANCE: High-end Bell -Shaped Crankshafts designed by the top tuners of the German-speaking scene and manufactured in Italy in a premium crankshaft forge. As SIP Performance version with polished forged Conrod or in the Premium version with a high-quality bronze Conrod.
SERIES PRO: Before the SIP PERFORMANCE Racing Crankshafts were available, worb5 updated the oldschool MAZZUCCHELLI Shafts for us. The Flowed Crankshafts are the result of many years of tuning experience.
MAZZUCCHELLI: More old-school with Full Circle Crankshafts. The Bell-Shaped Crankshaft was created in collaboration with SIP.
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 LIMA as well as CULU side
Oil Seal Crankshaft - replace both sides here too
NutLock Cap - if you have a Castle Nut on the Clutch, you need it:
