A high-end crank for the Vespa largeframe models. Increased stroke and the highest quality for engines in everyday use, with high torque values.
Together with the cylinder and piston, the crankshaft represents the beating heart of any internal combustion engine. It is amongst the hardest working components and the conversion of the pistons stroke to a rotary movement places the highest demands both quality and care taken during construction. The crankshaft should also be well balanced to reduce any unwanted vibrations and the oscillating mass kept to a minimum to support an efficient delivery of the power created by the motor. The big-end bearing rotates at the same rate as the motors RPM, receives lubrication from the petrol/two-stroke oil gas mixture and must withstand two abrupt changes in direction of the piston for each motor revolution. The crank-pin, connecting both crankshaft webs with the con rod, has to be pressed into the webs with a certain clearance to the openings in the webs. If this connection is not strong enough the crankshaft can twist and the crankshaft webs become misaligned and seize. To ensure the big end bearing receives sufficient lubrication the big end of the con rod should be provided with slots to facilitate this.
- Especially smooth running.
- Very high quality materials and production.
- Also available with a polished con rod.
The SIP crankshafts
This all-new range of performance crankshafts are produced for SIP in Italy and satisfy all of the above listed demands. We have concentrated our efforts to provide the highest quality combined with tried and tested technological features. Each crankshaft is balanced specifically to suit the stroke, con rod length and model of scooter for which it is intended.
The crankshafts available in this range can be split into two main types:
The 'Premium' are equipped with a 'standard' high end con rod type, meaning that its surface finish remains unmodified. It is provided with lubrication slots and holes, for the big and small end bearings respectively. The 'Performance' crankshaft models include a con rod of extremely high quality and they are made more enduring with an intensive polishing procedure that provides a more stable molecular structure. The smooth polished flanks of the con rod also help reduce turbulence. The polished con rods also have been optimised with a reduction in weight. They possess an gas-flowed profile and been modified around the big end to improve the bearings lubrication.
Long stroke crankshaft PX 62mm
The 62mm stroke provided by this long stroke crankshaft for the Vespa 200cc models has 5mm more stroke than the original crankshafts. This increases the cubic capacity of the cylinder fitted by approximately 8%. The improved relation between the stroke and bore not only raises the power out put, but also noticeably raises the torque delivery. The crank is designed to enhance road tuned motors with strong torque values. The 62mm stroke is not suited to the original crankcase. To be more specific, not into the smaller flywheel side of the casings. This requires machining to a internal diameter of 99.5mm.
The disc-valve port timings
125°/-5°: Including around 20° of extended port timing. The longer inlet port timing is ideal for 'Sport' orientated tuning. The port timings remain conservative enough for everyday use. This enables the motor to retain a decent performance at low revs and is also relatively simple to set up correctly. The 'blowback' from the crankcase is also kept at an acceptable level. The disc-valve web is specially designed to make the gas flow through the crankcase more efficient. Another aspect in the development of the crankshaft webs was to provide a more effective balancing and a smoother running motor.
The con rod lengths
We have these long stroke crankshafts available with the following con rod lengths:
- 105mm: For the 125-150cc Vespa largeframe models.
- 110mm: For the 200cc Vespa largeframe models.
- 127mm: For the QUATTRINI M244/M232.
The extra millimetres of length it possesses over the QUATTRINI type enables a more satisfactory adjustment of the port timings. Two small tungsten insert weights are also included to ensure a perfect balance.
Mounting information: Do not forget to modify the smaller half of the engine casings, this requires machining to a internal diameter of 99.5mm.
Conclusion ; The ideal crankshaft for mild, reliable tuning projects. It can enhance a wide range of uses, from a slightly tuned standard set up through to a Malossi sport cylinder combined with a big-box exhaust with a motorway friendly 20 PS.
The best set up - our SIP–TIP:
- Do not forget to also replace all seals and bearings when replacing the crankshaft, (e.g. # M6615466 & # M6617236).
- The extra stroke should be compensated for with a 2.5mm cylinder head gasket (such as # 90779500).
- New reinforced woodruff-keys (# 87059200) are also a good complementary component.
