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- Vespa Classic
- Cylinder - VMC Type R 50 - 85cc, Ø50, stroke=43mm, aluminum - Vespa V50, PK50
Torque-optimized aluminum cylinder kit with a 50 mm bore, Nikasil coating, and modern porting for Vespa small-frame engines with a 43 mm short-stroke.
The VMC Type R 50 cylinder kit increases the displacement of a Vespa 50 short-stroke engine to approximately 85 cm³. The combination of a 50 mm bore, 43 mm crankshaft stroke, six transfer ports, and a Nikasil-coated aluminum cylinder liner is designed to deliver strong torque at low and mid-range RPMs.
This makes the Type R 50 ideal for riders who want to give their Vespa V50 or PK50 engine more low-end torque and a broader usable power range without having to convert to a long-stroke crankshaft. The cylinder remains part of the classic short-stroke design and uses a crankshaft with a 43 mm stroke.
The valve timing—approximately 124° intake and 172° exhaust —reflects the design goal: The Type R 50 is not an extreme high-rev cylinder, but rather a modern street and touring cylinder with power that kicks in early and a well-utilizable mid-range.
VMC Type R 50 85 cc 43 mm short-stroke Aluminum Nikasil 6 over-the-head valves Torque-oriented
Many Vespa V50 and PK50 engines come factory-equipped with a 43-mm-stroke crankshaft. The VMC Type R 50 retains this short-stroke principle and achieves the additional displacement through its bore, which has been enlarged to 50 mm.
A bore of Ø50 mm and a stroke of 43 mm result in a calculated displacement of approximately 84.4 cm³, which is typically referred to as 85 cm³. This places the Type R 50 above classic 75-cm³ kits without requiring the design change to a 51-mm long-stroke crankshaft.
| Bore | Ø50 mm |
|---|---|
| Crankshaft stroke | 43 mm |
| Calculated displacement | approx. 84.4 cm³ |
| Rated displacement | 85 cm³ |
| Engine design | Vespa small-frame short-stroke |
VMC has designed the port configuration of the Type R 50 so that the cylinder fills efficiently even at low and medium RPMs. This ensures that the engine doesn’t have to wait until high RPMs to deliver power, but instead responds quickly to throttle inputs and provides better acceleration during normal road use.
Especially with a small Vespa small-frame engine, a wide usable RPM range ensures a more pleasant riding experience. The engine can handle inclines and headwinds more effectively and does not need to be revved as high during acceleration.
The Type R 50 features six overflow channels. These channel the fresh fuel-air mixture from the crankcase into the combustion chamber and help flush out residual exhaust gases.
It is not just the number of bleed ports that matters. Their shape, cross-section, and entry angle influence how the gas flow moves within the cylinder. VMC has designed the port layout to ensure good filling at low and medium RPMs.
As a result, the Type R 50 utilizes a more modern flow design than many classic short-stroke cylinders, whose construction is still based on significantly older channel shapes.
VMC specifies valve timing for the Type R 50 of approximately 124° at the intake ports and 172° at the exhaust. This results in a calculated early exhaust angle of around 24°.
These valve timing angles support the cylinder’s torque-oriented character. The exhaust valve does not open extremely early, which prevents the power band from being shifted unnecessarily far into high RPM ranges.
| Intake Timing | approx. 124° |
|---|---|
| Exhaust timing | approx. 172° |
| Calculated advance exhaust | approx. 24° |
| Basic Characteristics | Early torque and a wide usable mid-range |
Actual valve timing may vary slightly from the specified reference values due to manufacturing tolerances, gasket thickness, and the base engine used.
The Type R 50 features an aluminum cylinder block. The material rapidly transfers the heat generated during combustion from the cylinder bore to the cooling fins.
The actual cylinder bore is formed by a Nikasil coating. This thin, hard coating serves as a wear-resistant contact surface for the piston and piston rings.
On the Type R 50, the cylinder head is not clamped together with the cylinder using four long through-bolts. Instead, the head is mounted separately directly to the cylinder using four M6 Allen screws.
The kit includes four specific M7 studs for mounting the cylinder to the engine case. In this way, VMC avoids the mounting system used on various other small-frame short-stroke cylinders, in which the head and cylinder are held together using the same long studs.
The kit includes a cast aluminum cylinder head. The spark plug is located on the side of the head and uses a long thread.
When selecting the spark plug, ensure that the thread length, heat range, and electrode configuration match the engine configuration. A spark plug with the wrong thread length can result in an unfavorable position within the combustion chamber or cause mechanical problems.
The exhaust port has a diameter of 28 mm. The distance between the two exhaust studs is 52 mm.
The exhaust system must be mechanically compatible with these dimensions and, in terms of performance, suited to the cylinder. Given the torque-oriented character of the Type R 50, an exhaust system that is effective even at low and medium RPMs is ideal.
On some large-bore short-stroke cylinders, the cylinder base collides with the crescent-shaped dust protection contour at the base of the Vespa engine housing. This area must then normally be removed or modified.
According to the manufacturer, the VMC Type R 50 is designed so that this machining is not necessary. The existing crescent-shaped contour on the engine housing can remain intact.
The Type R 50 can be configured in various ways depending on the carburetor, crankshaft, exhaust, and gear ratio. Its fundamental character remains focused on early torque and a well-utilized mid-range.
The increase in displacement from 50 to approximately 85 cm³ significantly changes the requirements for fuel, air, and gear ratio. Therefore, the stock carburetor jet settings must not be used without verification.
The carburetor must supply sufficient fuel and be tuned to match the exhaust system being used. The stock gear ratio of a 50-cm³ engine may also prove too short for the additional torque.
The key factor is the engine base used, which must have a 43-mm short-stroke crankshaft. The model designation, engine number, and any modifications already made should be verified before ordering.
| Manufacturer | VMC |
|---|---|
| Series | Type R 50 |
| Type | Cylinder kit |
| Displacement | approx. 85 cm³ |
| Bore | Ø50 mm |
| Crankpin diameter | 43 mm |
| Cylinder material | Aluminum |
| Bearing surface | Nikasil coating |
| Bypass channels | 6 |
| Overflow time | approx. 124° |
| Exhaust timing | approx. 172° |
| Calculated advance angle | approx. 24° |
| Exhaust valve diameter | Ø28 mm |
| Exhaust stud spacing | 52 mm |
| Cylinder head | Cast aluminum |
| Spark plug position | Side |
| Spark plug thread | Long thread |
| Head fastening | 4 M6 Allen screws |
| Cylinder studs | 4 specific M7 studs |
| Housing machining | No machining of the crescent-shaped dust protection contour is required |
| Compatible with | Vespa V50 and PK50 with 43-mm short-stroke engine |
Other components included in the package are not explicitly listed in the manufacturer’s specifications provided here. The specific package contents listed for the product in the store are authoritative.
The VMC Type R 50 combines the classic Vespa short-stroke concept with a modern cylinder design. A 50 mm bore and 43 mm stroke result in approximately 85 cm³, without necessarily requiring a conversion to a long-stroke crankshaft.
The aluminum cylinder with a Nikasil coating, six transfer ports, and moderate valve timing of approximately 124°/172° is designed for early torque and a well-utilized mid-range. This makes the kit suitable for everyday and touring-oriented Vespa V50 and PK50 engines as well as for sport-oriented short-stroke setups.
The separate cylinder head mounting with four M6 bolts and the included M7 cylinder studs provide a clearly defined mounting. At the same time, according to the manufacturer, the crescent-shaped dust protection contour on the engine casing can remain unmodified.
