Malossi MHR 47mm "70cc" cylinder kit for Vertical Minarelli engines.
These were commonly found on early pre-bug type Yamaha Zuma, BW'S, MBK Booster, etc.
This is an absolute powerhouse of a kit and we recommend only experienced tuners give it a go. You absolutely should pair this with a performance crankshaft, a good exhaust like the Malossi MHR, and a large carburetor.
From Malossi themselves:
CYLINDER KIT MHR
- Material: special aluminium alloy with high percentage of silicon and titanium that guarantees exceptional strain strength even at high temperatures.
- Heat treatment: special quenching and stabilizing treatment that gives the material increased toughness and strength, guaranteeing that mechanical and size specifications will remain unaltered for temperatures of up to 250 °C.
- Chip-forming machining: carried out on NC machining centres with extremely-limited size and shape tolerance (roundness, perpendicularity).
- Inner surface coating: effected using silicon carbide on a nickel matrix with heat treatment that guarantees extreme hardness (around 600 HVO, 1/5) and excellent resistance to wear.
- Internal machining of cylinder: using special machines that allow a degree of finish on the cylinder barrel walls whose roughness corresponds with the angles set at the design stage (grinding process using special stone).
- Port and exhaust diagrams: designed and manufactured especially for racing. The definition of the port and exhaust diagrams has requested considerable effort on the part of our engineers both on engine test stands and the circuits on which the trophy is held.
- Material: special aluminium alloy with a very high percentage of silicon and titanium that guarantees both excellent heat resistance and strain strength upon temperature variation.
- External coating: graphite coating that guarantees a very low friction coefficient
- Structure: reinforced in order to offer resistance to the stress suffered by cylinder units used for top-level competition, but at the same time light enough to reduce inertial force.
- Ring: 1 mm nodular-cast-iron single ring with rectangular cross section and hard-chromium coating on outer surface.
- Rings in very strong modular cast iron with ground, wear-resistant, hard chrome metal-spray coating on the contact surface.
- Material: special alluminium alloy with a very high heat exchange coefficient.
- Geometry of heat exchange surfaces recalculated and increased.
- Combustion chamber completely-designed to obtain a high compression ratio with a very high turbolece.
- Machining: numerically controlled machines.
Malossi Part Number 31 7559