72 mm bore, 60 mm stroke, nikasil-coated aluminium cylinder.
Valve timings: Exhaust 182°, transfer ports 128°, blow-down 27°, intake: reed-controlled.
With the RB25 Kit, AF has created a “big brother” to the approved TS1, surpassing the latter in terms of displacement and performance.
The cylinder layout carries strong influences from the MotoX sector.
The intake is controlled through four very large reed valves, which are aligned in a “V”-angle.
Concerning layout, the intake port is directly connected to the transfer ports. In addition, there is a boost-port.
Apart from that, the exhaust port was increased by means of two auxiliary exhaust ports.
AF uses the ASSO piston with two thin chrome rings (1 mm) known from the Rapido 250.
The RB25 is designed for a 60 mm stroke crankshaft. Due to the 72 mm bore diameter of the piston, the spigot is enlarged in diameter. Therefore, the crankcase needs machining in order to fit the cylinder. Fortunately, the studs do not need moving.
Included in delivery are piston, reed blocks, intake manifold, alongside the cylinder.
Concerning cast and coating quality, the RB25 does not keep up to the quality of the TS1 which was manufactured by renowned foundry “Gilardoni”.
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