SPECIAL REED VALVES: TESTING ON THE ENGINE BENCH

Max Bernardi

15 May 2019

Every detail is useful to increase performance when preparing an engine. The machining of the intake and cylinder of the crankcase is the crucial way to maximize power, but also to assemble the right reed valve and the right reed valves give advantages. Let's see how the reed valve, a simple component at first sight, can affect the performance of a kart’s engine.

REED VALVES, WHAT THEY ARE

Reed valves they are components of reed valve suction engines. There are real "tabs" located inside reed valve packs that, due to their movement, allow the entry of the air/petrol mixture depending on the engine cycle: in the compression phase, the piston, rising from the LDP (lower dead point) to UDP (upper dead centre point), clogs the transfer ducts on the cylinder barrel generating a depression in the crank chamber (where the crankshaft is located). This depression causes the reed valves to open so that the fresh air/petrol mixture can flow into the crankshaft, to then be poured back into the combustion chamber by means of the transfer ducts in in the next phase of the cycle. When the piston ends its rising phase, the spark plug ignites the spark that ignites the mixture: the combustion generated in this way pushes the piston towards the LDP, the depression in the chamber weakens, thus causing the reed valves to close. At this point, while the piston continues to descend, the pressure in the pump casing increases, helping the mixture to enter the combustion chamber through the transfer ducts, expelling the combustion gases once the exhaust ports are uncovered.

A reed valve pack with reed valves, ready to be mounted on an engine.

The tuner modifies the reed valves to vary the bending

REED VALVES, WHAT THEY DO

Without reed valves, it would be impossible to create and use the depressions created by the piston in its stroke and, therefore, effectively "transport" the air/petrol mixture into the combustion chamber. This is why the reed valves must open and close with each cycle, withstanding very high and very stressful oscillation frequencies that sometimes lead to the yielding and deformation of the valves, with harmful effects on the engine.

The bending capacity of the reed valves depends on the material they are made of