Here is the big bore kit proposed by ATHENA to increase the displacement of your motocross / enduro YAMAHA YZ 125cc 2 stroke from 2005 to 2015. This kit in Ø58mm against Ø54mm of origin thus makes it possible to pass your motor bike of 125cc has 144cc real! A gain of torque and performance will be immediately felt. It allows a gain of 5 HP on average which is huge on this vehicle. Enough to have fun on the tracks or in the forest. ATHENA has also planned things well because this top engine is sold complete. It includes the cylinder, piston, ring, cylinder head and all the gaskets you need for a quality and tight reassembly. The advantage of taking this engine is that it is designed to be mounted on the original connecting rod. No adaptation is necessary to mount it. You will only have to mount the nozzle of an average of 10 points. You do not have any modification to make or adjustment! Attached is the power curve so that you can see for yourself the difference between the original and the big bore. You will also find a detailed list of vehicles on which this cylinder can be mounted.