To replace the front oil seal, the crankshaft pulley have to be removed The front seal can be removed by use of a screw driver or a hook tool being used to remove the seal gently and keenly so as not to cause any damages on the engine front cover bore and the sealing surface of the crankshaft. Another way is to make small holes with the drill on each side of the field seal and, after that, use self-tapping screws to remove the thing. Scrub the sealing areas on the engine cover and crankshaft then apply clean engine oil to the surfaces of the two parts. Starting with the front of the engine install the new seal making certain it is seated in a upright position. After starting applying the seal driver or a worthy socket to screw the seal tightly on the space until it comes to lay flat on the surface of the engine cover. After the roughing process apply clean engine oil on the lip of the seal. The rear oil seal is an assembly and as such, if the bike is fitted with a transmission and clutch, then remove the transmission and clutch assembly you then remove the flywheel followed by the oil pan. Removing the oil seal and carrier and then roughing up the surfaces where the two are joining on the cylinder block and crankshaft alike, polished burrs included. Detailed, lightly apply clean engine oil on the inner lip of new seal and affording a thin liner of a plastic material. With considerable care, whilst supporting the carrier, install the new oil seal and carrier onto the crankshaft and engage the carrier bolts; tighten the bolts while in this position. Some of the 'using knowledge from experience' might include, if there was a plastic liner it should be taken off to allow contact with the crankshaft before tightening the oil seal carrier to the appropriate torque. Last of all perform visible checks for evidence of oil leakage when the engine is running.