Tappet`s knocking on my kymco ck 125 - 2005 Kymco Stryker 125

Option 1: Go to mechanic

Option 2: Adjust the tappets. If you have never adjusted tappets or worked with engines before it is better to have someone experienced with you. The following is the procedure I use.

1: Carefully remove side panels.
2: Close fuel tap and disconnect pipe.
3: Carefully remove fuel tank. (undo the bolt under the seat and slide the tank 2 inches back, then lift it upwards)
4: Undo the bolts of the cylinder head cover (3 bolts with 12mm head, one of them also holds a small bracket for the throttle cable or ignition wire, I can't remember).
5: Remove the cylinder head cover. If you find this difficult put the bike in 5th gear and rotate the engine (by rotating the rear wheel) to the "inlet valve open" position so that the cover clears the "inlet valve rocker". Be careful that you do not damage the top cover gasket (made of rubber) or you will have an oil leak and no lubrication to the rockers.
6: Rotate the engine to a position with both valves closed, as close as possible to "top dead centre of compression/power strokes". There is a notch on the flywheel indicating top dead centre - you see this by opening the cap on the top of the flywheel cover on the left side of the bike. (do not stay at "top dead centre of exhaust/intake strokes")
7: Check the free play of the rockers on the valves. The service manual recommends a clearance between the valve and the rocker of 0.08mm with the engine cold (left to cool overnight). Maximum acceptable is 0.10mm and minimum is 0.06mm. The gap is checked using a feeler gauge (you know that you have a gap of 0.08mm by sliding a feeler that is 0.08mm thick and there is just a little friction slowing you down - if the feeler is hard to pull the gap is less than 0.08 and if the feeler passes with nothing resisting it then the gap is larger than 0.08mm).
8: If the tappets are knocking then the gap is too large. Undo the locknut on the tappet adjuster (10mm nut at the end of the rocker) just enough to let you turn the tappet adjuster. Then rotate the tappet adjuster until you get the right gap and tighten the locknut. Be sure to hold the tappet adjuster with pliers or something else while tightening the locknut so that the adjuster does not rotate.
9: Check and re-check that the gap between the adjuster and the valve is as specified. Incorrectly adjusted tappets are very bad for the engine, especially "tight" tappets with no gap between adjuster screw and valve. The first time you adjust tappets you might have to repeat from step 7 several times until you get used to it.
10: Assemble everything in the reverse order of disassembly. You might have to rotate the engine to "intake valve open" position again to place the cylinder head cover easily. During assembly be careful the the rubber gasket of the cover is not damaged or out of place. There is an oil path from the head to a nozzle above the rockers and the gasket must seal this well.
10: Once you assemble everything start the engine and once it is hot enjoy a more silent bike. It is normal on these engines to have some tappet noise when cold, but if the tappets are adjusted right they are nearly silent when hot.

Always refer to an expert when you are not sure. Maybe the first time it is safer to watch your trusted mechanic do this work.