This guide will take you through the procedure for adjusting the valves on a GY6 125 or 150cc engine.
Tools you will need:
– Socket wrench with metric sockets in sizes from 8mm to 12mm (Box wrenches will work too).
– Crescent wrench
– Feeler gauges with sizes from 0.003″ to 0.007″
– Torque wrench (optional)
1. Remove passenger seat
3, Remove the valve cover to expose the camshaft and rocker arm assembly. Rotate the camshaft until the big hole in the sprocket end points straight out of the top of the engine and the two smaller holes are lined up with the flat plane of the cylinder head. (Your camshaft may have lines instead of smaller holes, but they need to line up the same way). You can do this by rotating the variator in the CVT transmission counter clockwise by hand until the holes line up properly.
5. Using a feeler gauge (Harbor Freight sells a good set for $3), measure the gap between the top of the valve and the tappet of the rocker arm. Turn the tappet in or out as necessary to adjust. You want to set your valve clearances to 0.004″ – 0.005″ on both the intake and exhaust valves.
7. Tighten down the retainer nuts and re-check clearances (they sometimes tighten up a bit when you tighten the retainer.)
8. Replace the valve cover. Torque spec for the cover bolts is 6-9ft/lbs (72-108 in/lbs).
9. Replace the passenger seat, and you’re good to go!