Q. Does my scooter have 64mm or 69mm valves & why does it matter?
64mm and 69mm are the to the two common lengths of intake and exhaust valves in 139QMB cylinder heads. It doesn't really matter which your engine has unless you are replacing the cylinder head, rocker arms or rocker assembly, or the valves themselves or you are planning to port your cylinder head. 64mm valves need to be used with rocker arms intended for 64mm valves, and 69mm valves need to be used with rocker arms intended for 69mm valves. As long as you match the valve length to rocker arms or an entire rocker assembly for them, you can use either style of head.
Some big valve and big bore heads are only available with 64mm valves, so those with 69mm valves either buy rocker arms or the rocker assembly for an engine with 64mm valves to go along with the performance 64mm head. Some kits even include rocker arms with them. They can be swapped into the rocker assembly and then the kit may be used on either type without needing additional parts. If you need rocker arms, Parts For Scooters
carries both 64mm (part #151-101) and 69mm (part #151-247).
There are a couple of ways to look at the cylinder head with the valve cover removed and tell if your engine has 64mm or 69mm valves. One is to look across the top of the head and see how far the valve and valve spring protrude above the flat surface of the head. The 69mm valve will sit up higher above the head as shown in the photo below. You can see the whole top of the valve spring and retainer while looking across the 69mm valved head.
Another way is to look at the base of the valve spring on the intake side of the head. You should see that 69mm valved heads raise the spring assembly up compared to 64mm heads. The images below illustrate this. It's a bit difficult to see while the camshaft and rocker assembly are installed.
to watch a video that goes over the differences in 64mm and 69mm valves and heads in great detail.
<< Back to the Scoot F.A.Q.