Assembly:
Wrap a clean rag around the connecting rod, making sure to fill in area over crankshaft. This is to prevent foreign objects from falling down into crankcase. Install rings on piston.

Piston: Make sure opening in the ring straddles the ring locating pin on the ring land. After installing on the piston make sure it expand and contract freely. If they do not, swap the two rings. (On single ring pistons this does not apply.) Check for free movement.

Install wrist pin bearing on the rod. Use a drop of oil on and rotate to spread on inner race of rod.
Install one circlip. Make sure it seats in the groove properly. Slip piston over small end of rod. (Make sure the arrow on top of the piston points towards the exhaust.)
Install the wrist pin. Install the second circlip.
Remove rag that is protecting crankcase, and install cylinder base gasket.

Immediately before installation of the cylinder, WASH the cylinder with dishwashing soap and water. Scrub all the ports and the bore. Dry thoroughly with a lint free cloth. Make sure cylinder is both dry and clean.
Do Not smear oil in the cylinder. It wants to be installed "dry."

Slip the cylinder over the piston while compressing the ring(s) with one hand. Make sure ring ends are straddling the ring locating pin on the piston ring land. Rotate crankshaft and make sure piston moves up and down freely. Install head gasket. (if Head gasket has a raised ridge. It goes up.) Install head. Torque head nuts to 11-ft lbs. using a cross pattern. (If you are using the oil injector, don't forget to hook up oil line!) (Do not add oil to the gas tank!!!!)
Do not over tighten spark plug! (14ft/lbs torque)

Break In:
Do not ride at a sustained RPM for a long time.
Operate scooter in a "normal" manner. Ride for 5 minutes. Turn off and let cool down for 5 minutes. Then ride for 10 minutes and the turn off and cool for 5 minutes. Continue this adding 5 minutes of run time until you reach 30 minutes. Bike is then broken in. (This procedure takes time and patience. When done properly the rewards are great.)

It is important that during this break in time the RPM is varied constantly. Do not run at a sustained RPM for a long time. If you are cruising at 35mph for a minute, change to 40mph, etc. Do not put on the stand and let idle for any part of the break in period. Engine needs to have air going past it and the RPM constantly varied.

The Athena kit comes with several different base gaskets. Here's the deal:
The PAPER BASE GASKET is the one to use for general purpose reliable riding.
if you want to adjust the squish band to the optimum .9mm then use the different gaskets to achieve that spec.
(If you don't know what a squish band is, or how to adjust, please skip this step!)

Yamaha circlips are difficult at best. Pay particular attention to seating them properly. Yamaha head gaskets have a ridge on them. The ridge goes up.

Polini requires the use of a "long reach" spark plug such as an NGK B9ES

EXHAUST GASKET:
1. If you are using Arrow, Leo Vince ZX or ZXR pipe use the stock exhaust gasket.
2. If you are using the Leo Vince HandMade 70cc pipe use the exhaust gasket supplied with kit