INSPECTING AND INSTALLING THE PISTON:
With the Piston removed, if there’s no abnormal wear, cracks, or damage, then measure the diameter of it at 90º from the pin hole and at about 15mm (.6 in)
from the bottom of the piston skirt. The Piston should be replaced it is or less then 84.88 mm (3.3417 in).
Compare this measurement with the measurement of the Cylinder to get the Piston to Cylinder clearance.
If the Piston is good and will be reused then spread each Ring at the gap and remove them by lifting the other side of the ring up and over the top of the Piston and clean the ring grooves in the Piston with the end of one of the old rings.
Insert the new top and second Piston Rings (one at a time)
in the bottom of the Cylinder and square it up using the Piston and measure the gap between the ends of the Piston Ring. The Top Ring should be no more then .50 mm (.02 in)
and the Second Ring should be no more then .65 mm (.026 in)
and the Oil Side Rails should be no more then .9 mm (.04 in)
Next insert the new Rings onto the Piston by starting with the Oil Ring Spacer making sure not to overlap the ends and then the (2) Oil Side Rails (one at the top and one at the bottom of the spacer).
Then the Second Ring and then the Top Ring with the mark at the gap facing up. (Look carefully at the rings case there is a difference between the two of them. See pic for an idea of the difference in them).
Starting with spreading the gap in the ring and inserting into the grove and sliding the other side down over the side of the Piston. Then check that the rings move freely around in the groove without catching.
With new rings you shouldn’t have to worry about this, but it doesn’t hurt to check the ring to groove clearance. While pushing the ring in until the outer surface is flush to the side of the Piston, measure the clearance between the ring and the top of the groove. The top ring should be no more then .14 mm (.006 in)
and the second ring should be no more then .12 mm (.005 in).
NOTE: Sometime with the Second Ring it’s easier to go to the top ring groove then move it down to the second.
Next stagger the rings as shown here.
I usually like to space the ring gaps like this.
To install the Piston:
Apply molybdenum oil solution to the Piston Pin and the Connecting Rod and install the Piston with the “IN” mark toward the intake side and insert the Piston Pin through the Piston and the Connecting Rod. Then install new Piston Clips in the grooves of the Piston and make sure they are fully seated. Don’t align the gap in the Piston Clips with the small cutout in the Piston.
INSPECTING AND INSTALLING THE CYLINDER:
Start by checking the inside of the Cylinder for any cracks or scratches. Then the top of the Cylinder for warpage with a good straight edge and a feeler gauge. Lay the straight edge across the machined surface and up against the studs, checking in all four directions. If there’s more then .1 mm .004 in()
of space anywhere along the straight edge then it will need to be resurfaced.
You’ll need a Dial Indicator to do this next step, but most machine or bike shop should be able to check it for you too if you don’t have one.
Measure the inside diameter of the Cylinder at the top, middle, and the bottom and use the maximum reading to determine the wear. This should be less then 85.1 mm (13.35 in).
If exceeding this measurement you’ll need a New Piston and have the Cylinder re-bored.
NOTE: Never have the Cylinder re-bored without having the piston first. If a machine shop says they can do it without the piston, go to another machine shop.
The Cylinder to Piston clearance should not exceed .1 mm (.004 in).
This can be determined by subtracting the Piston’s diameter from the Cylinder’s diameter
To install the Cylinder:
If you haven’t already clean up the gasket surfaces of the Crankcase and the Cylinder as mentioned above and install the Dowel Pins and a new gasket. Coat a new O-ring with oil and install it in the groove on the bottom of the Cylinder.
Apply oil to the Cylinder wall, Piston, and Rings and double check the Ring spacing. Route the Cam Chain through the Cylinder and slide the Cylinder over the Piston while compressing the Piston Rings with your fingers. Don’t force the Cylinder down over the Piston Rings.
With the Cylinder fully seated, apply a light coat of oil or anti-seize to the threads of the 10mm Cylinder Head Bolts and install them with the washers. Tighten them down in a crisscross pattern in 2-3 steps to a final torque of 33 ft lbs.
Install the (2) 6mm bolt to bottom right side of the Cylinder and tighten them securely (about 10 ft lbs).
Install the Cam Chain Guide into the Cylinder and Crankcase aligning the knobs on the guide with the grooves on the Cylinder.