Yamaha GT1 Service Manual page 27

2)
Always replace the cylinder base gasket when
reassembling.
Fig. 4-4-2
B. Checking the Cylinder for Wear
1) Measure the amount of wear of the cylinder
wall with a cylinder bore measuring micrometer
or cylinder gauge. (Measure it at four depths
while positioning the instrument at right angles
to the crankshaft.) If the difference between
the maximum and minimum diameter exceeds
0.05 mm. (0.009"), rebore and hone the
cylinder.
Fig. 4-4-3
2) The standard clearance between the piston and
the cylinder is 0.035~0.040 mm. (0.0014"
and 0.0016").
-21-
ENBINE -
Cylinder
C. Cylinder Reconditioning
1) Pistons are available in 0.25 and 0.50 mm.
(0.010" and 0.020") oversizes.
2) The cylinder should be rebored and honed to
the diameter of the oversize piston plus the
minimum allowable clearance. (4-4-B-2}
3) The error between the maximum and minimum
diameters after honing should be no more than
0.04 mm. (0.0015").
4} If cylinde·r rebore is necessary be sure to cham-
fer all port edges to prevent the rings from
catching, breaking on a sharp port edge.
D. Removing Carbon Deposits
Scrape off the carbon accumulation in the exhaust
port of the cylinder with the dulled end of a hacksaw
blade.
Fig. 4-4-4
E. Installing the Cylinder
Put your fingers at each end of the piston ring,
expand the ring, and slip it onto the piston. Align
both ends of the ring with the knock pin in each ring
groove. Next, insert the piston into the cylinder.
Take care not to damage the rings on the bottom of
the cylinder with the rings.
Fig. 4-4-5