Cylinder; Removal; Maintenance - Yamaha YTZ250S 1986 Service Manual

CYLINDER
Removal
1. Remove the exhaust pipe.
2.
Remove the cylinder head.
3. Remove the carburetor assembly.
4. Disconnect the C.D.I magneto lead from
the clamp and remove the cylinder
holding nuts and cylinder.
Cylinder holding nut:
35 Nm (3.5 m.kg, 25 ft ·Ib)
5. With the piston at top dead center, raise
the cylinder just enough to stuff a clean
shop towel into the crankcase around the
connecting rod; this will prevent dirt from
entering the crankcase. Remove the
cylinder and base gasket and discard the
gasket.
3-13
Maintenance
1. Using a rounded scraper, remove carbon
deposits from the exhaust port.
2. Check cylinder bore. Using a cylinder
hone, remove any scoring. Hone lightly,
using smooth stones. Hone no more than
required to avoid excess piston clearance.
3. Using a cylinder gauge set to standard
bore size, measure the cylinder. Measure
front-to-rear and side-to-side at top,
center and bottom just above exhaust
port.
4. Compare minimum and maximum mea-
surements. If over tolerance and not
correctable by honing, rebore to next
oversize.
Max. allowable taper:
0.05 mm (0.0020 in)
Max. allowable out-of-round:
0.01 mm (0.0005 in)