4-36 ENGINE TOP END
Piston/Cylinder Clearance Inspection
The most accurate way to find the piston clearance is
by making separate piston and cylinder diameter measure-
ments and then computing the difference between the two
values. Measure the piston diameter as just described, and
measure the cylinder diameter at the very bottom of the
0.010 ∼ 0.022 mm (0.00039 ∼ 0.00086 in.)
Whenever the piston or cylinder has been replaced with
a new one, the motorcycle must be broken in the same
as with a new machine.
Boring, Honing Performance
When boring and honing a cylinder, note the following:
There are two sizes of oversize pistons available. Over-
size pistons require oversize rings.
Oversize Pistons and Rings
0.50 mm (0.0197 in.)
1.0 mm (0.0394 in.)
Before boring a cylinder [A], first measure the exact di-
ameter of the oversize piston, and then, according to the
standard clearance in the specifications section, deter-
mine the rebore diameter. However, if the amount of bor-
ing necessary would make the inside diameter greater
than 1.0 mm (0.0394 in.) oversize, the cylinder block must
Cylinder inside diameter must not vary more than 0.01
mm (0.0004 in.) at any point.
Be wary of measurements taken immediately after boring
since the heat affects cylinder diameter.
In the case of a rebored cylinder and oversize piston, the
service limit for the cylinder is the diameter that the cylin-
der was bored to plus 0.1 mm (0.004 in.) and the service
limit for the piston is the oversize piston original diameter
minus 0.20 mm (0.0079 in.). If the exact figure for the re-
bored diameter is unknown, it can be roughly determined
by measuring the diameter at the base of the cylinder.