Yamaha WR250FM Cylinder bore C 77.00 ~ 77.01 mm 0315 ~ 3.0319, 05 mm 0.002, 2nd step, Standard

CYLINDER AND PISTON

ENG

Cylinder bore “C”	77.00 ~ 77.01 mm
	(3.0315 ~ 3.0319 in)
Taper limit “T”	0.05 mm (0.002 in)
Out of round “R”	0.05 mm (0.002 in)
“C” = Maximum D

“T” = (Maximum D1 or D2) – (Maximum D5 or D6)

“R” = (Maximum D1, D3 or D5) – (Minimum D2, D4 or D6)

•If out of specification, replace the cylinder, and replace the piston and piston rings as set.

2nd step:

•Measure the piston skirt diameter “P” with

a micrometer.

a 8 mm (0.31 in) from the piston bottom edge

	Piston size “P”
Standard	76.955 ~ 76.970 mm
	(3.0297 ~ 3.0303 in)

•If out of specification, replace the piston

and piston rings as a set.

3rd step:

•Calculate the piston-to-cylinder clearance with following formula:

Piston-to-cylinder clearance = Cylinder bore “C” – Piston skirt diameter “P”

Piston-to-cylinder clearance: 0.040 ~ 0.065 mm

(0.0016 ~ 0.0026 in) <Limit>: 0.1 mm (0.004 in)

•If out of specification, replace the cylinder, and replace the piston and piston rings as set.

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