Subaru 2009 IMPREZA Service Manual page 1150

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2. CYLINDER AND PISTON

1) The cylinder bore size is stamped on the front

upper face of the cylinder block.

• Measurement should be performed at a temper-

ature of 20°C (68°F).

• Standard sized pistons are classified into two

grades, "A" and "B". These grades should be used

as guide lines in selecting a standard piston.

Standard diameter:

A: 99.505 — 99.515 mm (3.9175 — 3.9179 in)

B: 99.495 — 99.505 mm (3.9171 — 3.9175 in)

(A) Main journal size mark

(B) Cylinder block (RH) – (LH) combination mark

(D) #2 cylinder bore size mark

(E) #3 cylinder bore size mark

(F) #4 cylinder bore size mark

Cylinder Block

ME(H4DOTC)-92

2) Measure inner diameter of each cylinder.

Measure the inner diameter of each cylinder in both

the thrust and piston pin directions at the heights as

shown in the figure, using a cylinder bore gauge.

Measurement should be performed at a tempera-

ture of 20°C (68°F).

0.015 mm (0.0006 in)

Out-of-roundness:

0.010 mm (0.0004 in)

(A) Piston pin direction

(B) Thrust direction

H1: 10 mm (0.39 in)

H2: 45 mm (1.77 in)

H3: 80 mm (3.15 in)

H4: 115 mm (4.53 in)

3) When the piston is to be replaced due to general

or cylinder wear, select a suitable sized piston by

measuring the piston clearance.