Cylinder And Piston

WARNING: This page is about a different car, the 2006 Subaru Outback. However, it is still accessible from the selected car via links, so may be relevant.

The cylinder bore size is stamped on the cylinder block front upper surface.
NOTE:
- Measurement should be performed at a temperature 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: 89.205 - 89.215 mm (3.5120 - 3.5124 in)

B: 89.195 - 89.205 mm (3.5116 - 3.5120 in)

Fig 1: Identifying Standard Sized Pistons
How to measure the 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.

NOTE: Measurement should be performed at a temperature of 20°C (68°F).

Cylindrically:

Standard

0.030 mm (0.0012 in)

Out-of-roundness:

Standard

0.010 mm (0.0004 in)

Fig 2: Checking Inner Diameter Of Cylinder
When the piston is to be replaced due to general or cylinder wear, determine a suitable sized piston by measuring the piston clearance.
How to measure the outer diameter of each piston:
Measure the outer diameter of each piston at the height as shown in the figure. (Thrust direction)

NOTE: Measurement should be performed at a temperature of 20°C (68°F).

Piston grade point H:

37.3 mm (1.4685 in)

Piston outer diameter:

Standard

A: 89.205 - 89.215 mm (3.5120 - 3.5124 in)

B: 89.195 - 89.205 mm (3.5116 - 3.5120 in)

0.25 mm (0.0098 in) oversize

89.445 - 89.465 mm (3.5215 - 3.5222 in)

0.50 mm (0.0197 in) oversize

89.695 - 89.715 mm (3.5313 - 3.5321 in)

Fig 3: Measuring Outer Diameter Of Piston
Calculate the clearance between cylinder and piston.
NOTE: Measurement should be performed at a temperature of 20°C (68° F).

Cylinder to piston clearance at 20°C (68°F):

Standard

-0.010 - 0.010 mm (-0.0004 - 0.0004 in)
Boring and honing:
1. If the value of cylindrically, out-of-roundness, or cylinder-to-piston clearance measured is out of standard or if there is any damage on the cylinder wall, rebore it to use an oversize piston.
  CAUTION: When any of the cylinders needs reboring, all other cylinders must be bored at the same time, and use oversize pistons. Do not perform boring on one cylinder only. Nor use an oversize piston for one cylinder only.
2. If the cylinder inner diameter exceeds 89.715 mm (3.5321 in) after boring and honing, replace the crankcase.
  NOTE: Immediately after reboring, the cylinder diameter may differ from its real diameter due to temperature rise. Thus, pay attention to this when measuring the cylinder diameter.