Subaru Impreza 3 / Impreza WRX / Impreza WRX STI. Manual — part 84

ME(STI)-98

Cylinder Block

MECHANICAL

(2) If the cylinder inner diameter exceeds the

limit after boring and honing, replace the cylin-

der block.

NOTE:

Immediately after reboring, the cylinder diameter

may differ from its real diameter due to temperature

rise. Thus, when measuring the cylinder diameter,

wait until it has cooled to room temperature.
Cylinder inner diameter boring limit (diameter):

To 100.005 mm (3.9372 in)

3. PISTON AND PISTON PIN

1) Check the piston and piston pin for damage,

cracks or wear. Replace if faulty.

2) Check the piston ring groove for wear or dam-

age. Replace if faulty.

3) Make sure that the piston pin can be inserted

into the piston pin hole with a thumb at 20°C (68°F).

Replace if faulty.
Clearance between piston pin hole and piston

pin:

Standard

0.004 — 0.008 mm (0.0002 — 0.0003 in)

4) Check the snap ring installation groove (A) on

the piston for burr. If necessary, remove burr from

the groove so that the piston pin can lightly move.

5) Check the snap ring for distortion, cracks and

wear.

4. PISTON RING

1) If the piston ring is broken, damaged or worn, or

if its tension is insufficient, or when the piston is re-

placed, replace the piston ring with a new part of

the same size as piston.
NOTE:

• The top ring and second ring have the mark to

determine the direction for installing. When install-

ing the ring to piston, face marks to the top side.

• Oil ring consists of the upper rail, expander and

lower rail. When installing oil ring on piston, be

careful of the direction of each rail.

ME-00173

ME-00174

(A) Upper rail
(B) Expander

(C) Lower rail

ME-00175

(A)

ME-02480

(A)

(B)

(C)

(A)

(B)

(C)

ME(STI)-99

Cylinder Block

MECHANICAL

2) Using the piston, insert the piston ring and oil

ring into the cylinder block so that they are perpen-

dicular to the cylinder wall, and measure the piston

ring gap using a thickness gauge.

3) Fit the piston ring straight into the piston ring

groove, then measure the clearance between pis-

ton ring and piston ring groove with a thickness

gauge.
NOTE:

Before measuring the clearance, clean the piston

ring groove and piston ring.

5. CONNECTING ROD

1) Replace the connecting rod, if the large or small

end thrust surface is damaged.

2) Check for bend or twist using a connecting rod

aligner. Replace the connecting rod if the bend or

twist exceeds the limit.
Limit of bend or twist per 100 mm (3.94 in) in

length:

0.10 mm (0.0039 in)

3) Install the connecting rod with bearings attached

to the crankshaft, and using a thickness gauge,

measure the thrust clearance. If the thrust clear-

ance exceeds the standard or uneven wear is

found, replace the connecting rod.
Connecting rod thrust clearance:

Standard

0.070 — 0.330 mm (0.0028 — 0.0130 in)

4) Inspect the connecting rod bearing for scar,

peeling, seizure, melting, wear, etc.

Standard

mm (in)

Piston ring gap

Top ring

0.23 — 0.28

(0.0091 — 0.0110)

Second ring

0.37 — 0.52

(0.015 — 0.020)

Oil ring rail

0.20 — 0.50

(0.0079 — 0.0197)

Standard

mm (in)

Clearance between
piston ring and pis-
ton ring groove

Top ring

0.040 — 0.080

(0.0016 — 0.0031)

Second ring

0.030 — 0.070

(0.0012 — 0.0028)

ME-00177

ME-00178

(A) Thickness gauge
(B) Connecting rod

(A)

(A)

(B)

(B)

ME-05475

ME-00180

ME(STI)-100

Cylinder Block

MECHANICAL

5) Measure the oil clearance on each connecting

rod bearing using plastigauge. If any oil clearance

is not within the standard, replace the defective

bearing with a new part of standard size or under-

size as necessary.
Connecting rod oil clearance:

Standard

0.017 — 0.045 mm (0.0007 — 0.0018 in)

6) Inspect the bushing at connecting rod small end,

and replace the connecting rod if it is worn or dam-

aged.

7) Measure the piston pin clearance at connecting

rod small end. If the measured value is not within

the standard, replace the connecting rod and piston

pin as a set.
Clearance between piston pin and bushing:

Standard

0 — 0.022 mm (0 — 0.0009 in)

6. CRANKSHAFT AND CRANKSHAFT

BEARING

1) Clean the crankshaft completely, and check it for

cracks using liquid penetrant tester. If defective, re-

place the crankshaft.

2) Measure warping of the crankshaft. If it exceeds

the limit, correct or replace it.
NOTE:

If a suitable V-block is not available, using just the

#1 and #5 crankshaft bearings on cylinder block,

position the crankshaft on cylinder block. Then,

measure the crankshaft bend using a dial gauge.
Crankshaft bend limit:

0.035 mm (0.0014 in)

Unit: mm (in)

Bearing

Bearing size

(Thickness at cen-

ter)

Outer diameter of

crank pin

Standard

1.490 — 1.506

(0.0587 — 0.0593)

51.976 — 52.000

(2.0463 — 2.0472)

0.03 (0.0012)

Undersize

1.504 — 1.512

(0.0592 — 0.0595)

51.954 — 51.970

(2.0454 — 2.0461)

0.05 (0.0020)

Undersize

1.514 — 1.522

(0.0596 — 0.0599)

51.934 — 51.950

(2.0447 — 2.0453)

0.25 (0.0098)

Undersize

1.614 — 1.622

(0.0635 — 0.0639)

51.734 — 51.750

(2.0368 — 2.0374)

ME-00181

ME-00174

ME-00183

ME(STI)-101

Cylinder Block

MECHANICAL

3) Inspect the crank journal and crank pin for wear. If they are not within the standard, replace the bearing

with a suitable (undersize) one, and replace or grind to correct the crankshaft as necessary. When grinding

the crank journal or crank pin, finish them to the specified dimensions according to the undersize bearing to

be used.
Crank pin:

Cylindricality

Limit

0.006 mm (0.0002 in)

Out-of-roundness

Limit

0.005 mm (0.0002 in)

Grinding limit (dia.)

To 51.750 mm (2.0374 in)

Crank journal:

Cylindricality

Limit

0.006 mm (0.0002 in)

Out-of-roundness

Limit

0.005 mm (0.0002 in)

Grinding limit (dia.)

To 59.758 mm (2.3527 in)

ME-00184

Unit: mm (in)

Crank journal diameter

Crank pin outer diameter

#1, #3

#2, #4, #5

Standard

Journal O.D.

59.984 — 60.008

(2.3616 — 2.3625)

59.984 — 60.008

(2.3616 — 2.3625)

51.976 — 52.000

(2.0463 — 2.0472)

Bearing size
(Thickness at center)

1.998 — 2.015

(0.0787 — 0.0793)

2.000 — 2.017

(0.0787 — 0.0794)

1.490 — 1.506

(0.0587 — 0.0593)

0.03 (0.0012)
Undersize

Journal O.D.

59.962 — 59.978

(2.3607 — 2.3613)

59.962 — 59.978

(2.3607 — 2.3613)

51.954 — 51.970

(2.0454 — 2.0461)

Bearing size
(Thickness at center)

2.017 — 2.020

(0.0794 — 0.0795)

2.019 — 2.022

(0.0795 — 0.0796)

1.504 — 1.512

(0.0592 — 0.0595)

0.05 (0.0020)
Undersize

Journal O.D.

59.942 — 59.958

(2.3599 — 2.3605)

59.942 — 59.958

(2.3599 — 2.3605)

51.934 — 51.950

(2.0447 — 2.0453)

Bearing size
(Thickness at center)

2.027 — 2.030

(0.0798 — 0.0799)

2.029 — 2.032

(0.0799 — 0.0800)

1.514 — 1.522

(0.0596 — 0.0599)

0.25 (0.0098)
Undersize

Journal O.D.

59.742 — 59.758

(2.3520 — 2.3527)

59.742 — 59.758

(2.3520 — 2.3527)

51.734 — 51.750

(2.0368 — 2.0374)

Bearing size
(Thickness at center)

2.127 — 2.130

(0.0837 — 0.0839)

2.129 — 2.132

(0.0838 — 0.0839)

1.614 — 1.622

(0.0635 — 0.0639)