Subaru Impreza 3 / Impreza WRX / Impreza WRX STI. Service manual — part 60
ME(STI)-2
General Description
MECHANICAL
1. General Description
A: SPECIFICATION
Engine
Model
2.5 L
Cylinder arrangement
Horizontally opposed, liquid cooled, 4-cylinder,
4-stroke gasoline engine
Valve system mechanism
Belt driven, double overhead camshaft,
4-valve/cylinder
Bore × Stroke
mm (in)
99.5 × 79.0 (3.92 × 3.11)
Displacement
cm
3
(cu in)
2,457 (149.94)
Compression ratio
8.2
Compression pressure
(at 200 — 300 rpm)
kPa (kg/cm
2
, psi) Standard
981 — 1,177 (10 — 12, 142 — 171)
Number of piston rings
Pressure ring: 2, Oil ring: 1
Intake valve timing
Open
Max. retard
ATDC 5°
Min. advance
BTDC 25°
Close
Max. retard
ABDC 65°
Min. advance
ABDC 35°
Exhaust valve timing
Open
Max. retard
BBDC 32°
Min. advance
BBDC 72°
Close
Max. retard
ATDC 28°
Min. advance
BTDC 12°
Valve clearance
mm (in)
Inspection
value
Intake
0.20
+0.04
–0.06
(0.0079
+0.0016
–0.0024
)
Exhaust
0.35±0.05 (0.0138±0.0020)
Adjustment
value
Intake
0.20
+0.01
–0.03
(0.0079
+0.0004
–0.0012
)
Exhaust
0.35±0.02 (0.0138±0.0008)
Idle speed (Gear shift lever is
in neutral)
rpm
No
load
Standard
700±100
A/C
ON
Standard
750±100
Ignition order
1 → 3 → 2 → 4
Ignition timing
BTDC/rpm Standard
15°±10°/700
ME(STI)-3
General Description
MECHANICAL
NOTE:
OS: Oversize US: Undersize
Belt ten-
sion
adjuster
Adjuster rod protrusion amount
mm (in)
5.2 — 6.2 (0.205 — 0.244)
Camshaft
Bending limit
mm (in)
0.020 (0.00079)
Cam lobe height
mm (in)
Intake
Standard
46.55 — 46.65 (1.833 — 1.837)
Exhaust
Standard
46.75 — 46.85 (1.841 — 1.844)
Cam base circle diameter
mm (in) Standard
37.0 (1.457)
Journal O.D.
mm (in)
Front
Standard
37.946 — 37.963 (1.4939 — 1.4946)
Center, rear
Standard
29.946 — 29.963 (1.1790 — 1.1796)
Oil clearance
mm (in) Standard
0.037 — 0.072 (0.0015 — 0.0028)
Thrust clearance
mm (in) Standard
0.068 — 0.116 (0.0027 — 0.0047)
Cylinder
head
Warping limit
(Mating surface with cylinder block)
mm (in)
0.035 (0.0014)
Grinding limit
mm (in)
0.3 (0.012)
Standard height
mm (in)
127.5 (5.02)
Valve seat
Seating angle between valve and valve seat
90°
Contacting width
between valve and
valve seat
mm (in)
Intake
Standard
0.6 — 1.4 (0.024 — 0.055)
Exhaust
Standard
1.2 — 1.8 (0.047 — 0.071)
Valve guide
Clearance between the
valve guide and valve
stem
mm (in)
Intake
Standard
0.030 — 0.057 (0.0012 — 0.0022)
Exhaust
Standard
0.040 — 0.067 (0.0016 — 0.0026)
Inside diameter
mm (in)
6.000 — 6.012 (0.2362 — 0.2367)
Valve stem outer diameters
mm (in)
Intake
5.955 — 5.970 (0.2344 — 0.2350)
Exhaust
5.945 — 5.960 (0.2341 — 0.2346)
Valve guide protrusion amount
mm (in)
15.8 — 16.2 (0.622 — 0.638)
Valve
Head edge thickness
mm (in)
Intake
Standard
1.0 — 1.4 (0.039 — 0.055)
Exhaust
Standard
1.3 — 1.7 (0.051 — 0.067)
Overall length
mm (in)
Intake
104.4 (4.110)
Exhaust
104.65 (4.1201)
Valve spring
Free length
mm (in)
53.48 (2.106)
Tension/spring height
N (kgf, lb)/mm (in)
Set
204.6 — 235.4
(20.86 — 24.00, 46.00 — 52.93)/36.0 (1.417)
Lift
363.5 — 401.7
(37.07 — 40.96, 81.73 — 90.32)/26.7 (1.051)
Squareness
2.5°, 2.3 mm (0.091 in) or less
Valve lifter
Outer diameter
mm (in) Standard
34.959 — 34.975 (1.3763 — 1.3770)
Valve lifter mating surface inner diameter
mm (in) Standard
34.994 — 35.016 (1.3777 — 1.3786)
Valve lifter and valve lifter mating surface
clearance
mm (in) Standard
0.019 — 0.057 (0.0007 — 0.0022)
Cylinder
block
Warping limit
(Mating surface with cylinder head)
mm (in)
0.025 (0.0098)
Grinding limit
mm (in)
0.1 (0.004)
Standard height
mm (in)
201.0 (7.91)
Cylindricality
mm (in) Limit
0.015 (0.0006)
Out-of-roundness
mm (in) Limit
0.010 (0.0004)
Clearance between cylinder and piston at
20°C (68°F)
mm (in) Standard
–0.010 — 0.010 (–0.00039 — 0.00039)
Cylinder inner diameter boring limit (diameter)
mm (in)
To 100.005 (3.9372)
ME(STI)-4
General Description
MECHANICAL
Piston
Piston grade point
mm (in)
38.2 (1.50)
Outer diameter
mm (in)
Standard
A
99.505 — 99.515 (3.9175 — 3.9179)
B
99.495 — 99.505 (3.9171 — 3.9175)
0.25 (0.0098) OS
99.745 — 99.765 (3.9270 — 3.9278)
0.50 (0.0197) OS
99.995 — 100.015 (3.9368 — 3.9376)
Piston pin
Degree of fit
Piston pin must be fitted into position with
thumb at 20°C (68°F).
Clearance between piston pin hole and pis-
ton pin
mm (in) Standard
0.004 — 0.008 (0.0002 — 0.0003)
Piston ring
Piston ring gap
mm (in)
Top ring
Standard
0.23 — 0.28 (0.0091 — 0.0110)
Second ring
Standard
0.37 — 0.52 (0.015 — 0.0203)
Oil ring
Standard
0.20 — 0.50 (0.0079 — 0.0197)
Clearance between
piston ring and piston
ring groove
mm (in)
Top ring
Standard
0.040 — 0.080 (0.0016 — 0.0031)
Second ring
Standard
0.030 — 0.070 (0.0012 — 0.0028)
Connecting
rod and
connecting
rod bearing
Bend or twist per 100 mm (3.94 in) in
length
mm (in) Limit
0.1 (0.0039)
Thrust clearance
mm (in) Standard
0.070 — 0.330 (0.0028 — 0.0130)
Oil clearance
mm (in) Standard
0.017 — 0.045 (0.0007 — 0.0018)
Bearing size
(Thickness at center)
mm (in)
Standard
1.490 — 1.506 (0.0587 — 0.0593)
0.03 (0.0012) US
1.504 — 1.512 (0.0592 — 0.0595)
0.05 (0.0020) US
1.514 — 1.522 (0.0596 — 0.0599)
0.25 (0.0098) US
1.614 — 1.622 (0.0635 — 0.0639)
Bushing of
small end
Clearance between piston pin and bushing
mm (in) Standard
0 — 0.022 (0 — 0.0009)
Crankshaft
and crank-
shaft bear-
ing
Bending limit
mm (in)
0.035 (0.0014)
Crank pin
Cylindricality
mm (in) Limit
0.006 (0.0002)
Out-of-roundness
mm (in) Limit
0.005 (0.0002)
Grinding limit (dia.)
mm (in)
To 51.750 (2.0374)
Crank journal
Cylindricality
mm (in) Limit
0.006 (0.0002)
Out-of-roundness
mm (in) Limit
0.005 (0.0002)
Grinding limit (dia.)
mm (in)
To 59.758 (2.3527)
Crank pin outer diameter
mm (in)
Standard
51.976 — 52.000 (2.0463 — 2.0472)
0.03 (0.0012) US
51.954 — 51.970 (2.0454 — 2.0461)
0.05 (0.0020) US
51.934 — 51.950 (2.0447 — 2.0453)
0.25 (0.0098) US
51.734 — 51.750 (2.0368 — 2.0374)
Crank journal outer diameter
mm (in)
Standard
59.984 — 60.008 (2.3616 — 2.3625)
0.03 (0.0012) US
59.962 — 59.978 (2.3607 — 2.3613)
0.05 (0.0020) US
59.942 — 59.958 (2.3599 — 2.3605)
0.25 (0.0098) US
59.742 — 59.758 (2.3520 — 2.3527)
Bearing size
(Thickness at center)
mm (in)
#1, #3
Standard
1.998 — 2.015 (0.0787 — 0.0793)
0.03 (0.0012) US
2.017 — 2.020 (0.0794 — 0.0795)
0.05 (0.0020) US
2.027 — 2.030 (0.0798 — 0.0799)
0.25 (0.0098) US
2.127 — 2.130 (0.0837 — 0.0839)
#2, #4,
#5
Standard
2.000 — 2.017 (0.0787 — 0.0794)
0.03 (0.0012) US
2.019 — 2.022 (0.0795 — 0.0796)
0.05 (0.0020) US
2.029 — 2.032 (0.0799 — 0.0800)
0.25 (0.0098) US
2.129 — 2.132 (0.0838 — 0.0839)
Thrust clearance
mm (in) Standard
0.030 — 0.115 (0.0012 — 0.0045)
Oil clearance
mm (in) Standard
0.010 — 0.030 (0.00039 — 0.0012)
ME(STI)-5
General Description
MECHANICAL
B: COMPONENT
1. TIMING BELT
ME-04961
(7)
(6)
(10)
(5)
(23)
(11)
(15)
(17)
(9)
(13)
(14)
(12)
(16)
(8)
(19)
(19)
(19)
(19)
(21)
(22)
(22)
(21)
(2)
(3)
(4)
(1)
(20)
(20)
(20)
T3
T4
T2
T2
T2
T2
T2
T1
T7
T1
T7
T7
T8
T1
T3
T8
T3
T2
T2
T6
T2
T5
T2
(18)
T9
(24)
T2
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