Mitsubishi Evolution X. Manual - part 52

BASE ENGINE

TSB Revision

ENGINE

11-6

PISTONS

The pistons are made of a special aluminum alloy.
Their weight has been reduced by lowering their
overall height and increasing the depression at each
end of the piston pin.
The piston pin hole center is offset 0.5 mm (0.020 in)
towards the thrust side of the piston center.
The skirt portion along the perimeter of the piston is
finished with streaks that excel in oil retention and
seizure resistance.

PISTON PINS

The full floating type of piston is used to improve the
reliability by reducing the friction.

AK703206AC

Front mark

Piston offset

ITEM

SPECIFICATIONS

Basic diameter mm (in)

86 (3.4)

Pin hole diameter mm (in) 23 (0.9)
Overall height mm (in)

54.87 (2.160)

AK703727

ITEM

SPECIFICATIONS

Outer diameter (D) mm
(in)

23 (0.9)

Inner diameter (d1) mm
(in)

11.5 (0.45)

Inner diameter (d2) mm
(in)

10.5 (0.41)

Overall length (h) mm (in) 60 (2.4)

BASE ENGINE

TSB Revision

ENGINE

11-7

PISTON RINGS

The piston rings consist of No. 1 and No. 2 rings and
an oil ring.

AK703207AC

Oil ring

Spacer

Rail

Maker mark

Piston ring No. 1

Piston ring No. 2

Oil ring

Item

Piston ring No. 1

Piston ring No. 2

Oil ring

Shape

Inside bevel

Taper undercut

3-piece

Surface treatment (cylinder
contact surface)

Ion plating

Parkerizing

Ion plating

Supplier mark

None

BASE ENGINE

TSB Revision

ENGINE

11-8

CONNECTING RODS

The connecting rods are made of highly rigid, forged
carbon steel. The cross section of the rod portion is
shaped like the letter H.
A fracture-split process has been adopted for split-
ting the big end of the connecting rod.
The fracture split connecting rod has the high inser-
tion force between the rod and the cap as well as the
high installation location accuracy.
The oil holes that feed oil from the main journals of
the crankshaft to the crankshaft pins lubricate the
bearings at the big ends of the connecting rods.

CONNECTING ROD BEARINGS

The upper and lower connecting rod bearings are the
same. Each connecting rod bearing is provided with
a backing plate. Its bearing portion is made of an
kelmet alloy and its backing plate is made of ordinary
sheet steel.
The width of the connecting rod bearing has been
made as narrow as possible in proportion to the
bearing cap in order to reduce friction loss.

AK703208AC

Item

Specifications

Small end hole diameter
(d) mm (in)

23 (0.9)

Big end hole diameter (D)
mm (in)

55 (2.2)

Center-to-center distance
(L) mm (in)

143.75 (5.659)

AK502492AH

Item

Specifications

Width (H) mm (in)

17 (0.7)

Thickness (A) mm (in)

1.5 (0.06)

BASE ENGINE

TSB Revision

ENGINE

11-9

CRANKSHAFT

A forged crankshaft has been adopted.
It has 5 main bearings and 8 balance weights.
The crankshaft pins are located at equal 180

° inter-

vals.
The oil holes feed engine oil from the journals to the
pins.
A crankshaft sprocket and an oil pump drive shaft are
press-fit to the front of the crankshaft.

CRANKSHAFT BEARINGS, THRUST BEARINGS

The upper crankshaft bearings have oil grooves and
the lower crankshaft bearings do not.

Each crankshaft bearing is provided with a backing
plate. Its bearing portion is made of an kelmet alloy
and its backing plate is made of ordinary sheet steel.
A thrust bearing, which sustains the load in the thrust
direction, is provided at each end of the No. 3 bear-
ing.

AK502493AD

Balance weight

Oil hole

Item

Specifications

Pin outer diameter mm
(in)

48 (1.9)

Journal outer diameter
mm (in)

52 (2.0)

AK703628AC

Oil hole

Oil groove

Upper bearing

Lower bearing

Engine front

Thrust bearing

Groove

Content .. 50 51 52 53 ..