Subaru 2002 Impreza Service Manual page 154

PISTON
Mechanical
IO. Piston
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The pistons are of a slipper skirt design for reduced weight and friction. The oil control ring
groove utilizes a thermal design.
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The piston pin is offset either downward (Nos. 1 and 3 pistons) or upward (Nos. 2 and 4 pistons).
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The piston head has recesses to prevent interference with the intake and exhaust valves. It also
has engraved marks to identify the piston size and the direction of installation. All the pistons are
common in their design.
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Three piston rings are used for each piston
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two compression rings and one oil control ring.
The top piston ring has inner bevels and the second piston ring has an interrupt (cut) on the bottom
outside to reduce oil consumption.
(1) Location mark (Engine front side)
(2) Identification mark (Piston size)
(3) Engine capacity (2500 cc)
A
A: Top ring
B: Second ring
C: Oil ring
NF0449
(a) Inner-bevel
(b) Interrupt (cut)
(c) Upper rail
(d) Spacer
(e) Lower rail
ME-12