Honda Motorcycle Service Manual page 158

CYLINDERIPISTON
The oil ring is needed to remove oil from the cylinder wall and
return the residue from the hole of the oil ring groove. If the oil
ring fails, oil flows into the combustion chamber and burns,
causing smoke. The oil ring is either of a split type arranged
with two side rails and a slotted expander, or an integral type
with a slotted square edge.
2-STROKE
As the 2-strol :e engine has a differer ibrication sy: item, it is
arranged with only the top and second rings and without an oil
ring. As the 2-stroke engine has a cylinder wall with a port, a
piston ring dowel is added to the ring groove of the piston, to
prevent the rings from moving and hooking an edge in a port,
causing breakage. The piston rings of the 2-stroke engine
must therefore be assembled by aligning the end gaps to the
dowels.
The design and shape of piston rings for 2-stroke engines are
different than that of Cstroke engines. A taper is provided
over the entire cross section in 2-stroke ring design.
This is because with the 2-stroke engine burning engine oil.
carbon tends to adhere to the ring groove. If not remedied, the
ring sticks t o the groove, causing it to lose tension and re-
sulting in decreased compression. The ring and the ring groove
therefore have a taDered form to remove the carbon in the rino
"
groove when the ring is compressed during engine movement.
The rings of this type are called keystone rings.
Some 2-stroke piston rings are provided with an expansion
ring inserted between the inside of the second ring and the
piston. The tension of the expansion ring absorbs the impact
generated when the piston contacts the cylinder wail, with a
resultant decrease in engine noise.
*
OIL RlNG
Steel Rail with
Slotted Expander
Slotted Expander
COMPRESSION
RING.GROOVES
/RECESS
PISTON PIN
HOLE
SNAP RING
GROOVE
V
PISTON PIN BOSS
-
PISTON RlNG DOWELS
A piston ring dowel is press fitted to
each ring groove to prevent the ring from
rotating in the groove. After fitting the
ring in the ring groove, check that the
dowel engages the ring end gap properly.
1
TOP RlNG PlSTON
Date of Issue: Nov., 1 9 8 9
0
HONDA MOTOR CO.. LTD.