Polaris 1999 Sportsman 400 Service Manual page 132

126
Do not attempt to remove carbonfrom
the sides of the piston above the lop
ring or from the cy linder bore near
the top. Removal ofcarbonfro m these
two areas may C(II/se increased oil
consumption.
3. Aft er cleaning the piston , ex amine the crown
(Figure 127). Th e crown sho uld show no signs of
wear or dama ge . If the crow n appears pecked or
spongy- loo king, also check the spark plug, valves
and combustion cha mbe r fo r a luminum deposits. If
these dep osits are found, the engine is ove rheating.
4 . Examine ea ch ring groove (A, Fi gure 128) for
burrs, dented edge s or other dam age. Pay particu lar
attention to the top compression ring groove as it
usually wears more than the others. Because the oil
rings are con stan tly bath ed in oiled, these rings and
grooves wear little compared to compression rings
and the ir grooves. If there is evidence of oil ring
groove wear or if the oi l rin g asse mbly is tigh t and
difficult to remo ve, the piston skirt may have col-
lapsed du e to excessive heat and is perm anent ly de-
formed. Repla ce the piston.
5. Ch eck the oil co ntro l ho les in the piston (Fi gu re
129) for carbon or oil sludg e buildup. C lean the
ho les w ith wi re and blow out w ith compresse d air.
6. Check the piston skirt (B, Figure 128) for cra cks
or oth er damage. I
f a
piston shows signs of partial
se izure (b its of a luminum bui ld-up on the piston
skirt), rep lace the piston and bo re the cylinder over-
size if necessary to red uce the possib ility of eng ine
noi se and further piston seizu re.
NOTE
If the piston skirt is worn or scuffed
unevenlyfrom side
10
side, the con-
necting rod may he bent or twisted.
7. Check the retaining clip groov e (Figure (30 ) on
each side for wea r, cracks or oth er damage. If the
groove s are qu estio nab le, check the retai ning clip
fit
by insta lling a new retaini ng clip into each
groove and then attempt to mo ve the retaini ng clip
from side- to-side. If the retai ning clip has any side
play, the groove is wo rn. Replace the piston .
8. To chec k the pisto n pin-to-piston clearance , per-
form the fo llow ing:
a. Measure the a liter diamete r of the piston pin
wit h a microm eter (Figu re 131 ).
b. Measure the piston pin bore inner diam eter in
the piston w ith a snap ga uge ( Fig ur e 132).
CHA PTE R FO UR