Piston Inspection/Measurement; Piston Ring Installed Gap - Polaris INDY TRAIL RMK Service Manual

Piston Inspection/Measurement

1. Check piston for scoring or cracks in piston crown or
pin area. Excessive carbon buildup below the ring
lands is an indication of piston, ring or cylinder wear.
2. Measure piston outside diameter at a point 10 mm
(3/8²) up from the bottom of the skirt at a 90° angle to
the direction of the piston pin (domestic engines). For
Fuji engines, measure 1/2² (12.7mm) up from the
bottom of the piston skirt. Record the measurement
for each piston.
NOTE:The piston must be measured at this point to pro-
vide accurate piston-to-cylinder clearance measurement.
3. Subtract this measurement from the minimum
cylinder measurement recorded previously.
clearance exceeds the service limit, the cylinder
should be re-bored and new pistons and rings
installed.

Piston Ring Installed Gap

1. Position ring 1/2I (1.3 cm) from the top of the cylinder
using the piston to push it squarely into place.
Measure installed gap with a feeler gauge at both the
top and bottom of the cylinder.
NOTE:A difference in end gap indicates cylinder taper.
The cylinder should be measured for excessive taper and
out of round. Replace rings if the installed end gap ex-
ceeds the service limit.
NOTE:Always check piston ring installed gap after re-bor-
ing a cylinder or when installing new rings.
NOTE:Piston rings are installed with marking or beveled
side up.
FUJI ENGINES - Measure 1/2²
(12.7mm) up from bottom of skirt
If
Cylinder
Piston Ring
Cylinder
Piston Ring
Straight Edge
Piston Ring Cutaway
Keystone Piston Ring
ENGINES
90° to pin
1/2² (1.3cm)
Feeler Gauge
1/2² (1.3cm)
Up
3.61