3.35
ENGINE
3
9923412 - 2012 Sportsman 400/500 and EFI Tractor Service Manual
© Copyright 2011 Polaris Sales Inc.
4. Measure piston ring to groove clearance by placing
the ring in the ring land and measuring with a
thickness gauge. Replace piston and rings if ring-to-
groove clearance exceeds service limits.
Piston Identification
The piston may have an identification mark or the
piston
may not have an identification mark for piston
placement. If the piston has an identification mark, fol
-
low the directions for piston placement below. If the pis-
ton does not have an identification mark, the direction for
placement of the piston does not matter.
Note the directional and identification marks when viewing
the pistons from the top. The letter “F”, “
g”, “ 4” or “:” must
always be toward the flywheel side of the engine. The
other numbers are used for identification as to diameter,
length and design. Four stroke engine rings have a
rectangular profile. See text for oil control ring upper rail
installation. Use the information below to identify pistons
and rings.
*Pistons and rings marked 25 equal .25mm (.010”) over-
sized
*Pistons and rings marked 50 equal .50mm (.020”)
oversized
Piston Ring Installed Gap
1. Place each piston ring inside cylinder using piston to
push ring squarely into place as shown at right.
2. 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.
3. If the bottom installed gap measurement exceeds the
service limit, replace the rings. If ring gap is below
specified limit, file ring ends until gap is within
specified range.
NOTE: Always check piston ring installed gap after
re-boring a cylinder or when installing new rings. A
re-bored cylinder should always be scrubbed
thoroughly with hot soapy water, rinsed, and dried
completely. Wipe cylinder bore with an oiled rag
immediately to remove residue and prevent rust.
Piston Ring-to-Groove Clearance
Top Ring Std: .0016-.0031" (.040-.080 mm)
Limit: .0059" (15 mm)
Second Ring Std: .0012-.0028" (.030-.070 mm)
Limit: .0059" (15 mm)
Piston Ring Installed Gap
Top Ring
Std: .0079-.0138" (.20-.36 mm)
Limit: .039" (1.0 mm)
Second Ring
Std: .0079-.0138" (.20-.36 mm)
Limit: .039" (1.0 mm)
Oil Ring
Std: .0079-.0276" (.20-.70 mm)
Limit: .059" (1.5 mm)
Feeler Gauge
Piston ring
Cylinder
25-50 mm
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