Chapter 5. Piston And Rings, Connecting Rods And Crankshafts; Section 1. Piston And Rings - Tecumseh HH100 Handbook

CHAPTER 5. PISTON AND RINGS, CONNECTING RODS
PISTON AND RING DISASSEMBLY. Always remove
ridge and carbon buildup before attempting to remove
the piston and ring assembly from the cylinder.
Always deglaze the cylinder when replacing the piston
and rings. This must be done to allow the rings to
seat.
Make sure surfaces are clean, then place new head
gasket on cylinder and position head.
Always use a new head gasket if the cylinder head
has been removed.
POSSIBLE RIDGE
BUILD UP AREA
RING AND WRIST PIN ASSEMBLY. Stagger the piston
ring gaps 90° apart when installing piston and ring
assembly in cylinder.
The wrist pin retainers must be seated in the groove.
Move the wrist pin if necessary. Failure to correctly
seat the retainers may result in costly repairs.
The wrist pin is a palm press fit (pressed in by hand
with some resistance). If loose, check connecting
rod for seizing. Replace piston and wrist pin if loose.
RING GAPS
EXPANDER
AND CRANKSHAFTS

SECTION 1. PISTON AND RINGS

WRIST PIN AND RETAINER
RING GROOVE CHECK. Check the side clearance
of the ring in the groove using a feeler gauge. If
excessive, replace the piston. See Specifications.
TOP PISTON LAND CLEARANCE
PISTON
CYLINDER
WALL
2nd
COMPRESSION RING
PISTON DIAMETER MEASUREMENT. Check piston
diameter on the bottom of the skirt. Check at 90° to
center line of wrist pin hole. This is a cam ground
piston and the diameter will not be the same when
checked at another point.
Pistons and rings may be available in either .010''
(.254 mm), .020'' (.508 mm), .030'' (.762 mm) and
.040'' (1.016 mm) oversize.
RING END GAP MEASUREMENT. Before installing
the rings, insert each ring into the cylinder bore to
check the end gap. This gap check should be made
in a worn cylinder, a reconditioned cylinder and a
new cylinder.
An inverted piston should be used to push the ring
into the cylinder to a point that would be the center
of ring travel. The ring travel area will be the most
worn area in a used cylinder. Insert the piston ring
into the cylinder and place the top side of the piston
on the ring to position the ring squarely in the bore;
remove piston. Measure the end gap by inserting a
feeler gauge between the ring ends. Check each
ring using the same procedure.
The end gap dimensions are shown in the specification
division of this manual. If end gap is greater than
the maximum specification, then the cylinder must
be measured and perhaps bored oversize. If the
end gap is too small, carefully remeasure the bore
for undersize dimension and enlarge if necessary.
1st
COMPRESSION RING
SIDE
CLEARANCE
3rd
OIL CONTROL RING
CHECK PISTON DIAMETER
AT THIS POINT
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