CHAPTER 11 u PISTON RINGS u Page 295 Class u Page 306 Lab

PISTON RINGS u Piston rings seal combustion pressures. u Piston rings control oil consumption. u Piston rings help cool the piston. u Most modern engines use 2 compression & 1 oil rings.

RING OVERSIZES u Rings sizes are standard,.030”,.040”,.060”. u Metric sizes are standard, 0.50 mm, 0.75 mm, 1.0 mm,

COMPRESSION RINGS u Compression rings are forced against the cylinder wall by combustion pressure at the top and back of the ring. u A square ring groove is a must. u Heavy rings tend to flutter.

COMPRESSION RING DESIGN u There are many ring designs. See figure 10.32a. u The purpose of all designs is to cause the ring to contact the cylinder wall with a narrow part of the face. u This helps to cause quicker seating.

TORSIONAL TWIST RINGS u A torsional twist ring is chamfered on its top inside edge. u A reverse twist ring is chamfered on its bottom inside edge. u A barrel faced ring has less than.001” curve to its face. u Low-tension rings - Have less depth than standard rings. u Deck plates are advised when honing thinwall blocks.

RING COATINGS u Cast Iron is the common ring material. u Moly Rings - Have molten molybdenum sprayed on surface. u Chrome Rings - Have a chrome plated outer surface. u Moly barrel shaped top, reverse torsion second, 3 piece oil.

PLASMA CERAMIC

OIL CONTROL RINGS u 1 drop each power stroke = 1 quart every 2 miles. u Oil rings fail if they become plugged. u Reasons for failure improper maintenance, temp, lead. u Stainless steel expander with 2 chrome rails - common.

RING WEAR u Major cause of ring wear is abrasion. u Causes of wear Honing grit, poor air filter, dirty oil. u Signs of abrasive wear are vertical scratches on rings.

RING GAP CLEARANCE u Before installing rings check end gap. u Gap specs are in repair manual. u Gap will be.030” to much for each.010” error in size. u Too small a end gap can cause rings to seize in bore. Page 312 Fig

INSTALLING RINGS ON PISTONS u Rings may be installed by hand. u Rings may be installed with a ring expander. u Do NOT spiral rings onto pistons. u Do NOT overexpand rings during installation. u Install rings with I D marks up. Page 312 Fig

RING GAP POSITIONS u Place gaps at opposite sides of piston. u Dana says the reason for staggering gaps is to prevent scuffing. u Many opinions on gap placement. Page 315 Fig

OIL RING GAPS u Do NOT overlap ends of the expander. u Expander end gap over pin. u Rail end gaps 180 degrees apart.

WRIST PINS u Pistons attach to rods with pins. u Oversize pins are not common today. Page 311 Fig

PIN RETAINING METHODS u Press fit is the most common. u dismount with a press and proper adapters. u Install with rod furnace.

PIN RETAINING METHODS u Full floating pins - high performance. u Uses retaining rings to hold pin in place. u Opening in lock ring should face bottom of piston. u Be sure install piston on rod correctly.

CONNECTING RODS u Made from forged or cast steel.