CHAPTER 11 Main and Rod Bearings u Page 271 Classroom Manual u Page 273 Lab Manual

BEARINGS u Check bearing clearance with Plastigauge. u Cut Plastigauge full width of journal, 1/4 off center. u Green Plastigauge range is.001” to.003” u Red Plastigauge range is.003” to.006”

MEASURING CLEARANCE u Doubling oil clearance will through five times as much oil onto the cylinder wall. u This increases oil consumption. u Excessive oil clearance will cause low oil pressure at idle.

BEARING PROPERTIES u Bearing surface has four properties. u Surface Action u Embedability u Conformability u Fatigue Resistance Page 272

BEARING INSERTS u Bearing shells are a steel back. u Bearings have babbit, copper-lead, or aluminum alloy. u Some bearing have multilayered lining material. Page 272

BEARING SPREAD, CRUSH u Bearings have a property known as spread. u Bearings have a property known as crush. Page 272

LOCATING LUG, OIL GROOVE u Bearings are positioned in the bore by a tang (most), or a dowel (some). u Main bearings with a hole are upper bearings. u Some upper bearings are also grooved. Page 272

BEARING UNDERSIZES u Are marked on the back of the bearing. u For some engines a.001” is available u.010” u.020” u.030” Page 275

BEARING INSPECTION u Keep bearings in order during disassembly. u Main cause of short bearing life is DIRT. u Check for metallic particles on bearing surface.

EXCESSIVE LOADS ON BEARINGS u Pressure from the flame front against the piston. u Centrifugal force from rotating weight of the rod. u Inertia from the up-and-down motion of the piston & rod. u These loads increase with RPM.

EXCESSIVE LOADS ON BEARINGS u Upper rod bearings have the most load. u Lower main bearings have the most load. u Using high viscosity oil can fatigue bearings. u Dry starts. u Excessive drive belt tension.

THRUST BEARING WEAR u Improper clutch adjustment, no free play. u Riding the clutch, improper driving habits. u Damaged pilot hole in crankshaft.