CHAPTER 11

Crankshaft and Bearings Piston and Rods Page 276 Classroom Manual Page 276 Lab Manual

CHAPTER OBJECTIVES Analyze wear & damage to Crank &

Bearings. Analyze wear & damage to Piston and

Rods Select the most appropriate repairs to

perform. Explain theory of engine balancing. Describe related theory of Pistons, Rings,

Bearings

CHAPTER INTRODUCTION

This chapter deals with Crank, Pistons, and Rods.

These parts are called the lower end. This chapter will deal with

procedures for the lower end.

THE CRANKSHAFT Cast Iron Nodular Iron Forged Steel Do NOT store crankshafts laying down. Lube and place in plastic bag. Stood on end to prevent warping. Or hung to prevent warping.

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CRANKSHAFT DESIGN Crank converts reciprocating motion to

rotary motion. Polished bearing surfaces are called

Journals. Main and Rod Journals. Rod journals are also called crank pins. Crank has drilled passages from the

main to rod journals.

COUNTERWEIGHTS Opposite each rod journal is a

counterweight. In-line engines have a separate rod

journal for each rod. V-8 and some V-6’s have rod journals

for two rods. V-6’s with 90 degree have splayed rod

journals.Page 279

CRANK END THRUST

Crank is pushed forward by converter and clutch.

One main journal is ground on sides to provide bearing surface - Thrust.

Flanged bearing to control end play. Thrust inserts - half washers - some

imports.Page 279

CRANK CONSTRUCTION

Gray Cast Iron Nodular Iron Forged Medium-Carbon Steel Forged Chrome-Moly steel Some cranks are hardened.

Ion Nitriding

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CHECKING CRANK CONDITION

Keep bearings in order during disassembly.

Bent forged cranks can be straitened. Bent cast cranks should be replaced. To check for straightness use front

and rear bearings In block and a dial indicator

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CHECKING FOR CRACKS

More accurate to use wet magnaflux. Disadvantage only works on ferrous

metals.

CRANKSHAFT WEAR

Cranks wear because of abrasives in the oil.

Out-of-round maximum is .0005” Taper Clean and polish all cranks before

reuse.

REGRINDING CRANKS

Standard undersizes are .010”, .020”, .030”

Main and rod journals can be ground to different sizes.

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POLISHING THE CRANK

Polishing only removes approximately .0002”

Belt must travel across crank in direction of rotation.

Do NOT hand polish crankshaft.

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WELDING CRANKSHAFTS

Acceptable to buildup undersize. Not acceptable to repair a crack.

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