Page 67 - The Tribology Handbook

AI 1 Crankshaft bearings

SELECTION OF PLAIN OR ROLLING BEARINGS

Charactnistic Rolling Plain
Relative cost High Low
Weight Heavier Lighter
Space requirements :
Length Smaller Larger
Diameter Larger Smaller

Shaft hardness Unimportant Important with harder bearings
Housing requirements Usually not critical Rigidity and clamping most important
Radial clearance Smaller Larger
~ ~~~ ~
Toleration of shaft deflections Poor Moderate
Toleration of dirt particles Poor with hard particles Moderate, depending on bearing hard-
ness
Noise in operation Tend to be noisy Generally quiet

Running friction :
Low speeds Very low Generally higher
High speeds May be high Moderate at usual crank speeds
Lubrication requirements Easy to arrange. Flow small except at Critically important pressure feed and
high speeds large flow
~ ~~ ~~~~~~~ ~
Assembly on crankshaft Virtually impossible except with very Bearings usually split, and assembly no
short or built-up crankshafts problem
At the present time the choice is almost invariably in favour of plain bearings, except in special cases such as very high-
speed small engines, and particularly petroil two-strokes.

SELECTION OF TYPE OF PLAIN BEARING
Journal bearings
Direct lined Insert liners

Accuracy depends on facilities and skill Precision components
available
~ ~~~~~~ ~ ~~
Consistency of quality doubtful Consistent quality
First cost may be lower First cost may be higher

Repair difficult and costly Repair by replacement easy
~ ~ ~~ ~
Liable to be weak in fatigue Will generally sustain higher peak loads
Material generally limited to white metal Range of available materials extensive

Thrust bearings
Flanged journal bearings Separate thrust washer
Costly to manufacture Much lower first cost
Replacement involves whole journal/thrust Easily replaced without moving journal bearing
component

Material of thrust face limited in larger sizes Range of materials extensive
Aids assembly on a production line Aligns itself with the housing
AI 1.1