Machine Design
In replacing the V-belts, a complete set of new belts is used instead of replacing a single damaged belt because

Only one belt cannot be fitted with other used belts
The new belt will carry more than its share and result in short life
New and old belts will cause vibrations
Belts are available in sets

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Machine Design
In oilness bearings

Grease required to be applied after some intervals
Do not require external supply of lubricant
The oil film pressure is generated only by the rotation of the journal
The oil film is maintained by supplying oil under pressure

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Machine Design
The cracks in helical springs used in railway carriages usually start on the inner side of the coil because of the fact that

It is more stretched than the outer side during the manufacturing process
It is subjected to a higher stress than the outer side
It is subjected to a higher cyclic loading than the outer side
It has a lower curvature than the outer side

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