Automobile Engineering in ME
The function of a second ring is that it is a

Back up oil control ring which will work in place of the bottom ring when it is broken
Back up compression ring which will work in place of the top ring when it is broken
Cushion ring which prevents piston slap and knock
Compression ring and aids the top ring in sealing and cooling

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Automobile Engineering in ME
An imbalance wheel during vehicle operation

Creates a standing wave
Makes large noise when its heavy point hits the road surface
Bounces vertically or deflects from side to side (as seen from front or rear)
Deflects in the vehicle's longitudinal direction

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