What are signs of blow-by in engine cylinder and how to fix it?

asked 10 Apr '17, 10:32

April 10, 2017, 10:32 a.m.
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edited 10 Apr '17, 10:33


Answer:

Blow-by is a failure of piston rings to retain expanding gases inside combustion chamber. Combustion gases flow into under piston space (crosshead engines) or crank case (trunk piston engines). This leads to several negative consequences: unit efficiency drops, liner lubrication film destroyed, increases possibility of under piston spaces fire, crank case pressure and oil mist concentration increases.
Piston rings may fail in two ways:

  • Neighbor rings's got their gaps vertically aligned and stuck in this position

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  • Ring broken

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Blow-by can be noticed by:

  • specific sound of passing gasses during combustion stroke

  • reduced cylinder cycle compression pressure Pc

  • excessive smoke/oil mist in the crank case

  • increased temperature of under piston space inspection cover

Most common root causes of blow-by are

  • over extension of overhaul period: accumulation of solid combustion products leads rings to stuck in the groove
  • high risk of rings breaking due to use of sub standard not original parts
  • insufficient cylinder liner lubrication leads to higher wear of rings and increasing possibility of their breaking

Sometimes on early stage of blow-by it may be eliminated by temporary increased cylinder lubrication which could make rings moving freely in groves. But blow-by itself is always a sign of overhaul required.
Overhaul periods should never be extended.

Liner surface of cylinder with blow-by:

alt text

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answered 10 Apr '17, 11:43

April 10, 2017, 11:43 a.m.
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edited 24 May '17, 03:31

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