Bore Glazing
This is when the cross-hatch honing marks on the inner surface of the cylinder liner fill up with combustion residue during long periods of low-load running and turn into a shiny surface. The marks lose their function of holding the oil film; the rings can no longer seal and oil consumption rises. It arises from the same operating condition as wet stacking.
A new cylinder liner is not smooth; its surface has cross-hatch channels cut at a certain angle. These channels have two functions: to hold oil and to let the rings bed in. When the engine runs at sufficient load, cylinder pressure presses the ring against the wall, the ring cuts its own seat and the seal is established.
At low load, cylinder pressure cannot apply this pressing sufficiently. Because combustion is incomplete, carbon residue fills the channels and the surface becomes shiny. The consequences are cumulative:
- Increased oil consumption and blue exhaust smoke.
- Loss of compression, hard starting and drop in power.
- Rise in crankcase pressure.
At an advanced stage the only solution is re-honing the liner, which means opening the engine. Prevention is far cheaper: do not keep the engine idling for hours unnecessarily, run it regularly at sufficient load. The stored work speed and drop-to-idle-during-pauses functions indirectly reduce this risk by shortening total idling time.
Context in which this term is used: Electronic speed and throttle control on diesel engines