The piston ring is designed, to seal the gap, between the piston and the cylinder wall.
While doing this, they also remove heat, from the piston, transferring it to the cylinder wall.
Piston rings usually come in a set of three, but each ring has, a completely different job.
The piston ring, also come in all different sizes, to fit different size cylinder bores. When installed, each ring has to have, a gap of a specific size.
If this gap were too small, thermal expansion of the piston could make the piston seizes in the cylinder.
However, a large gap would cause, insufficient sealing, against the cylinder walls. Consequently, resulting in, excessive blow-by (combustion gases entering the crankcase) and less pressure in the cylinder, reducing engine power.
So, The main functions of a piston ring are:
- To seal the combustion chamber. So, that there is minimal loss of gases to the crankcase.
- Improve heat transfer, from the piston to the cylinder wall.
- Maintain the proper quantity of oil, between the piston and the cylinder wall
- Regulate engine oil consumption, by scraping the oil from the cylinder walls, back into the oil pan.
So, during the compression and power strokes, the compression rings; seal the combustion gases and prevents blow-by. As a result, blow-by stays at an acceptable limit.
Also, engine oil lubricates the cylinder walls. Consequently, the oil comes from throw off, from the connecting rod bearings. Finally, the rings wipe off any excess oil.
Consequently, leaving a fine layer of oil, on the cylinder wall, to provide lubrication for the following ring. But, as rings wear, the ability to perform these functions is decreased. Finally, resulting in, oil consumption and blow-by.
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