Well, this is my understanding of how piston rings work, but I am not specifically a trained mechanic.Originally Posted by VX KAT
The top ring is solid in cross section, and slides hard against the cylinder wall. It has the primary function of keeping the combustion gasses and compression, in the combustion chamber. Excessive blowby occurs if this ring, or the cylinder walls, are worn or scratched. Also, if the ring groove in the piston is worn, the ring can stick so that it is not hard against the cylinder wall.
The bottom ring has special contours in cross section. Its prime function is to take most of the oil (not all) off of the cylinder walls. This oil is thrown up by splashing of the crankshaft etc as it rotates, and also from the oily mist that is always in the sump when an engine is operating. This ring actually guides some of the oil back into the ring groove and back to sump through drain holes in the piston skirt. That is why there has been some talk about the piston drain holes being responsible for the VX burning oil. If the drain holes clog up, or the ring wears or sticks, you have an oil burner.
The middle ring helps restrict any blowby that gets past the top ring, and any oil that gets past the bottom ring. It also covers the "gap" area in the top and bottom rings. But it is not 100% efficient in either role, so if the other rings are worn, some of the excess still gets past.
Depending on what is worn and how much, you can have an oil burner that still has good compression and no blowby. You can also have excessive blowby and not be a large consumer of oil.
However, the normal would be for relatively even wear, and you have both blowby and oil burning.
Note that the rings are never 100% efficient.
If the oil rings took every little bit of oil off the cylinder walls, the top ring would wear very quickly, so a small film of oil is always there to lubricate the top ring.
This is what is considered "normal" oil consumption, and different manufacturers will rate their engines differently.
Now, you guys have to decide if I have blinded you with science, or baffled you with bull scat??
PK
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