Quote:
Originally Posted by s20525xxx
Sorry, if i didnt describe it clearly. Is the second ring on piston designed to scrap off oil from bore prevent oil burnt in combustion chamber while piston travel downwards? If gap increases, more oil will get consumed?
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The Scraper ring is the piston ring with a tapered face located in the ring groove between the compression ring and the oil ring. The scraper ring is used to further seal the combustion chamber and to wipe the cylinder wall clean of excess oil. Combustion gases that sneak past the compression ring are stopped by the scraper ring - if it's doing it's job.
If the second ring is knackered you usually have a lot of blowby at all engine loads.
Ring 'gap' is the clearance between the ends of a ring when compressed against the cylinder wall - this gap changes very, very little over a motors lifetime.
Rings are held under tension against the bores by nature of their shape & are designed to use combustion pressure (behind the ring) to increase the seal with load.
Ring to piston clearance can & does if the piston material is operating to hot or the material is too soft to begin with - ala 2.5L chocolate pistons.
No one has mentioned bore glazing which is a possibility too.