Quote:
Originally Posted by Jolly Green Monster
My understanding is that the vaccum on overrun pulls the rings out against the bore wall, therefore by law of opposites I would expect boost to push them in.
Simon
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Really.......If that was the case then when you have boost you would have no compression..which equates to no power..I dont think so
Put it this way if you crank an engine over with say a 10:1cr (keeps it simple) at bdc the engine has drawn in air at atmospheric pressure (14.7psi) then go to tdc and the airs been compressed by 10:1 which equates to 147psi. If the rings did not expand to seal the gap then a compression test would reveal zilch or less puff than a sparrows fart. So rings expand under boost Simon. They have to and they dont need running in, any miniscule high spots off the bores would be gone in a few minutes. If your running at 3000rpm at say for 300 miles that took 3 hrs to do that means the engine has made about 544,000 revolutions: 180 minutes x 3000 revs. More than enough.
Top Ring
- The top ring, or compression ring, helps make piston rings work because during the combustion process, it doesn't allow it to lose any pressure. The compression ring maintains any pressure build-up as the piston in the engine makes its way to the top of the stroke. A mixture is ignited when the piston arrives at the top, and the pressure builds-up to bring the piston back down. The piston rings are able to control this pressure because the top ring acts as a barrier, and transfers any of the heat through the cylinder wall.
The Second Ring
- The second ring, or secondary compression ring, is designed similarly to the top ring. The second ring allows hot gases to penetrate into the crank case oil through the cylinder wall. When this happens it is called blow-by, and it helps mix the oil with carbon particles. This increases the acid level and makes the oil hotter and the oxidation process faster. This causes a slowdown of the oil from lubricating, and prevents the carbon particles from wearing out the parts of the engine. The second ring is also known as the oil scraper ring, which effectively minimizes any oil from gathering between the compression ring and oil ring.
The Oil Rings
- The oil rings works with the piston in the engine to lubricate the cylinder walls, pistons, rings and wrist pins without it getting into the combustion process. The oil rings help the thermal control because it cools the piston by directing oil straight into it.