Saturday, 27 August 2016 @ 07:00 AM ICT
Contributed by: news
Piston rings never fully prevent combustion gases from escaping into the crankcase when an engine is running. Leakage happens even when the best cylinder finishing and highest quality piston rings are employed, inevitably getting worse over time, and the issue creates two distinct problems.
One, some amount of power is continually lost to this leakage. And two, the engine designer must find a way to minimize the buildup of blow-by in the crankcase, which creates both corrosive contamination of the oil supply as well as excess pressure that must not be allowed to blow out seals and gaskets.
There are two readily available methods to determine ring sealing: the simple ‘compression test’ and the more accurate ‘leak-down test.’ To perform a compression test, a pressure gauge is screwed into a spark plug hole, and while the throttle are held wide open so as not to restrict airflow, the engine is cranked over for several seconds until the gauge stops rising. Each cylinder is tested in turn and the pressures are compared to one another. We’d like to find them all within 10 percent of one another and close to the maximum pressure specified in the service manual.