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Old 10-25-2013, 11:23 PM
Skyskiguy Skyskiguy is offline
MC Fanatic
Join Date: May 2012
Boat: 2006 X30
Location: Utah
Posts: 781
Pretty sure I was TDC on each one. Performed the tests just as the dealer instructed. I found TDC by holding my thumb over the air hose threaded into the sparkplug hole and bumped the starter until I felt pressure. When I connected the gauge to apply air pressure from the compressor it was pretty obvious whether it was at the top of the stroke with valves closed. If it was short of TDC, the compressed air would actually push the piston back down. Or, if I was past TDC, the pressure would complete the stroke. If it was in any other position the compressed air would just flow right out either the intake or the exhaust. It usually took some fine tuning with several small bumps of the starter to get it just right.
When I say "low" range, I am assuming that because I could clearly hear air moving through the intake (cylinders 3 & 5) or exhaust (cylinders 4 & 6) that the leakage into the crankcase in those cylinders is probably similar to the good cylinders - which was 15-25%.
Also, with the good cylinders (1, 2, 7 & 8), if I plugged the PCV ports in the valve covers and had the dipstick in place then held my palm over the oil filler hole while pressurizing the cylinder, pressure would slowly build in the valve cover/crankcase, confirming the "low" (15-25%) ring leakage in those cylinders. With the other cylinders (3, 4, 5 & 6) the pressure that built in the crankcase, under the same conditions, seemed about the same - thus my assumption of ring leakage percentage being similar to the others. I don't know of a way to determine what percentage of the leakage is past the rings vs. thru the valve in a particular cylinder.
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