[hurryinhoosier62]

Originally Posted by Schurkey

Leakdown testing with oil? I'd expect the air pressure to blow the oil past the rings in short order, leaving no difference with or without oil added to the cylinders.

You use the oil to seal the rings AFTER you have established a base line reading. IF the pressure goes UP, the rings aren't sealing correctly. If it stays the same or DECREASES, start looking for leaking valves(especially exhaust valves). We've been doing this for DECADES on recip aircraft engines. I know many here will not agree, but cylinder glazing is the prime reason why I DO NOT use engine oil on the pistons and rings when assembling an engine.

[Schurkey]

Originally Posted by rtanner

its the way its done,

Originally Posted by hurryinhoosier62

You use the oil to seal the rings AFTER you have established a base line reading. IF the pressure goes UP, the rings aren't sealing correctly. If it stays the same or DECREASES, start looking for leaking valves(especially exhaust valves). We've been doing this for DECADES on recip aircraft engines.

1. How can adding oil decrease the pressure? What in a combustion chamber leaks MORE when oiled?

2. The FAA does not suggest a "wet" leakdown test where oil is added to the cylinder via the spark plug hole. They do accept an "oiled" re-test that involves running the engine in "CHAPTER 8. ENGINES, FUEL, EXHAUST, AND PROPELLERS; page 8".
http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/list/AC%2043.13-1B/$FILE/Chapter%2008.pdf

Originally Posted by FAA

recheck the readings after operating the engine for at least 3 minutes to allow for sealing of the rings with oil.

My concern still stands: Does added oil via the spark-plug hole just blow out the ring gaps or other ring leakage points when the cylinder is pressurized? The result would be no difference in "wet" versus "dry" cylinder leakdown testing once the oil has moved down the piston.

[rtanner]

Originally Posted by Schurkey

1. How can adding oil decrease the pressure? What in a combustion chamber leaks MORE when oiled?

2. The FAA does not suggest a "wet" leakdown test where oil is added to the cylinder via the spark plug hole. They do accept an "oiled" re-test that involves running the engine in "CHAPTER 8. ENGINES, FUEL, EXHAUST, AND PROPELLERS; page 8".
http://rgl.faa.gov/Regulatory_and_Gu...apter%2008.pdf


My concern still stands: Does added oil via the spark-plug hole just blow out the ring gaps or other ring leakage points when the cylinder is pressurized? The result would be no difference in "wet" versus "dry" cylinder leakdown testing once the oil has moved down the piston.

Do it however you want then! Thanks for the FAA info come in handy if I ever work on a airplane.

[madokie]

i agree with hurrinhooser62, i don't use engine oil when installing piston w rings in bore, oil is like water is wont compress, i have seen in car mags a pan full of oil and piston dunked in oil and then assembled in bore, not needed !!!!, a light spray lube in bore and on piston is all you need for assembly.