Thread: oil burner-did leak down test

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hey everyone: the motor fails the leak down test. You can literatly feel the air come out the oil fill tube, (all 8 the same). Question for ya all: although the leak down test points to the rings, I feel our pistons don't have adequate drain back holes behind the oil ring. I've looked at over 17 sets of pistons, and despite they be stock or racing, chevy or other, there are twice as many holes, and the holes are a bit larger in diameter as well. Could excessive oil on the cylinder walls prevent the rings to seal, or explain the oil burning problem in any way? I was thinking maybe excessive oil would kinda act like a "hydrolic seal" and prevent cylinder pressure from getting behind the rings to seal them. Total Seal rings said that about the grease doing this, and wondered if excessive oil could do the same? Any idea's on that one? My boss just handed me a 1957 wheat penny. Is that good or bad? Maybe a bit of luck, for it looks like I'm going to have to tear her apart again. Hopefully 3rd time is the charm. (or he's putting his one cent's worth in). Later all

After two rebuilds with the same problem, I'd get new pistons. I've seen and used pistons with few small holes successfully, but in your case there's nothing else to do.

the bottom oil ring shouldnt have anything to do with a leak down test. you could take the bottom ring off of the piston and your leak down test would be the same. the top 2 rings does all of the sealing work. if air is getting into the pan then you have the wrong pistons, rings, or rings on wrong, or the block is to big for the piston. i think you're putting the top rings on up side down. you ned to check that close.

LEAK DOWN TEST HAS NOTHING TO DO WITH OIL RINGS , IT'S TESTING THE VALVES AND FIRST AND SECOND RINGS. if the air comes out the oil tube then the first and second rings are the problem. Are the pistons and rings the correct sise ie. standard / 10 over / 30over etc. . Make sure the pistons and ring are for the same size bore. The first ring is what seals the cylinder on the compression stroke. Thats all it's job is in life nothing else. The second is a double duty ring so to speak. It counter seals the the top rings " gap " , thats why you don't line them up. So make sure you put the rings on the pistons the correct way. They have a top and bottom as well as a final location to be in when in the cylinder. The second ring second job is a final oil scrape. the oil rings just do a fast heavy oil scrape to make sure the second and fist ring don't get coverd !
I don't think you have to rebuild completely just recheck the end gap of the rings and their sizes and correct position installed.



air out the exhaust is e-valve
air out intake= intake valve
out radiator (bubbles ) head/block or head gasket

End gap alone isn't enough to make it burn that much oil. If the cylinders are round and the rings are any good at all it should run cleaner than that.. The pistons must be wrong somehow.

Hi It1s10, dozzer, r pope: I realize the oil rings have nothing to do with the test, but was wondering if oil couldn't escape fast enough behind the oil rings-which are drain back holes-if excessive oil couldn't escape fast enough and build up in the cylinder. I don't think this my trouble, just a thought. On the second rebuild all things associated with clearances, rings installed right, etc. checked out 100% (had two other motor heads there at tear down on the second rebuild so they could give me some extra eyes on the problem). Also, our machinist rechecked everything when it was re-honed. (our piston to cylinder is .0025) Between multiple people you would of thought one of us would catch a flaw. that's why this one is killing me. Although the grease may not be the problem, it'll be put together with oil this next time, and like you guys said it could be a boo boo I made, so we'll recheck everything again and find out. I'm human all the way, so when this happened the first time, I was twice as picky on the second rebuild of all clearances, etc. as one would suspect. I think your right (pope) on considering new pistons. Dozzer: our machinist wants piston in hand before he finishes the cylinder with hone machine. On second rebuild machinist measured a few cylinders with me there, plus I measured them too back at the shop. Got to go for now. thanks.

forgot to mention that no air leaked by any of the valves, or had no water shoot out the radiator. (no air sound out the carb or exhaust, none by the guides. Also pressurizing the intake manifold yielded no leaks. (the test I did a week ago). later