Leak Down test results

Offical Complete results of the Leak down test with the proper fitting is as follows:

#1 -- 14.4% #2 -- 24.5% #3 -- 17.7% #4 -- 11.1% #5 -- 10.0% #6 -- 13.3%

Just for the record.

Reply to
William Oliveri
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BTW, on a cold engine.

Reply to
William Oliveri

William Oliveri wrote: > BTW, on a cold engine.

Wonder if doing it to a warm engine might be revealing?

I'm curious not having used a leak down tester, what does the percentage signify?

If I was you the first thing I'd do is run around testing every car I had that is running well... At the very least you can get an idea of what kind of variation is common with the tester you have. If you find a number of 10% variations then that 24.5% number doesn't look so scary ;) If not then you may be looking at the gasket between #2 and #3 :(

Reply to
Simon Juncal

Bill,

When you tested #2 and #3 cylinder, did you check to see where the leakage was? #2 is a bit high and #3 is iffy. remember, a new engine can have as much as 8%, so the rest of them appear to be ok.

Chris

Reply to
c

Chris,

When I originally did the valve seal change I was concerned about the sound of air leaking as I had never had experience with putting air into the cylinder to hold up the valves. So I did several examinations. I looked in my radiator for bubbles (that doesn't pan out anyway as I'm not getting water in the oil) and saw no bubbles. I put a sandwich baggie loosely over the tail pipe with a rubber band to see if it would move the plastic, no effect. Also, couldn't hear anything from the tail pipe. I put the valve cover back on and took the hose from the pcv valve and put it up to my cheek to feel for air, here I felt something. I forgot to close off the hose from the valve cover to the air filter housing so I think if I did I would have felt much stronger feeling through the pcv valve. However, I don't know if this air is coming up through the valve guide or down through the cylinder. I didn't test the oil dip stick for air.

Earlier, before the valve seal change I had a mechanic do a compression test. The results were 150 psi across all cylinders. I double checked #1 and #2 on Tuesday (ran out of time to get the rest) and I got the same results on both #1 and #2, 150 psi. So I confirmed the compression results the mechanic had.

Bill

Reply to
William Oliveri

Ok, I am curious...

Do you have any idea just what those numbers represent or mean? I really don't.

I am taking a wild assed guess and am thinking those represent the shape of the valve seats. You did say you had some play in the valve stems on #2 right? This will make a strange oval wear pattern on the valve seating area.

I mean the compression is way up there like a new engine, so things like rings and gaskets are fine. The book says a new 258 should have 140-150 psi compression, but most important is even compression.

Your compression is 'perfect'.

It must be the seats of the metal parts that the leak down test tests???

I honestly have never seen or heard of in person anyone doing that kind of test. I have only heard about it on the internet and thought it was a way to test a racing engine after a fresh rebuild like they do every second race or so.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

William Oliveri wrote:

Reply to
Mike Romain

Mike,

It is most common for racers to use leakdown to test the condition of their engine, but there is much more you can diagnose with it. An engine can show relatively good compression numbers and still have a problem, but not necessarily all the time. For instance, a head gasket that has started to seep (and will fail eventually) doesn't always get detected with a compression test due to the short time the cylinder sees pressure while cranking the engine. A leakdown test will find that seeping gasket if the air is left on long enough. I have also detected a bad exhaust valve with a leakdown that wasn't detected with a compression test. This particular engine ran fine, except for an very infrequent pop out the exhaust pipe. The leakdown showed it was only holding 40% as compared to 80-85 for the other cylinders. When we tore the heads off, there was an exhaust valve with a small crack from the stem out to the valve seat. I would bet that eventually this valve would have broke and caused some serious damage. It was on a Dodge 440 that got driven pretty hard.

After looking at the numbers Bill got, and thinking about it a bit, he "might" have a problem with one of the rings on that piston. I wouldn't diagnose it as this until all the of other possibilities are checked. I didn't want to scare him by posting this, and I think you were also right in saying that he should check the injector for that cylinder before he tears into the engine. Without any of us actually seeing his plug coloring, it is hard to diagnose the problem. It may not be oil on the plug, or the oil may be getting there because the extra gas is washing the cylinder down which will not let the oil control ring work like it should. I hope for his sake it is something like a bad injector, and because he bought his EFI kit used, there is a good possibility of that.

Chris

Reply to
c

Chris,

Thank you for your reply. You won't scare me as I am not mentally ready for the worse but hoping for the best.

Thanks,

Reply to
William Oliveri

Correction. That is, I AM mentally ready for the worse but hoping for the best.

Reply to
William Oliveri

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