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Leak down testing results - all cyls.

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1958 rambler super View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 1958 rambler super Quote  Post ReplyReply Direct Link To This Post Topic: Leak down testing results - all cyls.
    Posted: Feb/06/2023 at 9:04pm
So I got all that stuff I talked about to do the leak down test
 (or at least I think so). 
the leak down test kit, and a 125psi air compressor, so now I have these tools. 
I gotta say, it's cool buying new tools! 
Now I have an air compressor! 
I didn't have time to get into it this morning after bussing home with the goods, with only an hour and a half to be on the bus to go to work, I decided to wait untill my days off tomorrow ....
Here's those dirty spark plugs too... 



Edited by 1958 rambler super - Feb/08/2023 at 5:53pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 1958 rambler super Quote  Post ReplyReply Direct Link To This Post Posted: Feb/08/2023 at 5:52pm
I followed the instructions to the letter that came with the leak down kit, followed the instructions on how to use the air compressor to the letter. 

the results I got from the leak down test starting at whatever cylinder was on a compression stroke (cyl5) and i orientated it to top dead center, then following the firing order to the next cylinder on a compression stroke are as follows....

Afyer filling the air compressor to 100psi, turning the regulator valve all the way down, connecting the leak down instrument, turning open the regulator valve to allow 100psi to flow into the leak down instru. Turning the leak down gauge all the way to the yellow part of the gauge at 0, then Connecting by hand the adapter that threads into the cylinder to be tested, and connecting that hose to the leak down instru. The sound of air escaping in whatever way was the weakest part of the seal in the engine was always coming from the oil filler tube, not the intake, no bubbles in the radiator, no sound from the exhaust.

The leak down indicator gauge slowly went from the green part  of the gauge which is ok, all the way to the red part of the gauge indicating 100% leakege which is really bad, the needle passing all the way to the 100% leakege area took maybe more then one minute but not much more, it was fast. 

I was thinking, that this result tells the tester where the leak is, in this case, the leak sounding from the oil filler tube means the air being introduced into the cylinder is escaping through the cylinder, past the rings and into the crank case were the oil and crank shaft are and then out the oil filler tube. 

This is supposed to let you know there is maybe damage to the cyl walls, or a problem with the rings. 

What I started thinking is that I have done the 20 minute break in, but not the 500 miles break in which is supposed to help seat the rings. 
I think the rings haven't seated and that is why the air is escaping from the cylinders, and I suppose you guys would say the same thing. 

What do you guys think? 


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Trader View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Trader Quote  Post ReplyReply Direct Link To This Post Posted: Feb/08/2023 at 9:45pm
Well it does indicate the rings have not seated, but unsure of the tool use and sequence.
It reads like you fill the leak down tool with 100psi, turn off the air and plug the tool into the cylinder. If that's the case, every cylinder will go to 0psi after the tool is emptied of pressure.
The tool should have 100psi flow to the cylinder and the second gauge should be showing either a pressure in the cylinder to calculate % loss or the other type that just give an indication of good to bad based on the cylinder vs tool pressure difference.
All cylinders will go to 0psi without constant air flowing into them, none are perfect.
A minute to loose the volume of air in the tool, hose and cylinder with piston at TDC does not seem that bad if that is what was done.
So the second type of tool which is what it looks like you have.
1 - set the piston TDC compression stroke
2 - set the compressor to 100 PSI
3 - install the hose into the spark plug hole
4 - set the tool regulator so the second gauge reads 0, first gauge should be reading 100psi
5 - plug the hose into the tool
6 - read the second gauge when stable
7 - turn the regulator counter clockwise all the way to remove pressure from the tool
8 - remove the tool 
Some of these aftermarket "interpreted tool instructions" will tell you to back off the pressure to the tool after the second gauge reaches 0. That's wrong.
IMO the 2 pressure gauge tools are better, just a little math required.

If I'm way off and the first gauge is reading 100psi, the regulator is not backed off and all the cylinders go to red on the second gauge in about a minute, you need to re-hone and re-ring. That's a lot of leakage and hard to believe.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote farna Quote  Post ReplyReply Direct Link To This Post Posted: Feb/09/2023 at 8:12am
Yep, rings not yet seated. Dirty plugs indicate the same. I've never used a leak-down tester, Trader sounds like he has though!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote FSJunkie Quote  Post ReplyReply Direct Link To This Post Posted: Feb/10/2023 at 1:22am
I've leak-down tested AMC engines before.

Assuming you are calibrating your tester properly beforehand...each one is a little different. Some you plug the hose and adjust to "0", others you leave the hose open and adjust to 100%.

10%-15% is about as good as they get. That's just leakage past the rings...mostly through the ring gaps. 

You will know if the cylinder is not on TDC when you do it. 100 PSI will kick the engine over with a good amount of force.

I do it by watching the valves and placing the companion cylinder on valve overlap. That means the cylinder I am testing is on TDC compression stroke. You can also mark the distributor rotor. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Trader Quote  Post ReplyReply Direct Link To This Post Posted: Feb/10/2023 at 7:22am
These leak down test tools can be misleading to the average user. Adjusting the second gauge to 100% or 0 depending on the tool is exactly the same thing. Your setting the tool gauges to the same supply air  pressure. 
Then you attaching the tool to the cylinder. A calibrated orifice in the tool is allowing a specific air flow and the second gauge when connected will read the difference between the supply air pressure and the cylinder pressure, hence supply - leakage = leakage rate.
You listen/observe for the constant air flow to determine were the leak is occurring.
A good fresh rebuild will be around 3% to 5%, and a good used engine running fine will be 10% or slightly more.
When you find a cylinder with 20% to 100% loss, there is a problem.
Odds of getting all cylinders to read 100% loss is like winning a lottery and loosing the ticket. The tool is not being use correctly or defective.
There are so many cheap knock off tools now, don't rule out a defective tool. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote wittsend Quote  Post ReplyReply Direct Link To This Post Posted: Feb/10/2023 at 10:28am
I watched a how to video. A number of things to consider seem logical:

The 100 PSI air coming in should be sustained. If the compressor volume is not sufficient to maintain the set pressure there would be an eventual imbalance. I did not see a time interval that this test was suppose to occur but I'd think that a near immediate reading (after a few seconds to stabilize) would be the most accurate. Even the best cylinder should bleed the air down eventually (assuming a non-running compressor). While small, the ring end gaps assures that.

It would seem logical that repeated tests will eventually force oil out of the ring area and decrease the reading. Just like I did not see an emphasis on sustained compressor pressure that would be associated by a large compressor, nor a stated time interval to read the test there was no statement as to hot or cold or even cold cranking to splash oil on the cylinder.

Admittedly it was just one video I saw and and like others I have never done the test myself. That said, processes have a commonality and the things I state MIGHT be a factor in getting an accurate reading.

My question is why is this car not out on the road generating the miles needed to (hopefully/properly) break the rings in? What is it keeping that from happening? This car in question needs to get off the couch and get a life. Years ago I bought a 4 Cylinder Datsun that barely got home (the car had sat for some time). I kept cleaning the plugs over the course of a day (4 or 5 times) and eventually it ran on all four cylinders. From that point on the car never had a problem and rolled up 10's of thousands of miles. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Trader Quote  Post ReplyReply Direct Link To This Post Posted: Feb/10/2023 at 11:07am
Should add, if your doing this often on different engines, you really want a dual pressure gauge tool.
The reason is you can set the tool to read at different pressures and this is useful for different bore sizes.
A big bore will have much more ring area and bigger ring gap to leak through then a smaller bore.
2 tools as examples:
and 

The first one has 2 pressure gauges and you can set it to different pressures for the test. The second one can only get the second gauge to 0 when the pressure is set to 90% or better of the supply pressure.
The first tool, you can do a low pressure test for a smaller bore and a higher pressure test for a larger bore. Useful as a 290 is 11.69" circumference and a 401 is 13.06", 11% bigger and 11% more area to leak. If you test a 401 at 100PSI and get a leak rate, a 290 should be tested at 89psi if you want to compare equivalencies of leak rate.
The second tool does not allow this. You get one input pressure and one "indication" of leak rate that you cannot even calculate a % difference between cylinders.
Long winded, but IMO the first tool is the most useful. It can also be used as a compression tester for low compression engines!



Edited by Trader - Feb/10/2023 at 11:12am
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1958 rambler super View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 1958 rambler super Quote  Post ReplyReply Direct Link To This Post Posted: Feb/11/2023 at 10:07am
Well, the possibility the gauge is broken out of the box is a possibility, the chance I did the test wrong is low because I followed the printed instructions, unless they were wrong, I maybe have typed out the sequence wrong and didn't have the paper with the instructions on it when I did, so I have a pic of it and the gauges for you guys if your wondering what I was following.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote purple72Gremlin Quote  Post ReplyReply Direct Link To This Post Posted: Feb/11/2023 at 10:34am
I see its a PT brand.. 
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