# Can Someone Splain Dis 2 Me ???



## aegt5000 (Feb 22, 2004)

Leak Down Testers 

<img src="http://img.photobucket.com/albums/v155/aegt5000/LeakDownTester.jpg" alt="Image hosted by Photobucket.com">

<img src="http://img.photobucket.com/albums/v155/aegt5000/leakdn2.jpg" alt="Image hosted by Photobucket.com">

I’ve looked at a few Mfg’s sites that make these things and I think
I have a pretty good idea of how they work. The Regulator is adjusted
to 100 psig with the outlet of the test rig closed (100 psig = No Flow)
The Damper Valve is merely a fixed orifice downstream of the regulator
which limits the flow of air through the test rig. With the spark plug
hose connected to the rig, the gauge pressure is reflective of the 
balance between the air leaking out of the rig and the make-up air
flowing through the fixed orifice. The lower the pressure reading,
the poorer the engine’s condition. Sounds OK so far.

BUT…the fixed component here is the diameter of the orifice.
Since different size engines have different diameter Cylinders
and Valves it seems to me that a Big engine would always look
worse than a small engine. Even if the larger engine leaked a
lower percentage of its cylinder’s volume, the smaller engine
could leak a higher percentage, yet appear to better. 

Seems to me these things should have calibrated valves in place
of a fixed orifice. The instructions would then say, set the valve
at “X” for cylinder volumes between “A & B”, set the valve
at “Y” for cylinder volumes between “B & C” …….
Maybe I’m missing something, but I can’t see how these things
work with a “One size fits all” fixed orifice.
Like I said…Can Someone Splain Dis 2 Me ? :what101:


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## Archdean (Jul 15, 2004)

Anthony, commonly called compression testers and at one time exclusively used on (air cooled) aircraft engines normally used for differential values among cylinders not an absolute value as you are suggesting!!

I have a new (not used) if you would like it i'll send it to you!!

Dean


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## HarryG (Mar 28, 2004)

AEGT500,

I've used cylinder leak testers over the years in various shops in my employ. I think of these as a "go-no-go" sort of tester. The reason I say this is if you read the instructions they do not give acceptable/unacceptable readings for various engines. I as well as the other tech I worked with used it as a comparitor to see if the cylinders were somewhat equal in their sealing ability to hold compression. 
Don't get me wrong. They can be a very useful tool in finding a leaking valve, piston, cylinder, etc. But you have to intrepret what its telling you without good/bad spec numbers to go by.
I believe a compression tester should be used before even considering using a cylinder leak tester.
Regards, HarryG


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## Chris (Sep 15, 2003)

I have always used a compression tester...Good insight there Harry! Great for indentifying worn seals and leaky cylinders...especially gwhen doing wet and dry tests......never used a leak tester.....old Ns are notorious for developing problems with blowby and leaking past rings....works great for me...


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## Michael (Sep 16, 2003)

Leak down testers are basically used to determine the ability of the cylinder to hold pressure for a set amount of time. Just the other day I was doing a tuneup of my wifes car a 1994 Plymonth Acclaim with a 3.0 V-6, I always do a compression test and leakdown test when I do a tuneup. All the cylinders held pressure at 85-89 PSI, which is within the acceptable margin and the compression test read 110-115 PSI.

I have always used a both testers to get a general idea of the engines health. Leakdown testers are good at finding bad valves, rings and something most guys use them for but fail to mention testing the condition of the head gaskets.


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## aegt5000 (Feb 22, 2004)

The idea of using it as a Go / No-Go instrument or for differential 
readings against adjacent cylinders (or a comparable engine)
makes a lot more sense than looking for absolute values. 
I downloaded 2 instruction sheets and both represent 90 psi
as “Good”, 80 psi as “Fair” and anything below 80 psi as being in
need of some form of attention. 
That just didn’t sit right with me.

I like the advantages it offers over a simple compression tester:
Exhaust Valve leaks…Air out the muffler
Piston Ring Rings…...Air out the dip stick and breather
Intake Valve Leaks….Air out the carburetor
Blank off the Intake and Exhaust manifolds, rotate to 
TDC on exhaust stroke and test valve seals.

Establishing a set of Base-line readings on a good running
engine and taking new readings at tune-up intervals would
be valuable information. 

Dean…Thanks for offering but you’re too far away for us
to start sharing the stuff in our sheds. Besides every time 
you give something away, you wind up needing it 2 days
later.
:furious:


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## Archdean (Jul 15, 2004)

Please remember when you use one that you are supplying air pressure to the top of the cylinder!! As long as your are TDD no problem BUT BE OFF JUST A SMIDGE AND YOU HAVE JUST STARTED THE POWER STROKE!! Blade /prop/egg beater what have you has just rotated /// Arm /leg OUCH!!

Dean


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## DrBailey (Nov 14, 2004)

aegt5000, I e-mailed you a link on testing , I might have made a mistake , uuh , are you working on aircraft or a tractor product ??


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## Carm (May 27, 2004)

We use them on aircraft as a way of measuring the integrity of the cylinder. Set to 80 PSI going into the Cylinder at TDC and then you read the other gauge and it will be at some point below 80. It was a general rule that anything below 68/80 was cause for rejection. But there are other criteria now as set out by the manucafturers. They can be useful in any engine to check where air is going...rings, valves, etc...


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## guest2 (Dec 27, 2003)

I sell them all the time. Common buyers are motorcylce shops and high-end dealers such as BMW and Mercedes. Probably have one on the truck. Like the others have said those who know how, use them often. 

Are you using it on your tractors or one of your vehicles? If you are trying to check a head gasket there is another tool that checks the coolant for exhaust gasses. Also popular with BMW and Mercedes techs.


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## Chris (Sep 15, 2003)

> _Originally posted by Carm _
> *We use them on aircraft as a way of measuring the integrity of the cylinder. Set to 80 PSI going into the Cylinder at TDC and then you read the other gauge and it will be at some point below 80. It was a general rule that anything below 68/80 was cause for rejection. But there are other criteria now as set out by the manucafturers. They can be useful in any engine to check where air is going...rings, valves, etc... *


Carm, great to see you again!!! Welcome back! :elephant:


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## Carm (May 27, 2004)

Thanks...nice to be back...sorry to hear abouth the bad year...it has affected us all, but it wasn't totally bad I guess. Anyhow, just picking up where I left off


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