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  #1  
Old 02-13-2003, 11:10 AM
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Leakdown Tester and ?'s

I am building one for general use... Actually prompted by harbour freight having a regualtor for only 2.99 on sale right now...

So I am building a manifold to do the testing. The following drawing depicts my simple design. I figure you could either have the guage mounted on the testing manifold or use the injector hole with a compression guage inserted and feed air to the system via the glow plug hole. Probably best to mount it on the manifold but I already have the compression tester and could use a gas tester that reaches 300 PSI if this is high enough. This one does not have a schrader valve in the intake end of the hose.

One other anomaly I noted in their testing procedure is that they state the pressure loss values atr various points but how in the world can you tell if you losing 15% at the rings and 10% at the valves? Put a flow control meter on the valve cover/tailpipe and intake/exhaust manifolds and... Well you get my point.

I was researching this procedure however and see no specs for the pressure constant (PSI) to load to the cylinder. It also seems a little odd to me that they would suggest this be done at TDC since what if you have a cracked block below the rings at TDC? Testing at TDC would not find this crack so wouldn't it be more effective to test at the bottom of the intake stroke? You also would not have to worry about your pressure pushing the piston down either at that point in the cycle.

Okay, be gentle I did this drawing in about 5 minutes....I did not pick the colors but let the program default...
Attached Thumbnails
Leakdown Tester and ?'s-leakdown-drawing.gif  
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  #2  
Old 02-13-2003, 12:17 PM
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UHG..... when one starts to answer the drawing goes away...LOL

I don't think you need the pressure regulartor ( that will be on your air compressor anyway)... keep the guage which you have listed as optional ... and forget the one which is listed as going into the injector spot... otherwise you will be set up where you can't use your tool with normal gas engines...

When you put air in you will be looking at the guage and turning off the switch when it gets to the amount you want for the starting point...then time it as it goes down...

Air supply to cut off switch, to guage , to hole in system ( glowplug for diesel, spark plug for gas)

I think the percentage for valves compared to rings is determined by squirting oil onto the piston, thus sealing up the rings... the leak which continues from it is from the valves...

I have warned before that using TDC for putting air into the cylinder WITH OUT SOME MECHANICAL MEANS OF LOCKING THE ENGINE..... IS DANGEROUS.....

One cylinder of a 300 , when 100 psi is put on top of it is 1200 pounds of force... THE ENGINE WILL TURN IF NOT PERFECTLY CENTERED AT TDC....

This will probably mean you have to adjust the valves or the intermediate device so that the valves are shut at BDC... a real pain... and the reason that compression tests are more popular in my opinion... (popular but not more useful for diagnosing where your problem is)

Also I do not think that the amount of air which you can squeeze into a diesel at TDC will give you enough time to measure anything correctly...

You need some air compressed into the cylinder and then let it leak out... not enough total air if you have the piston at TDC....

Last edited by leathermang; 02-13-2003 at 12:46 PM.
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Old 02-13-2003, 12:17 PM
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that looks like a good idea/plan. I might have to make one too.
From what I've read, you have to listen to where the air is coming from to tell if it is the valves or rings. Real scientific!!
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Old 02-13-2003, 03:06 PM
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Okay Greg,
I'll go along with your idea of not enough air at TDC. The questions still stands though that a cylinder at the bottom of the intake stroke should be "sealed" as it begins it's upward climb to compression firing shouldn't it?

So why couldn't you go to that point in which you eliminate the danger then of the engine cycling. Also more air...
There are no specs though for the psi maximum to use for this procedure and since I am no math wiz I will defer to your calculations and say that it appears to me that you could really blow something if you went over pressure. I guess then though you would know where the leak is!!

I need to find the spec for PSI....

Also the reason that I put the regulator on the manifold is:
1. You could use a portable air supply like a simple portable tank to apply air with this system.
2. In addition you can increase the pressure slowly since there is not a very high volume of air in a cylinder. I have blown test plugs out of plumbing systems with just a quick crack of the air valve before so I figured for the 2.99 regulator at Harbor that I could afford to add this instrument to the manifold.
3. If your leak is sufficient to cause a quick loss of air you could turn the valve on and leave it on at a regulated pressure to go stick your ear in the tailpipe etc... Love that picture!

McRoth, I agree. What do you do go "hey, that sounds like about 20% of my loss coming out this hole...!

I know there are some geniuses out there that have figured this out before I had the shadetree idea so jump in whenever you feel inclined....
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Old 02-13-2003, 04:38 PM
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One would assume that the valves would be completely closed at the start of the compression stroke, but that is not something you can assume...so you need to make sure....

Most air compressors are not going to give you more than about 175 lbs anyway...and that is a two stage compressor... most singles only about 125...
And your car is usually working with 300 PLUS... therefore I do not think you are going to blow anything from too much pressure...

I appreciate your defering on the specs.. but just for the record... I used four inches for the diameter of the piston,,, pi (about 3.14) times radius ( half the diameter ) squared is 2 times 2... so four times 3 is 12 square inches on the top of the piston... thus at 100 pounds per square inch makes 1200 pounds of pressure on top of the piston.

Putting oil into the cylinder is how you determine what part of the air is being lost at the valves..
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  #6  
Old 02-13-2003, 05:15 PM
Chris J.
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leak down tester

The one I made is like this: Compressor with regulator, shrader male disconnect into tee with 200lb. guage,close nipple, ball valve, close nipple, tee with another guage, then a flexable line to a quick disconnect, and then a glow plug adapter. This is all 1/4" brass. The flexable line has 1/8" threads on each end, so one would need two 1/4"x1/8" bell reducers. With ball valve closed, air goes in and brings the first guage up to 100lbs. Ball valve is opened to let air into cylinder. Then ball valve is closed and guage is watched for drop. If anyone see's any flaws in this design, I would like to hear them? I hope this helps.
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Old 02-14-2003, 03:00 AM
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Alrighty then....:)

You've obviously thought this through Chris and that would be the old configuration that I would worked with in the past.

I simplified this one to only the 4 elements needed.

It works and works well.
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  #8  
Old 02-14-2003, 09:27 AM
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Ok, then now it is time to share your results...

What psi did you use as the start number ?
How long did it take to leak to your goal number?
How long did it take after oil was applied to rings ?
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Old 02-14-2003, 10:54 AM
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Haven't done mine yet... My comment was directed to Chris' design.
I might try to put it together this weekend.
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'85 300SD Silver - Sold
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  #10  
Old 02-14-2003, 11:01 AM
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It would be nice if we could accumulate a sample from lots of people.... those with engines in good shape, those with rings problems but good valves, good rings but leaking valves.. etc...
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  #11  
Old 10-30-2005, 08:09 PM
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Thank you leathermang

for pointing this one out.

Last edited by whunter; 03-05-2010 at 01:49 PM.
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