Just READ my lines above .... it depends on the incoming pressure. If you apply 7 or more bars then you almost everytime end up with values below 10% which gives you -nothing- but nice looking numbers below 10.

Or do you think Hazet as one of the best tools manufacturer just sets wrong areas on their gauges to green? I dont think so.

At 50 psi or 100 psi, 20% leak down is too much for an air-cooled 911. The last time I did a leak down on my race engine, which was just a few weeks ago, I has the same leak down percentage at 50 psi and 100 psi......

Shure, because your setup (I guess) comes with two gauges where behind the first one an orifice keeps the internal prassure at a given level no matter what pressure comes in. Cheap Chinese ones internally even go down to 1 Bar. These even go up to 40% in their acceptable range. Watch the Sets shown in the www.

All depends on the actual pressure present in the combustion chamber.
Use a one-Manometer setup where you can set the an individual pressure at the output reaching the chamber and you will have diff. percentage results at diff. incoming pressures.

So a "20% is too much" answer is valid for your leak down test set and many others out there but not a rule of thumb in general.
Btw I personally also prefer a maximum here of 10% at 4 bar but ... thats my personal limit before I suggest an engine overhaul. But main focus is - as said - that rleak down esults within the cylinders are almost matching.

This sounds fishy. I have never seen an engine produce the same compression numbers with the throttle closed.

I try to be careful about things where I am not entirely certain. Aircraft mechanics use these things where there are more consequences if you don't get it right, and OK an engine which didn't actually meet FAA or someone's specs. Maybe someone with that experience will chime in.

A quick look at testers which are for aircraft shows plenty with two dials (though many also have two valves - don't know what those are for). Aircraft testers seem to denominated by the diameter of the piston, also.

From previous discussions about leakdown testers, I think the way they work - the two gauge ones - is that between the pressure you regulate for dial A, there is a small orifice leading to dial B. Because it is so small, negligible air flows/pressure is lost to dial A when dial B is connected to a cylinder. I analogize this to the tiny orifice in a CIS fuel distributor through the large diaphragm separating the top and bottom halves of the FD.

Or perhaps to a high value resistor which doesn't draw enough current from a circuit to lower its voltage? High impedance on volt meters in these days of good and inexpensive electronics (from one who grew up in the VTVM era)? Beyond some level of impedance, only for the most exacting scientific testing would more be better in practical terms.

My experience (all random) with air leaks is that if there is an opening, even if very small, near negligible pressure will show up in a soap bubble test. Maybe a rubber seal might work differently, as more pressure might force a seal to leak. But I don't see that kind of concern with engine leak downs. You aren't going to force valves off their seats, and my suspicion is that you won't move rings to where they don't seal as well.

Past discussions often involved the size of the orifice, and on how there was thought to be no standard for it.

With my first compressor, I couldn't get 100 psi on the inlet side, so used 80, or 50 to save the math, just like many others have. Now I can use 100, so I do.

My take on how Hazet has set up the one dial gauge is that its face is set to work properly only at a very specific inlet air pressure. It must still have a restriction between the inlet and the outlet. I suspect the adjustment knob is set so the one gauge is at 0, and its face is calibrated so 0 is for what their desired inlet side pressure is.

It seems to me that higher pressure just gives better analog dial resolution. Soon, I suspect, there will be electronic digital dials on the market - I just bought a digital tire gauge. Hard to know what its error range might be - anyone who has compared the several tire gauges we all collect has been a bit surprised to see how much they all vary. As mentioned, the gauges on my leakdown tester are quite probably not up to some technical institute standard of accuracy.

So I am not understanding the argument about why one and only one inlet pressure can work on a two gauge system, though it is critical on a single gauge system. Unless it has to do with internal orifice size. And it would seem that with a dual gauge system you could deal with that - after setting up the test, reset the inlet pressure so the inlet side is back to 100 or whatever you had chosen, and promptly read the outlet gauge.

I'd be leery about 20% leakage in an exhaust valve - if seat or valve is burned, it could get worse fairly quickly. Ring blowby you could live with for a while - maybe more frequent oil changes? Intake, I'd wonder why. But for a race or track motor, I'd not settle for 20% anywhere.

After blowing up a 2.7, I got a used replacement, with leakdowns in the 10-12% range per a mechanic with a big, fancy looking test rig. He said it should be OK, just not quite as fresh. I ran it a while, but persuaded myself that my lap times were suffering, and sold it - with full disclosure - to another racer. He said it worked fine for him until he built a 2.8 with carbs and cams and CR etc.

So Andrew, I think you will have some trouble convincing some of us (most of us aren't worried about being corrected - that's how you learn if you accept the fact that there is almost always someone out there who knows more than you do) that the the inlet pressure on a two dial tool will cause the percentage of leaking to vary if you operate it in the normal way.

A healthy engine should be under 5%.
When I tested my 964 engine I had leak down at 1% (could not hear any leaks at all), on the same tester we did a friends 968 turbo, set up with larger ring gap. It had 15+ something, mostly leaking through the rings.

What is "acceptable" is arbitrary. The manufacturer of that tool, Hazet, has 0-20% in the green zone. I wouldn't be happy with 20% on a newly rebuilt and broken in engine.

If I got 20% on a daily driver with 300k miles on it, I may be OK with that for now but I would be planning on replacing/rebuilding the engine.

I built my own leak down tester with parts I bought from the local hardware store.

http://forums.pelicanparts.com/uploa...1476761526.jpg

I've posted this picture before and I keep using it.

@ Otto
Read my explanation further above, ... it depends on the pressure which reaches the combustion chamber.
The Manufacturer Hazet of the tool above deals with an internal clamped pressure provided to the combustion chamber and thats why here "these" 20% are within the range.
Many people go with about approx 7 Bar at the combustion chamber when doing a leak down test there YES about 5% is ok and should not be exceeded.

BTW, YES, your gauge output is fully ok at approx 80 PSI. What is the sice of the ofrice you used on your DIY seutp? Nice btw!

Here's a reading I did a few weeks ago ... approx 2.5% loss when applying 4 Bar to the comb.chamber. Same very slight Noise on all six tests.

http://andrewcologne.bplaced.net/911/leak-down.jpg

Aircraft piston engines are measured using the two gauge leakdown tester, but the readings are listed as "compression tests," with the post orifice number listed first, then the inlet air. A reading would be advertised as, "Compression is 78/80." Even though we all know it's actually a leak down test.

At the risk of throwing too big a wrench in the works.....
I was thinking... what we are trying to measure is an amount of air flow at a given pressure (80-100? psi) applied to a cylinder. The pressure applied to each cylinder should be the same. If that's the case then why isn't the downstream gauge set to read a constant pressure? What would happen is the gauges would read 105-100 instead of 100-96 or something like that. I know it's a small difference and probably not worth worrying about.

No, you are measuring pressure difference. If the inlet pressure is 100 psi and the cylinder hold 95 psi, there is a 5 percent difference or leak down. I use a 2 gauge setup with one gauge showing the inlet pressure and the other showing the cylinder pressure.

ugh.. the FAA has some guidance of leak down tests

https://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/0/99c827db9baac81b86256b4500596c4e/$FILE/AC_43.13-1B_w-chg1.pdf

page 8-7

I built my tester 20 years ago and I think I just put a plug of epoxy in the pipe nipple that is in between the two gauges and let it cure and then drilled a hole with a .040" drill bit.

The FAA recommends a .040" orifice for engines with pistons 5" diameter or below and .060" for engines with pistons bigger than 5" diameter.

Henry

Your engine is good and you should be jumping with joy at getting those leak down readings. Those are very good numbers. You will have to find something else to worry about.

Small variations in upstream line pressure from your compressor won't matter. I try to keep the test between 100 and 80 psi. My compressor maxes out at 100.

Andrew - first off, why is the pressure which reaches the combustion chamber anything other than the regulated pressure before the orifice, minus what leaks out? We both know that if the filter in a WUR is blocked so the WUR can't reduce the CP, the CP ends up the same as system pressure. And if the line from the WUR to its next stop is blocked, you get the same result. If you have zero combustion leaks, you will have no difference between the two gauges, without regard to what the regulated pressure is, won't you? And with zero leaks, the orifice diameter won't matter, will it? Of course it will, some, when connected to the spark plug hole.

Second, how do you respond to the argument that the Hazet, which has to make things work with one fixed gauge with a "backward" face so it reads directly in percent, has to use a very specific regulated input pressure for their system to work? Certainly, if you used more or less pressure than specified, you'd get different readings (though you couldn't really use more -the needle would hit its stop).

More to the point, Hazet says you need an air pressure source of 6-12 bar, so their setting pressure can't be over ~90 psi. If you somehow measured what the regulated pressure is when set is 80 something psi, I believe you.

My suspicion is that the gauge they use isn't custom made for them, though they have a custom face. Perhaps some gauges available in metric countries are specified at 5 bar?

Two gradation lines difference between cylinders they say are 4% loss, which they say is acceptable if that is the greatest variance between the high and low cylinders. You set the pressure until the dial pointer is on 0. Then they say green area is up to 23% on the gauge.

Like others, I am mystified at accepting a 23% leakage. If I had a 19% leakage in five exhaust valves, but 23% in one, would I do more than, say, chance driving home or to a shop for a rebuild?

If I had my car home, I'd perform a 50 psi and a 100 psi leakdown test, to see if that confirms that (within the differences in resolution) the % results were the same.

And am I wrong to analogize pressure to voltage, and flow to current? The Ohms law analogy does suggest that different orifice sizes will lead to different leak percentages, though, if the orifice is taken as the resistance. However, we are measuring a whole circuit - the leakage from the cylinder is part of the circuit - maybe that makes orifice differences, at least if small, not as R1, and the leakage as R2. Resistance electrically is additive. Here we have the area of a 0.04" diameter orifice , R2 is infinite, and R1 is irrelevant. If we assign a small enough decimal number to R1, and some rather lower number to R2, would that work?

It appears that the length of the restrictor, as well as its diameter, affects the pressure drop. That is a term in the equations doctors use in figuring blood flow drops, which are pretty much like Ohms Law with some special cases. But maybe the length, if relatively short, doesn't matter all that much? I have never seen an engineering analysis of the length, compared to the diameter, of a dent in, say, an oil line in terms of flow.

If you have a tester with only 1 gauge, like the Hazet, it is dependent on the air source to be the "other" gauge and pressure regulator.
Its the orifice between the unrestricted air source and leaking chamber that do the magic in the test, it needs to be appropriately sized to the leakage of the piston rings. Its the only thing that can skew the test.
If you have a tester with a red/yellow/green zones and percentage instead of numbers you need the specific air pressure that the manufacturer of the gauge specifies. The Hazet pictured seems like a cheaper to manufacture and dumbed down tool.

The Hazet Tool is used by many well known Porsche Workshops here which also offer engine overhauling etc. Hazet Tools aren't cheap manufactured at all, its the other way around as they provide most reliable hardware and are here in Germnay the first choice of mechanics.

yes,IF the tester comes with no ofrice, but in case of the Hazet tool the source pressure should be within the specs above 5 Bar like mentioned above by Walt. Internally it works with reduced fixed 4 bar, thats why differnet source pressures will result in the same leak down values.
As you already know (as thats what you meant above), when just connecting a simple gauge shurely different incoming pressures will end up in diff. results.

Thats cause internally the pressure brought to the combustion chamber will remain the same.

I never said that I personally accept this. In case of Hazet and their specs, means their final reduced pressure brought to the combustion chamber, the green area on their gauge just tells the menachnic that the engine is ok. In our case where we want to archieve/keep maximum power at our engines, for shure I would be anything but not be happy with 20%. BUT ... I would also no accept 5-10% when using a tool providing much more pressure "to the combustion chamber" like real reaching 8 Bars or higher – Im not talking here only about the source pressure, the pressure "reaching the combustion chamber" here is relevant.

With the Hazet tool you you set the pressure from the compressor connetion to more than 6 Bar (length of hose must be taken into account) to the Testing tool. the next point in the way of the air is the ofrice in the Hazet tool (and also in case of other tools) which clambs the pressure – thats why diff input pressures here on such tools wont change the result. Its all depening on the ofrice used and IF one is used.
FAA following devices are shurely a way to go, ... but beside other FAA compilant ones I also built myself one DIY version of a tester which does not come with an ofrice as by this I can provide the Full 8-10 Bar to a combustion chamber, wich not only once showed me that there is a "leak" between the Head and the cylinder. Covering that area with some dishsoap/water mixture showed me in that particual case that ateh sealing ring was flawed – which was prooved when the engine was taken apart.

Shure

I know Hazet isn't cheap, but it is still cheaper to produce a tester with one gauge than two.

All leakdown testers MUST have an orifice/restrictor between the air source and combustion chamber otherwise you can't measure a pressure drop.

ok, ... but it works and gives correct outputs – I dont see your point as you point out the argument cheaper. But ... no matter.

I never mentioned something different. But thats not needed for measuring the pressure drop itself, its needed to clamb down the incoming source pressure which will be forwarded to the combustion chamber to a specific pressure value – and that makes the incoming pressure independand as log as you keep the incoming pressure above a specific value depending on the device. As you btw statet further abvove as well.

Just do a test: Take a one gauge device with no ofrice and set the inpout pressure to exactly matching 4 Bar while the output is closed/sealed. If then connecting the output to the combustion chamber the leak in the combustion chamber will show the proportional pressure drop on the gauge. I did the test often and the result is exaclty matching to the ofrice containing Hazet device with 5-8 Bar applied to its input.
The logic is simple ... i.E. Walt compared it to the WUR pressure affecting approach.

yup ...

I agree with you and I tend to worry too much about many things. Today for some reason I couldn't find the title. Wife is checking the safe deposit box at the bank today.

The wife is hiding the title so you cant sell it! 😁

Well, I think we are now pretty much on the same page in our diversion on how leakdown testers work, and what affects what.

I had forgotten about cylinder head leaks, as on our engines without a broken head stud, or maybe turbo hand grenades, this doesn't seem to be a common leak. More pressure at gauge A could cause a problem, though the 125 or 150 psi which is about most all home compressors can manage (?), seems way below what combustion pressures would be, and would be unlikely to lift the head and break the seal?

This statement by Andrew got some of us confused: giving 135 PSI to a combustion chamber for a leak down test is far too much for a precise test result. By this most test results are between 2% and 5% which looks good on the first view.

Andrew: I calculate that if the pressure before the orifice is 135 (on a system with a gauge or gauges which go up that high), and the pressure shown on the (final or only) gauge is 128, then the leakdown is about 5%?

Opinions vary, but I tend to favor the leakdown over a compression test - it tells you what is leaking. In fact, you can learn a lot by just putting compressor air in through the spark plug, and using a piece of hose in your ear to listen for where the leaks are, and perhaps how loud they are.

Despite all this back and forth (interesting to others than hcoles), he got his car sold, or almost so.

I know a good solution to your problem.

Buy a 68 Triumph Bonneville and restore it in your living room and watch the fireworks with the missus..

<iframe width="560" height="315" src="https://www.youtube.com/embed/DiMRDAAJTcg" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>

Walt, just look here:
https://nineelevenheaven.wordpress.com/die-druckverlustmessung/

Dumb translation option via Google as engl. version will follow.
https://nineelevenheaven-wordpress-com.translate.goog/die-druckverlustmessung/?_x_tr_sl=de&_x_tr_tl=en&_x_tr_hl=de&_x_tr_pto=nui ,elem

Andrew - the translation is actually very good, and the illustrations are superb. And I see your orifice is only a little smaller in diameter than the US aircraft 0.04".

I can see how more pressure could conceal very small valve leaks by pressing valves a bit tighter. Typical seat pressures are in the 110-130 psi range, and seat pressure only needs to be strong enough to control valve bounce and the like. A 49mm intake is (if my math is correct) ~2.9 square inches, about 300 pounds with a 100 psi combustion chamber pressure, roughly triple what normal static seat pressure is, though the compression cycle pressures will have more effective seat pressure, and the combustion seat pressures will be what - 10X that?.

When I have ground valves or seats, or just used valve lapping abrasive paste and rotated the valves, I test by clamping a gasketed plate with a fitting in the center over the chamber. I put some soapy water in the ports, and blow through a hose attached to the plate. If I get any bubbles, I go back to lapping until that quits. Shops doubtless have more efficient methods of testing. However, I have never tested like this with a head fresh from a running engine, just after removing a valve for whatever reason.

Perhaps the cylinder pressure component of valve sealing is why small intake or exhaust leaks are generally ignored? In a running engine they seal fully?

The mystery here seems to be the difference between your tests at three regulated pre restriction pressures, and what others have recorded, typically using 50 and 100 for ease of calculating percentages. You get different percentages of leakage, and others don't. The general methods and procedures and equipment are fundamentally the same. There is better resolution on a gauge with 0-100 on its face if you use 100 psi as your input.

I would stay away from the differential pressure leak down test tools. How do you know when the tool isn't working?

On my home built tool, I have a quick disconnect fitting and when the hose is off the fitting acts like a valve and is shut, In that condition the pressure across the orifice is equalized and the gauges should read the same. As I increase pressure from the regulator on the compressor, both gauges should read the same. This tells me the tool is functioning properly.

On a tool with a differential pressure gauge, with the hose blocked off so no air can flow, the gauge should not move at all as I increase the pressure.

What if the gauge isn't working at all, or what if it works only some of the time? And if it does break, can I fix it myself or do I have to scrap it and buy a new one?

With my home made tool, I will know immediately when the tool has a problem and I can go to harbor freight and buy two new gauges, or order them on Amazon. I can buy cheap gauges or spend some more money on better gauges.

Maybe this is why I have a Volkswagon and not a Mercedes. I like things simple.

Otto - you must mean single gauge instruments for this purpose? All of them work on a differential pressure basis, don't they.

all gauges are differential,

I was trying to avoid going into this but here i go

the simple dial gauge uses something called a Bourdon tube

https://cdn.britannica.com/s:700x450...4-1259877B.jpg

The bourdon tube is shaped like a banana and when the internal volume is pressurized it wants to become straight. The tube is attached to a linkage that is attached to a pointer and it rotates on the face of the gauge.

The simple gauge has one signal pressure and a reference pressure. In the case of a tire pressure gauge, the signal is the the pressure in the tire and the reference is the atmosphere. The atmosphere is 1 Bar and the tire is around 3 to 4 Bar above atmosphere.

the differential pressure gauge has two signals. In the case of the leak down tester sold by Hazet, the signal is the down stream pressure (combustion chamber) and the reference is the upstream (compressor). It could be the other way around too.

The mechanism in the gauge is having a tug-of-war between the two signals and its connected to a pointer on a dial. When both signal and reference are the same the needle doesn't move and reads 0. Atmospheric pressure is ignored.

I just looked up that test rig and I found the biggest reason I would avoid it

$384

https://hausoftools.com/products/hazet-4795-1-engine-leakage-tester?variant=39351876878359&msclkid=e6b8c6fbd373 13515adea7ac161a5d0e&utm_source=bing&utm_medium=cp c&utm_campaign=Shopify_Bing-Shopping_53502967831&utm_term=4586818916556693&utm _content=ShopifyImportAdGroup

I built my tester for maybe $10. I cannibalized the hose from my compression tester so add the price of that tool.

the only advantage I can see of the Hazet tool is speed. If I was in a production environment where I had to take many measurements an hour, a single gauge would be prefered. Its easier to read and if your workers are semi skilled, there is less chance of a mistake.

The point is, not everybody got skills to build a tester in a DIY way.
And btw. the offer you linked to is exorbitant expensive ... here its offered for about 150€ exclusive 14mm adaptor/hose. But shure still to expensive for a DIY'er.

Even I built my tester with 2 gauges as well, ... two gauges are simply not needed. And testing btw is not faster. IMHO the only advantage of a two gauge set is, that you have a clear info via gauge display of what compression is internally on the way to the combustion chamber used, i.E. 1,5, 4 or 7 Bar - its explained in the link above


Actually mine comes with 0.04", means 1mm, as well.

Get this for leak down:

https://www.amazon.com/OTC-5609-Cylinder-Leakage-Tester/dp/B0030EVL60

and this for compression:

https://www.amazon.com/OTC-5605-Deluxe-Compression-Tester/dp/B004K2FSXI/ref=asc_df_B004K2FSXI/?tag=hyprod-20&linkCode=df0&hvadid=312158556601&hvpos=&hvnetw= g&hvrand=12518946887999855819&hvpone=&hvptwo=&hvqm t=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9032150&hv targid=pla-338189074226&psc=1

If you are smart enough to use a tester, you are smart enough to build a tester. But I understand some people would rather buy and they can get a tester from Aircraft Spruce for a reasonable amount.

https://www.aircraftspruce.com/catalog/topages/15-05209.php?clickkey=121314

or here at Pelican

https://www.pelicanparts.com/Porsche/catalog/ShopCart/tool/POR_TOOL_MT0286_pg8.htm


My point in the 1 gauge test being faster is its faster to interpret the reading on the dial. The actual time to do the test is the same but our brains have to process the information and 1 gauge is easier to read than 2.

I have no idea why Hausoftools has such a high markup on that tester. They won't be selling many if customers figure out they can order the same tool from a company in Europe and get it in the same time for a third of the price.

I found the same Hazet tool on Amazon for a little cheaper

https://www.amazon.com/Hazet-4795-1-Engine-leakage-tester/dp/B001C9TFAE/ref=sr_1_31?dchild=1&keywords=hazet+leak+down&qid= 1633284358&sr=8-31

$333

still not a bargain

a leak down terster would make a good Christmas or birthday gift so a new one would be better than a home made tool

ok, price rised from approx 150€ to 185€ but .... its still worth comparing prices also outside the US.
https://www.hazet-freak.de/HAZET-Druckverlust-Tester-4795-1/4795-1
But ... honestly the Hazet one mentioned above was – beside quality – just mentioned as one example of an internally 4 Bar pressure operating unit.

BGS btw. also provides excellent quality:
https://www.werkstatt-produkte.de/werkzeuge/kfz-spezialwerkzeuge/pruefwerkzeuge-testgeraete/25694/druckverlust-test-set-7-tlg.-bgs-art.-62645
Maybe also offered somewhere within the US ...

Otto, thanks for finding the great graphic.
I like the one gauge method. In general gauges are not exactly the same. If you use one gauge - that issue is eliminated. A helpful spec. which I haven't found would be that the air flow rate across the orifice at a given delta P. This would be a way to compare different orifices. Everything else is straightforward IMO.

Not really, If you have 2 gauges you can see that they show the same if you block the output, that they are calibrated to each other.
With one gauge you have no idea that its still calibrated to the pressure it regulates too.

Ok, in case of using a tester where both gauges do display a range of "0 to 100 Psi" its true.
BUT in case of testers where the gauge on the right displays 100%-0% leakage, here many testers out there actually do show on the right gauge at set up the target position"set" or "0%" if the left side gauge is just at 20 Psi! So not matching at all.
A two gauge set -with a right side gauge display of 100%-0% leakage- gives you only one advantage: You can see on the first gauge the pressure the test is actually done with. But in case of such tester models thats not really needed, so one gauge here in this case makes sense.

Good point. I'm using two gauges. I open and close a valve to confirm they read the same or very close.
What about the idea of adjusting the inlet pressure until the downstream pressure reads the same? Then each cylinder is seeing the same pressure, no?

In my opinion, no buyer who knows what is going on will demand a compression test when you have solid leak down numbers. Especially when the runs well.

^^^ I tend to agree. However, on certain auction sites the bidders/commenters can stink up the proceedings if the compression numbers are not provided or are up around e.g. 155 or higher.

Here's my homemade leakdown tester. It has a single gauge and uses a scavenged pressure regulator. The air supply line attaches to the left side of the regulator. The orange hose connects to the spark plug adapter for a compression tester. (Ignore the stickers on the gauge, those are CIS pressure range indications).

With the valve closed, the gauge reads the static pressure controlled by the regulator. I usually set it to 80 PSIG, but can run up to whatever my anemic compressor can handle. With the valve open, it reads the pressure of the cylinder. Since I'm reading actual pressures, I need to do a bit of math to get leakdown numbers (e.g. 76 PSIG is 5% leakdown for 80 PSIG supply)

http://forums.pelicanparts.com/uploa...1634920573.JPG

The flow restriction is built into the quick connect fitting that connects to the pressure regulator. It's a 1/4" long piece of plastic tubing with a 0.40" ID epoxied into the fitting. Those dimensions match the only spec I could find for leakdown testers. (As I recall, those numbers come from the aviation world and were quoted somewhere on Pelican).

http://forums.pelicanparts.com/uploa...1634920632.JPG