Need advice - Leak-down great, Compression test not so much

[safe]

Originally Posted by hcoles

I Wife is checking the safe deposit box at the bank today.

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

[Walt Fricke]

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.

[otto_kretschmer]

Originally Posted by hcoles

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.

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..

[AndrewCologne]

Originally Posted by Walt Fricke

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

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.

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

[Walt Fricke]

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.

[otto_kretschmer]

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.

[Walt Fricke]

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

[otto_kretschmer]

Originally Posted by Walt Fricke

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



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=e6b8c6fbd37313515adea7ac161a5d0e&utm_source=bing&utm_medium=cpc&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.

[AndrewCologne]

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=e6b8c6fbd37313515adea7ac161a5d0e&utm_source=bing&utm_medium=cpc&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 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.

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.

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

Originally Posted by Walt Fricke

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".

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

[winders]

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=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9032150&hvtargid=pla-338189074226&psc=1

[otto_kretschmer]

Originally Posted by AndrewCologne

The point is, not everybody got skills to build a tester in a DIY way.

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

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.

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.

[otto_kretschmer]

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

[AndrewCologne]

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.

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 ...

[hcoles]

Originally Posted by otto_kretschmer

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



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=e6b8c6fbd37313515adea7ac161a5d0e&utm_source=bing&utm_medium=cpc&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.

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.

[safe]

Originally Posted by hcoles

I like the one gauge method. In general gauges are not exactly the same. If you use one gauge - that issue is eliminated.

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.

[AndrewCologne]

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.

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.

[hcoles]

Originally Posted by safe

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.

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?

[David Borden]

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.

[hcoles]

^^^ 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.

['78 SC]

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)



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).