Leak down testing?

[Schurkey]

Two things to add:

1. Orifice size can be effectively changed by the addition of rust flake(s) from crappy compressed-air plumbing. If there's any restriction to flow through the orifice beyond the designed-in restriction, the leakdown tester will indicate greater leakage than "true".

2. Use of a "master orifice" as suggested (required) by Continental Teledyne can help a guy discover a contamination-restricted main orifice, and allows the leakdown tester operator to "know which way is up" by providing a way to "test the tester". That said, the official Conti-Tele "master orifice" is too large for performance automotive use. The concept is valid, but the allowable leakage is too high. A smaller orifice would serve our purposes better.

[rebelrouser]

I use a leak down tester a lot. The numbers others mentioned are in the ballpark. My suggestion is to leak your engine on the engine stand before firing, this tells you if your assembly was correct. Have had plenty of aftermarket heads leak the valve job, and catch it before it goes in the car. After you have made a few runs leak it again, you should expect it to leak better after rings seat. Write down the numbers, and then leak the engine while in service. You have a baseline, and now you can determine much easier when it is time to freshen the engine.

[hoodeng]

I read the PDF that Bill posted and agree with him that a P1/P2 gauge setup is the most accurate , but a little quandary creeps in here .With some race vehicles you use the leak down tester for another purpose other than checking cylinder seal and that is setting your barrel valve .So if the standard tester used by your team is a Snap-on single gauge type you would use the same one for all tasks .
Also pointed out earlier was the potential for error caused by partial obstruction of the metering orifice , a quick open end test should read 100% leakage if any percentage showed on the gauge that would confirm an obstruction.

Cheers.

[hoodeng]

Here is a shot of what was used to test leakage/comp and set up Hilborn /Kinsler /Enderle fuel bike system some years back ,i still use one of the master gauges and regulator to set up the Snap-on tester each time i use it .Under the foam in the gauge case was a pill for every ill and every conceivable concoction of fittings to test anything.

Cheers.

[Schurkey]

Also pointed out earlier was the potential for error caused by partial obstruction of the metering orifice , a quick open end test should read 100% leakage if any percentage showed on the gauge that would confirm an obstruction.

Cheers.

The orifice is upstream of the gauge. A restricted orifice won't produce pressure at the gauge when the hose is "open end". A symptom of a restricted orifice is that the gauge will indicate "higher" leakage than is actually called-for based on the true leakage.

The way to test these leakdown testers is with a "master orifice"--a calibrated leak that simulates a good but not perfectly-sealing cylinder. You'd want to see reasonably consistent indicated leakage when using the master orifice over the life of the tool.

[hoodeng]

You're right ,sorry about that.

Cheers,

[induction apprentice]

A proper calibrated leak checker using 100 psi regulated inlet pressure should show a leak value of 80@.080.
80% leakage using a flowed .080" jet on the output side. If it does not flow 80 at 80 and most dont. Then it is moot information. IMO.

Second part of this is the rellevents of leak readings in a cylinder in the first place. To many factors to read into when comparing 4,5, or6 percent leak figgures and what they mean. But it can be handy for helping locate a specific problem area within a si engine. IMO. A hose threaded into the cylinder coupled streight to shop air is just as usefull and also helps with changing out dead valve springs.

[swampbuggy]

question for piston guy-----can you say for SURE that gapless rings will provide MORE power?? NOW i am talking about two brand new engines built EXACTLY the same except the rings. (OR) possibly the SAME engine with a ring change ? thanks Mark, BTW which piston Company do you work for if you don't mind saying ? .

[Schurkey]

A proper calibrated leak checker using 100 psi regulated inlet pressure should show a leak value of 80@.080.
80% leakage using a flowed .080" jet on the output side. If it does not flow 80 at 80 and most dont. Then it is moot information. IMO.

I've heard similar, although I think the guy I heard if from was suggesting a #78 jet.

Point being, these may be useful suggestions, but they're not an industry standard.

[MadBill]

A proper calibrated leak checker using 100 psi regulated inlet pressure should show a leak value of 80@.080.
80% leakage using a flowed .080" jet on the output side. If it does not flow 80 at 80 and most dont. Then it is moot information. IMO.

I've heard similar, although I think the guy I heard if from was suggesting a #78 jet.

Point being, these may be useful suggestions, but they're not an industry standard.

The only standard I'm aware of is the FAA one as referenced here: https://www.faasafety.gov/SPANS/noticeV ... x?nid=3416 I'm sure an FAA-certified tester (as opposed to one merely built to the same orifice dimensions) would have an extra zero on the price compared to a top grade automotive one..

[Steve.k]

Well everyone this is very interesting info for sure. As you know we were trying to find out why we had our engine dropping like a brick at 4300 rpm. We had changed everything and were looking at everything. Dyno operator suggested leak down as he thought maybe lazy cylinder or two. But ended up faulty lifters(hyd) from comp.

[Schurkey]

The only standard I'm aware of is the FAA one as referenced here: https://www.faasafety.gov/SPANS/noticeV ... x?nid=3416 I'm sure an FAA-certified tester (as opposed to one merely built to the same orifice dimensions) would have an extra zero on the price compared to a top grade automotive one..

Surprisingly...no.

I bought an aircraft tester for about a hundred dollars. Had to tell them to ship it with a 14mm spark-plug hole adapter instead of the aircraft-style 18mm adapter. The price is now up to about $120.
https://www.amazon.com/Aircraft-Tool-Su ... er+orifice

The specific brand mentioned by Continental Teledyne (Eastern Technology) was about $40 more. Even so, that would have been under $150 then. I don't see that brand listed on Amazon any more.

[MadBill]

Maybe if it was Coast Guard-certified...

[induction apprentice]

The only standard I'm aware of is the FAA one as referenced here: https://www.faasafety.gov/SPANS/noticeV ... x?nid=3416 I'm sure an FAA-certified tester (as opposed to one merely built to the same orifice dimensions) would have an extra zero on the price compared to a top grade automotive one..

Surprisingly...no.

I bought an aircraft tester for about a hundred dollars. Had to tell them to ship it with a 14mm spark-plug hole adapter instead of the aircraft-style 18mm adapter. The price is now up to about $120.
https://www.amazon.com/Aircraft-Tool-Su ... er+orifice

The specific brand mentioned by Continental Teledyne (Eastern Technology) was about $40 more. Even so, that would have been under $150 then. I don't see that brand listed on Amazon any more.

the .040" orifice mentioned in the linked article will calibrate the tester to approximately a leak percentage of "80 @ 80" 80% using a .080" flowed jet on the plug end and 100 psi inlet pressure which is the standard also typically used in racing. Particularly when setting up constant flow injection. If this standard is not used. It is very difficult to offer help tuning in the alcohol and top fuel catagory as any tuning done with a tester of unknown values means absolutely zero. Leakdown of any engine presents the same challenge as the leak numbers have no value if the testers used are not calibrated to a known constant. So if anyone on here cares if their tester is usefull or not. They need plug a .080" jet on the end and see what it reads. If it is wrong. They are easily re callibrated. But on another point to testers. Don't waist your time if it has a shit regulator on it. If you can adjust the regulator knob a little each way without a change on the gauge and or it is not a sampling type reg with a very small controlled air leak. Then in my opinion. throw it out or mail it back to china and get a proper regulator to start with.

[Fireonthemountain]

Well everyone this is very interesting info for sure. As you know we were trying to find out why we had our engine dropping like a brick at 4300 rpm. We had changed everything and were looking at everything. Dyno operator suggested leak down as he thought maybe lazy cylinder or two. But ended up faulty lifters(hyd) from comp.

Sounds like something else besides a leak a tester would pick up, to drop like a brick at 4300. More like valve springs, spark or fuel or air failure either in or out. The higher the rpms the more those are prone towards failure to keep up. Leakage effects lower rpms more and high rpms less.