[Ted B]

A local EVO owner recently asked me to assist him in conducting a leakdown test. When he arrived, his leakdown tester was a Chinese/Ebay/Harbor Freight unit that proved to be completely worthless. Not having replaced my leakdown tester since it was destroyed by Hurricane Katrina, I checked around and found units ranging from $25-$100+, with none of them mentioning any standard or specification in their product descriptions. When one measures leakage, it must be measured with respect to a standard that is engineered into the tester itself. Unless the tester is constructed to a specific standard, there is no way of knowing what it's telling us. This is like a chassis dyno generating a chart, but with numbers that don't reflect hp or any other known standard of measurement. Being dissatisfied with this, I decided I could do better by making my own, while saving a few bucks at the same time.

Anyone who knows anything about the FAA (Federal Aviation Administration) knows the FAA doesn't screw around when it comes to engine maintenance standards. The FAA established the standard for leakdown testing, and that requires a 1mm (.040") orifice be placed between the two gauges. In other words, when pressure is applied (e.g. 100psi), what we are looking for is leakage in the cylinder as compared to the airflow through a 1mm orifice at that pressure.


Parts:
(2) 100psi 2.0"- 2.25"1/8 NPT gauges (Ebay) - don't get larger than 2.25" or there may not be enough space to fit them!

(1) 1/4" NPT air pressure regulator (100psi capable) - Ebay

(1) 1/4" NPT male Quick Connect fitting

(1) 1/4" NPT female Quick Connect fitting

(1) 1/8" NPT plug (for regulator gauge port)

(2) 1/8" NPT male to 1/4" NPT female adapters

(2) 1/8" NPT male/male unions

(2) 1/8" NPT 'T' fittings (all female)

(1) 1/8" NPT union (1-3/4" long)

(1) 1mm (.040") precision drill bit. This can be found on Ebay, and possibly through Dremel tool parts listings.

(1) Spark plug hose of correct size for your engine, with male Quick Connect fitting - if you have a compression tester, you may be able to use that one. Otherwise, check Ebay and auto parts outlets. Be sure it doesn't have an integral check valve, or it won't work!

The fittings and such are available from better hardware stores, Home Depot, Ebay, etc.

Assemble everything as shown in the photo, with the exception of the long 1/8" NPT union. Carefully apply one wrap of Teflon tape to all threads.
[Image: LD1.jpg]


Now, to make the critical feature, the 1mm (.040") orifice ...

This is easy to do with a bit of JB Weld "JB-KWIK" epoxy.
[Image: LD2.jpg]

Mix a small amount of the epoxy. Take the 1/8" union and insert one end into the mixed epoxy, getting enough inside to create a plug and seal the tube.
[Image: LD3.jpg]

Be sure to carefully wipe any excess from the threads. Let the epoxy set for ~30 min, or until it becomes fairly hard.
[Image: LD4.jpg]

Using the 1mm (.040") drill bit, carefully drill a hole through the epoxy plug. If you don't have a Dremel tool handy, you can even do this with your fingers if you're careful. Be sure to check that the hole remains intact after the epoxy is completely dry.
[Image: LD5.jpg]

Again, if you have a compression tester with a removable spark plug hose, you're already set. Be sure to remove the check valve before using the hose for the leakdown tester.
[Image: LD6.jpg]


All things considered, this cost me <$50 in parts, and I can be assured that I have a tester that gives me readings that make sense, and are relative to leakdown readings as described and discussed in professional terms.

[Dolphin1]

thank you for doing a really nice job of this for everyone to use.

[The Flying Clutchman]

This could top the list of correct do it yourself tools. Great Thread!

[johnk&triumph]

Thanks for posting, I had lost the drill size needed.

This works great. Been using a home made one like this for years.....I think about 15.

I think the standard way of reading this is in percentage , as in Pressure Drop / Pressure in.

IE: (In gauge - out Gauge) / In gauge

( 100psi - 90psi) / 100 Psi = 10% leakage

Below 10% leakage is excellent , 20% to 35% is good, 35% to 50% is fair. Over 50% leakage is time for a rebuild...

Some pre-made leak-down gauges just give good/fair/poor....


jk

[Ted B]

Originally posted by johnk&triumph:

I think the standard way of reading this is in percentage , as in Pressure Drop / Pressure in.

IE: (In gauge - out Gauge) / In gauge

(100psi - 90psi) / 100 Psi = 10% leakage

That is correct.

<10% = Excellent
10-15% = Good
15=25% = Fair
>25% = Weak

[onesillynotch]

pretty cool.. i def ganna make one!

thanks

[b-blown]

i made one from a website that is basically identicle ..I used a multiport air manifold for mine and looked just like one from a major manufacturer ,,,and worked perfect (good enough that someone borrowed it from my toolbox without my knowledge) been meaning to build another

[bfm_]

excellent tutorial man, thanks, will be building one as well when funds allow

[Robert Camp]

The orifice is a little more detailed. The one you made is good if you always compare the before and after with your gauge, but will not necessarily be the same as another gauge built this way.

From Wikipedia:
In the United States, FAA specifications[1] state that engines up to 1,000 cu in (16 L) displacement require a 0.040 in (1.0 mm) orifice diameter, 0.250 in (6.4 mm) long, 60-degree approach angle. The input pressure is set for 80 psi (550 kPa), and 60 psi (410 kPa) minimum cylinder pressure is the accepted standard.

[Ted B]

That's correct, but the variation should be so minor (especially at low leakdown rates), that I seriously doubt and disparity could be truly significant. My orifice is about .25" long, but the approach angle is probably closer to 45 deg. I think the FAA specifies such detail out of a necessity for exacting consistency, as obviously, a solid shaft with a 1mm orifice all the way through it is going to read differently.

Already, this particular gauge has proven itself to be very, very sensitive and well worth the small amount of effort. Take 4 cyls that give identical compression test readings, and it reveals the differences between them with ease.