Leak down test

[2rods]

How do you do a proper leak down test? I made a tester and am wondering if I am doing the test properly? I have 110psi coming in which is regulated to 100 psi and then goes to the cyl. I am getting 100 psi on both gauges. If I shut off the air it bleeds off pretty fast. The leakage is past the rings as I can hear air from the VC breather and the dipstick. If there is leakage the 2 gauges should not be the same indicating the % of leakage assuming you start at 100 psi. Is this right ?

Thanks for any help. Dave.

[Bruce Dorsi]

How do you do a proper leak down test? I made a tester and am wondering if I am doing the test properly? I have 110psi coming in which is regulated to 100 psi and then goes to the cyl. I am getting 100 psi on both gauges. If I shut off the air it bleeds off pretty fast. The leakage is past the rings as I can hear air from the VC breather and the dipstick. If there is leakage the 2 gauges should not be the same indicating the % of leakage assuming you start at 100 psi. Is this right ?

Thanks for any help. Dave.

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How did you make your tester?  

Did you incorporate a restrictor orifice between the two gauges?  .....Without this restriction, the two gauges will always read the same.   (The restrictor orifice creates a pressure drop between the two gauges if the cylinder leaks air faster than it is replenished.) ...However, if the orifice is too small, you may not get an accurate test.

I have tested engines that have had considerable "blow-by" based on sound, but those cylinders passed leak-down test, and had a good compression test.

Best results are obtained if the leakdown test is done on a warm engine, but that isn't always possible.

Info I have been able to find indicates the following leakdown rates:

3%-5% leakdown = good racing engine

5%-7% leakdown = good street engine

10% leakdown = weak

20% leakdown = shot

Another source specified:

0-10% leakdown = good
10%-20% leakdown = needs rebuild

[2rods]

I was looking at some on the net and just realized I need the orifice. I am going to put a needle valve between the gauges and adjust to get proper balance. Thanks.

[Ed ke6bnl]

I was looking at some on the net and just realized I need the orifice. I am going to put a needle valve between the gauges and adjust to get proper balance. Thanks.

the one I made called for a number 60 drill bit with a set spacing distance between the ports. I can't recall the space or length of the 60 drill bit port, must have it in my files somewhere. Ed ke6bnl

[1FATGMC]

This came up on Chevy Talk the other day:

http://www.chevytalk.org/threads/showflat.php?Cat=&Number=894010&page=2&view=collapsed&sb=5&o=14&fpart=1

If that doesn't get you there then go to the "Perforamance Forum" on http://www.chevytalk.org/

In that post there is a link to building a leakdown tester and it talks about the orfice:

http://www.xs11.com/tips/misc/misc3.shtml

Like a lot of testers it sound like you should be looking for differences between cylinders.

c ya, Sum