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hcoles hcoles is offline
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Join Date: Mar 2005
Location: Saratoga CA
Posts: 3,298
A while back I attempted to find out about leak down testers and see if there were any specifications that they are made from or conform to. In general they are all different, there is no automotive industry spec. for these. The airplane engine industry has the most regarding the specifications for these. For example you can find for a given cylinder circumference the leakage should be X.XX or less at say 100 psig. Smaller pistons have lower leakage all things being equal and the valves not leaking much.

I would like to start a thread or we can continue on this one with a discusion on leak down tester specs./etc. The result will be that people can easily build their own tester and also understand what the numbers really mean.

Here is my take to start with....

Leak down testers come in two styles: - one gauge and two gauges.
The "tester" is really only a device that measures pressure drop across a restriction. The restriction is usually just a fixed orfice in the "leakdown" tester. When pressure is applied against the cylinder there is flow across the restriction and past the rings and valves and a corresponding pressure drop compared to no flow.

What you really want to know is how much air volume flows at a given pressure that the cylinder sees. The fact that everyone talks about this or that % leakdown doesn't really provide too much information because all of the testers are made different.

History - my interest started when a friend purchased a BMW 530 (V8). As you may know there was a big reall because some of the engines were not made with Nickicil cylinders. The check that BMW did to determine if you get a new engine was a leak down test. People all over the world started getting thier engines tested and then wanted to verify the test that the dealer did. It turns out that BMW wouldn't let out exactly how thier tester was constructed or calibrated and what the numbers really meant. So my friend did quite a bit of investigation and built a few testers to see how they match the factory numbers/etc.

Anyway...if there is another thread or past set of threads I'll go look at those.

Anyone interested on taking off on this subject...let me know and I'll start a thread..if you think I'm mistaken on what I've said...by all means please respond also.

Cheers,

-Henry
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1989 3.2 coupe, DIY top end at 77k, now 112k
Old 07-25-2005, 07:59 AM
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