I'm thinking of building a leak down tester myself for something to do.
I have access to a new regulator 3/8" or 1/4"npt .
Thought about using the gauge off my compression tester for the leak side (engine side). Use the quick connect hose from the compression tester to thread into the spark plug hole with schrader valve removed.
........Fill the inside of a nipple with epoxy between the regulator and a Tee, drill it out .040" for a restriction. Add the compression tester gauge to the top off the tee and compression tester hose to outlet of the tee,

Will this work properly?
Has anyone made one?
Or am I wasting my time?

 

Look at the FAA requirements for a leakdown tester. They have a drawing of how it all goes together. The 0.040 orifice needs an inlet taper at 45 degrees. The illustration shows an outlet taper, too.

http://rvplane.com/pdf/AC43.13-Chapter%2008.pdf
(8-14 Compression testing of Aircraft engine cylinders, especially Figure 8-1)

As long as you're building stuff, make a Master Orifice so you can "test the tester".
http://rvplane.com/pdf/AC43.13-Chapter%2008.pdf
But note that while the concept as explained in the .pdf is valid, the actual orifice used in the Aircraft testing is too large to be of value for performance automotive engines--it allows too much leakage. A smaller Master Orifice is needed for our purposes. I'm told that a Holley main jet of a certain size works well...but I don't remember what size the jet is supposed to be. Perhaps #89?

I just bought a leakdown tester with a built-in Master Orifice; I use ~2/3 of the "allowable" leakage to be my limit for leakage (Less leakage than allowed for Aircraft engines.)
https://www.aircraft-tool.com/shop/d...ookieSupport=1
Comes with an 18mm spark plug adapter unless you request a 14mm adapter. Other size adapters also available.

 

Thankyou very much for the info
Jeff