i've suggested the use of this tool to several people lately, and though i had access to one, i didnt have my own. so i figure'd i'd build one and document it for you guys so you can build your own.
if you're working on your own engines, this thing is almost a must have in your garage. i've seen alot of guys condeming their engines, saying that they need a whole new engine for whatever reason. spending a couple dollars and building yourself one of these testers can save you hundreds of dollars very easily.
its a leakdown tester for those of you who dont know. basically its used to tell you how much compression you're losing in your engine, and will do a very good job of pinpointing where its leaking. it will also tell you if you're leaking an excessive amount, or an acceptable amount. if you've got a leaking head gasket (into the cylinder) you'll likely see bubbles in the radiator, valve you'll hear at the end of their respective ports(intake = throttle body or carb, exhaust = tailpipe) and rings you'll be able to hear (and perhaps feel) air escaping through the crankcase vents.
heres what you'll need...
1 spark plug pressurizing adapter
1 air pressure regulator (make sure it goes to 100psi output!)
1 air pressure gauge.
1 spark plug pressure adapter
1 Female air hose fitting
2 male air hose fittings
1 0-100 psi air pressure gauge w/ 1/8" NPT input (if your regulator comes with one, it can be used in addition to this gauge)
1 1/4" NPT tee fitting
3 1/4" NPT to 1/8" NPT reducing hex bushings
1 1/4" NPT pipe nipple
1 1/8" NPT grease gun hose
and a tube of your favorite epoxy
my parts all layed out.
i'll go through its build, and then get into the workings of it...
i started out with this...
its an adapter for your spark plug holes to pressurize the combustion chamber with the piston at TDC and both valves closed, allowing you to remove and change the valve springs, seals, etc. without removing the heads. i've had this for quite a while, and used it several times, so i figured i wouldnt canibalize it to build the leakdown tester, but make it a part of it while still retaining its original functionality.
i began by taking the pipe nipple and filling the inside of it with the epoxy.
after letting it harden i took a #60 drill bit (.040") and drilled a hole right through the middle of the epoxy. this is the heart of the tool, the airline restriction which makes it all work.
next install your restriction to the output side of the regulator.
in this pic i have already installed the tee fitting, which is the next step.
then install the hex bushings in the two remaining ports on the tee, like so.
next intstll your gauge to one of the ports that you just put a hex bushing in.
install the remaining hex bushing onto your grease gun hose.
then install your grease gun hose into the tester.
install the female air line fitting onto the end of the grease gun hose.
then plug in your spark plug pressurizer.
finally, install the male air hose fitting into the input side of the regulator.
COMPLETED!
now to use it...
bring cylinder to be tested to TDC, and ensure both valves are fully seated. now install your spark plug adapter. then simply hook the leakdown tester to the adapter. plug it in to an air supply, set the regulator to 100 psi (this is critical!). you'll notice your secondary gauge drop if you have leakage. dropping to 90 psi indicates 10% leakage, 80 psi = 20% leakage, etc.
generally an engine in good running condition wont leak down more than 5%, if it still runs decent with more leakage, the choice of what to do is up to you, run it or fix it... after 10%, its done, time for some major work.
one thing i will add is watch the cheap pressure gauges that often come with your run of the mill cheap regulators. the gauge that came with my regulator (a $20 TSC special) isnt accurate at all. even looking at the thing i can tell you that its crap. i'm planning on replacing it with another VDO gauge just like the one i have placed after the restriction. this is simply to verify that i still have my 100psi input pressure while testing a cylinder.