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Leakdown testing explained in depth
Posted 11 March 2004 - 10:23 AM
First you need a leakdown tester. There are 2 types: One and Two gauge. Either will work, they are both equal. The two gauge one simply shows line pressure (from your compressor or air tank, and it isn't vital. Two gauge testers abound on ebay, they are about $70, i bought a used Snap-on one for about $40.
First, You need to get whatever cylinder you are going to test on Top dead center, both valves closed. It's fairly important to get the piston near the top of the bore, as this is where most of the wear is, and it's more accurate. It might be easier to take the valve cover(s) off so you can see the valves working. Pop the radiator cap (if it's a H/g, you don't wanna blow up your heater core/radiator if pressure gets into the cooling system.. Plug the tester into a source of compressed air, and zero the gauge. A line screws into the spark plug hole, with a quick connect hooking to the gauge. Connect the two. Hold the crankshaft so it doesn't turn. Read the gauge.
2% or less-race engine quality ring seal
under 20% Reasonable. You shouldn't see any problems
over 20%- um, there is some wear, or leakage, or something.
With compressed air in the cylinder, if there is a leak, then you can pinpoint it. If it's a h/g leak, bubbles should form in the coolant. If your rings are worn the hell out, you can hear air coming out of the dipstick tube or open valve cover. Intake valve leak- You can hear a change inpitch if you open and shut the throttle. You can put your ear over the intake.
Exhaust valve leak- you can hear air coming out of the tailpipe.
You can do this test in a junkyard if you bring a full air tank and work quickly. Only 30psi (approx) enters the cylinder, and if it doesn't leak too much, you should have more than enough air, maybe enough to do a V8.
Mods- i'd like to submit this to the Repair Manual. And If someone want's to link it to the new Gen Forum, or the Alliance Board, Or wherever else, fell free.
Posted 11 March 2004 - 11:43 AM
Posted 11 March 2004 - 04:48 PM
Posted 11 March 2004 - 04:53 PM
Posted 11 March 2004 - 05:26 PM
Besides, the thing I wrote was how to use the leakdown tester, not how to avoid using one.
That wasn't meant to sound harsh.
I've done it with just compressed air.
It IS nice to have quantifiable numbers, though.
Posted 11 March 2004 - 07:04 PM
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