Well, I was thinking that the videos I posted on this pretty much told the story but Brian (EuropaTC) suggested I post the results of my leakdown tester build so here it is.
I used some of the parts from the Harbor Freight leakdown tester: one pressure gauge and the hoses. I used an old Sears air pressure regulator I had lying around figuring it is of better quality than the one that came on the HF leakdown tester. I had to buy a 100 psi gauge to replace the gauge that didn't work. In addition to that, I had to get some brass plumbing parts such as a union, a 'T', and an adapter. Which size you get will be determined by your gauge, regulator, and hose.
Making the tester was pretty much as the videos say. I used JB Weld to plug up the union and got a #60 drill bit from a hardware store to drill the 0.040" hole in the JB Weld. After that, it was just screwing it all together. I used Teflon tape to seal the threads (and because it looks so professional) but I really have had better luck using silicone sealer for sealing threads for air joints. As I say, I used the hoses that came with my old HF leakdown tester but I think some of the nicer compression testers have similar hoses so you might want to buy one of those and trade hoses between them.
How to use it:
Take off the valve or cam cover so you can make sure the valves are closed on the cylinder you're testing and take out all the spark plugs. Rotate the engine so that the cylinder your testing is at or near TDC with both valves closed and put it in gear (or the air pressure might try to turn the engine). Screw the hose into the spark plug hole and make sure your compressor or other compressed air source is providing more than 100 psi. Plug the hose of the tester onto the hose in the spark plug hole and adjust the regulator so that your regulator gauge reads 100 psi. Read the second gauge and that is the percentage of air retention. It's that easy. You won't get 100 psi on the second gauge because there will be leakage out the rings. A reading below 80 psi on the second gauge is cause for concern. If you have your headers and carbs off, you can listen from the exhaust or intake ports to see if your valves and which ones are leaking. You might have a leak in your head gasket so check for bubbles in your header tank and air from your dipstick tube for leakage into the water or oil passages in the head and check for leakage to an adjoining cylinder for leakage through that part of the head gasket.
This is a very useful tool, it's inexpensive to make, and it's easy to use.
