63super88

I was gonna do some leak down tests on the engine today, I watched a bunch of tutorials and I think Ive got the process down, just never actually done it before. I know the cylinder being tested has to be top dead center, on compression stroke. I saw a guy use a long screwdriver or socket wrench extension and crank it until it fully rises then begins to fall, then ease it back to center. is this method reliable enough, if not what other ways are there? (I saw one with a vacuum gauge which I don't have)

chadman

You can just mark your damper every 90 deg. from TDC and use the timing pointer. Every 90 deg. one piston will be at TDC. Just follow the firing order.

MDchanic

1. Get a vacuum gauge. You need one. Everybody does. There is no excuse.

2. The goal when doing a leakdown test, as the "tutorials" may or may not have mentioned, is to have both of the valves closed. To that end, the exact position of the piston is not important, only that it is close enough to TDC on compression stroke that the valves are definitely closed.
If you have the valve covers off, then this is extremely easy, as all you have to do is be sure that the tension is off of the rockers (usually indicated by the pushrods spinning easily if you have hydraulic lifters).
If you have the valve covers on, then just turn the crank 90° at a time, starting at #1, and follow the firing order, one cylinder at a time.
To confirm the position of each piston, yes, sticking something in a spark plug hole and feeling for when it's at the top is adequate for a leakdown test (though not for timing the engine).

- Eric

edit: Chad, you beat me.

63super88

thanks fellas, I warmed up the car, added some fluids and am now letting it cool off a second so I could take out the plugs and let the pressure in the rad go down so I could take the cap off to listen. I understand the concept, getting the cylinders valves closed to check the pressure loss, and check the fluid holes/ exhaust/ open throttle carb for air leaks. I have actually been nervous and the real reason im jumping on this is because im noticing lots of watery green condensation under the filler/breather cap and in the pcv and am hoping its not a head leak (the oil looks ok I guess, but I had thought it was a bit funny and might of been contaminated with water so I dropped it and added 4 1/2 qts 5w 30 synth blend and a qt of marvel mystery.) I actually noticed that the element int he breather cap was dry so I oiled it up really good with motor oil got a nice film in the cap too, maybe it was letting in to much ice cold air into the tube and forming condensation (which is probably forming small water puddles in the oil)? hopefully if this is the case or even possible the oily foam element will screen some of this out and ill see a diff. ill be listening in on the rad cap for leaks, and might even go get a block tester fluid pump type kit which is pretty simple to operate ( long as no coolant gets in it to give a false reading) but that's later on if the problems persist or this test reveals something else. thanks for the tips and if theres anything else I should know about this test and such let me know!

63super88

welp I only got a chance to do the first cylinder before it started to snow, so im gonna open up a new thread about leakdown tests, but heres what I came up with. undid coil wire, set the timing mark to center which centered #1, got tester to read 0% then plugged it into the hose in the plug hole. what I found was strange I think, it read just above 20% in the green which seemed good, but I heard hissing through the oil filler hole and pcv. usually if theres a cracked cylinder or bad ring youd lose compression right? so then why am I hearing it? is it just typical wear around 95,000 miles?

Octania

The ring seal is never perfect. The rings have gaps, and there must be clearance of some sort between piston and ring and between ring and cylinder.

Hopefully the only place the leakage is observed is into the crankcase. The valves must form a perfect seal, and there should be no leakage to/from the cooling system of course.