Heads 3.0L V6 1992 Ranger

[Tom58]

I just put a set of rebuilt heads on my truck. I decided to check for leaks befroe putting the intake and exhaust on the engine. I put 80 psi of air into the cylinder through the spark plag hole. I can hear air and barely feel air in the intake and exhaust ports. The bleeds down from 80 psi to 30 psi in 7 seconds. It takes 17 to reach 0 psi. I have never checked a head or cylinder this way before. I no it won't retain the pressure for very long.

Does this mean the rebuilt heads are no good?

How long should it hold pressure?

Thanks for any help in advance.

Waiting for some infor before continuing work on truck.

 

[Haywire6000]

How are you putting air into the engine? Are you using an air compressor? IF so make sure that that cylinder is between strokes. The Cylinder should be at TCD(I think) so both valves are closed.

 

[Andy D]

I dunno about your method. I used to test heads by putting plugs in, turning the head upside down and filling the chambers with gas. If you were worried after you put the heads on, do a compression test. Get it running and hook up a vacuum gauge. Leak down test equipment is too much money for this shade tree hacker.

 

[RonD]

I think this was answered already?

Metal valves and metal valve seats are not air tight.
Metal cylinders, metal pistons and metal rings are not air tight.

So ............a cylinder will not hold air pressure, cold or hot.

If you want to test a cylinder for "leak down" then that is done with a compressor and a gauge.
Tested cylinder needs to be at it's TDC(compression stroke)
You set the compressor for a specific pressure, like 80psi or 90psi or 100psi and then test that it is 80psi, 90 or 100.
Now hook up the compressor with an inline gauge to the cylinder, if you start with 100psi and gauge reads 99psi then you have 1% leak down, if its 98psi the 2% leak down.
If you want to test the rings then add some oil to cylinder, rotate engine and then back to TDC for that cylinder, repeat test, this will tell you what % is going out the valves and what is going out the rings.

Holding pressure time after shutting off the air doesn't really "mean" anything, at least I can't think of any application for that data.
Fuel pressure yes, cooling system pressure yes, these were designed to be air tight, rubber and felt seals, compression fittings, ect....
Cylinders just were not, can not, be designed to be air tight, at 1,000deg not sure of a seal that would work.