leak down test

[flyinlow]

Did a leak down test on my 446 . Cold engine. No way you can get the plugs out hot.    48 K. miles on engine. SRP lightweight forged pistons/rings  and + .030  .Eddy heads. Plugs looked normal. Engine runs well. Uses /leaks a quart of oil every 2000 miles. On cold start some piston noise is heard with the hood open, disappears in a couple minutes. Has always done this.

Jegs basic tester. It recommends warm engine. I recommend skin on fingers.

#1   100/91
#8   100/82
#4   100/92
#3   100/82
#6   100/82
#5   100/88
#7   100/84
#2   100/88

No air leakage was heard thru the throttle body or tailpipes  on any cylinder.  slight air leakage thru breather on all cylinders. Was expecting 90+  (less than ten percent leakage) How much change would a warm engine make?

[cdr]

A hot engine will make of difference, I would run what you have !!!!  

[flyinlow]

Did a cold Compression test .  170 PSI +/- 5 psi all cylinders.  Again not sure how much being cold effects the readings. I can't find any numbers from a test on I did warm on the three plugs you can get out after about an hour . This was done when the engine was first build. I was thinking about 175-180 psi.

I looked in four of the cylinders with my Milwaukee inspection camera. (more for home inspections rather then a bore scope) Some carbon deposits on the pistons and cylinders above the ring travel. The side of the cylinders opposite the plug hole had some minor scoffing. Do short skirt forged pistons do this? Crosshatching was still visible.

I am doing this in preparation for a thrust bearing repair attempt. The cylinders while not great,  appear to be serviceable .

[c00nhunterjoe]

Readings will vary alot cold to hot. You cant get any plugs out hot? The piston noise that goes away once warm shows you how much things expand with heat. Im betting your numbers will be acceptable on a warm engine. The 90s will be 95s and the 82s will probably be mid 90s. Cold engine doesnt have any oil film on the cylinder walls either.

[flyinlow]

Two plugs (7& could be removed . When I get it back together after trust bearing/ oil pan replacement I will try those warm and compare.

[elacruze]

The most important consideration while performing leakdown is that you are very careful to seat the rings to the bottom land in the ring groove. To do that, you *must* be moving the piston towards TDC last thing before the test. Even a tiny reversal will unseat the rings, and if they're in good shape they'll have enough friction on the cylinder walls that the air can't blow them back down on the land. So if you're not absolutely certain, re-test. After that, give a shot of WD40 in the plug hole, run the piston around a lap and test again. With oiled cylinders, wait at least 10 seconds to see if the reading falls any which it will if it's blowing the oil out.

With short-skirted, wide-clearance forged pistons the rings aren't held as squarely to the walls as with a stock piston, so I expect a couple percent just on that data. You can rock the crank back and forth a few degrees and watch the reading, sometimes you can seal it up significantly better than it finds that first time.

If you really want to be thorough and have a helper to hold the crank, check the leak at ~20* ATDC. That's about where peak cylinder pressure should happen.

If you have any carbon build-up on the valves or pistons that will also reduce a static leak test- go out and thrash it good and re-test again.