leakdown results!!??

[dude]

Just pulled the engine from my 82 SC, this winter for a tranny O/H.
Out of interest, did a leak down test as I thought the car was getting weaker over the last few months prior to storage.

A borrowed tester with no directions, but used 72 psi on the first gauge, got 74 on the second gauge. Cyl 456 all same results. Cyl 123 all leaked alot, seems to be head gasket area - can feel the air whistling out. Further investigation - found a head barrel nut on the #2 cyl just lying around under the valve cover. I've replaced all my studs last year with steel, studs are good, re rung the engine as well and it ran well. Everything was triple checked at assembly so why the loose nut? Can this cause all three cyls to leak at the head gasket? Elapsed mileage since last years work roughly 8000 miles.

Now, what can I expect when the heads come off???/ Other than more dough to spend.

[Wayne 962]

Head stud lying there typically means broken head stud. However, the steel studs *just do not break*. Never seen one break - I don't think John Walker has either. I've never heard of one breaking.

2nd thought is that they weren't torqued down properly, or weren't installed with red Loctite in the case.

Did you retorque your heads after the rebuild last year?

-Wayne

[dude]

No I did not. To clarify, the nut was just that, the nut. The studs are still fine, and I did install them w/ red loctite. So, I'll go get my torquewrench calibrated for this go around, and do a retorque. How long after for a re-torque do you recommend?

The engine never seemed to sound different could the leak go away with heat as it warms up?

[Rot 911]

Are you sure you were at TDC on each cylinder you checked? If not, a valve can be open and you will hear all kinds of air whistling around.

[Grady Clay]

Hey Dude (no pun intended),

Kurt and Wayne are right on with their advice.

A Cylinder Leakage Tester is one of the best diagnostics for the mechanical performance of an engine. A cranking compression gauge (one that screws into the sparkplug hole) is useful also but tells you different things and should be used as secondary to a leak tester. The other really good instrument is a bore scope that fits the plug hole and will fit past the open valves.

Some cylinder leak test basics:

The test is done with low pressure compressed air, say 5 PSI, and the tool measures the small amount of air flow. The tool has a regulator that brings shop air pressure (70-200PSI) down for safe use.

The test is done on each cylinder in firing order sequence with that piston at TDC compression. I take that plug out only when the piston is in place as some carbon on the plug could get under the exhaust valve and prevent an accurate measurement. The piston has to be at exactly TDC as the compressed air can turn the engine. Don’t leave a wrench on the crank bolt and be prepared for the engine to inadvertently spin.

The beauty of this test is that it both tells you if there is a problem and, if so, where the problem is. My gauge reads from 0% to 80% air flow. I disconnect the gauge from the engine and set the regulator to 0%. I then reconnect to the engine (it has a homemade screw-in-the-head quick disconnect to fit 911) and take a measurement. I disconnect and re-connect to take several measurements and to insure the “zero” hasn’t changed.

On my particular instrument, a normal, perfect running, best-you-can-get reading is about 1%. Most read 1-2%. That is all past the rings (you put your ear to the oil filler.) If I get readings approaching 4% past the rings, I put the plugs in and drive on the highway for a while and then re-test. If the numbers come back down, to say 3% or less, I know it need to be driven more.
If there is any detectable leakage past the valves (you put your ear to the intake and exhaust), again go drive the car on the highway and re-test. If there is still leakage past a valve then measure the valve clearance next. If it has opened up since your last valve adjustment or is much looser that the other valves, the next place to look is something between the valve and the seat or UGH a bent valve. I have had skilled mechanics tell me that when they get to this point they hammer on the rocker adjusting screw while pressure is on the cylinder. I don’t like that approach but some seem to think it works.
If there is any leakage past the head gasket, stop and torque the head nuts. If you find one (some) that turn to take torque, note which ones, and test drive, and re-torque. The critical issue here is they need to hold torque, particularly on mag-case engines.

Some put shop air to a cylinder. I don’t think that is ever a good idea. A 100mm cylinder and 125 PSI air is putting 484 pounds force on the static piston and trying to lift the head by the same amount or more. You do the math.

FYI, I have two archaic (circa ‘60s) Sun Electric Corporation, Model 228, Cylinder Leakage Testers. They work great, are repeatable and agree with each other within their resolution (about 0.2%). I went on line and tried to find the company to no avail. I’m sure they have long since been bought out.

What are the current good testers?

Best,
Grady

[dude]

Well crew - lesson learned. Bad leakdown test was the result of failure to spend the money a Porsche adapter so I could use my engine stand last year. This led to assembly of my motor lying on the bench. I must have bumped the head gaskets somehow as I put the head on. (I left the cams intact so 3 heads, etc went on all at once.). Gravity no doubt acted upon said gaskets, they got a bit out of their groove and now will be replaced.

Learn from my mistake gentlemen!

Now, if i have a shop clean up the sealing area on the head and cyl tops, do I machine the other side an equal amount? It doesn't leak, and so far I have not disassembled it. What's the max that can be removed without fear of impinging on valve/piston clearance?

Somber dude.