Cylinder leak-down test procedure (with percentage gauge)

km7648 · #1 (**permalink**) 01-08-07, 09:54 PM

I've got a little smoke on start-up and before doing the anticipated valve stem seals, I wanted to be sure I didn't have any other problems.

Well I bought an engine leak-down test kit (with poorly translated instructions) but haven't been successful using it.

Do any of you know how to test using a setup like the one in the picture?

The left gauge show PSI and the right shows percentage loss. While it sounds easy enough, I'll be darned if I can find the right procedure anywhere (and I've looked).

So far, my engine is either perfect or totally pooched <grin>

**Ranger** · #2 (**permalink**) 01-08-07, 10:01 PM

What are you testing for? Head gaskets or burnt valves? What engine?

km7648 · #3 (**permalink**) 01-08-07, 11:12 PM

It's in a sand rail but from a 1996 Seville - a Northstar.

While I think the motor is OK, I wanted to be sure the smoke is the valve stem seals that I expect.

**Ranger** · #4 (**permalink**) 01-08-07, 11:23 PM

I don't see how that is going to tell you anything about valve stem seals. That is more for testing compression, rings & valve seats. You could also use the separate hose for a cylinder pressure test to check for bad head gaskets.

km7648 · #5 (**permalink**) 01-09-07, 12:54 AM

I "know" that I need valve stem seals and I don't need the leak down test to tell me that.

I just want to be sure that I don't need anything else.

I could still use help re. the proper usage of the leak down tool with a 2nd percentage gauge.

zonie77 · #6 (**permalink**) 01-09-07, 01:10 AM

Found these quickly.

http://members.boardhost.com/Mustang...160701958.html

http://vmaxoutlaw.com/tech/leakdown_tester.htm

http://www.tavia.com/08015_instructions.html

clarkz71 · #7 (**permalink**) 01-09-07, 10:41 AM

To be accurate, you need to regulate the supply air to 100 psi, then a 10% reading on the leak-down tester is actually 10 %. A leak-down tester will help determine if an oil consumption/smoking problem is valve guides/seals or rings. If you hear air coming from the oil fill hole in the valve cover, and the percentage of leakage is high, you have a ring problem. Likewise, if air is heard from the throttle body, intake valve, exhaust pipes, exhaust valve. You want to see all 8 cylinders within 10% of each other. To use this tester, you need to have the piston at TDC on the compression stroke.

km7648 · #8 (**permalink**) 01-09-07, 10:42 AM

Thanks Zonie77

My problem is with the style of gauges that I've got. The left one is a standard PSI gauge but the right one shows percentage of leak.

I'm just trying to figure out how to calibrate and use it.

The only links that I've found (and those you sent) show a PSI gauge on the left and right. Kinda' thinking I should buy one of those anyway...

clarkz71 · #9 (**permalink**) 01-09-07, 10:45 AM

The left gauge is the supply air, set the regulator to 100 psi. The right gauge is the percentage of leakage. IE: 50 on the gauge would be 50% leakage. (bad) You want to see no more then 20 or 30%.

clarkz71 · #10 (**permalink**) 01-09-07, 10:54 AM

Quote:

Originally Posted by Ranger

I don't see how that is going to tell you anything about valve stem seals. That is more for testing compression, rings & valve seats. You could also use the separate hose for a cylinder pressure test to check for bad head gaskets.

Larry, a leak-down tester puts air in the cylinder at a lower psi then direct shop air (120 psi or more). You can hold your finger over the fitting. It measures the percentage of air leaking past the rings & or valves. If the leakage is 20% or less and you have an oil consumption problem, you know it's the guides/seals. If it's high, 40% or higher, the rings are suspect. You'll also hear the air coming from the crankcase.

**Ranger** · #11 (**permalink**) 01-09-07, 12:27 PM

Understand that Clark. Just don't understand how it relates to valve stem seals. Shouldn't be any pressure there, right?

clarkz71 · #12 (**permalink**) 01-09-07, 12:34 PM

Right, if you don't hear air from the crankcase. If leakage is in specification (20-30%), and you have an oil consumption problem, it's the seals & or guides.

km7648 · #13 (**permalink**) 01-09-07, 01:13 PM

OK, I contacted the manufacturer and indeed, the instructions are in fact incorrect.

For those following this thread, the correct procedure is:

1) Bring the cylinder to be tested to top dead center, valves closed.
2) Thread the hose into the the spark plug hole.
3) Set the incoming air pressure to the tester at pressure 30-100 psi
4) Slowly turn the regulator on the tester until the percentage gauge reads "0". This calibrates the gauge.
5) Connect the hose from the cylinder to the tester.
6) Read the percentage of leakage on the gauge that previously read "0" when calibrated. This will be the percentage of leakage.

The instructions had step #5 before #4 and it made no sense to me.

*Thanks to those that offerered assistance.

clarkz71 · #14 (**permalink**) 01-09-07, 03:52 PM

Your gauge must be set up different then mine. Let us know what readings you get.

km7648 · #15 (**permalink**) 01-15-07, 11:26 PM

First, I did a compression test and for all cylinders got reading of 195-200.

Then I did the leak-down test and per the gauge, got readings right in the center of "low" leakage for all cylinders. The gauge indicates that the middle of "low" is about 30% OK for their gauge but lousy by other 100psi gauge tests.

I did each of these tests while the engine was at about 60 degrees so I understand these readings would be even higher/better if the motor was warm.

The attached photo shows the gauge dial face. You can read the numbers if you squint just right <grin>

Then to be paranoid, I cranked up each cylinder to ~80psi and listened for any leaks, hisses, gurgles in the coolant etc. and - nada.

Sounds like the motor is A-OK and I should go ahead with my valve seals and not tear down the motor?