leak down test - how to?

[Alan L]

I've searched the threads, and found lots of numbers and diagnoses. But what I'm looking for is the info on how to do a leak down test. I may be wrong, but I am under the impression there are two techniques. One measures the pressure drop over a period of time, and one measures the gas flow to maintain a pressure?
What is required in terms of equipment to do these, and is one right/wrong, or will either do.
Thanks
Alan

[304065]

Alan,

This is well covered in the archives but it might be worth a reprise here.

First, obtain required tools.

Spark Plug socket-- factory "spring" type or HAZET

10mm Hex bit and 3/8" drive ratchet to remove plugs

Air compressor

Leakdown tester

Leakdown adapter such as Stomski SR031 or HAZET 3428, this is long enough to stick down into the spark plug hole through the valve cover. If you try to use the 14mm adapter that comes with the tool, it will work fine, but it's hard to get it seated because you have to tighten it using the rubber hose instead of the metal part of the adapter. Guys have adapted old spark plugs to the same jobs, more work but cheap.



22mm socket from toolkit for fan pulley nut-- used to rotate engine CLOCKWISE only

"Whistle" attachment for finding TDC on the compression stroke. I know that you should be able to do this by aligning the Z1 mark with the notch in the blower housing while the distributor rotor points to the notch in the distributor body. This is the ignition point and should roughly correspond to the static distributor timing, you get it in the ballpark and then set it to TDC by turning the crank pulley. I use the whistle instead, turn the engine until the whistle stops and that's the end of the compression stroke, line up the pulley mark with the notch in the blower housing.

Procedure. Peformed on a WARM (not hot) engine.

1) Start compressor

2) Remove all spark plugs

3) Turn engine to #1 TDC

4) Insert compressed air adapter, do NOT destroy the aluminum threads!

5) Set leakdown tester to zero with air supply DISCONNECTED. This should result in an air pressure around 35 PSI. Do NOT send all 150 PSI into the cylinder, it's too much. Also, BE CAREFUL THAT WHEN YOU CONNECT THE AIR SUPPLY YOU FIRMLY KEEP THE ENGINE FROM ROTATING. The engine could begin to rotate and the wrench could fly off the pulley and hit you in the Jaw, leading to infection and death (old Charles Kettering reference)- at a minimum it will throw off the reading.

6) Note reading. If it's reading zero, you probably bumped the valve open, so rotate the engine back until the hissing stops and the gauge reads the leakdown. Record reading.

7) Next cylinder. Follow firing order to save time, 1 6 2 4 3 5

8) Repeat measurements.

Good:


Bad:


Cause:


The most important thing besides the leakdown percentage is WHERE the leaking is coming from. Carbs or induction system: Intake Valve leak. Tailpipe: Exhaust Valve. Crankcase breather: Rings or pistons.

Don't ever believe someone who tells you they can't localize the source of the leak.


Did I leave anything out?

[Alan L]

Many thanks. I searched about 20 pages of search thread, but could not find this.
Plenty to go on with. Any suggestions as to how to lock the engine? Will the fan pulley be enough?
Will poking something down the plug hole be sufficient to find TDC?
Regards
Alan

[BoxxerSix]

Great post. On older motors I tend to use a little dab of copper anti seize on the spark plug adapter oring. I do this as some older motors tend to have a bit of corrosion or burnt-on debris down in the head that can disrupt the little oring from sealing and causing a small leak which throws the readings off a bit. The anti seize helps the adaptor seal a little better I use copper anti seize as it doesn't affect spark current on the plugs when reinstalled. WD40 is an alternative as it too doesn't affect electrical current if left behind on the spark threads.