Small Engine Repair: Using a Harbor Freight Leak-Down Tester on a Briggs & Stratton Engine



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**Always follow the instructions in your repair manual when doing repair or maintenance work on Outdoor Power Equipment. Manuals can be found at the manufacturers website.**

This video is about how to use a Harbor Freight Leak-Down Tester on a small engine. I wasn’t able to get the tester to work correctly using the instructions provided with the tester, so I made one change, and the tester seems to work correctly. The instructions say to connect the tester to the engine before you apply compressed air and adjust the regulator, but it didn’t seem to work correctly, so I applied the compressed and adjusted the regulator before connecting the tester to the engine. This correction made the difference, and I was able to use the tester to determine the condition of the engine. It would be interesting to hear about other experiences with this tester, so please leave a comment, and thanks for watching.

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33 Replies to “Small Engine Repair: Using a Harbor Freight Leak-Down Tester on a Briggs & Stratton Engine”

  1. The Harbor Freight leak-down tester is useless. The tool has two fatal design flaws. A true leak-down tester is a differential pressure gauge. There are many web sites that explain how to easily make a true cylinder leak-down tester that actually works.

  2. @FuriousHondaBoy from PredatorOmnivore. it won't let me post a link just search to make your own leak-down tester you need to apply 100 psi to input, you need to measure actual pressure differential between two gauges. The HF tool only allows 15 psi as test pressure 520536-make-your-own-cyl-leakdown-tester

  3. yes, for a cylinder leakage test, aviation and automotive engine service manuals specify that you must be able to inject 100 psi into cylinder, however, the cylinder will not hold 100 psi because of normal leakage past the rings. So you inject 100 psi, but you measure the amount of pressure that the cylinder can hold. if the cylinder can hold 80 psi with a 100 psi input, then you have a 20% leak rate. ther are many web sites with long explanations. I have reported this defective tool to uscpsc

  4. BTW – You don't have to keep the pressure at your compressor below 100lbs. The regulator on the gauge should be able to handle up to 200 lbs + at the input, as long as you don't dial in more than 100 lbs; actually 15 lbs, because the second gauge maxes out at 15 psi.

  5. Same tool as mine. What do you call the input connection was different from my other air tools. I ended up holding it by hand. My output valve leaked as well when the pipe was disconnected. Nice that it does not move the crank even if it is not at tdc. Had to repeat the test a few times as the calibration is not very stable.

  6. If you just had the spark plug hole adapter hoses that you could plug your air compressor into couldn't you just use that and listen for how bad the leak is and where it's coming from to diagnose the engine? Do you really need the gauges? Great video by the way.

  7. Leak down test is more thorough, accurate and honest test than compression test alone. Sometimes compression test can be normal but leakdown will show that it is leaking down compression.

  8. Introducing cold air into a hot engine can warp or fracture
    valves and/or other engine parts. Always test a cold engine. A standard compression test is done with a warm engine.

  9. Nice video, this tool would be good for small engines with automatic compression release like the kohler k engines. A compression tester doesn't cut it then.

  10. Thanks for the info on the Harbor Freight tester. even though it may not be 100 % accurate it will still pinpoint the leak. My tester is an ADT brand (USA). Really nice tool and gauges. .

  11. That's an excellent summary and review of the equipment. It took me a while to understand how this works. I was a little puzzled why they didn't label the second gauge with units of pressure. That's all it is! Simply, there is a small orifice separating two chambers, each connected to a pressure valve. When the first chamber is filled, the air slowly flows through the orifice into the second chamber and the second pressure valve responds to the increase in pressure. It's understandable there may be a small delay, for air to get across and equalize pressures in the two chambers. Then when the second chamber is attached to the cylinder, the pressure in the second chamber falls. If the cylinder has an external leak, pressure falls a lot and the gauge measures the big drop down into the red zone. Because the orifice restricts flow from the compressor, air can't flow fast enough through the orifice to restore a drop in pressure. So, it becomes a competition between the resistance to filling through the orifice vs declining pressure out the external leak. In that sense, it's exactly analogous to a voltage drop test when testing electronic circuits. A big drop across the known resistance of the orifice means there is significant flow, caused by a downstream air leak….

  12. What if your engine does not have any pressure loss when you do a leak down test? I have a Briggs 17.5 HP OHV that I did this on and did not indicate any pressure loss at all. I understand that this is not normal, if so do I have the valves adjusted incorrectly? Thanks again.

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