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cylinder leak down pressure

Discussion in 'Mechanic and Repair' started by bbahun, Nov 19, 2007.

  1. bbahun

    bbahun LawnSite Member
    Messages: 31

    I have a couple of questions about checking the compression on an engine using a leak down tester.

    1. How much pressure do you adjust the regulator on the tester to?
    2. What is the best way to hold the engine at TDC when adding the pressure?
    3. What is an acceptable percentage of loss on both 2 and 4 stroke?

  2. tomo

    tomo LawnSite Senior Member
    Messages: 660

    hello ,r u using the single guage type or a twin guage type ??

    In the simple form a single guage type has a regulator then a guage then a ball valve then a hose to a spark plug fitting .
    Set the regulator to 100 psi and open ball valve [hose connected to cylinder ]the needle should only drop 2--4 psi .Over 5 psi, there is an issue some where in engine .

    The off the shelf leak down units have instructions .Typically they r set at 100 psi also at this point u have to zero the the leakage guage and then connect to engine . Open the tap etc and hey presto u have a reading . The twin guage type have a regulated orifice feeding the second gauge and therefore they only function as per there maker intended . U need the instructions !!! On my particular guage allowable leakage is up to 10-15 % .My own engine reads 5--10%

    It is not always required to lock the engine ,but if u have to the OEM typically has a tool or u can fabricate a tool .

    2-4 r most likely going to be similar . On 2 strokes a dedicated compression guage will give a good indication .[the 2 stroke guages i have seen are small compared to a automotive type ,mainly 4 accuracy small internal volume ]
    I have never done a leak down test on a 2 stroke ,generally the machines i have had, have been worn out in all the other areas also --replacement is the easy answer

    Remember a leak down test is only an indication not a hard and fast result . Eg A piston typically has 3 x rings ,some times the oil ring may be worn out but the compression ring ok .This situation will give false readings on your test guages . Most likely the first symptoms of rings starting to fail .

  3. bbahun

    bbahun LawnSite Member
    Messages: 31

    Thanks for the info Tomo. I have a Thexton guage with two guages on it. It has some instructions but they did not cover everything. Thanks again.
  4. fixer67

    fixer67 LawnSite Silver Member
    Messages: 2,098

    This is for the one from Kohler but it should help.

    Leak down tester.JPG

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