Leak Down Procedure (Pic Heavy)

Small Block Mopar Engine

  1. seabee

    seabee FABO Gold Member FABO Gold Member

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    Did a leak down test on the 273 today and took some pics on how I did it for the next guy that searches it. Please add any , corrections, advice, or tips.

    1. Find Top Dead Center on Piston #1. I used a piston stop to make sure the balancer hadn't shifted.
    [​IMG]
    [​IMG]

    Using a small level I made horizontal and vertical marks:
    [​IMG]
    [​IMG]

    Each 1/4 turn of the crank will put the next cylinder in the firing order at top dead center. Firing Order: 1 8 4 3 6 5 7 2
    [​IMG]
    [​IMG]

    Next I checked the gap (solid, non hydraulic lifters) to make sure the valves were fully closed. I could also just remove the rocker arms completely.
    [​IMG]

    Then I used the piston stop on the cylinder opposite the firing order to prevent the crank from turning under the air pressure. Opposite pistons: 1:6, 2:3, 4:7, 5:8
    [​IMG]

    Then Applied 100PSI to get the first reading. Number 8 cylinder is losing 20%.
    [​IMG]

    Then I put the spark plugs into the neighboring cylinders to help rule out a head gasket breach between cylinders.
    [​IMG]

    Next I use a piece of hose to my ear and listen to locate where the 20% of air is going to.
    Carb: Intake Valve
    Exhaust:Exhaust Valve
    Dip Stick (Crankcase): Past the piston rings (Normal)
    Radiator: Cracked head or cylinder wall.

    I wrote down all the results:
    [​IMG]

    Might be time for a rebuild, what do you think?
     
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    • Abodybomber

      Abodybomber Breaking street machines , since 1983.....:) Legendary Member

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      Nice idea,See bee. Hopefully a mod will sticky it.....
       
    • adiffrentcity

      adiffrentcity Bent Rodder

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      x2!
       
    • Daves69

      Daves69 Well-Known Member

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      Curious, what's up with the retainer next to the valve you're checking gap on?
       
    • seabee

      seabee FABO Gold Member FABO Gold Member

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      The spacer shims? (circular thin washers)
       
    • 67Dart273

      67Dart273 FABO Gold Member FABO Gold Member

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      Only thing I know to add:

      With valve gear in place, you must check piston at TDC. If you have something like a rough/ cracked cylinder wall, this wont' show up. Better to run at TDC, then pull rockers and run again all cylinders at BDC

      Also, this test will show different results hot and cold.
       
    • Daves69

      Daves69 Well-Known Member

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      On the on the spring retainer, runs around the top. What is that?
       

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    • seabee

      seabee FABO Gold Member FABO Gold Member

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      Marks from manufacturing I guess. Several of the retainers have them, which is why I didn't notice.
       
    • 4spdragtop

      4spdragtop CONGRATS NORTH AMERICA! FABO Gold Member

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      Del, just curious as to what the difference would be BDC vs TDC?

      Great thread, thanks Seabee!
       
    • Rocket

      Rocket FABO Gold Member FABO Gold Member

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      Question. Is the test performed when the engine is cold or after warming to operating temperature?
       
    • Norway-dart

      Norway-dart Well-Known Member

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      usually you get a VERY good Reading @ BDC, because the cylinder isnt worn in that area!
       
    • Tech857

      Tech857 Well-Known Member

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    • mech1nxh

      mech1nxh CUSTOM TITLE FABO Gold Member

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      First, excellent post ! THX added.
      Second, I (with Your permission Sir). would like to add an note on the hot/cold test
      parameters.
      Pistons are, always have been, and always will be of an 'cam ground' design--- read the larger mass across the pin bosses , when heated, 'pulls' the smaller mass of the casting/forging into a circle.

      Apologies, suffice to say, do the test no more than 10 min after normal operating temp has been reached.

      Now Sir on to My humble answer on Your rebuild 'Q'.


      Left bank total % = 56.
      Right bank total %= 60.

      total variance 4%...bank to bank anyway. further,

      #1-#2 delta , 4%.
      #3-#4 delta , 4%.
      #5-#6 delta , 5%.
      #7-#8 delta , 1%.

      'Delta' an term used for 'total' overall engine 'sealing' health. as it were.

      In Your case Sir 14% total delta = changing #8 when it oil fouls, probably
      after 3-4k miles

      Thx to the board for My long winded reply !!!!
       
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