Leak Down Procedure (Pic Heavy)

  1. seabee

    seabee FABO Gold Member FABO Gold Member

    Messages:
    2,488
    Likes Received:
    657
    Joined:
    Dec 20, 2009
    Location:
    Bonita, CA
    Local Time:
    4:46 AM
    seabee submitted a new Article:

    Leak Down Procedure (Pic Heavy)

    Read more about this article here...
     
    Last edited by a moderator: Oct 26, 2016
  2. Abodybomber

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

    Messages:
    30,853
    Likes Received:
    10250
    Joined:
    May 21, 2011
    Location:
    Arroyo grande ca
    Local Time:
    4:46 AM
    Nice idea,See bee. Hopefully a mod will sticky it.....
     
  3. adiffrentcity

    adiffrentcity Bent Rodder

    Messages:
    303
    Likes Received:
    12
    Joined:
    Feb 17, 2013
    Location:
    Smyrna TN
    Local Time:
    6:46 AM
    x2!
     
  4. Daves69

    Daves69 Well-Known Member

    Messages:
    6,038
    Likes Received:
    4565
    Joined:
    Feb 20, 2011
    Location:
    WestOfChi
    Local Time:
    6:46 AM
    Curious, what's up with the retainer next to the valve you're checking gap on?
     
  5. Oklacarcollecto

    Oklacarcollecto Life is an experiment

    Messages:
    17,036
    Likes Received:
    297
    Joined:
    Mar 13, 2009
    Location:
    North Central Oklahoma
    Local Time:
    6:46 AM
    Done.
     
  6. seabee

    seabee FABO Gold Member FABO Gold Member

    Messages:
    2,488
    Likes Received:
    657
    Joined:
    Dec 20, 2009
    Location:
    Bonita, CA
    Local Time:
    4:46 AM

    The spacer shims? (circular thin washers)
     
  7. 67Dart273

    67Dart273 FABO Gold Member FABO Gold Member

    Messages:
    51,424
    Likes Received:
    20378
    Joined:
    Oct 14, 2010
    Location:
    Idaho
    Local Time:
    4:46 AM
    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.
     
  8. Daves69

    Daves69 Well-Known Member

    Messages:
    6,038
    Likes Received:
    4565
    Joined:
    Feb 20, 2011
    Location:
    WestOfChi
    Local Time:
    6:46 AM
    On the on the spring retainer, runs around the top. What is that?

    Leak Down Procedure 7-1.jpg
     
    Last edited by a moderator: Oct 26, 2016
  9. seabee

    seabee FABO Gold Member FABO Gold Member

    Messages:
    2,488
    Likes Received:
    657
    Joined:
    Dec 20, 2009
    Location:
    Bonita, CA
    Local Time:
    4:46 AM
    Marks from manufacturing I guess. Several of the retainers have them, which is why I didn't notice.
     
  10. 4spdragtop

    4spdragtop CONGRATS NORTH AMERICA! FABO Gold Member

    Messages:
    32,426
    Likes Received:
    13528
    Joined:
    Aug 28, 2009
    Location:
    Wasting time here
    Local Time:
    6:46 AM
    Del, just curious as to what the difference would be BDC vs TDC?

    Great thread, thanks Seabee!
     
  11. Rocket

    Rocket FABO Gold Member FABO Gold Member

    Messages:
    2,288
    Likes Received:
    381
    Joined:
    Apr 22, 2005
    Location:
    U.S.A.
    Local Time:
    12:46 PM
    Question. Is the test performed when the engine is cold or after warming to operating temperature?
     
  12. Norway-dart

    Norway-dart Well-Known Member

    Messages:
    146
    Likes Received:
    13
    Joined:
    Oct 6, 2009
    Location:
    1 hour south of oslo
    Local Time:
    1:46 PM
    usually you get a VERY good Reading @ BDC, because the cylinder isnt worn in that area!
     
  13. Tech857

    Tech857 Well-Known Member

    Messages:
    188
    Likes Received:
    40
    Joined:
    Jun 29, 2012
    Location:
    NH
    Local Time:
    7:46 AM
  14. mech1nxh

    mech1nxh CUSTOM TITLE FABO Gold Member

    Messages:
    5,432
    Likes Received:
    2749
    Joined:
    Jan 20, 2009
    Local Time:
    4:46 AM
    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 !!!!
     
    • Like Like x 1
    • RLF Cuda

      RLF Cuda Barracuda Bob

      Messages:
      81
      Likes Received:
      14
      Joined:
      Jan 7, 2012
      Location:
      Aurora, CO
      Local Time:
      5:46 AM
      A low cost leak down gauge can be built from two 0-100 gauges, a pressure regulator, and a plug between the gauges with a 0.040" hole. This is what the piston engine aircraft rebuilders use to check leak down.
      It can also be used to check manifold leaks by pressurizing the intake. You will need to make a plate to cover the carb side of the manifold and tap for a fitting. Pressurizing the intake and using the leak down gauge will help identify if there is an intake leak and where it is. You will need to remove the rocker arm assembly to make sure all intake valves are closed.
       
    • jimjimjimmy

      jimjimjimmy lobsterman FABO Gold Member

      Messages:
      4,706
      Likes Received:
      1558
      Joined:
      Nov 2, 2010
      Location:
      p. e. i.
      Local Time:
      8:46 AM
      pressurizing the intake you would be able to check the condition of the valve guides and check if there was any leaks from cnc porting also?
       
    • 67Dart273

      67Dart273 FABO Gold Member FABO Gold Member

      Messages:
      51,424
      Likes Received:
      20378
      Joined:
      Oct 14, 2010
      Location:
      Idaho
      Local Time:
      4:46 AM
      ..............Hmmmmmmmmmmmmmmmmm.......... Now there's one I had not thought of..........

      Might be better, though, to come up with a vacuum tester rather than high pressure.. Not too sure the intake gaskets would reliably hold 100 psi, and certainly not something like the "bottom pan" design of the magnums.
       
    • jimjimjimmy

      jimjimjimmy lobsterman FABO Gold Member

      Messages:
      4,706
      Likes Received:
      1558
      Joined:
      Nov 2, 2010
      Location:
      p. e. i.
      Local Time:
      8:46 AM
      I was thinking in the 25psi range like the amount of a good turbo ?
       
    • Hipo65

      Hipo65 Yeah I'm "That Guy"

      Messages:
      646
      Likes Received:
      51
      Joined:
      Aug 9, 2013
      Location:
      Lincoln Nebraska
      Local Time:
      6:46 AM
      So how much difference will there be (avg) in hot vs cold? I ask because my very fresh & very strong running 273 with no oil usage whatso ever cold has rite @ 20% (cold). I checked it only to compare with my 60 hp mercury outboard as a "new motor"base line. Out board (cold) was the same 20% using the matco dual gauge set up in carcraft mentioned above. Is there that much diffrence hot vs cold? The 273 runs flawless plenty of power no oil usage at all & keeps oil clean.
       
    • 67Dart273

      67Dart273 FABO Gold Member FABO Gold Member

      Messages:
      51,424
      Likes Received:
      20378
      Joined:
      Oct 14, 2010
      Location:
      Idaho
      Local Time:
      4:46 AM
      X2 I would think so
       
    • AJ/FormS

      AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

      Messages:
      21,732
      Likes Received:
      8967
      Joined:
      Jan 19, 2014
      Location:
      South-Central Manitoba,Canada, 900ftelevation
      Local Time:
      6:46 AM
      I've done them hot and cold on fresh engines with little measurable difference.But we are talking numbers in the zero to 3-4 percent!

      On a used engine, there is a possibility for the pistons to be slightly cocked in the bore,due to the earlier mentioned cam-ground design,(post #13) which would tip the rings ever so slightly, and allow them to leak.Further more,with the cold used pistons, the worn ring faces may not be flat in the worn grooves, or centered on the piston, or there could be carbon involved or huge ring gaps.

      However the amount of leakage is a concern. Here's a quote from Smokey Yunick talking about leakage over 8%.
      " This doesn't sound like very much to worry about,but you have to remember that only 1/3 of the heat energy(pressure) developed by each cylinder is actually going to push the piston down. So, if 8% of the cylinder pressure is leaking away, you are theoretically losing 24% of the recoverable flywheel horsepower."
      He goes on to say that around 5-8%, should be considered rebuild time.
      If your tool is truthful...........There is a problem!
      ------------------------------------------------
      2-cycle outboard engines are a whole different animal. These engines are cooled by sea/lake water. They go from idle to full load-WOT, and back. They spend huge amounts of time at full-load WOT. To cope with this abuse the pistons are laughably loose in the bores. When cold, there is no way to keep the pistons from rocking, and thus no way to keep the rings in full contact with the cylinder walls. I'm not surprised to see 20% leakage on an outboard. They also have huge head chambers and low compression, due to the 2-cycle design.They make power because they fire twice as often as a 4-stroker, and usually operate in a very narrow rpm band, allowing the designer to optimize the port layout.
       
    • Hipo65

      Hipo65 Yeah I'm "That Guy"

      Messages:
      646
      Likes Received:
      51
      Joined:
      Aug 9, 2013
      Location:
      Lincoln Nebraska
      Local Time:
      6:46 AM
      I checked the motor on my very low hours go-devil mud motor (v-twin vanguard briggs) same deal it's saying 18%! That gauge set has got to be goofy! It's saying that my 273,my merc & my mud motor are all worn out! It's gotta be the gauge set! I havnt had eny thing ever read better than 18%! None of the them burn oil have great power. As for the 60 hp merc (or any 2 stroke) ring seal is a MAJOR factor in how they will run mainly @ idle. Without good ring seal it will not have the power/vacuum to draw in the next air/fuel charge. Until the Rpm is higher to cover it up. Like I'm thinking my gauge set has got to be somthin wrong with it. The big gauge when set is 25-30 psi it seems alot lower than any other set I've seen before. So it's putting in 25-30 psi & loseing 18-20% of that. The 273 is a year old with apx 3000 miles on it & runs great!
       
    • Hipo65

      Hipo65 Yeah I'm "That Guy"

      Messages:
      646
      Likes Received:
      51
      Joined:
      Aug 9, 2013
      Location:
      Lincoln Nebraska
      Local Time:
      6:46 AM
      I think after doing some resurch that I'm getting diffrent readings is becouse of the psi my gauge set is testing @. His is testing from the more common 100 psi. Mine is testing from 25-27 psi! I bet of I get a gauge set that tests from the more "standard" 100 psi my % goes waaaaay down!
       
    • 67Dart273

      67Dart273 FABO Gold Member FABO Gold Member

      Messages:
      51,424
      Likes Received:
      20378
      Joined:
      Oct 14, 2010
      Location:
      Idaho
      Local Time:
      4:46 AM
      Even at 100 psi, gauge readings are not going to "compute" very well from gauge to gauge, as there are variables. What you need to do is to get clear back to the ORIGIN of leak down testing

      These are sometimes called "differential pressure testers" and reference is made to a "master orifice tool"

      7ts0.com/manuals/continental/Service%20Bulletins/MB%2084-15.PDF

      Originally, the orifice........which is the key to the whole deal.........was a precision flowed orifice, not just a sharp cornered, rough drilled "somewhere around" .040" hole, with internal flaws and of unknown length, friction, and flow characteristics.

      This thing is claimed to be such an orifice

      http://www.skygeek.com/aircraft-too...aign=froogle&gclid=CN6AxsDP0cgCFRSEfgodcEEGQA

      If you google the part no. in the pdf for the master orifice, it seems to be "unobtainium"

      https://www.google.com/search?num=2....0....0...1c.1.64.serp..4.23.1325.oYwL9Vgm65M


      A little 'bit from the FAA

      http://www.avweb.com/news/savvyaviator/188758-1.html

      and yet more

      http://www.vansairforce.com/community/showthread.php?t=94870
       
    • 67Dart273

      67Dart273 FABO Gold Member FABO Gold Member

      Messages:
      51,424
      Likes Received:
      20378
      Joined:
      Oct 14, 2010
      Location:
      Idaho
      Local Time:
      4:46 AM
      The other factors which are probably going to have some effect on readings..........even from the same engine using the same tester.......

      Temp, humidity, weather conditions.

      Are you using dry air, or an air compressor?

      Certainly, any other pressurized gas is going to give skewed results. CO2, EG is WAY more dense than is N2 or compressed air.
       
    1. This site uses cookies to help personalize content, tailor your experience and to keep you logged in if you register.
      By continuing to use this site, you are consenting to our use of cookies.