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  1. #1
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    How to do leak down test on a 2.4 EFI

    Hi there, I am hoping someone can explain how to do a leak down test on a 1989 Bridgeport 2.4 EFI.

    I have watched some videos and the procedure does not seem to always be the same. Some talk about finding top dead center and others state you must seal off the exhaust and intakes. How would you do that on a six cylinder? I am hoping there is a easier way.

    I was also wondering what the specs are regarding how much PSI to pump into cylinder and what percent and time allowance for leak by?

    Any help would be welcome

  2. #2
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    This is the way I've understood it ? Not an expert by all means.... But first of all ya need a good leak down gauge... (no harbor freight gauge) someone has good ones for sale on this site.... And when ya have a good one ya just follow the instructions .... !!! But here's how it works.... 1 cylinder at a time, ya bring the piston to TDC and hold it there, via a big wrench / breaker bar, on the crank (flywheel nut) and get as many buddies as it takes... 1 to operate the gauge / air & two, if necessary to hold the breaker bar (if the piston is exactly at TDC the bar should have no resistance) but if it's a little before or after and ya have 100 psi's of air in the cylinder and not a good handle on the crank.... It can break a face or arm or anything in the way.... So have someone hold on to the breaker bar tight.... and the gauge does the rest.... It lets ya know how much air passes by the rings / scratches or any other problems within the cylinder or piston by a percentage of air passing through a .040 orifice between the constant pressure gauge (i.e. compressor psi) and the leak down gauge that measures the amount of air that bypasses the piston / cylinder / rings... at the given constant incoming air pressure.... In which shows you the percentage of air that leaks by any and all escape paths..... 2-3 % very good (racing engine) 4-5% (good) 5-7% (acceptable) 8% and up ya might want to pull the heads and take a look ??? And that's just the way I've understood the procedure... The key is get a good gauge !!! And Instructions are very inclusive....
    '81 HS 18' Viking - 2.5 L 200 Merc
    '86 Cougar 21' MTR - Pro XB - 310 ish
    Thanks To: Joe, Todd, Chaz, Pete, Eric, Greg & Sandy
    And Special Thanks to Suzie !!!
    They are all super people... !

  3. #3
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    It's not actually a gauge..... It has two, connected together with a precise metering orifice and a regulator.... And the PSI's are relative, but the compression psi's are good to use as a constant, 100 to 120 psi's will usually work from your compressor as long as it has a constant volume .....
    '81 HS 18' Viking - 2.5 L 200 Merc
    '86 Cougar 21' MTR - Pro XB - 310 ish
    Thanks To: Joe, Todd, Chaz, Pete, Eric, Greg & Sandy
    And Special Thanks to Suzie !!!
    They are all super people... !

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    My opinions on leakdown testing procedure are a little different than most,and render the most accurate results,again my opinion.Most folks follow the directions and put the piston at top dead...where there's no wear,and usually get low leakdown results accordingly.A poor mans leakdown test is really better,and is faster,cheaper,and easier...do a comp check,just write down the compression numbers,squirt a couple shots of 30 wt oil in each cylinder,spin the motor over a few seconds and recheck the compression...the amount the compression goes up will be close to overall leakdown percents.
    Now my way.Follow the normal procedure but instead of locking the flywheel near tdc,pull the motor from ports open to tdc on every cylinder,stopping at several spots along the way,and look at the resulting leakdown along the working stroke of the cylinder.
    We do this with a ratchet on the flywheel nut,with a long bolted in place tube extention on the ratchet handle...(3 foot long,specificly for this task).
    DO NOT USE A BREAKER BAR for this job...when you pull the piston over tdc the 40-50 pounds of pull required will turn to push and may DE-BRAIN you...the ratchet will allow the flywheel to spin to to open the ports.
    This procedure will locate bulged cylinders,scoring above the ports etc.,that a locked flywheel test won't know about.
    I figure if you're going to test you might as well get the best results you can,I should'nt have to tell you to keep fingers clear,and be careful,as the flywheel is going to spin as it goes over tdc,but i will anyway,BE CAREFUL,Chris



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    There are many opinions on how to do leakdown test but I believe Chris Carson's method to be the best and it is shared by Lee Sanderson which should lend even further credibility to it not that it is needed when Chris is involved. Chris, please correct me if I am wrong but when testing the port side, you pull against the flywheel so it is going in a clockwise direction and when testing the starboard side, you pull against the flywheel in a counterclockwise direction. In addition, it is not necessary to apply 100 psi to conduct the test. You may use 50 psi going in, but remember then that when using the "2 gauge" leakdown tester, if you are showing 48 psi on the other gauge, the leakdown percentage is actually 4%. ( 2 divided by 50 is 4%) An other example would applying 80 psi going in and the other gauge reads 76 psi. (4 divided by 80 is 5%) It is much easier to pull against the flywheel with somewhat lesser than 100 psi and if you do the math correctly, the results should be the same. Again Chris, if any of this in your opinion is not correct, please let me know, but it has proven to me that it works and gives accurate results.
    Last edited by catfish123; 09-01-2016 at 07:37 AM.

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  7. #6
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    Quote Originally Posted by catfish123 View Post
    There are many opinions on how to do leakdown test but I believe Chris Carson's method to be the best and it is shared by Lee Sanderson which should lend even further credibility to it not that it is needed when Chris is involved. Chris, please correct me if I am wrong but when testing the port side, you pull against the flywheel so it is going in a clockwise direction and when testing the starboard side, you pull against the flywheel in a counterclockwise direction. In addition, it is not necessary to apply 100 psi to conduct the test. You may use 50 psi going in, but remember then that when using the "2 gauge" leakdown tester, if you are showing 48 psi on the other gauge, the leakdown percentage is actually 4%. ( 2 divided by 50 is 4%) An other example would applying 80 psi going in and the other gauge reads 76 psi. (4 divided by 80 is 5%) It is much easier to pull against the flywheel with somewhat lesser than 100 psi and if you do the math correctly, the results should be the same. Again Chris, if any of this in your opinion is not correct, please let me know, but it has proven to me that it works and gives accurate results.
    Yes,you are correct,clockwise port bank,counter starboard bank,I test at 75 pounds air pressure and just check the chart...try not to think anymore than necessary...Chris

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  9. #7
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    Wow guys.... that sure makes more sense than the way I explained.... I just read that somewhere...? But that's why I really like this site.... I'm always learning something..... Thanrks for straightening me out anyway..... ! And the other guy also !
    John
    '81 HS 18' Viking - 2.5 L 200 Merc
    '86 Cougar 21' MTR - Pro XB - 310 ish
    Thanks To: Joe, Todd, Chaz, Pete, Eric, Greg & Sandy
    And Special Thanks to Suzie !!!
    They are all super people... !

  10. #8
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    50 psi and ratchet like that !!!!
    Last edited by eli; 09-01-2016 at 09:52 PM.

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  12. #9
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    suggestion on warmed up/cold motor? how much oil ratio?? how much will difference between synthetic/petrroleum?-th

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    And here I have been trimming the motor up and counting days till it leaks back down all these years know wonder I keep getting 0% lol
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  15. #11
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    Thank you all very much for the time to reply back, I will do these tests and see what it indicates.

    Right now the engine fires right up and idles , five cylinders are showing 115 lbs compression and the one cylinder that is not firing at idle is reading 105-110 psi.
    I understand that a healthy Bridgeport should all be around 135 PSI

  16. #12
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    The only motor I've ever done a leak down on is my InLine. I use a Balz gauge and I've been using 50 PSI and going from ports open, over top to ports open. Stays about 4%, or 2 PSI difference. 125 plus or minus a couple for compression. And Michael Balz made me a special adaptor for the InLine bottom cylinder which makes it easy to get good numbers on all 6. And I do a careful TDC at 100 PSI and get less than 2% which shows the difference when you get off that TDC spot.
    I carry a gun because a cop won't fit in my pocket.

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  17. #13
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    Quote Originally Posted by Chris Carson's Marine View Post
    Yes,you are correct,clockwise port bank,counter starboard bank,I test at 75 pounds air pressure and just check the chart...try not to think anymore than necessary...Chris
    Why go in different directions? Clockwize and counter clockwise?

  18. #14
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    Quote Originally Posted by CircleHook View Post
    Why go in different directions? Clockwize and counter clockwise?
    The piston would like to go straight down the cylinder under power,and would,with no skirt loading,if it wasn't connected to the rod and crank.Because the push on the rod and crank is not aligned with the cylinder bore the skirt of the piston must support the angular push of the rod,That angular push of the rod loads the starboard skirt of both port and starboard pistons,also resulting in greater wear on the port bank pistons due to the skirt being less supported because if the large,hot exhaust port in the load bearing area of the cylinder wall.
    By changing the rotation direction the piston is cocked a bit in the cylinder and is pushed against its load bearing surfaces...skirt to cylinder.Hence,rotate clockwise to check the port bank,and ccw for the starboard,Chris

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    so if going both ways is it it best to take the lower unit off to do a leak down on a v6 due to messing up the water pump vanes turning in the wrong direction ?

    I dont have a v6 but just curious about this scenario and would that also be the same for a v4 crossflow omc ?

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