Announcement

Collapse
No announcement yet.

Compression Leak Down Testing

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • #16
    Re: Compression Leak Down Testing

    Not totally disagreeing with you TC, but the top of the cylinder sees a lot more friction and wear than the bottom. I'd be a lot more concerned with the seal at that end as opposed to the bottom where a great deal of the cylinder pressure has been bled off.
    ;)

    Comment


    • #17
      Re: Compression Leak Down Testing

      Originally posted by BlackoutSteve
      Not totally disagreeing with you TC, but the top of the cylinder sees a lot more friction and wear than the bottom. I'd be a lot more concerned with the seal at that end as opposed to the bottom where a great deal of the cylinder pressure has been bled off.
      ;)
      BUT AT THE SAME TOKEN, IF THE BOTTOM IS LEAKING BAD
      on compression stroke. you're gonna lose alot of air to compress..

      Comment


      • #18
        Re: Compression Leak Down Testing

        Originally posted by BlackoutSteve
        Not totally disagreeing with you TC, but the top of the cylinder sees a lot more friction and wear than the bottom. I'd be a lot more concerned with the seal at that end as opposed to the bottom where a great deal of the cylinder pressure has been bled off.
        ;)
        Not measuring volume, your checking for leakdown.
        Do it at TDC.

        Comment


        • #19
          Re: Compression Leak Down Testing

          thats what i was thinking, maybe you should do a compression test then.
          so, let me get this straight. i should start at TDC and turn the crank and leak it every couple of degrees until the piston is at BDC?
          Originally posted by TC
          also boost will make the cam act smaller

          Comment


          • #20
            Re: Compression Leak Down Testing

            Originally posted by A/Fuel
            thats what i was thinking, maybe you should do a compression test then.
            so, let me get this straight. i should start at TDC and turn the crank and leak it every couple of degrees until the piston is at BDC?
            I do it at tdc and again half way down and again at bdc..
            because if it seals great at the last 20% of the stroke.. but leaks the other 80%..
            you can have almost nothing in the cyl. compaired to the cyl volume
            I find alot of 12 to 1 pump gas engines are this way.. that was bored without torque plates and the bolts/studs to be used in the build

            Comment


            • #21
              Re: Compression Leak Down Testing

              Originally posted by A/Fuel
              thats what i was thinking, maybe you should do a compression test then.
              so, let me get this straight. i should start at TDC and turn the crank and leak it every couple of degrees until the piston is at BDC?
              Unless you hold the motor from turning there's going to be a good chance that the compressed air is going to move the piston downward. I also remove all rocker arms when doing a leak down, that way you don't have keep turning the motor over to make sure the valves are closed. And you guys know the only reason they say to put the piston at TDC is to make sure the valves are closed, right?? But since I loosen the rockers or remove them I don't worry about it, basically saying that it doesn't matter where the piston is, your checking for "Leakage", thus the term "Leak Down Test".

              Comment


              • #22
                Re: Compression Leak Down Testing

                Originally posted by MentalMuffinMan
                Originally posted by BlackoutSteve
                Not totally disagreeing with you TC, but the top of the cylinder sees a lot more friction and wear than the bottom. I'd be a lot more concerned with the seal at that end as opposed to the bottom where a great deal of the cylinder pressure has been bled off.
                ;)
                BUT AT THE SAME TOKEN, IF THE BOTTOM IS LEAKING BAD
                on compression stroke. you're gonna lose alot of air to compress..
                My intake valve closes at 72 ABDC, and my exhaust valve opens at 82 BBDC, so I'm really not that bothered with BDC testing. Knowing the quality of TDC is far more important. If TDC comes up good, you can bet that BDC will be at least as good or better..
                Not to say that I won't check BDC for the sake of checking it though.. ;)..

                Comment


                • #23
                  Re: Compression Leak Down Testing

                  I have tried a 1/2 dozen different leak down testers and the only one I can get to repeat is a Snap On that is well over 20 years old. The instructions for the Snap On have you adjust the supply to 60 PSI and that seems to work very well.
                  If your worried about the air pressure spinning the engine, you should try just putting the rocker arms on my deal. With 400# seat pressure on the springs, a needle bearing cam and low tension rings it takes 2 people, one to bolt the rockers on and one to hold the engine from turning.

                  Comment


                  • #24
                    Re: Compression Leak Down Testing

                    Originally posted by jfuelracer
                    I have tried a 1/2 dozen different leak down testers and the only one I can get to repeat is a Snap On that is well over 20 years old. The instructions for the Snap On have you adjust the supply to 60 PSI and that seems to work very well.
                    Unless the gauges are faulty , there is a poor seal at the sparkplug thread, or the air pressure is fluctuating, the only variable should be within the engine.

                    Comment


                    • #25
                      Re: Compression Leak Down Testing

                      You should be on a warm motor and at tdc but still your looking for a relitive reading if all of them are at 10% or if ones at 25 and the rest are at 10% you got troubles listen for the air to tell you whats leaking. dont get to wraped in the number it will depend on rings used and oil present. dont use to much pressure they all leak if enough is used
                      2007 SBN/A Drag Week Winner & First only SBN/A Car in the 9's Till 2012
                      First to run in the .90s .80s and .70's in SBN/A
                      2012 SSBN/A Drag Week Winner First in the 9.60's/ 9.67 @ 139 1.42 60'
                      2013 SSBN/A Drag Week, Lets quit sand bagging, and let it rip!

                      Comment


                      • #26
                        Re: Compression Leak Down Testing

                        Originally posted by JeffMcKC
                        You should be on a warm motor and at tdc but still your looking for a relitive reading if all of them are at 10% or if ones at 25 and the rest are at 10% you got troubles listen for the air to tell you whats leaking. dont get to wraped in the number it will depend on rings used and oil present. dont use to much pressure they all leak if enough is used
                        I have always used 100 psi, and with the 350 I used to run that had TotalSeal rings, I had cylinders with no leakage. That's right 100psi being shot in and 100psi staying in. Even after 5000 miles the most a cylinder had was 2%. The reason I use 100psi is it makes figuring your percentage of leakage easy.

                        And like I said the only reason you put the cylinder at TDC on the compression stroke is so both valves are closed, it has nothing to do with the readings your going to get.

                        Comment


                        • #27
                          Re: Compression Leak Down Testing

                          Originally posted by TubbedCamaro
                          I have always used 100 psi, and with the 350 I used to run that had TotalSeal rings, I had cylinders with no leakage. That's right 100psi being shot in and 100psi staying in. Even after 5000 miles the most a cylinder had was 2%. The reason I use 100psi is it makes figuring your percentage of leakage easy.
                          That's what I've heard about Total Seal.. The ring seal is extremely good.
                          I was going to use Total Seal's rings during my last rebuild (near 10 years ago now) and was actually talked out of using them. Not because they are bad, but because they are too good! The reason behind the advice was there aren't/weren't really good valve stem seals available that could control the amount of oil being pulled in with such high vacuum from the ring's seal..

                          Although it may be true, I wish had ignored the advice and fitted them anyway. I will next time.
                          Not totally disappointed though, I fitted Sealed Power file-fits and my leakdown was around 92-95%. I'm happy enough with that.

                          Comment


                          • #28
                            Re: Compression Leak Down Testing

                            All my roundy engines use TS rings, I swear by them.
                            I have used em on a few street/strip motors,
                            using new bronze guides, and PC seals.

                            Comment

                            Working...
                            X