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Weird Compression Readings - Advice Needed

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    #1

    Weird Compression Readings - Advice Needed

    Hey everyone, I am the new owner of a 2004 CB/IR 6mt with 113,000 miles and I recently did a compression test to check the status of the motor (with it warm) and I got some weird readings. Cylinders 1 & 6 are reading 150ish, and Cylinders 2, 3, 4, and 5 read 180ish. I know the headgasket was changed like 30,000ish miles ago (I assume it was blown) and that it is due for another valve adjustment. Does anyone have an idea whats up with these readings? If it was one cylinder I could see rings, or two adjacent cylinders I could see HG, but cylinders 1 & 6 which rotate up and down on the same stroke, I don't know what to make of it. Any engine builders out there with some advice?
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    #2
    Originally posted by M3_Worker_Bee View Post
    Hey everyone, I am the new owner of a 2004 CB/IR 6mt with 113,000 miles and I recently did a compression test to check the status of the motor (with it warm) and I got some weird readings. Cylinders 1 & 6 are reading 150ish, and Cylinders 2, 3, 4, and 5 read 180ish. I know the headgasket was changed like 30,000ish miles ago (I assume it was blown) and that it is due for another valve adjustment. Does anyone have an idea whats up with these readings? If it was one cylinder I could see rings, or two adjacent cylinders I could see HG, but cylinders 1 & 6 which rotate up and down on the same stroke, I don't know what to make of it. Any engine builders out there with some advice?
    Do a leakdown test. Should be more informative.


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      #3
      Originally posted by eacmen View Post

      Do a leakdown test. Should be more informative.


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      I have the tester on its way from Amazon, just wondering if anyone has come across this before.

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        #4
        Possibly rings or valve seals but it’s weird that it is cylinders 1 & 6 with the same readings and all other cylinders reading the same.


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        2004 M3 Coupe - Imola/Black | AA Supercharged (432 whp / 275 ft/lbs) | ARP Head Studs | ACL | Besian | Mishimoto CC | AA Headers w/ 100 Cell Race Cats | SS Section 2 | OEM Section 3 | TCK DA 400/500 | TMS Rear Camber Arms | Apex Arc-8 18x9 / 18x10 | 996 Brembo (In-Progress)

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          #5
          Update:

          Now I am at impasse and unsure of what to do. I did a leak test on Cylinders 1 & 6 and I am sitting at around 10-12% leakage on both with air coming from the PCV Valve, so it looks like rings on both. However, with leakage only 10ish% and pressures still within min spec (which should increase once oil is introduced), I am debating whether to leave it for now and just change it in the future when I take the engine out. I have a catch can for any excess oil and I haven't noticed any oil loss yet. Thoughts?

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            #6
            Originally posted by M3_Worker_Bee View Post
            Update:

            Now I am at impasse and unsure of what to do. I did a leak test on Cylinders 1 & 6 and I am sitting at around 10-12% leakage on both with air coming from the PCV Valve, so it looks like rings on both. However, with leakage only 10ish% and pressures still within min spec (which should increase once oil is introduced), I am debating whether to leave it for now and just change it in the future when I take the engine out. I have a catch can for any excess oil and I haven't noticed any oil loss yet. Thoughts?
            Did you do leakdown on the other cylinders as well?


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              #7
              Originally posted by eacmen View Post

              Did you do leakdown on the other cylinders as well?


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              Yea, I was sitting at 6-7% on the rest of the cylinders.

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                #8
                Originally posted by M3_Worker_Bee View Post

                Yea, I was sitting at 6-7% on the rest of the cylinders.
                10-12 percent isn't good but isn't bad either. It you have no other symptoms i would leave it alone.


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                  #9
                  Originally posted by eacmen View Post

                  10-12 percent isn't good but isn't bad either. It you have no other symptoms i would leave it alone.


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                  That was my line of thinking as well. I just wasn't sure how fast piston rings degrade. I guess I will wait and see.

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                    #10
                    Originally posted by M3_Worker_Bee View Post

                    That was my line of thinking as well. I just wasn't sure how fast piston rings degrade. I guess I will wait and see.
                    Clearly the compression and leakdown test both verified there is an issue with 1 and 6. Unless you're building a race engine that needs peak performance I would treat this as informational and plan to address it sometime in the future.

                    I don't want you to think it's not an issue but without any symptoms hard to justify tearing into it.


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