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    Head Gasket/Low compression test numbers.

    I think i got my head gasket at the last track day. Had a red flag and stopped in the pits but they let us go again and just on pit exit i saw the temp at the hot line. Fresh 80+mph airflow solved the temp issue and it ran just fine and after discovered a disconnected wire to my aux fan. Fixed that and Ran the rest of the day without issue, no power loss, or other symptoms. Over the break my project has been extensive. CMP reinforcement, full solid bushings etc, etc, among many other things. I decided to flush the coolant and it was pretty dusky, greyish. Its only been in 2 years 5% coolant to water and strictly track days 8/10 per year. Refilled thinking it just must have gotten dirty and on refiring the car yesterday letting the new coolant circulate i saw a few puffs of white come out the exhaust. I couldn't believe that short time in the red got the gasket. But its a 150k mile engine so i did compression test. Not knowing what im doing my numbers were 1-6: 145, 130, 145, 145, 95 and 145. Terrible numbers. Added the oil to cylinder 1 and i got 280?? I guess i dont know what im doing. But cylinder 5 spark plug hole had rusty material in it and the plug had what looked like water deposits and also a good bit of corrosion.

    Does this sound like a head/valve job and new gaskets or full on pull the engine and rebuild with new rings and other rebuild items? Ive recently (in miles) done the rod bearings, so its not like those are needed.

    What do we think about sending the head to Lange for the stage 3? Is that treatment worth the coin or is a local rebuild nearly as good?

    Thanks for the input.

    Pic shows cylinder 5plug down on compression.
    Attached Files

    #2
    Not too much input I can give here, as my engine diagnosing expertise is mostly on the N54. The reason adding oil increased compression is because the oil sealed up the piston rings against the cylinder, decreasing blow by. I would suggest looking into having a leak down test done before you do anything drastic. Also try posting this in the right subforum (E36 or E46) for better responses.
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      #3
      right but the compression number should have gone back to normal....~200 not 280. I guess it was too much oil i added. Im not sure what a leak down adds at this point since i believe if at best its a head gasket and i pull the head and do a full head rebuild while im in there any way. A leak down will tell me which cylinder (already know its #5) and if theres an exhaust valve or intake valve problem....or am i missing something.

      If these numbers are to be trusted i guess i have blow by(pretty bad) on all cylinders, correct?

      Comment


        #4
        Perform the test on a warm engine w/the throttle open and crank each cylinder about 5-8 times, and try to crank it the same number of times for each cylinder to keep results consistent. Your results should be from 165-180 (for a factory S54) with a variance of less than 10%...and less than 5% would be ideal.

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          #5
          Have you performed valve adjustments regularly? And compression test with engine warm/ normal hot temp? If so, do a leakdown test before you take the engine apart because It will get very expensive very quickly. Trust me, I rebuilt my engine myself.

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            #6
            The valves were checked recently and needed no adjustment for the last 2 checks. I didnt do compression warm so maybe ill give that a try to see if the other numbers come up. But the one cylinder definitely out and theres signs of a problem on that cylinder on the plug and in the hole. If you knew you had that problem would you then run the engine to get it hot just to recheck the compression? I dont have a leakdown tester yet and wasnt planning on getting one bc the head is coming off at a minumum and going for a build. Is there a value in doing a leakdown if im already sending the head??

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              #7
              Leak down test would be more informative and not that much harder than compression test. Just need shop air. I use this one; https://www.amazon.com/OTC-5609-Cyli...dp/B0030EVL60/

              Also when I was looking at used cars I used this kit to quickly check for head gasket issues: https://www.amazon.com/gp/product/B06VVBSFTF/

              You could also do an oil analysis looking for coolant in the oil.

              I would do al of these before pulling the head. I had temps in the red in the pits on track before and did not suffer a hg issue. Really depends on how much in the red you were.

              Comment


                #8
                I know I am late here, but just discovered that tapatalk is finally working, so I'm back .

                Have to do it on engine at operating temp.

                Min. results should be between 160-174psi with max variance of 7psi.

                One thing I can tell you about a compression test I recently ran on my car and a friend's car. You need to make sure you have good seals on the tester you use. On the tester I use, I needed to use an adapter for the right threads to match the spark plugs, there is a rubber oring on it. You need to make sure it is screwed onto the tester tube TIGHT. Also, if your adapter is tall/long and does not have a valve on the very end of it, it will count as part of the cylinder pressure volume, resulting in lower compression numbers. You need to make sure that the valve is as close as possible to the actual piston. Last thing, you need to make sure that the threads from the spark plugs in the head are clean, if they are not you will think that the tester is on tight since you will feel resistance when screwing it in, but it actually wont be, especially if all the leverage you have to screw on the tester is the rubber hose which flexes. You need to use an extension adapter since s54 spark plug tubes are so deep, but make sure you use the kind with the valve in the bottom of it, otherwise it will count as volume of the cylinder and result in lower numbers.

                Sent from my SM-G950U using Tapatalk



                All jobs done as diy - clutch, rod bearings, rear subframe rebush, vanos, headers, cooling, suspension, etc.

                PM for help in NorCal. Have a lot of specialty tools - vanos, pilot bearing puller, bushing press kit, valve adjustment, fcab, wheel bearing, engine support bar, etc.

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                  #9
                  Thanks for the reply, but the engine is almost ready for reassembly! Lol. One cylinder verifiably down by 40% repeatedly. Even if the other numbers came up to spec with the engine warm id be leary to keep using it on track. In any case whats done is done.

                  Comment


                    #10
                    Originally posted by F1Dryvr View Post
                    Thanks for the reply, but the engine is almost ready for reassembly! Lol. One cylinder verifiably down by 40% repeatedly. Even if the other numbers came up to spec with the engine warm id be leary to keep using it on track. In any case whats done is done.
                    What did the problem end up being? Headgasket?

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                      #11
                      Not really sure. Nothing obvious from the block head or gasket. Maybe engine specialists here see something i dont. The head only needed .003 to clean it up. I did have dusky coolant which prompted the search for low compression. The spark plug on cyl 5 was badly corroded while the others were normal. Cyl 5 was the one with compression loss. I didnt do a leakdown.

                      Attached Files

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