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Need advice from experience for an M42 rebuild

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    Nope, not the right o-ring. The correct one is a lot beefier and fills the slot it rests in, protruding past the outside radius of the plastic as well. Make sure to get he Genuine BMW water pipe, not the aftermarket one, since the aftermarket one is prone to cracking. The parts you want:
    11531714738
    11531709157

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      Yep got it. Compression tested again and it’s all good. Replaced it put everything back and tested the cooling system. Finally no new leaks. Temp held steady around half. Took it around the neighborhood and no overheating. Gonna take another compression test after to cools down afterwards cuz I’m paranoid. Good news is that the oil doesnt look milky.
      Last edited by JonsE30; 05-24-2020, 02:02 PM.

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        Nice, yeah that is great to hear. Also, try doing the compression test when it is hot (after removing all spark plugs) and post the numbers. I'm curious to see what the values for a freshly built stock M42 are.

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          bmwman91 did the compression test while hot. i am getting 175-180 per cylinder.

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            Aren't those the same numbers from the cold test? I would've expected some change, but it could be a different tester giving different readings.

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              yeah the first time was a rented one, this one is from amazon that had some good ratings. i took some pics and zoomed in and was off buy a little. i've read people getting over 200

              cylinder 1 170
              cylinder 2 177
              cylinder 3 180
              cylinder 4 176


              update: took readings again after its cooled down for several hours

              cylinder 1 185
              cylinder 2 190
              cylinder 3 197
              cylinder 4 190

              are these readings still good?
              Last edited by JonsE30; 05-26-2020, 07:14 PM.

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                Those numbers are fine, ideally there would be less variation between cylinders, and you'd typically see about that amount of change hot versus cold.

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