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Loud Metallic Pop After First Run

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    Loud Metallic Pop After First Run

    Something has been bugging me a little since I put the head back on the block. It was off due to a busted valve spring and I had that dealt with by the builder. This is a 1991 318iS (well, 321iS now )

    After the first test drive for a few miles, I parked it in my parents driveway. We were standing out there talking about 5 minutes later and we heard a very loud metallic pop from the front of the car, almost like if someone dropped a socket on the fender. The logical answer is that something was just settling after the initial run as it cooled and contracted. Now, the dark side of my mind is imagining the head popping a big crack in the exhaust valve area, the block cracking or a head bolt popping apart. After I drove it the 17 or so miles home and left it over night, there were zero drips of anything on the ground and no funny smells under the hood. I did notice that my coolant expansion tank was empty, but I also forgot to turn the heater on when I was bleeding it, more air bleeds from the system in the first hour or so of driving, and I am sure that the hoses that sat for months expanded after use and are holding more coolant. I do not recall any white smoke, although it was dark and I was not looking for it, but as I left my parents' house they were watching and they didn't see white smoke (and you usually get it after a start if you have a bad HG or cracked head). Has anyone had a similar experience with a loud "pop" noise as the engine cools?

    Anyway, I am 500 miles from home for a family member's graduation so my imagination and paranoia are running wild lol. We sure as hell didn't drive my E30 down here, and it is sitting at home.
    Last edited by bmwman91; 06-15-2013, 01:47 PM.

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    #2
    It was probably the exhaust system.

    I'd check the manifold studs (to see if they're still tight- and all there)
    and the downpipe bolts/studs first.

    Then look for stuff.

    No, you won't hear the head crack!!!

    It's probably just fine.

    And yes, it seems like the coolant tank always sucks itself dry at first, no matter how carefully you bleed it...

    t
    now, sometimes I just mess with people. It's more entertaining that way. george graves

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      #3
      Thanks Toby.

      All of the exhaust studs were there, although I didn't have a socket handy to check them. I also pulled the valve cover and took a look, but nothing was out of line. All head bolts were there and tight.

      I then proceeded to do what I paid to do with this engine: 7700RPM runs up on-ramps and the like. No issues. All coolant is accounted for now that I topped it off. Rings and everything were seated a long time ago (valve spring broke ~1100 miles in, had the head off to get that dealt with by the builder). It certainly pulls hard for an NA M42 lol (granted, there is not a single stock moving part, and even some big stationary ones lol).

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        #4
        What tach are you using for 7700 rpm redline?

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          #5
          Stock. The chip's programmed limiter lets me know when I hit it lol.

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