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Thread: Whine/squeal following top end rebuild M70 V12

  1. #1
    Join Date
    Sep 2015
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    UK
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    35
    My Cars
    1988 BMW 750i

    Whine/squeal following top end rebuild M70 V12

    Hi all,

    Following a top end rebuild on my M70 V12 i've got a weird squeal/whine from the top end. There's a video of it here;

    https://www.youtube.com/watch?v=8Uc6u195k9g

    Any ideas? i can't decide if it's an air leak or more of a dry bearing/metal on metal noise.

    Also one of the injector rails doesn't seat the injectors as low into the inlet manifold as the other. Is this normal? On the one side you can see pretty much all of the plastic ring on the base of the injector whereas on the other side it sits deeper.

    Thanks
    Simon

  2. #2
    Join Date
    Jan 2005
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    Japan
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    54,654
    My Cars
    11/88 E32 750iL+98 E36M3
    Do you have a mechanics stethoscope? Try with that to find the source of the whine, helped me a lot.
    Just a shot in the dark: maybe the water pump bearing?
    The injector rails are fixed with 2 bolts, total 4 x # 3 http://www.realoem.com/bmw/enUS/show...diagId=13_1387
    if they are in and there is no change in idle when you spray brake cleaner in the area of the fuel injector o-rings, it should be o.k.
    Shogun tricks and tips for the E32 series are HERE!

  3. #3
    Join Date
    Sep 2015
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    UK
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    My Cars
    1988 BMW 750i
    H Shogun,

    I do have a stethoscope but the plan has been scuppered by finding out that one of the plastic caps on the injectors has fallen through the inlet manifold and into the engine. I've removed the manifolds but there's no sign off it so i assume it's been eaten by the engine - hopefully as it's light plastic there will be no damage.

    I'll re-assemble paying particular attention to the manifold joints so that should at least rule out any air leaks.

    Thanks
    Simon

  4. #4
    Join Date
    Mar 2013
    Location
    Green Bay, WI
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    1992 750il / 1991 560 SE
    Thats an odd sound. Did you place the cam caps back onto the exact same locations?
    ______________________________
    1992 750iL

  5. #5
    Join Date
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    99 840ci Sport Indv
    If that were an M60 I would immediately say it is the PCV valve (crankcase ventilation valve) - it is certainly worth checking them on the M70 as they can make the same noise.
    Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i


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  6. #6
    Join Date
    Sep 2015
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    UK
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    My Cars
    1988 BMW 750i
    I've removed the cam covers and checked the cam caps - thankfully they are all in the correct place. The PCV's were replaced about 3000 miles ago so i'm hoping they're ok.

    What i have noticed though is the poor fit of the intake manifolds to the gaskets. I fitted the gaskets to the manifolds off the car and was surprised at how warped they are - not terrible but enough that they don't sit perfectly flush. Anyway i've gone ahead and re-installed them using Reinzosil in the hope it closes the gap and sorts the noise if it's coming from there.

    Thanks for your help, i'll report back tomorrow night.

  7. #7
    Join Date
    Jul 2015
    Location
    Dallas, Texas
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    582
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    98 750iL, 01 740iL
    that should do it! if not, try a smoke test. next time i do the job, i'll get the max lumens kit

    good luck

  8. #8
    Join Date
    Sep 2015
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    UK
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    My Cars
    1988 BMW 750i
    Well i can report there has been a dramatic improvement - still a very small bit of noise but so much better. I probably should have been more patient and let the Reinzosil cure for a few days before starting the car but i'm happy at the moment.

    Thanks all for your help, much appreciated.

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