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Thread: the build back

  1. #1
    Join Date
    Sep 2017
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    1994 840, 2013 X5 335d

    the build back

    After overheating my 94 840 due to a broken aux. water pump, the build back has begun. With the cold weather and work, I've managed to gather the parts required, purchase a replacement set of heads, have them completed rebuilt and begin tear down. I'll be investing time over each week to methodologically tear down the top end. It is clear though that as I get deeper in, more parts continue to be needed. As an example, the knock sensors literally came apart with one twist of the bolt. That's OK though as I want to have a reliable motor and already know this is not about penny pinching.

    Lastly, I am continually encouraged by this forum. thank you. It does help jump start one's motivation when it wanes. And so it begins!

    IMG_3380[1].jpghead1.jpgparts.jpgengine.jpg

  2. #2
    Join Date
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    Those knock sensors seem to be made of exploding plastic - but overheating them certainly doesn't help them! All the rubbery bits need replacing including the hollow fixings for the manifold - they will have been permanently compressed at this age anyway.

    But well done for taking it on!
    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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  3. #3
    Join Date
    Jan 2012
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    Upstate South Carolina
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    1996 840Ci / 2007 B7
    Good luck! I am just finishing up something similar on my '96 840. Here's mine about as far down as I went while the engine was still in the car. Tim is a far more experienced resource, but hopefully I can help out if you run into issues
    Attached Images Attached Images

  4. #4
    tvjake2's Avatar
    tvjake2 is offline SoCalEights - CA BMW CCA Member
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    '97 840Ci, '89 635CSi
    Quote Originally Posted by Timm View Post
    Those knock sensors seem to be made of exploding plastic - but overheating them certainly doesn't help them! All the rubbery bits need replacing including the hollow fixings for the manifold - they will have been permanently compressed at this age anyway.

    But well done for taking it on!
    Timm - Are the knock sensors important to replace? I've got two showing they are not working properly but I have no engine pinging, even in hot SoCal weather.

  5. #5
    Join Date
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    Without the knock sensors working the engine will not deliver its full power or economy - many owners would not even notice the slight reduction in power. This is because the ignition timing will have been retarded to a 'safe' setting - whereas the ECU (with the knock sensors working) will attempt to squeeze more power by advancing the timing to the point of detonation.
    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


    My Current 840ci Sport Individual
    My Current 650ci Sport Individual
    My E31 Repair and Information Website
    My E38 Repair and Information Website
    My E63/E64 Repair and Information Website

    Chase - Heroes to a generation

  6. #6
    Join Date
    Sep 2017
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    1994 840, 2013 X5 335d
    Thanks Tim, agree on all rubber being replaced. While cleaning the throttle body a "fine" looking rubber plug was cracked. It would be poor form not to ring fence all the perishable rubber hoses while I'm in there.

    Thanks Spandrel. Appreciate the offer. How close are you to running again? Any tips?

    Now that i'm back in the swing of it, today I disassembled the intake manifold and cleaned the throttle body and traction control body as well. The neat thing was I used a 200W ultrasonic cleaner I bought off Facebook to degrease. Using Grease Lighting and a 45 minute sonic bath for each part, I'm quite pleased. Next update next weekend. The plan is to remove the front end of the engine and including the valley pan. If all goes well, I start on the drivers head and plan to do one head at a time, given I have a replacement set ready to go.

    body.jpg elbow.jpg cleaner.jpg
    Last edited by Gregsgroup; 02-11-2018 at 07:17 PM.

  7. #7
    Join Date
    Jan 2012
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    1996 840Ci / 2007 B7
    I'm down to adding fluids. Hopefully try to crank it over sometime this week. The ultrasonic cleaner is a good idea - I made do with a couple of bottles of Fast505 and a lot of elbow grease. Definitely replace anything rubber that you can see - it will just crumble if mine was any indication. And take pictures. LOTS of pictures, at every step. The crank bolt stymied me for a while - needed an 1100 ft-lb impact gun to get it off after the 9 foot cheater bar just tore my counterhold bar instead. Also be sure to put marker dots on the new head bolts and holes so that you can track the multiple 60° turns to properly set them (remembering that 60° is one corner to another on the hex head) (and you'll need a hell of a cheater bar for the last step)

  8. #8
    Join Date
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    2001 BMW 540i6
    Make sure when you tighten the knock sensors you torque them to spec, that’s what calibrates them.

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