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Thread: M70 (V12) Engine rebuild questions.

  1. #1
    Join Date
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    91 850i, 01 740i, 06 760

    M70 (V12) Engine rebuild questions.

    I'm almost ready to send the heads out to be checked, cleaned, resurfaced, valve job etc. They only have 65K mi so not sure if the guides will need to be replaced or not. I've ben quoted $500 ea labor (parts are extra). Does this seem reasonable? Any advice what to ask for as not been down this road before? I'm in San Diego.

    I will most likely have the block cleaned since I'm finding quite a lot of crud in the coolant passageways under the head gasket. I was quoted $100 for this.

    M70.jpg

    block.jpg
    Last edited by BMSman; 11-25-2017 at 12:29 AM.

  2. #2
    Join Date
    Jan 2004
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    Toronto, Canada
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    BMW 850CSi
    Does the rest of the engine only have 65k mi too? Why the rebuild at such low mileage?

  3. #3
    Join Date
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    Vena, Sweden
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    Looking forward for more pictures.

  4. #4
    Join Date
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    91 Dinan860 & 91 850 6sp
    "If it ain't broke, don't fix it." ... thats an old country rule for things like this. What actual reason do you have to break down that bottom end? Yeah, didnt think so... leave it alone

  5. #5
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    Those are actually great prices, but a total waste on an engine that can easily do 400,000 - 500,000 miles.
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    ...the price of cool ain't cheap!

  6. #6
    Join Date
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    Westfield, IN
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    '91 e31 M70
    Quote Originally Posted by BMSman View Post
    I'm almost ready to send the heads out to be checked, cleaned, resurfaced, valve job etc. They only have 65K mi so not sure if the guides will need to be replaced or not. I've ben quoted $500 ea labor (parts are extra). Does this seem reasonable? Any advice what to ask for as not been down this road before? I'm in San Diego.

    I will most likely have the block cleaned since I'm finding quite a lot of crud in the coolant passageways under the head gasket. I was quoted $100 for this.

    M70.jpg

    block.jpg
    Where are you having the heads done? Shopping for a place to do mine.


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  7. #7
    Join Date
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    Have not sent them out yet but I plan to use a local machine shop. I would not recommend shipping them as they are quite large and heavy. There are several machine shops in San Diego that do this type of thing and I plan to visit a few of them before choosing one.

    This is a spare engine for me that came out of a wrecked 850i with only 65K mi. The main reason for stripping it down was to check for damage but i'm also doing this for fun and will eventually put it in my car. Many gaskets needed replacing as is typical with these engines. I found the upper timing case was damaged and the pin securing the cam chain sprocket sheared on one side (distrib cap was hit and broke which locked up the rotor and shared the pin). I've replaced the timing cover. I was a bit nervous about pulling the pistons but i've been practicing on a different spare engine block I acquired a few years ago and with an ARP ring compressor finding it very easy to pop the pistons out and reinstall them without breaking anything. This block has all new bearings and rings in it so I have plenty of spares if I need them. I work at a leisurely pace, no rush to finish this.
    Last edited by BMSman; 12-07-2017 at 06:57 PM.

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