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Thread: Help identifying an M20 motor

  1. #1
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    Help identifying an M20 motor

    Well the obvious was not so abvious.

    I pulled a motor from a 1990 525i supposed to be a M20B25
    now im not so sure.

    after taking motor apart with intentions to replace all gaskets and seals before placing in car here is what i found.

    motor from 1989 325i:
    Engine block casting 1-289-575
    Head casting 1-705-885

    Motor from 1990 525i
    Engine block casting 1-289-575
    Head casting 1-264-200

    this is according to what I have found an "e" or "es" to my knowledge
    no 525i was ever produced with this motor so maybe someone replaced
    it with a motor from an "e" or "es" 325

    Even though both blocks have the same casting numbers the pistons on them are not the same ( i did not get a chance to measure the stroke) they are as follows:

    My 1989 325i has the following:
    Engine block casting 1-289-575
    Pistons stick out past the top edge of the block

    and

    Motor from 1990 525i
    Engine block casting 1-289-575
    pistons have a slight inward dome dish

    Question here is what can i do with what i have what can i combine
    and still have a better running motor.

    any help greatly appreciated

    Thanks
    Xavier

  2. #2
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    It sounds like your donor is a genuine eta motor with a 200 head. All E34 525i M20s would have had the 885 head.

    You could just run the engine as installed in your donor car. That would work, but would be a somewhat inferior package as compared with an M20b25.

    Edit: you cannot combine an i bottom end with an eta head (the 200) for what should be obvious reasons lol.
    Last edited by strad; 05-23-2010 at 10:04 PM.
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  3. #3
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    Another consideration is that if the block is from an E34 525i, the holes for the motor mount arms are different. They castings are the same, but the bosses where the holes are drilled and tapped for the mount arms are not drilled and tapped in the right place to use the block in and E30.


    Are you sure you didn't pull that engine out of an E28 528e?

  4. #4
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    Quote Originally Posted by Rigmaster View Post
    Another consideration is that if the block is from an E34 525i, the holes for the motor mount arms are different. They castings are the same, but the bosses where the holes are drilled and tapped for the mount arms are not drilled and tapped in the right place to use the block in and E30.
    That isn't necessarily true for all E34 M20B25/B27 engines, though it might be true for some of the production. I have an M20B25 from a 91 E34 that I used in my previous Spec E30. The only thing I had to do with the engine to use it was to install the engine mounted dipstick and plug the sump where the E34 dipstick was.
    The car makes it possible, but the driver makes it happen.
    Jim Levie, Huntsville, AL

  5. #5
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    Quote Originally Posted by thejlevie View Post
    That isn't necessarily true for all E34 M20B25/B27 engines, though it might be true for some of the production. I have an M20B25 from a 91 E34 that I used in my previous Spec E30. The only thing I had to do with the engine to use it was to install the engine mounted dipstick and plug the sump where the E34 dipstick was.
    Thanks Jim, I stand corrected.


    I know for sure that it is the case with at least some of the production, I don't have any idea what the mfg date break is.

  6. #6
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    Quote Originally Posted by Rigmaster View Post
    Another consideration is that if the block is from an E34 525i, the holes for the motor mount arms are different. They castings are the same, but the bosses where the holes are drilled and tapped for the mount arms are not drilled and tapped in the right place to use the block in and E30.


    Are you sure you didn't pull that engine out of an E28 528e?

    The car was a 1990 525i and I pulled out the motor myself I know the owner of the yard and he put the car in a shaded area so I could do my work with the help of one of the guys from the yard, all I had to do was tip the guy for helping me.

    About the motor mount holes I think your wrong same casting means identical blocks besides this is the 5th M20 from a 525i I pull to replace motors on E30's there are more 525i than E30's with M20 all E30's i find are 1.8's even the E36's

    Thanks
    Xavier

    Quote Originally Posted by Rigmaster View Post
    Thanks Jim, I stand corrected.


    I know for sure that it is the case with at least some of the production, I don't have any idea what the mfg date break is.

    Why didn't you keep the E34 oil pan and dip stick that is what i allways do!!

    OK guys so after all is said the motor I pulled out is useless for me
    unless I want to make my E30 an eta.

    No possible combinations? this bottom end is in better shape than mine
    I got the E30 because it had been recently painted and the interiors are in excellent condition except the dash which I have one the car had been sitting in a garage for 3 years it stopped running a few months after it had been painted and sat there till i pulled it out for $600.

    the motor had the water in it like orange sludge, maybe i should pull the lower end out strip it and have the block dipped to clean it then just reassemble with the same parts just new rod bolts and maybe new bearings and rings.

    Anyone need an eta engine? make me an offer and come get it.

    Xavier
    Last edited by Xavier; 05-24-2010 at 08:59 PM. Reason: Automerged Doublepost

  7. #7
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    If you put an 885 head on the eta block you can have a motor that is arguably better than an M20B25. Get super eta pistons, bigger injectors and intake, and you'll have a nice little M20.
    1998 Technoviolet M3 Convertible

  8. #8
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    Quote Originally Posted by Strelok View Post
    If you put an 885 head on the eta block you can have a motor that is arguably better than an M20B25. Get super eta pistons, bigger injectors and intake, and you'll have a nice little M20.

    Ok the 885 head on an eta block?
    I noticed the eta block has dish style pistons which at TDC are lower than the edge of the block but the regular pistons on my 89 are higher than the
    edge of the block, they stick out at a slant about 5mm that tells me it would have higher comression than the combo you mentioned could you elaborate why the 885 head on an eta block renders a motor better than a M20B25

    Thanks

  9. #9
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    With the stroker setup as they call it, you get the full 2.7 liters of displacement, with the superior valvesprings, intake, TB, etc. of the B25. There's not much of an HP increase (sometimes less) but quite a bit more torque than a standard B25.

    I've heard that i pistons don't work, there's not enough clearance. The ideal pistons for this setup are super eta pistons, which can be found only on 1988 325e's. They have less of the dish style, allowing for higher compression. Strokers with eta pistons (like mine) have inherently lower compression. You could go this route if you're considering FI, as it's an ideal platform.
    1998 Technoviolet M3 Convertible

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