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Thread: 1979 528i with mystery motor. Might be an M90?

  1. #1
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    1979 528i with mystery motor. Might be an M90?

    Hi everyone,

    my name is Marius. I live in Switzerland and have recently acquired a 1979 E12 528i in Polaris silver with several added ALPINA pieces, such as 16" wheels, front and rear spoilers, steering wheel and additional gauges for oil temp and pressure as well as voltage. Besides the cool lok, what really sparked my interest in the car was the previous owner mentioning it having a more powerful replacement engine.
    Well, fast forward a few weeks, and here I am devouring all I can learn about M30 and M90 engines from various sources on the web. However, there are a few, well, let's say, irregularities with my engine that I'd like to share with you. Any input is highly appreciated.

    1. I checked the serial number stamped on the flat spot towards the back and the gearbox. It reads "6560685" which corresponds to the VIN. The rest of the flat spot is empty.

    2. On the right hand side of the block, there is the number "1270006" above "BMW" and the date code "24K79" (meaning November 24th, 1979, right?) below "1Z". My car papers say that the E12 was first registered in Switzerland on March 5th, 1979. So it definitely is a later produced and thus a replacement engine.

    3. It gets even better once we turn to the left hand side of the block: clearly visible is a raised water jacket running from cylinders 1-4, like I've seen on pictures of M90 engines. However, whereas in those pictures it usually says "3.5" on that said water jacket, in my case it says "2.5 / 2.8". I have never seen this combination of raised water jacket and 2.5/2.8 inscription anywhere before. Also, it seems that the color and surface texture of the part of the water jacket that has the numbers on it differs quite visibly from the other parts to the left and right.

    4. I then turned my attention to the cylinder head. It reads "1304473" but then to the right, between the inlets for cyl. 5&6, thee is no "3.5". Instead, that area seems to have been fileed or ground, maybe in order to remove evidence of the "3.5"L displacement? Remember, my car is titled as a 528i, and in Switzerland, swapping a 3.5L motor would mean immense administrative effort and costs to get it titled and approved for road use. If at all.

    5. Well, what else? I thought... and had a look at the DME. It's a Bosch unit "0 280 001 114", which seems to have been used exclusively with 3.4/3.5L engines in the M535i or early 635CSi. Smaller engines used a different Bosch part (0280001108).

    6. Finally, I checked some auxiliary part numbers like the L-jetronic ("banana") plenum (1 266 599 225), which appears to have been used on the 635CSi as well. But that might not necessarily mean as much as the previous findings.

    By the way, the car is equipped with a GETRAG 265/6 long geared 5-speed transmission and a side-loader differential which is supposed to be a 25% LSD. But I haven't checked its part number yet.

    Anyways, thank you for reading/listening. What do you think, which engine might it be?

    And how would you proceed from here on? Examine the piston tops, I heard, would be one way. Or of course, open up the engine and measure the bore...

    Best regards, Marius

    I added a few pictures:
    IMG_20201017_161410.jpg IMG_20210102_170435.jpgIMG_20210105_180447.jpgIMG_20210105_175008.jpgIMG_20210105_175027.jpg
    Last edited by E12mysterymotor; 01-06-2021 at 02:16 AM.

  2. #2
    Join Date
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    here it says: the M90 has a water jacket running horizontally on the outside of the block from cylinder 1 to cylinder 5.
    https://www.bimmerforums.com/forum/s...450-M30-vs-M90
    Shogun tricks and tips for the E32 series are HERE!

  3. #3
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    Thank you, @shogun.

    Does anybody know whether this long water jacket is unique to the M90 engine (M88 block, respectively) or are there other blocks with it?

    EDIT: I have found one example of a 2.5/2.8 block with a long raised water jacket. LINK. Albeit with a cyl head for a B25/28/30 engine, unlike the 35 head on mine.
    Last edited by E12mysterymotor; 01-07-2021 at 07:39 AM.

  4. #4
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    I'm still hung up on this picture: long raised water jacket, but saying "2.5/2.8", combined with obvious differences in the surface.

    IMG_20210105_175008.jpg IMG_20210105_175027.jpg

    EDIT: I have found one example of a 2.5/2.8 block with a long raised water jacket. LINK. Albeit with a cyl head for a B25/28/30 engine, unlike the 35 head on mine.


    Also, the ground or filed off area on the cylinder head where it's supposed to say "3.5". Head is #1304473 (a 3.5L head, right?). Coincidence? I doubt it...

    IMG_20210105_180447.jpg
    Last edited by E12mysterymotor; 01-07-2021 at 07:38 AM.

  5. #5
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    Just a note that a discussion about this engine has developed in this thread here: https://www.bimmerforums.com/forum/s...y-motor-(M90-)

  6. #6
    Join Date
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    BMW 325i
    Quote Originally Posted by E12mysterymotor View Post
    Just a note that a discussion about this engine has developed in this thread here: https://www.bimmerforums.com/forum/s...y-motor-(M90-)
    I'm sure you have a 3.5l engine. You are correct with all your assumptions. The punched in number on the back above the starter does not look original. The casting numbers 1270006 and 1304239 are definitely for a 3.5 block.

    P2170004.jpgP2170010.jpgM88.jpg
    Last edited by mg681; 01-28-2021 at 12:55 PM.

  7. #7
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    Thank you, mg681!

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