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Thread: Let The M73 Swap Begin!

  1. #1
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    Let The M73 Swap Begin!

    I've just placed an order for an M73 (non N) engine with 70k miles on the clock for a swap into my '91. I plan to document the swap here for the purpose of 1) helping others who are interested in the swap, and 2) begging for assistance from all the folks on the forum here who are smarter than me when I run into the inevitable snags on the swap.

    I picked up a hoist and a stand to make the process a bit easier. I do have a 4 post lift, but that doesn't really help with this project.

    Question related to prepping the new engine. I would obviously like to seal everything up while I have it on an engine stand as that's the time to do it. I plan to replace all of the obvious gaskets. Should I also plan on the head gaskets while I have access or is that asking for trouble to disturb the heads?

    Thanks in advance for the help!
    MY SPEEDO ON THE 'BAHN!!! - @155!
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    '01 e38|M73 - Anthrazit Metallic|Schwarz|Shadow-Line
    '91 e31|M70 - Schwarz|Schwarz|M70

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  2. #2
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    search here for the step by step from WOKKE - he has it down to a science, having done about 10 of these already...
    The key is to swapping some M70 parts onto your M73, so the fabrication headaches are kept to a minimum. The biggest thing I found was that the M73 downpipes, don't match the exhaust pipes - you need to make sure that you get the downpipes (if your M73 came out of an E31 - if it came out of an E38, then those pipes won't work. WOKKE also sells custom fabricated solution for this issue.
    '93 850Ci - Mineralweiss Metallic
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  3. #3
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    Quote Originally Posted by TxGR8White View Post
    search here for the step by step from WOKKE - he has it down to a science, having done about 10 of these already...
    The key is to swapping some M70 parts onto your M73, so the fabrication headaches are kept to a minimum. The biggest thing I found was that the M73 downpipes, don't match the exhaust pipes - you need to make sure that you get the downpipes (if your M73 came out of an E31 - if it came out of an E38, then those pipes won't work. WOKKE also sells custom fabricated solution for this issue.
    Yes sir... I've read those threads multiple times and have them bookmarked for reference. My M73 is from an E38.

    I was curious on the downpipes though. If I buy the replacement downpipes for the E31 M73, wouldn't they bolt right up to my exhaust?
    MY SPEEDO ON THE 'BAHN!!! - @155!
    '07 e65|N62 - Alpina B7 - Black Sapphire|Black|Loaded
    '02 e46|M54 - Orient Blue|Beige|'Vert
    '00 e39|M52 - Anthrazit Metallic|Grey (Daughter's)
    '01 e38|M73 - Anthrazit Metallic|Schwarz|Shadow-Line
    '91 e31|M70 - Schwarz|Schwarz|M70

    '13 328i Auto - Black Sapphire|Coral Red|Sport Line|GONE
    '05 545i SMG - Jet Black|Black|Bamboo Anthracite|GONE
    '07 335i Auto - Montego Blue|Grey|GONE
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  4. #4
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    Whee!

    Let the fun begin. That should keep you busy over the winter. Heated garage?
    1993 850Ci.....159,600 miles and counting!

  5. #5
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    Quote Originally Posted by adwebinc View Post
    Yes sir... I've read those threads multiple times and have them bookmarked for reference. My M73 is from an E38.

    I was curious on the downpipes though. If I buy the replacement downpipes for the E31 M73, wouldn't they bolt right up to my exhaust?
    Yes they will, but used ones from an E31 are hard to find, and new ones are $$$$$.
    Talk to WOKKE, his are excellent and less than new OEM.
    '93 850Ci - Mineralweiss Metallic
    ALPINA B7 -Alpinweiss III


    ...the price of cool ain't cheap!

  6. #6
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    Quote Originally Posted by adwebinc View Post
    I've just placed an order for an M73 (non N) engine with 70k miles on the clock for a swap into my '91. I plan to document the swap here for the purpose of 1) helping others who are interested in the swap, and 2) begging for assistance from all the folks on the forum here who are smarter than me when I run into the inevitable snags on the swap.

    I picked up a hoist and a stand to make the process a bit easier. I do have a 4 post lift, but that doesn't really help with this project.

    Question related to prepping the new engine. I would obviously like to seal everything up while I have it on an engine stand as that's the time to do it. I plan to replace all of the obvious gaskets. Should I also plan on the head gaskets while I have access or is that asking for trouble to disturb the heads?

    Thanks in advance for the help!
    I'd do a leakdown test to check condition of the new motor. Look it over real carefully if it came out of a wrecked car. There may be damage that was overlooked (as my spare engine had).

    It was my understanding that Wokke used M70 heads on the M73 block to avoid the need for new down pipes.

    Looking forward to seeing your progress.

  7. #7
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    Quote Originally Posted by BMSman View Post
    I'd do a leakdown test to check condition of the new motor. Look it over real carefully if it came out of a wrecked car. There may be damage that was overlooked (as my spare engine had).

    It was my understanding that Wokke used M70 heads on the M73 block to avoid the need for new down pipes.

    Looking forward to seeing your progress.
    Yes sir. Planning on full leak down test. Although this engine has a 5 year, 50k warranty on it, so I donít anticipate any issues.

    Wolf did use M70 heads on some of his earlier projects, but there are more benefits to using the M73 heads and now that he has a way to address the exhaust issues. It seems the right way to go.


    Sent from my iPhone using Tapatalk
    MY SPEEDO ON THE 'BAHN!!! - @155!
    '07 e65|N62 - Alpina B7 - Black Sapphire|Black|Loaded
    '02 e46|M54 - Orient Blue|Beige|'Vert
    '00 e39|M52 - Anthrazit Metallic|Grey (Daughter's)
    '01 e38|M73 - Anthrazit Metallic|Schwarz|Shadow-Line
    '91 e31|M70 - Schwarz|Schwarz|M70

    '13 328i Auto - Black Sapphire|Coral Red|Sport Line|GONE
    '05 545i SMG - Jet Black|Black|Bamboo Anthracite|GONE
    '07 335i Auto - Montego Blue|Grey|GONE
    '05 545i SMG - (Euro Delivery 7/22/05)|Black Sapphire|Auburn|GONE
    '97 528i Auto - GONE

  8. #8
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    Quote Originally Posted by TedBobo View Post
    Whee!

    Let the fun begin. That should keep you busy over the winter. Heated garage?
    Yes sir! Heated, but not too far from a cold beer. If you, for some strange reason, at your house here in Indy this winter, stop by! Hopefully you are planning to be in the so cal weather though.


    Sent from my iPhone using Tapatalk
    MY SPEEDO ON THE 'BAHN!!! - @155!
    '07 e65|N62 - Alpina B7 - Black Sapphire|Black|Loaded
    '02 e46|M54 - Orient Blue|Beige|'Vert
    '00 e39|M52 - Anthrazit Metallic|Grey (Daughter's)
    '01 e38|M73 - Anthrazit Metallic|Schwarz|Shadow-Line
    '91 e31|M70 - Schwarz|Schwarz|M70

    '13 328i Auto - Black Sapphire|Coral Red|Sport Line|GONE
    '05 545i SMG - Jet Black|Black|Bamboo Anthracite|GONE
    '07 335i Auto - Montego Blue|Grey|GONE
    '05 545i SMG - (Euro Delivery 7/22/05)|Black Sapphire|Auburn|GONE
    '97 528i Auto - GONE

  9. #9
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    Quote Originally Posted by adwebinc View Post
    Yes sir! Heated, but not too far from a cold beer. If you, for some strange reason, at your house here in Indy this winter, stop by! Hopefully you are planning to be in the so cal weather though.


    Sent from my iPhone using Tapatalk

    Will be there for Christmas (against my wishes but wife has spoken) I'll give you a call.
    1993 850Ci.....159,600 miles and counting!

  10. #10
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    Bookmarking this thread - looking forward to following your progress!

  11. #11
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    Quote Originally Posted by TedBobo View Post
    Will be there for Christmas (against my wishes but wife has spoken) I'll give you a call.
    Funny how easily we get overruled by the domestic CEO.


    Sent from my iPhone using Tapatalk
    MY SPEEDO ON THE 'BAHN!!! - @155!
    '07 e65|N62 - Alpina B7 - Black Sapphire|Black|Loaded
    '02 e46|M54 - Orient Blue|Beige|'Vert
    '00 e39|M52 - Anthrazit Metallic|Grey (Daughter's)
    '01 e38|M73 - Anthrazit Metallic|Schwarz|Shadow-Line
    '91 e31|M70 - Schwarz|Schwarz|M70

    '13 328i Auto - Black Sapphire|Coral Red|Sport Line|GONE
    '05 545i SMG - Jet Black|Black|Bamboo Anthracite|GONE
    '07 335i Auto - Montego Blue|Grey|GONE
    '05 545i SMG - (Euro Delivery 7/22/05)|Black Sapphire|Auburn|GONE
    '97 528i Auto - GONE

  12. #12
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    So, Wolf is strongly recommending the M73 bottom end and M70 heads with cams. So, that certainly changes my game plan a bit.

    I was planning to simply refresh the M73 heads with valve stem seals and obviously refreshing gaskets. Now, if I am actually pulling the M70 heads, I need to decide if Iím going to get them machined, etc. Gut says yes, itís just Scope and budget creep (plus the cost of the cams).


    Sent from my iPhone using Tapatalk
    MY SPEEDO ON THE 'BAHN!!! - @155!
    '07 e65|N62 - Alpina B7 - Black Sapphire|Black|Loaded
    '02 e46|M54 - Orient Blue|Beige|'Vert
    '00 e39|M52 - Anthrazit Metallic|Grey (Daughter's)
    '01 e38|M73 - Anthrazit Metallic|Schwarz|Shadow-Line
    '91 e31|M70 - Schwarz|Schwarz|M70

    '13 328i Auto - Black Sapphire|Coral Red|Sport Line|GONE
    '05 545i SMG - Jet Black|Black|Bamboo Anthracite|GONE
    '07 335i Auto - Montego Blue|Grey|GONE
    '05 545i SMG - (Euro Delivery 7/22/05)|Black Sapphire|Auburn|GONE
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  13. #13
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    Are the M73 downpipes not able to be reproduced by a competent muffler shop?
    Last edited by 72tpik5; 12-07-2017 at 03:41 PM.
    Desecrator of all things Sacred

  14. #14
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    Let The M73 Swap Begin!

    Quote Originally Posted by 72tpik5 View Post
    Are the M73 downpipes not able to reproduced by a competent muffler shop?
    Actually, I believe itís possible to use the M73 E31 downpipes. I havenít confirmed with ECS, but it appears they are available for around $540 for the set.

    Wolfís position is that the performance gains are easier to attain via the M70 heads. But Iím still on the fence as for me the direct M73 transplant would be easier and a lot cheaper.

    Would love to hear from those who have done the full M73 swap (M73 heads) regarding performance.


    Sent from my iPhone using Tapatalk
    Last edited by adwebinc; 12-07-2017 at 03:59 PM.
    MY SPEEDO ON THE 'BAHN!!! - @155!
    '07 e65|N62 - Alpina B7 - Black Sapphire|Black|Loaded
    '02 e46|M54 - Orient Blue|Beige|'Vert
    '00 e39|M52 - Anthrazit Metallic|Grey (Daughter's)
    '01 e38|M73 - Anthrazit Metallic|Schwarz|Shadow-Line
    '91 e31|M70 - Schwarz|Schwarz|M70

    '13 328i Auto - Black Sapphire|Coral Red|Sport Line|GONE
    '05 545i SMG - Jet Black|Black|Bamboo Anthracite|GONE
    '07 335i Auto - Montego Blue|Grey|GONE
    '05 545i SMG - (Euro Delivery 7/22/05)|Black Sapphire|Auburn|GONE
    '97 528i Auto - GONE

  15. #15
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    Right. Using all the performance parts for the M70 with the increased displacement of the M73 bottom end makes the most sense. And power no doubt.
    Desecrator of all things Sacred

  16. #16
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    M73 direct transplant with proper tuning is the way to go. dont mess around with M70 heads.

  17. #17
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    Quote Originally Posted by dragon850 View Post
    M73 direct transplant with proper tuning is the way to go. dont mess around with M70 heads.
    The suspense is killing me.... Iíll send you a PM. Need to know how I get the tune!


    Sent from my iPhone using Tapatalk
    MY SPEEDO ON THE 'BAHN!!! - @155!
    '07 e65|N62 - Alpina B7 - Black Sapphire|Black|Loaded
    '02 e46|M54 - Orient Blue|Beige|'Vert
    '00 e39|M52 - Anthrazit Metallic|Grey (Daughter's)
    '01 e38|M73 - Anthrazit Metallic|Schwarz|Shadow-Line
    '91 e31|M70 - Schwarz|Schwarz|M70

    '13 328i Auto - Black Sapphire|Coral Red|Sport Line|GONE
    '05 545i SMG - Jet Black|Black|Bamboo Anthracite|GONE
    '07 335i Auto - Montego Blue|Grey|GONE
    '05 545i SMG - (Euro Delivery 7/22/05)|Black Sapphire|Auburn|GONE
    '97 528i Auto - GONE

  18. #18
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    I remember reading the various m70/m73 threads over the past few years and getting confused as to the "best" approach - hybrid or full m73 transplant. Very excited to see this thread and thinking that I would get the definitive answer - hah!
    Just an intellectual exercise for me at this point - but who knows what the next 12 months will bring...

  19. #19
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    I can make a tune for M73 no problem, its not a huge deal.

  20. #20
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    Why do people see so much trouble to change the engine to a car that will still be slow?
    seriously, if you want this heavy car to move you have to put TC or SC under the hood. Everything else is just money waste.
    Last edited by mikae31; 12-08-2017 at 11:10 AM.

  21. #21
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    Quote Originally Posted by mikae31 View Post
    Why do people see so much trouble to change the engine to a car that will still be slow?
    seriously, if you want this heavy car to move you have to put TC or SC under the hood. Everything else is just money waste.
    My M70 needs a refresh anyway, so why not swap in an M73 for a couple of thousand dollars vs. $10k+ on FI. If I can get ~370+ (along with my 3.91 LSD) out of this as my fun summer cruise car, then I will be happy. When I want to drive a SC car, I'll jump in my E65 B7 for 500+ HP.
    MY SPEEDO ON THE 'BAHN!!! - @155!
    '07 e65|N62 - Alpina B7 - Black Sapphire|Black|Loaded
    '02 e46|M54 - Orient Blue|Beige|'Vert
    '00 e39|M52 - Anthrazit Metallic|Grey (Daughter's)
    '01 e38|M73 - Anthrazit Metallic|Schwarz|Shadow-Line
    '91 e31|M70 - Schwarz|Schwarz|M70

    '13 328i Auto - Black Sapphire|Coral Red|Sport Line|GONE
    '05 545i SMG - Jet Black|Black|Bamboo Anthracite|GONE
    '07 335i Auto - Montego Blue|Grey|GONE
    '05 545i SMG - (Euro Delivery 7/22/05)|Black Sapphire|Auburn|GONE
    '97 528i Auto - GONE

  22. #22
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    Quote Originally Posted by mikae31 View Post
    Why do people see so much trouble to change the engine to a car that will still be slow?
    seriously, if you want this heavy car to move you have to put TC or SC under the hood. Everything else is just money waste.
    As if owning an 8 is a sound financial decision. I say if you don't like it the way it is, change it.
    Desecrator of all things Sacred

  23. #23
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    No regrets here on going FI. Just be sure to upgrade the brakes.

  24. #24
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    The slight gain in HP using the M70/Schrick combo, is not worth the extra work in my book. Also, the camshaft oiling spraybar on the M73 is 1000x better, and let's not forget the M73 has roller rockers. I agree with you, change out the front lower timing cover and just drop that baby in. You will be just as happy(especially with the 3.91),with a lot less work. I do the same thing: when I want a kick in the pants, I climb into the cockpit of the B7.
    Last edited by TxGR8White; 12-10-2017 at 11:15 AM.
    '93 850Ci - Mineralweiss Metallic
    ALPINA B7 -Alpinweiss III


    ...the price of cool ain't cheap!

  25. #25
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    Quote Originally Posted by TxGR8White View Post
    The slight gain in HP using the M70/Schrick combo, is not worth the extra work in my book. Also, the camshaft oiling spraybar on the M73 is 1000x better, and let's not forget the M73 has roller rockers. I agree with you, change out the front lower timing cover and just drop that baby in. You will be just as happy(especially with the 3.91),with a lot less work. I do the same thing: when I want a kick in the pants, I climb into the cockpit of the B7.
    Appreciate the feedback sir! Question for you and Ed (Dragon)... how deep do I go with replacing gaskets proactively since I will have this on the stand? Obviously, I will do all the timing cases and the upper and lower oil pans. I will also be using the valve covers and intakes from my M70 as I had those powder coated 2 years ago. So likely makes sense to go for the full gasket kit, but do I actually disturb the heads and replace the head gaskets? What about the valley pan gasket? I assume it makes sense to replace the valve stem seals proactively as well.

    This engine only has 70k, but I want to replace what makes sense to replace before I drop it in. Thanks in advance for the help!
    MY SPEEDO ON THE 'BAHN!!! - @155!
    '07 e65|N62 - Alpina B7 - Black Sapphire|Black|Loaded
    '02 e46|M54 - Orient Blue|Beige|'Vert
    '00 e39|M52 - Anthrazit Metallic|Grey (Daughter's)
    '01 e38|M73 - Anthrazit Metallic|Schwarz|Shadow-Line
    '91 e31|M70 - Schwarz|Schwarz|M70

    '13 328i Auto - Black Sapphire|Coral Red|Sport Line|GONE
    '05 545i SMG - Jet Black|Black|Bamboo Anthracite|GONE
    '07 335i Auto - Montego Blue|Grey|GONE
    '05 545i SMG - (Euro Delivery 7/22/05)|Black Sapphire|Auburn|GONE
    '97 528i Auto - GONE

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