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M20 Conversion For Dummies

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(edited)

R3vlimited has a big thread on it, with tons of people cross referencing all the specs. Wiki also matches.

 

Right, I'm one of those guys on there (skifree).  A lot of that can be rather convoluted and confusing right off the bat.  A good straight forward intro can be found here .....

 

http://www.strictlyeta.net/technical/328i_1.html

 

In fact that site in general is a great intro.

Edited by AceAndrew

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Will a m20 out of 1988 e320ix work in 2002 for a swap... thanks guys

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I have been looking through the forums, and everyone always talks about a E30 325i as the donor car for an M20 swap.

Would the M20B25 motor out of a BMW e34 525i not work great ? In fact I have never seen a E34 525i mentioned as a donor car, but it should work fine? Could it be because so few E34 with M20B25 engines was sold in the US (BMW2002faq.com has primarily US members)?

 

The only items I get using an E30 donor car over the E34 is the right hand side engine mount (if you would reuse that), and some of the radiator hoses. Everything else in regards to the engine should be the same. Can anyone confirm this?

 

E34 and E30 headers are the same.

E34 525i also uses a 228mm flywheel (at least for the stick shift versions)

 

I will be Installing the engine with the following components:

  • Getrag 245 5-speed with overdrive out of an E21 323i (M20 housing).
  • E21 323i radiator
  • E21 LSD Diff 3.45 - Late model 6-bolts converted to 8mm output shafts.
  • E21 3-bolt drive shaft
  • E30 318is in tank fuel pump (1990-1991)

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It is essentially the same except for a couple minor details.  The E34 M20 dip stick goes into the oilpan rather than the engine block (the hole on the block is filled with a metal plug).

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Thanks Andrew,

 

I looked further into whole E34 M20B25 vs E30 M20B25 thing.

The oil pan and engine mounts are different. The E34 M20B25 does not have an oil cooler fited from the factory. Tubing to AFM sensor are slightly different. Parts are interchangeable between the two "engines".

 

However mixed information exists on the M20B25 motor mount bosses when comparing an E34 to an E30! They seem to be different on the block depending on year of engine (pre or post March 1988?) or transmission type? I'm not sure. Can anyone elaborate on this?

 

Different findings on the matter...

http://forums.bimmerforums.com/forum/archive/index.php?t-1770154.html search for "M20 block (post 3/88)" on the page.

http://forums.bimmerforums.com/forum/showthread.php?745611-e34-M20-into-an-e30&highlight=e34%20m20

 

For those who can read a bit of German;

http://e30-talk.com/allgemeines/t-unterschied-m20b25-aus-5er-e34-und-3er-e30-nfl-48348.html

http://e30-talk.com/antrieb/t-motortausch-320i-cabrio-89-a-36843.html

 

Especially this post is interesting, but my German is not that good (something about engines build until 10.87 do not  have the mount bosses for both E30 and E34???):

http://e30-talk.com/antrieb/t-m20b25-aus-e34-e30-88835.html

 

It is clear from the German forum that some E34 M20B25 engines do have motor mount bosses that accept both E34 and E30 motor mounts just fine, will some people say they have encountered engines that don't.

 

 

The M20B25 E30 and E34 oil pans are interchangeable.

E30 oil pan - Note that the dip stick is mounted on the engine block (1 hole):

ODlfcA==.png

 

E34 oil pan - Note the dip stick is mounted on the oil pan next to the oil sensor (2 holes):

OTRfcA==.png

 

Some work is required to enabe the E30 dipstick installation on a E34 block. The metal plug/dowel can be removed from the E34 engine block, but is not my idea of a lot of fun. Any knowledge about this operation?

 

Reusing the original E34 oil pan would be optimal (no work required). It should work on an BMW 2002 E10, as AceAndrew is using one on his M20 triple weber-build (http://www.bmw2002faq.com/topic/116731-m20-triple-weber-build-x2/)

 

So All-in-All it seem possible to use an E34 engine when executing a M20 swap, if the engine in question do have both the E34 and e30 mount bosses. If it does not the engine mount in the 6into2.pdf guide will not work, as it is baed on the E30. A new custom engine mount design could be created for the E34 mount bosses, but this is a cumbersome task if possible at all.

 

 

Does anybody know if the ECU wires do have the same color coding on the E34s and E30s? At lest the C101 connector plug should have the same order/pin location, right?

Edited by Thorbjorn

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I have done some more research on the M20B25 engines out of the 5-series E34.

 

All M20 engines produced since November 1987 will have mount bosses that will accept both the E30 and E34 engine mounts. This is based on information from the German forums. I did have a friend help me out with some of the German.

 

M20 engines produced before November 1987 will have vehicle specific engine mount bosses. E.g. an M20B27 from an E24 will not accept the engine mounts from an E30, and vice a versa.

 

Since the first E34 are produced in 1988, all M20B25 engines from these cars will accept E30 engine mounts, and work in the 2002 (E10). Chris from Only02.com has confirmed two installations using his 2002 engine mounts and the E34 M20B25 engine.

 

I speculate that people stating otherwise in regards to the engine compatibility have come across engines that were removed from the original car, and was misinformed about the source.

 

The part no. for the M20B25 exhaust header is the same for both E34 and E30 cars, so it will work in a M20 swap as well.

 

The AFM piping is different on the E34 and E30. I will post if they fit or not when I get around to the engine installation.

Edited by Thorbjorn

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(edited)

I'e been off the forum for quite a while due to a pretty serious brain injury, but I'm 85% back. I'm trying to get the 2002 M20 conversion running again, but I need to replace the in-tank fuel pump. Here's the prob. I bought a 1990 318 fuel pump from Oreilly, but the wiring plug is wrong. There is one available from Autozone with the right plug, but it only has 1-tube coming out of the top. My old pump has 2 tubes.. Here are views from the top.

 

 

http://www.oreillyauto.com/site/c/detail/IDF0/A30159/02535.oap?year=1991&make=BMW&model=318i&vi=1011249&ck=Search_C0401_1011249_668&pt=C0401&ppt=C0025

 

http://www.autozone.com/fuel-delivery/fuel-pump/airtex-fuel-pump/bmw/318i/1991/4-cylinders-1-8l-fi-dohc/896081_917696_4921_1543/

 

 

 

Any ideas?

 

Thanks,

Doug

post-9199-0-21541600-1414945211_thumb.jp

Edited by punchesdfw

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Any reason the guide specifies those particular Ecu's? 153/173? I have an M20B25 with the Getrag 260 that came without an ecu and now have the opportunity to buy an active autowerke chipped 308 ecu that came out of a same year E30. It's a good price, am I asking for headaches if I go with that Ecu?

Thanks

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Sorry, that should read 380 from what the owner told me. I realized that the 308 is on the list. My apologies.

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FWIW, the M10 and M20 flywheels ARE identical (if comparing two flywheels with the same clutch size, and single mass), but the ring gears are not. You have to swap the ring gear if you're moving the flywheel from one engine to another. 

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Well i have been trying to get my 02 undergo a e30 system. But when i start it dies after 4-6 seconds? I have only the e30 green and black from the ECU to coil and and black from ecu to taxo, green from ECU to ignition, what is wrong? Her is how i have spliced the wire to 02 system:   


So here are the 9 wires that go to the round connector:
1. Black/yellow - Starter signal - Black on 02 engine loom. edit:black/white from 72/73 on, check colour at ignition switch. 
2. Green - Coil +ve - Green on 02, this is the wire that goes to the coil along the bulkhead. 
3. Brown/white - Temp sender - Brown/white or Brown/yellow on 02 engine loom. 
4. Brown/green - Oil pressure light - Brown/green on 02, on the bulkhead. 
5. Blue - ignition (charge) light - Blue on 02 engine loom.
6. Green/violet - Fuel pump +ve - Green/white on 02, follow this wire along your drivers side inner sill from the rear, it connects to the car loom near where the main harness goes through the bulkhead and on to the fuse box. Upgrade this connection, consider adding an inline fuse. 
7. Green/yellow - diagnostic socket - do not connect on 02
8. White/blue - diagnostic socket - do not connect on 02
9. White/black - diagnostic socket - do not connect on 02

Fuel pump relay:
Red - ecu/injection main power - battery +ve on 02. I mounted the fuel pump relay on the inner wing and had to extend this wire to the battery. Edit: some e30/28 looms connect this to +ve via the alternator, otherwise connect directly to the battery. 

Small 3 pin connector near ecu main plug, 3 wires. 
1. Green - ecu/main relay 'on' signal - Green on 02,from ignition switch. You can connect to the small 3 pin connector by the ecu, or connect into the same wire at the other end of the E30 loom near the fuel pump/main relay, and extend it to the fuse box and find an ignition +ve there. Must be +ve on start and on run. 
2. Black or Black/blue - rpm (tach) signal - small black on 02, coil -ve, you can extend the wire from the 3 pin connector to the tachometer connection on the cluster, or leave disconnected and leave the original tach wiring (black) from the 02 coil. 
3. Brown/yellow - do not connect on 02

The pump primes and starts when the engine runs the 6-8 seconds then dies?
Where have i gone wrong

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