M20 to M30 Swap Considerations in a 528e Chassis
Posted: Dec 06, 2024 10:35 AM
M20 to M30 Engine Swap Differences in a BMW E28 528e Chassis
FWIW - My 528e is a 1986. The M30 engine I swapped in was from a 1986 535. And the wiring harness I used was from a 1986 535. Are there model year differences? I don't know. RealOEM is your friend for those questions.
This is NOT a manual swap shopping list. I’ll assume you have the appropriate transmission and driveshaft for the result you’re looking to achieve. I had a manual transmission equipped ’88 535is to refer to while doing the swap so I could see what “right looked like” when I invariably got stymied. Here are the “I didn’t think of that” things I encountered:
The M30 engine uses different mounting brackets, wiring harness, flywheel (M30 does NOT use the dual mass flywheel!), exhaust manifolds, and ECU.
You can reuse the power steering pump, alternator, A/C condenser, and coil. However, the first three all require M30 specific brackets to mount to the engine. AND the PS pump requires a different pulley! Belts are unique to the M30.
Radiator is different. Hose connections are reversed as to which side the top and bottom connect to. Need a fan shroud too. Fan can be reused. Oh, and the wiring for the sensors can be reused. You just need to free up the wiring behind the grill and run it from the driver’s side to the passenger side. Hoses are unique to the M30.
Radiator overflow tank mounts on the other (driver’s) side of the engine bay, is a unique shape, and there’s really nothing to mount it to so you’ll have to fab up a bracket. You can probably use the one from the 528e. I had one from a 535 so I just used that. You’ll have to extend the coolant level sensor wiring from the passenger to the driver’s side of the car. I thought there was wiring on driver’s side for the coolant sensor as there is a matching connector, but it didn’t work.
The 528e is a vacuum assisted brake set up, so you’ll need to tap the manifold and install a connection to provide the vacuum. The good news is the “brake bomb”, et. al. go away so at least one leak source disappears!
If running a manual tranny, you’ll need the longer bell housing sensors unique to the M30. The M20 ones aren’t long enough.
You’ll have to source an M30-specific exhaust system. OE systems are bordering on unobtainable, and even if you could find one the shipping would be ridiculous. A competent exhaust tech/welder could build you one for the shipping cost it would seem.
The bracket that supports the cruise control and throttle cables on top of the engine is different for the M30.
Starter is different, maybe. I put the M20 one next to the M30. They look the same, except that the M20 one is about ¼” shorter. Running the M20 part number through RealOEM.com showed no commonality. I took that as gospel and ran the M30 one. I will say, bench test your starter and mount it (and the flywheel) on the engine before you put the engine in the car!
Air Conditioning lines from the compressor to the firewall are different in the 528e. They run a little higher along the frame rail and interfere with where the M30 air filter assembly wants to be positioned. The solution is some form of after-market conical air filter. Like the coolant reservoir, you’ll need to fab up some sort of support.
I went manual to manual on my swap. That made things simple regarding clutch master and slave, pedal assembly, etc. The only issue you may run into is the shifter carrier (i.e. sheet metal one versus the longer rod type). My 528e M20/265 setup used the sheet metal carrier. My M30/260 setup came with the longer rod type carrier which requires a bracket in the tranny tunnel to support the carrier. Not that big a deal if you have to fab/drill/weld, but I was able to reuse the sheet metal one.
Corrections always welcome. PM for questions. Pix available.
FWIW - My 528e is a 1986. The M30 engine I swapped in was from a 1986 535. And the wiring harness I used was from a 1986 535. Are there model year differences? I don't know. RealOEM is your friend for those questions.
This is NOT a manual swap shopping list. I’ll assume you have the appropriate transmission and driveshaft for the result you’re looking to achieve. I had a manual transmission equipped ’88 535is to refer to while doing the swap so I could see what “right looked like” when I invariably got stymied. Here are the “I didn’t think of that” things I encountered:
The M30 engine uses different mounting brackets, wiring harness, flywheel (M30 does NOT use the dual mass flywheel!), exhaust manifolds, and ECU.
You can reuse the power steering pump, alternator, A/C condenser, and coil. However, the first three all require M30 specific brackets to mount to the engine. AND the PS pump requires a different pulley! Belts are unique to the M30.
Radiator is different. Hose connections are reversed as to which side the top and bottom connect to. Need a fan shroud too. Fan can be reused. Oh, and the wiring for the sensors can be reused. You just need to free up the wiring behind the grill and run it from the driver’s side to the passenger side. Hoses are unique to the M30.
Radiator overflow tank mounts on the other (driver’s) side of the engine bay, is a unique shape, and there’s really nothing to mount it to so you’ll have to fab up a bracket. You can probably use the one from the 528e. I had one from a 535 so I just used that. You’ll have to extend the coolant level sensor wiring from the passenger to the driver’s side of the car. I thought there was wiring on driver’s side for the coolant sensor as there is a matching connector, but it didn’t work.
The 528e is a vacuum assisted brake set up, so you’ll need to tap the manifold and install a connection to provide the vacuum. The good news is the “brake bomb”, et. al. go away so at least one leak source disappears!
If running a manual tranny, you’ll need the longer bell housing sensors unique to the M30. The M20 ones aren’t long enough.
You’ll have to source an M30-specific exhaust system. OE systems are bordering on unobtainable, and even if you could find one the shipping would be ridiculous. A competent exhaust tech/welder could build you one for the shipping cost it would seem.
The bracket that supports the cruise control and throttle cables on top of the engine is different for the M30.
Starter is different, maybe. I put the M20 one next to the M30. They look the same, except that the M20 one is about ¼” shorter. Running the M20 part number through RealOEM.com showed no commonality. I took that as gospel and ran the M30 one. I will say, bench test your starter and mount it (and the flywheel) on the engine before you put the engine in the car!
Air Conditioning lines from the compressor to the firewall are different in the 528e. They run a little higher along the frame rail and interfere with where the M30 air filter assembly wants to be positioned. The solution is some form of after-market conical air filter. Like the coolant reservoir, you’ll need to fab up some sort of support.
I went manual to manual on my swap. That made things simple regarding clutch master and slave, pedal assembly, etc. The only issue you may run into is the shifter carrier (i.e. sheet metal one versus the longer rod type). My 528e M20/265 setup used the sheet metal carrier. My M30/260 setup came with the longer rod type carrier which requires a bracket in the tranny tunnel to support the carrier. Not that big a deal if you have to fab/drill/weld, but I was able to reuse the sheet metal one.
Corrections always welcome. PM for questions. Pix available.