m54 swap into 1975 e12 520i

[Pete K]

I’m swapping an m45b30 into my 1975 e12 520i. I found lots of info about e28s with m52 swaps and some with m54, but not much of anything on e12s. There differences from the e28 seem to be just enough to make most of it irrelevant, so I thought I’d post some info here in case someone else is doing the same project.

Here’s what I started with.

From the start, a 4 cylinder was a challenge. The different front panel cut down space, but it was what I had to work with. My 520i has been a track car since 2000 and became track only in about 2007. I went down the path of building a really high spec “race” engine with high compression, big cams, big valves, ITBs, etc, etc and it was fantastic…for two track days before blowing up! It’s been off the track since 2015 and I wanted a reliable engine, I could leave stock, but still make good power. My “new” track car is an e46 320ci with an m54b30 swapped in. This is my fourth e46, so I’m pretty familiar with them and really like the m54's smooth power. The m54b30 is 10 kW more powerful than my m535i’s m90 but is around 60 kg lighter (depending on which source you read).
Another complicating factor is that I’m in Australia, so my car is right hand drive. This put all the steering components in the way of the exhaust.

The first step was actually to check the driveline angles of the donor car. There’s a lot of opinions and guides online, but I couldn’t find any actual factory specs, so we were looking at 1-3 degrees, parallel crank/gearbox and diff and rear section of tailshaft at least 1 degree different. Diff and engine came out at 2.5 degrees and rear half of tail shaft at 3.2 degrees. Keep in mind, this is not absolute. We didn’t have a reference, so essentially, just the 0.7 degree difference was what we knew.

IMG_6087 - lo res.jpg (42.68 KiB) Viewed 2018 times

We then took the radiator, fuel supply system, computer and exhaust manifolds from the e46 to use in the e12.


We finally took the engine and gearbox out of the e12. Once this works, I’ll sell off the m10 parts to recoup some cash.



We trial fitted the engine to make sure it would actually fit (and as practice for the next 20 times we’d put it in!). The engine leveler is an absolutely essential tool. It would be hell without it.



With proof it would physically fit, I had to remove the radiator mount. It’s the 4 cylinder one that moves the radiator closer to the engine so the fan worked. That first cut was tough, but once I got started, it went pretty easily.



We had to take the oil pan off as you need the front sump. I ordered one, but it was coming from Belarus, so was weeks away. Luckily, I had a spare engine that came out of the 320ci, so it didn’t matter that the oil pan was off. The oil pick up and dip stick are also different. The “new” pan came with the right oil pick up but I’ll have to work something out for the dip stick.

IMG_5847 - lo res.jpg (64.98 KiB) Viewed 2018 times

We then fitted the engine again and made some temporary engine mounts.

Engine back out and fitted the gearbox. We’re using the ZF S5-31 that came in the 330ci (and other things). I see a lot of m50/m52 swaps that use the smaller gearbox. I already have that set up in the e46 320ci with an m54b30 and the gearbox is already suffering. I wanted to do it properly and use the right gearbox. This caused a fair amount of extra work as it is a bit larger.



I'll post more info as we go along. I've got the gearbox and shifter in, and I'll post some updates with videos and pics once I have them.

Wish me luck!

[Mike W.]

Wow, looks like an interesting and ambitious project. Question though, what happened to the M10? It's a pretty rugged engine, though I can see why the M54 swap.

[Pete K]

The poor old m10 ended up with a cracked block. It pressurised the sump and pumped all the oil out the breather. Then this happened.
No shade on the m10 though. That thing was bored out, had way too much compression, etc, etc, so it was only a matter of time.

[Pete K]

We got a bit more work done and some more videos loaded.

The ZF S5-31 is a lot bigger than the old Getrag 242 and even a fair bit bigger than the Getrag 250G in the smaller engine e46. It's a definitely bigger than the 240 series boxes you see in e28 swaps. It meant there was no way the engine and gearbox together were going to fit at the right angle.


Since we would be cutting the tunnel, I removed the rubber external protection and the foam and rubber internal sound deadening. I'll have to get on to the bitumen sound deadening later.


We marked out the parts of the transmission tunnel to cut by the simple expedient of "bumping" the gearbox into some undercoat sprayed under the car. Wherever the marks were had to go. We initially cut it with the grinder, but I got some proper steel cutting blades for the reciprocating saw and that was much easier, smoother and way less chance of fire in the car!


Once I had the gearbox actually sitting in the car, I could make up a transmission mount so it was at the correct angle. This was supposed to be a temporary mount, but it worked out so well I think I might just keep it. Laying the plates on the old mount to get the angles right worked beautifully.


I'm still waiting on the e34 m50b25 sump to arrive, but I had the 3D printed version. It wouldn't fit because of the oil pick up on the windage tray. I'm not sure if I need a new windage tray or not, so I just removed the spot welds and took the pick up mount off.


Once I'd done that, the 3D printed one fitted perfectly. There was about 5 mm clearance at least at each point, so I'm going to call that done.


Now the engine and gearbox were solid, I moved on to the tailshaft. I only had an e46 325i (manual) and e12 520i 4 speed shafts to work with. The output flange from the ZF is the large 96 mm PCD compared to the 76 mm for the Getrag in the 325i. I solved that by cutting the ends of the bolt holes out on the shaft flange. Once I'd done that, amazingly, the 325i shaft was the exact right length from gearbox to diff. A couple of problems though; 1 the spigot on the diff end of the e46 shaft is much deeper than the e12, so even though it was the right diameter and the flange bolt holes correct, it wouldn't pull the shaft flange all the way to the diff flange, and; 2 the location of the centre support bearing was right at the back of the e12 location, so needed modified mounts and because it was so far back, I couldn't get the bearing up high enough to get the same angle as the motor/gearbox. So that meant I had to move the centre bearing to in front of the existing mount and that meant cutting the shafts anyway. That meant I could use the front of the e46 shaft and the rear of the e12 shaft. I measured way more than 6 times, but I lost count. It worked out in the end though with the angle measuring up perfectly and it fitting like it was made for it. I had to make a "step up" for the centre mount out of angle iron and tube, and then the shaft angles were dead on.


My last things was to shorten the shifter support. There might be one out there that is the right length but this one will work fine when I get someone who can weld aluminium properly.


The drivetrain is "in the car" and all the angles and heights are correct, so it's time to start doing things to make it run like fuel, power, exhaust, cooling, etc. Still lots to do if we're getting this done by November!