Project goals: motor, transmission & chassis

When I first went to see this car, I immediately created a project plan. My plans are typically pretty mundane; there are so many ways to waste money on cars. I always try to stay within my means, feet firmly on the ground. I’ve seen far too many projects that just ran off the rails. Primarily, I strive not to exceed the net sales value of the car. What’s the point of that? Once I’ve gotten that number, it becomes a baseline budget estimate. Then I can narrow down the possibilities. Should I make it a decent daily driver? I’m not typically interested in like-new restorations. If it’s a little ratty, should I modify it instead? If the choice is ‘mod’ instead of ‘resto,’ how far should it go?

BMW is – first and foremost – an engine manufacturer. They’d been designing aeromotors long before they started with motorcycles & cars. It’s their middle name, literally. In my small way, a few of my fondest automotive memories are the result of their vaunted inline-six motors. Much of that mystique is due to the M30 “Big Six” motor. Basically just a modified M10 four-cylinder (fortified with 50% more cylinders), BMW produced them over a quarter century. They provided much of the basis for BMW’s racing successes in the 70s and the resulting sales successes in the 80s. These motors are still not to be underestimated, even today.

Of course, I didn’t want just any old M30…I wanted the best version I could afford. I decided to ignore the expensive racing variants (the Motorsport M88, M90 and S38) due to high maintenance costs. Two of the more pedestrian M30 motors stand out. The European version of the M30B34 was significantly more powerful than the North American-market M30B32 version. It was built for more demanding customers, driving higher speed European highways, and sloppier emissions regulations. This motor was bored & stroked with higher compression pistons, hotter cam and a better-flowing exhaust system. It was also typically fitted with an oil cooler, a single-mass flywheel and a heavy-duty drivetrain. Nicknamed the “dirty M30” due to a lack of any emissions controls whatsoever, it’s about 25% more powerful and a lot more fun than any of the US versions. Eventually, BMW retired this motor and replaced it with a “world-model” engine, the M30B35. That version got better flowing manifolds, a more efficient head casting with larger valves, and an updated version of Bosch Motronic. It was better in many ways than the earlier Euro motor and almost as powerful. It’s also cheaper & far more common; the Euro motor was never offered for sale here because it couldn’t pass long-term emissions testing in the USA. So my project would have to have one of those two…but just to get it back on the road. I’ll be building my own motor later, combining the best of these two motors into a naturally-aspirated beast!

So how did it turn out? I patiently waited to find the proper donor. I passed up a Euro E23 735i because it was a flood victim, the seller wouldn’t negotiate, and I didn’t have enough cash. Then I stumbled across a complete ’82 Euro 635CSi right next door in Ohio, desperate for redemption. In this case the “dirty” moniker was more than apt…this car had been trapped in a freshwater flood, totaled by an insurance company, auctioned for scrap, then left in a field to rot. It was a moldy rusted-out disaster, fit only for mice. The powertrain was a hidden treasure…certainly good enough to bring it back to life. It was fitted with one of Getrag’s toughest transmissions: the excellent 265/5 overdrive 5-speed gearbox. The only mechanical disappointment was the differential…unfortunately an open non-locking type. Oddly, it appeared to be a 188mm ring in a 210mm case. Never seen anything like it from BMW. I ended up finding a far superior diff somewhere else. Read all about that process here.

I also lucked out with a few choice parts that came along with these cars. I couldn’t use them, so I sold them to fund the project. The ’86 donated a full OEM M5 exhaust, M5 quad-piston front brakes and the M5 radiator, among other pieces. I sold a lot off the ’82 Euro as well: desirable manual transmission parts, an original Becker stereo, the rare trunk-mounted spoiler, a few decent trim parts like windows, rear seats & mirrors. I also scrapped the chassis & wheels.

I did keep a few of the tasty upgrades. I lucked out on the ’86 because it already had Bilstein Sport struts/shocks, Ireland Engineering springs & M5 sway bars. I installed the Euro’s front calipers onto the ’86 to replace the M5 parts I’d sold off. But then I found a nice ’95 740i, so I swapped those big E32 brakes onto my E24 knuckles. The key to fitting these larger brakes is to use E34 540i parts. The E32 front calipers had one more bonus, they fit very nicely onto a spare set of E28 M5 300x20mm rotors left over from when I bought the car. Check out that project here. These aren’t difficult parts to source, the E34 540i kit is available from many BMW specialists. You could easily do it from most online parts houses. They certainly perform as advertised, even with the stock master cylinder.

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