Future plans for the 635CSi

July ’18

After taking a little time off for fundraising, I’ve turned my attention back to the E24. There are a few significant problems I’ve been pondering. In no particular order:

• Significant battery drain (I have no good ideas yet but I’ll start pulling fuses soon).
• Smoking a lot (probably oil seeping past the valve seals).
• Tends to idle and run really lean when the car warms up (temp sensor? vac leak? No real idea).
• Has some troubles with shifting once the lube gets warmed up (synchros are worn, or I’m running the wrong lube).

To solve those problems, I pulled my spare B35 head out. Irritatingly, the seller lied about the condition of this motor. I’m not too annoyed, it was a bargain. The head is bowed significantly, with overheating being the most likely contender. Maximum out-of-flatness is 0.012″, this one is a little over 0.030″.

So it’s back to square one. I started researching B34 combos, came across this lovely article from Fritz’s Bits. Very common sense stuff, seems to contradict a lot of other articles I’ve read. This does seem more my cup of tea, so I’ll be rebuilding the Euro M30B34 with B35 controls instead of the full B35 head upgrade.

To accomplish this chore, I pulled out my last spare M30 cylinder head, a filthy old B32 part. This was removed from my old ’81 633CSi due to bent valves. I’ve pulled it all apart to see if anything can be salvaged. Although it was clearly neglected…lot of roasted oil…it actually doesn’t look awful. Check it out:

What are your thoughts? Looks to me that number 5 had a very bad day a few years back. I had to use a great deal of persuasion to drive those valves out. That #5 exhaust valve was quite the struggle: firmly clamped down on the retainers…dead-blow hammer to the face…penetrant right into the keepers…you have to take your time with fun like that! Things didn’t look awful once they were all fished out. They look good, but I’m still learning here…not drawing any conclusions yet.

The first job for my new parts washer is the M30 stuff. I’m listening to it munch on a set of pistons currently. Updates will follow!

March ’18

I’ve grown quite fond of the E24 during my short tenure of ownership. It has a few problems, but it’s been well worth the effort in my humble opinion. And (other than my wife) who else’s opinion would matter?

Whats next? The next phase…those inevitable upgrades! Let’s start off with the motor. I’ve considered several options. The larger BMW V8 and V12 motors aren’t really a good fit for my intended purpose, and BMW has already built that car. (Still, it’s tempting to daydream: how about a 640CSi running an M60 with a 6 speed? Or perhaps a 654CSi with an M73B54 V12?). IMHO the older inline-6 motors and a manual gearbox are essential to my understanding of Freude am Fahren. That leaves me with two basic choices. One is a hybrid M30, customized to enhance the tractable delight of those big old M30s. The other is a turbocharged M30 (or M106).

The hybrid M30 is simply bolting together all the best parts BMW offered. The M30 came in many versions with quite a lot of interchangeability. With a little skill it’s possible to develop a bespoke version. So what’s my current planned recipe?

1. It starts with the Euro B34 bottom end. It already has the 10:1 high-compression pistons.
2. The single mass flywheel will be staying, of course. I’ll never give that up! In all honesty, that flywheel is the most effective performance upgrade I’ve ever done to a car.
3. I’ll likely add an oil cooler and a windage tray to the B34 mid-sump pan.
4. The next component will be the B35 head. It has larger ports, larger valves, a more aggressive cam and better intake manifold design. There is a slight problem with the B35’s larger combustion chambers slightly dropping the compression ratio. I’ve been lucky enough to find a skimmed head that should mitigate that snag.
5. Likewise, I’ll keep the B35 electronics with the Bosch/Volvo EV6 injectors and AEM wideband. That 1.3 version of Motronic is a little quicker and a bit more reliable in my experience. I’ve also been doing a little research into an even newer Motronic, the 3.3.1 version. It supports a lot of extra goodies, and reacts far faster. The full sequential injection is what I’m really looking for. The individual coils and MAF are just icing on the cake.
6. I’ve also been researching other mods. There is a rumor floating around that aircooled 93mm VW pistons and 143mm Honda H22 rods will make a hellacious stroker. I’ve also been tinkering with setting up TunerStudio for a little monitoring. Eventually, a Moats Ostrich might find its way inside the DME too.

The M106 I just bought is also a strong contender (but then I caved in and sold it). If I stumble across another, it’s a worthwhile choice. It can be a really powerful engine and the big parts fit into an E24 very easily. There are significant downsides: the turbo is not an easy fit, electronics are crude and problematic and a complete exhaust system will need to be cobbled together.