The risks of buying old junk…

I’ve been looking to upgrade my high-compression M30B34. If you’ve been reading the other pages here, you might recall that the motor was salvaged from a flooded wreck of a parts car. The motor had been cleaned up and re-started after the flooding, but it must have sat for years afterwards. The oil pan had been cracked (most likely during a move), the engine was locked up, the original wiring harness was heavily rodent-damaged, and the Motronic DME had been flooded. A lot of condensation and corrosion problems were evident by the time I got to it.

Fast-forward a few months, and quite a few of those problems have been resolved. I managed to free up the motor, found an oil pan, cleaned up the intake, replaced most of the gaskets and adjusted the valves. But…I hadn’t resolved the wiring harness problems. Don’t worry – I had a plan!

A common upgrade is the later Motronic 1.3 engine management system from later BMWs. Although the M30B35 engine is nearly identical to my M30B34, mostly every part had been improved by BMW. Ten years of progress is well worth having. I did have a later E34 M30B35 harness but it wasn’t a full kit. The odds of finding a cheap working AFM and DME are pretty low, and I needed a lot of other stuff. It’s better (and usually cheaper) to have a whole running engine at your disposal, and they’re pretty cheap used.

So I set about finding an early ’90s 535i or 735i donor car. It took almost a year, but I found a good candidate a few hours away. Despite the high mileage (250K), I was interested. The engine looked great internally. The head was pretty fresh, no signs of overheating. The transmission shifted easily so I made an offer on the whole drivetrain. We agreed on a deal, pulled the motor, loaded it up into my minivan, and I brought it back home. With any luck, I could sell what I didn’t need as a complete motor and also a 5-speed manual conversion “kit.”

Unfortunately, I ran into a significant problem. Sometimes, there is only a very small indication of severe damage. If you know what to look for, it’s instantly visible. The block was cracked, right in the middle of the cooling jackets, on both sides. I had totally missed it until it sat outside for a week or two. Both sides of the block are very difficult to see in the car when the manifolds and accessories and fenders are in the way. But if ice is permitted to form in the coolant cavities, which will happen if the anti-freeze is diluted too far, the block will rupture since it can’t expand. In this case the cooling jacket was broken in at least one place. Considering the damage, I’d suspect the motor died of frostbite instead of overheating.

This is typically the result of improper storage. Fresh coolant could have prevented this from happening; that’s why they call it “anti-freeze,” right? Motors must be properly winterized – not only to protect against ice, but also the more insidious process of galvanic corrosion. Dissimilar metals generate a small electrical current in this process. Eventually this current will consume the sacrificial salts in the antifreeze (usually sodium phosphate or silicate) whether or not the motor has been run. Finally, this process will eat away at the higher-potential magnesium or aluminum components. If this was a rare engine, I’d consider having it repaired. It’s a pretty common motor; I’ll dismantle it, save a few goodies for myself, resell what I don’t need, and scrap the rest.

Despite the cracked block, it ended up being a slight gain. I managed to recoup my costs from selling many of the B35 parts. As a bonus, I kept the wiring harness & DME to upgrade the B34 in my 63CSi. I’m not done yet…the superior B35 intake & head might make their way into the E24. I also still have the reciprocating assembly (crankshaft, rods & pistons) to sell or re-use.