Last week, I was walking cheerfully down the path of dealing with Otto's low compression in the #3 cylinder—at least as cheerfully as one can walk when one is a mouse-click away from listing a car on eBay. Then I decided to do a compression test, got a bad result, and had to postpone the sale and yank Otto's head off.

    I’d brought the head into the machine shop, and Hal (the machinist) reported that the head was warped by 0.007”. This seemed to explain the symptoms, which in addition to low compression, included the radiator gurgling like a fish tank when I’d performed a leakdown test on #3. But the path was clear and straightforward: Mill the head, lap the valves for good measure, reassemble it, slap it back on, done.

    Ah, if life were only like that.

    Hal called me a couple of days ago to break the bad news. After the head was tanked and all the varnish cleaned off, two cracks became visible. One was a spreading crack (larger at one end than the other) in #3 chamber, between the chamber and the coolant passage. The other was, surprisingly, in #2, plainly visible between the valve seats.

    Although the car ran perfectly cool whenever I drove it, one can assume that a prior overheating incident caused both the warpage and the cracking. One can only speculate whether the low compression in #3 and the gurgling of the coolant were due to the warpage or the crack or both, and marvel that the crack in #2 was apparently asymptomatic. But none of it really matters. I need to replace the head.

    Although it is possible to weld a cracked head, Hal advised that, since E12 2002 heads are fairly plentiful and not terribly expensive, it would be cheaper to buy an uncracked used one than to pay to have this one welded and tested. Plus, because the crack in #3 is a spreading crack, there is the possibility that a weld job will fail.

    Initially, I thought, no problem—I have an entire spare tii motor sitting beneath my back porch. I bought it about this time last year when I was fixing Brian Ach’s tii. It reportedly ran when yanked ten years ago for an M20 conversion. I picked it up because it was cheap (about $400 complete). At the time, I was looking at it primarily as a source of spare fuel injectors. Now, I thought… free head. Yank it off, either slap it on Otto’s block as-is or disassemble it and take it in for R&R, but it’s available and already paid for. I’m all about the path of least resistance. 

    But the more I think about it, the less enamored I am of this solution. The problem is that if you cannibalize the head from a sitting motor, you’re essentially relegating the block to the scrap heap. Someone may want a whole used motor, or a used head, but few people want a used decapitated block that has been sitting exposed to the elements. The spare tii motor is really worth much more, to me or to someone else, as a whole intact motor, even if its provenance is unknown. I could yank Otto’s block and swap in the spare motor, but this simply transfers the problem—Otto’s block would then be the boat anchor.

    So, as I, ahem, head off to The Vintage, I’ll be scouring the vendor area for a crack-free straight E12 head. Otto, in the meantime, will need to get used to his acephalous state. Apparently he’s going to have to live that way a while.—Rob Siegel

    Rob’s book Memoirs of a Hack Mechanic is available through Bentley Publishers, Amazon, and Bavarian Autosport—or you can get a personally inscribed copy through Rob’s website: www.robsiegel.com. His new book, The Hack Mechanic Guide to European Automotive Electrical Systems, can be pre-ordered from Bentley Publishers. Use the coupon code “BMWCCAELECTRIC” for 30% off list.