Sorting Out The Shark, Part II: Tanks For The Memories
As I wrote several weeks ago, one of the things that allowed me to purchase the ’79 Euro 635CSi at a price I could afford was the curious choice that the previous owner made to spend money on things such as refinished vintage BBS RA wheels—while leaving unresolved such problems as a leaky gas tank. The tipping point in the purchase came when he agreed to sell me the car without the wheels; I literally had to show up with another set and swap them in his garage. Of course, I was trading away something cool and shiny, and accepting something rusty and leaky.
In other words, not only is there no free lunch, your sandwich stinks of gas.
The seller warned me that the tank leaked when filled above a certain level. Although this is consistent with rust at the seam—quite common in gas tanks on old cars—it’s also possible that it’s due to leakage at the O-ring sealing the fuel-level sender. I checked this from inside the trunk, but I didn’t see any discoloration around the O-ring.
The PO had been driving the car very little, putting only a few gallons of gas in it at a time, and I’d put no gas in it since buying it, so there was very little fuel in the tank, making removal easy. I suppose I could’ve filled it with fuel to definitively verify that it leaked from the seam, but the seam was the most likely location—and I didn’t want to have to drain and dispose of any more gas than necessary. Dropping a tank with one or two gallons in it, then tipping the tank and pouring the gas into a container is easy; dealing with a tank holding fifteen gallons is a total pain in the butt.
I did some research to find out which gas tanks fit a Euro E24 635CSi. Early E24s are E12-based, whereas later ones are derived from the E28 platform. According to Real OEM, one gas tank fits all U.S.-spec E12s, E24s, and E28s. Unfortunately, a different gas tank is specified for the Euro versions of these cars. Reading on bigcoupe.com, I found that the difference between the U.S. and Euro tanks appeared to be twofold. First, the U.S. tanks are smaller due to a notched area to accommodate the shocks for the big American bumpers—thus you can put a U.S. tank in a Euro, but not the other way around. Second, the U.S. tanks have an in-tank fuel pump and a flange with bolt holes to receive it, whereas the Euros have only the hole for the twist-lock level sender.
Of course, there’s also the possibility of repairing the existing tank.
I’m a practical guy who tries to save money wherever possible, so I figured I’d do whichever was the most cost-effective. The discounted dealer cost of both the U.S. and Euro tanks was similar, about $550, and the Euro tank was available, so there seemed to be little reason to go with the U.S.-spec tank and face the conversion issues. I also contacted German suppliers Walloth und Nesch (www.wallothnesch.com). Even with shipping from Germany, their quote for a new Euro tank was $440—not the end of the world, but hardly chump change. And no, I am not going to ask Maire Anne to get it for me for Christmas. She’s the best, she loves me, but that’s clearly over the line.
But no matter which path I took, the first task was to remove the old tank. Depending on the make and model of the car, a tank may drop in from the top—this is the case with 2002s, E3s, and E9s—or it may be bolted up from the bottom, as with E12s, E24s, and E28s. Unfortunately, one of the bolts holding up the tank also holds up the mount for the back of the muffler, so the muffler has to come off in order to pull the tank. Since, on an old car, the individual exhaust sections rarely come apart without a fight, the easiest thing to do is simply unbolt the headpipe(s) from the exhaust manifold(s) and drop the entire exhaust as a unit. Mercifully, on the Shark, it all came off without any of the manifold studs snapping.
With the exhaust out of the way, dropping the tank itself is very straightforward: Undo the fuel lines from inside the trunk, disconnect the three vapor lines from the neck of the tank, support the tank so it doesn’t crash to the ground, and remove the four 17-mm bolts holding it up (well, three; you’ve already removed the one doing double duty holding up the exhaust hanger). I was using my impact wrench to speed these off. Unfortunately, the one on the right side wouldn’t budge. Since it’s a gas tank, you don’t want to use heat near it. And I couldn’t reach or see what the bolt was screwed into to soak it with penetrating oil. I hit it with the impact wrench for maybe the eighth time, and then off it came—but it didn’t sound right; there wasn’t the gradual change in pitch accompanying threads slowly loosening. Then I realized that the bolt had sheared off. Damn! I knew instantly that this meant I had to allocate an entire evening at some point to drilling the damn thing out.
But at least the tank was now free to come out. When I pulled it and inspected it, I could see some flaking around the seam, but it didn’t look too bad. I called around to a few places for repair estimates, but no one wanted to quote me a price without seeing it. I took it into a hole-in-the-wall radiator shop in Framingham I’ve used before. It’s the kind of place I love—a family-owned business run by a grandfather, son, and grandson, with stuff absolutely everywhere and a propane heater throwing off a three-foot flame. The older gentleman explained that they could clean the tank, fix any obvious holes, then seal the inside of the tank with Red Kote, a flexible pour-in fuel-tank liner, sort of like an inner hot-water bottle. He estimated the cost at $275 to $325. I explained that, with a new tank costing as little as $440, if the cost could be held to $300, I’d do it, but any higher and I’d just buy a new tank. The gentleman agreed to do it for no more than $300 unless something truly exceptional came up.
While the tank was being repaired, I dealt with the snapped-off bolt. With the tank out, I could see that the bolt goes into a captured nut in the middle of a U-shaped hanger. When faced with drilling out a bolt, I first ask myself if there’s any other way; maybe I could simply replace the entire hanger. When I looked at it, though, I could see that it was welded to the underbody. Okay, I thought, maybe I could cut out the section with the captured nut and the snapped bolt and affix a new section. If I knew how to weld, this would probably be trivial—in my next life, it’s on my list—but looking at it, I thought, no, just get on with it and drill it out.
Now, this is not a process of drilling a hole and then using some sort of easy-out reverse-twist device to turn out the remaining bolt; we’re talking about drilling it out completely—that is, removing the bolt by drilling larger and larger holes through it, until there’s nothing left but a thin wall of steel left in the threads. When drilling through a bolt, you want to drill through as short a section as possible. On the bottom end, the bolt was snapped flush with the hanger, but it protruded quite a bit at the top, so I wanted to cut off that protrusion. My usual method of a cutting wheel on a Dremel tool wouldn’t work because the diameter of the wheel was larger than the gap in the hanger, but I found that my jigsaw had a blade just thin enough to do the trick.
From here on, there aren’t any shortcuts that I’m aware of; you have to put in the time with the drill. You center-punch the end of the bolt as accurately as possible, then start with a small drill bit—I use carbide bits—and if you have any question as to how old and sharp your bits are, just run to Home Depot and buy new ones; you won’t miss the thirty bucks once those beautiful metal shards start raining down.
Drill slowly, stopping to squirt a little oil. The first hole takes by far the longest. DON’T PUSH THE DRILL HARD! If you snap off a hardened bit in a hole, you’re screwed, as it’s really difficult to drill through or around it. Once you’re through, step up to the next-size bit. With the hole established, it goes more quickly.
What inevitably winds up happening, though, is that the hole is off-center due to its being punched slightly to one side, or the drill bit wobbling away from the punch point, or the drill not being exactly parallel with the bolt—–most likely a little bit of all three. Mine was off by a lot, with some of the original threads showing on one side of the hole, and quite a bit of the bolt left on the other. Drill bits are not routers; you don’t get much cutting action trying to lean the drill to the side, and it’s very easy to snap the bit if you do try this. I tried using my Dremel tool’s grinding bits, but the stone just withered away against the steel of the snapped bolt. I looked online and saw that Dremel sells tungsten cutting bits designed to bite into steel (Dremel attachments 9901 through 9904). The local Home Depot had one of them, 9903, in stock. I paid my $15, and was delighted at the short work it made of removing the rest of the bolt. Once the snapped-off piece occupied less than 180 degrees of the hole, I was able to pull the remainder out of the threads with a metal pick and needle-nosed pliers. Although I’d slightly enlarged the opposite end of the hole as part of the drilling process—oops!—once I retapped the threads, it held a new bolt very securely.
When I picked up the repaired tank, I was a bit disappointed. There was certainly no confusing it with a new tank; it had a thick rubbery coating on both the outside and the inside. As with many areas in which I try to save money, you can look at this a number of different ways. I probably should’ve just spent the extra money on a new tank, but I chose to view it from the standpoint of the Shark’s being a rarely-driven car, unlikely to encounter many miles of tank-rusting weather, and the $140 savings would be instantly lapped up by some other automotive or family need. Plus, the guy said that if it ever leaks, just bring it back to him for a free repair.
Obviously, while I was under the car, I changed the ancient rubber gas lines and the fuel filter. I’m cost-conscious, but I have a thing about old fuel-line rubber.
It’ll be a while before I get to fill up the tank and verify that it’s leak-free. The car’s not even inspected yet. But it feels great to be over this hump before the holidays. It’s one of my many little presents to myself.—Rob Siegel
Got a question for Rob Siegel, the Hack Mechanic? You can find him in the BMW CCA Forums here!
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.
