Ever been out in the middle of nowhere with less than half a tank of fuel and wonder if you'd have enough to get to the next station? That thought was on my mind a lot a few years ago during a trip to Saline Valley, just west of Death Valley. The distance to our camp was almost exactly a half tank away from the gas station, and it got to be a real drag planning to make the first stop after leaving in either Olancha, Lone Pine, or Beatty. Or remembering to make the last one a fuel stop at any of those places on the way in. And not just for me. My riding buddy Bob had an oversized Paris/Dakar tank from an R80G/S with almost nine gallons on tap, and he got drug along for all those gas stops, too. A year or two later when a crash badly damaged the standard tank, I decided to make lemonade out of lemons and get a P/D tank of my own. I'd been looking at options for more fuel, but the big prices that Touratech fielded and the iffy fit of the Acerbis offerings left me less than enthusiastic. Fortunately, a good fitting and realistically priced option comes right out of the BMW catalog, but not for the R100GS. Instead you have to look at the Paris Dakar version of the R80G/S, a bike that hasn't been made in almost twenty years. Gene and I had recently completed a coast-to-coast-to-coast run on the K bikes, and I'd spied a brand new P/D tank still in the primer sitting on the shelf at a St. Louis BMW dealership. Knowing that the chances of it still being there were slim, I called and was relieved to find it still available. Even better, the fella that had ordered it had backed out of the deal, and I was able to negotiate a small discount. I also ordered a gas cap to go with it (don't forget the new Roundels):

R80 G/S Paris Dakar Tank: 16111453914, $600.00
Locking Filler Cap: 16111453817, $31.25 (not 16131455063, a top vented alternative)
Tank Emblem: 16112325179, $6.89

When the tank arrived the first thing I did was put it on the frame to see how it fit. I'd heard rumors of what was needed to make it work, but wasn't sure what would be required. The first good news was that the rubber pad at the back underside of the standard tank was a drop on fit for the P/D, as was the wire bale that held the tank in place. The "U" bracket at the front was also a perfect fit. That was the end of the good news, though, as the fairing panels interfered badly on the side, and the new fuel cap had a breather vent sticking straight out of the top. The nice Rick Mayer solo saddle wouldn't mate up to the back of the tank without some pretty radical hacking, and I just couldn't bring myself to do it. Since I had time on my hands healing broken bones anyway, I started shopping around for a new saddle, and it wasn't long before one showed up on the IBMWR classifieds site, complete with P/D rack. I reasoned I could snag that and get Rick or his brother Rocky to alter it, then sell Rick's seat with the new rack. With that on the way I started in on the fairing panels.

I reasoned that the easiest solution was to shorten the panels until I had enough room for tank clearance. The photos above show the right side. Underneath (left photo) the panel was rubbing the tank, holding the upper section (right photo) away. Using a drum sander in the drill press I started removing material on the underside which brought all of the right side panel into contact with the tank. At that point it was clear that material would have to be removed from all along the trailing edge of the panel, so I used some masking tape to lay out an edge on the panel while it was mounted on the bike.

I then dismounted the panel and went at it with the drum sander until I'd reached the edge of the tape, at which point I reattached it to the bike for another fitting. This cycle was repeated five or six times until a gap was produced. Using an iterative process like this let me keep the gap pretty constant, since the panel was flexing in three dimensions as it moved in. When the right panel looked about right, I started in on the left panel. Again using the masking tape and repeatedly marking and sanding produced a fairly uniform gap.

Next up was the vent on the fuel cap. I reasoned that if I shortened it, then capped it with a sheet metal screw, it wouldn't interfere with the tank bag that would almost always ride on top of it. But then the fuel tank would have no vent at all, and the motor would starve for gas as it emptied. The old tank had such a vent, and it was plumbed from a small hole in the filler neck to the bottom underside via a steel line. I didn't see any way to rig a tube into the filler neck like the old tank because the well where the tube attached simple wasn't there on the P/D. What I could do, though, was rig the tube so that the top end terminated high in the filler neck, above the fuel line. But even then, I'd have to poke a hole in the brand new tank for the tube to exit. I was more concerned about picking the correct location than I was about sealing the tube to the hole, as I planned to use steel brake line for the tube and it would be easy to braze it into the steel of the fuel tank.

Looking at the underside of the tank showed that there was a little shelf above where the petcocks attached. Even better, there seemed to be plenty of room around the rear end of the shelf when the tank was mounted on the frame. All I needed was a bit of brake line, and I found plenty at the local auto parts store. When I got back I measured the tube and drilled the hole in the underside of the tank. Then I got some 1/8" welding wire and bent up a pattern I could experiment with until I had something that would work. I found that there was just a little bit of a lip on the filler neck, and decided to bend a "U" into the pattern that hugged the back side of the lip. I put a right angle bend into the end of the pattern to discourage gravity induced contamination while refueling, and another right angle bend on the other end of the "U" to get it headed down to the hole in the bottom of the tank. It took a few tries, but I eventually ended up with something that fit quite well. All I had to do was copy the pattern in real brake line. I'd never tried it before, but I'd heard that if you filled a tube with sand you could bend it without collapsing the walls. So I crimped one end of the tube shut and dribbled sand into the tube, stopping every inch or so to tamp the sand down with another length of welding rod. When the tube was full I crimped the other end as close to the sand as I could. I formed the "U" bend first, and it went smooth as silk. The other bends went just as well, using sockets and other round items held in a vise as mandrels, and sometimes just my fingers. When I had everything the way I wanted it, I cut the ends of the tube to length and shook out the sand. Just to make sure the tube was clean I shot some compressed air and contact cleaner through it to get the last grains out. I then drilled a small hole low in the lip of the filler neck and safety wired the upper end of the tube in place. I'd already used a flapper wheel to remove the paint from a quarter sized spot on the underside of the tank, so I propped the tank in place and surrounded the hole with damp rags to keep it as cool as possible while I brazed in the lower end of the tube. I got a little smoking while the torch applied the heat (especially on the inside where I couldn't reach to remove the paint), but the braze filleted up around the tube nicely.

With the fitting out of the way, it was time for paint. Again mounting the tank on the bike I tried to pick up the lines from the side panels and side covers, while keeping the top contours interesting. The result wasn't perfect, and there's a bit too much blue pearl in the black, but I'm pleased enough with the final result.

The PD tank is also a bit longer and taller than the R100GS tank, and that means I had to modify the front of the new seat. I never did care for the way the old seat covered the back of the tank, and made up my mind to fix that with some surgery and a custom job from Rocky down at Bill Mayer Saddles. I used a combination of saws and grinders to trim away material from the seat pan, then folded the old cover back into place before taping it down for the ride to Ojai. Rocky and his gang fit a couple of stiffeners to the pan, then cut a pocket for their special foam, and covered the result with a nice new piece of black leather. Happy butt, happy tank.

And just in time, too, as Gene and I were due to head out on an easy cruise south along California's coast, my first since getting whacked. The only problem that surfaced during the trip was a leaking fuel cap. It seems that I'd broken something in the breather assembly when I'd capped it, and with a full load of gas I got big drips down the side of the tank. Enough that it discolored the paint. Arrrgh!

Returning home I remembered seeing a flat locking cap on fellow NorCal member Greg's P/D tank, so I phoned him up to find out what it was. It turns out to be a BMW part, designed for just the same application I needed. It was also vented, but the tube outlet came out of the side of the rim, avoiding any problems with tank bags and such. Sure wish I'd have known about that cap before all the drilling and brazing started!

The new cap cured the leaking problem (I tapped the breather hole and used a machine screw for a plug), and a little color sanding removed the yellowed clear coat from the paint. The new tank holds almost 9 gallons of fuel, which puts another forty or so pounds on the fork springs and noticeably effects handling, not necessarily for the better. I've installed beefier springs for some improvement. After spending the money and working out the paint, was it worth it? I'd have to give this one a big thumbs up. The tank gives the bike a more solid look, and almost doubles its range (capacity is just shy of 9 gallons, up from 5.5 of the original). My knees are a bit more out into the air stream, but not uncomfortably so. I notice the added weight of a full tank and sometimes need help getting it onto the center stand when the bags are loaded with camping gear. And that weight is also a factor when the machine is on the move. Not so much on the pavement, but on dirt or sand it makes things just that much more "interesting". The riding position is also a bit more stretched out, just something else to get used to.

The only real misgiving I have about this upgrade is having waited so long. I could have saved myself a lot of trouble on the paint if I would have swapped the tank out when I did the first "zebra" paint scheme, but locating a new large capacity tank seemed like a big deal back then. It's funny how random events can combine to help things like this along. It's a good thing, too, because by 2004, a year or so after this conversion was completed, BMW no longer offered the R80G/S tank as a spare part, and prices for used ones (when they can be found) have skyrocketed.