Monday, 14 June 2010

Despite having assorted other things to attend to, I did actually manage to make a degree of progress with the BMW this week. As well as sorting out something on the GS 550 and more things of a one step forwards, two steps back nature on the Alfa trike.

Nothing overly dramatic I'm afraid, although, the tank did arrive. It turns out that an R80 has somewhat different fuel tank mounts than an R65, despite the frames appearing to be identical.

"Appearing to be identical" is deceptive though as the R80 front tank mount appears identical to the R65 one at first glance, but place the tank on the frame, and something is clearly amiss. The front mount consists of a "C" section channel bridging the tunnel of the tank, and a horizontal piece of tube welded to the frame down-tubes behind the headstock, with a rubber moulding that sits on the tube. The tube on the R65 frame is not only slightly longer, it's located lower too, and sitting your long awaited R80 tank onto the mounts reveals that there is no clearance between the starter motor and the fuel tank. Luckily I realised that the mounts were different before despondency set in.

I've got as far as making a new mount for the front of the tank, and I'm thinking of ordering the rubber cotton reels for the rear of it and making some suitable brackets to weld to the frame.

After a ridiculous amount of farting around, the motorcycle now has the makings of an exhaust. I say "an exhaust" as it may not be "the exhaust" since I'm not too sure about the way the pipes run under the engine. I feel they could do with following the line of the sump rather than floating around in mid air like that, which would pull them in a little closer at the front as well. Because the left side cylinder is further forward, the pipes converge to the right of the bikes centre line, making them near as damn it equal length and overall the effect isn't entirely unpleasant, and it seems that I'm the only person who isn't enamoured of it. I think I'm going to take one more stab at it as I have the tube to do that anyway, and the collector I made is a slip on one so that at least could be re-used.

I've also sawn the threaded stub off of the left hand cylinder head, which has left no means of securing the front pipes to the heads. I'm planning on removing the heads and drilling its fins to accept some springs which will hook onto the exhaust pipes, rather like you might see on a moto-cross machine. The pipes I've made are 1 1/2" OD, 1/16" wall, so and I've put short stubs of the 1 3/8" pipes that came on the motorcycle into the ends of those to locate in the exhaust ports.

The final thing I did was to make all the parts for a fork brace. I'd resolved to spend money more freely on this project as opposed to my usual "I can make that..." approach, and I knew you could buy fork braces not unlike this. However, I had been looking at what I had in the way of 7/8" tube formers, and looking at the one on a conduit bender I own, it looked to be about the right size to make the inverted "U" pieces. A test bend revealed that it was, in fact, exactly the right size when used with the tube I had lying around. Making the mounting brackets from some 1" x 1/4" steel strap was going to be easy enough so I made one and tacked it up. I don't really like the strap brackets, and am toying with the idea of jig sawing some from 1/4" plate, which would look better, and make the brace stiffer. It would also give me somewhere to drill some lightening holes, and I find the idea of adding some extra metal so I can drill lightening holes in it vaguely amusing.

The rear sub frame is causing me to lose some sleep. It's ugly, flimsy, and ridiculously heavy for the amount of stiffness it possesses. It wouldn't be beyond the wit of mortal man to make something stiffer and lighter from larger diameter tube and weld it in place, contributing to the overall stiffness of the frame, which is a department where it is sadly lacking. The other side of that coin is that part of what makes a BMW café racer a BMW café racer to me, is that skinny subframe stripped of the side panels and battery mount.

Different is not a synonym for "better", but that doesn't exclude the possibility.

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