Below are the issues that we are considering for the rebirth of my beloved R100RS.
Need to get engine and frame dimensions into the CAD program at home.
We are planning on making a simple space frame, something along the lines of this MKM1000 frame (from Mick Walker's "BMW Twins..." restoration book), out of mild steel (1026) tubing. I'll probably buy the stuff from MetalMart.com; they seem pretty cool about small orders, they have exactly what I need, and they do unlimited cuts to 1/8". Not sure if we are sticking with 1" tubing all the way through, or perhaps mixing and matching with thicker tubes for major structural elements and thinner tubes for bracings.
Geometry considerations: if I just slap on race bike forks (see Suspension below) then I keep stock on race bike forks (see Suspension below) then I keep stock steering head angle (27 degrees, i believe). Fancier front suspension systems will make this way different, probably raking it out a bit since braking forces will be taken care of separately in that situation. The Telelevers are around 34 degrees, or something absurdly large like that. To the first approximation, I'm just going to start welding my tubes onto the straight, stock frame now (well, I hope it's straight) and then cut away interfering stock tubes as they get in the way. This way I'll preserve the steering head/swingarm locations right now.
The original Gummikah featherbed frame means the engine mounts are on the bottom of the type 247 Airhead block, where mounts to the steel cradle tubes live. I'm still not sure what the best solution is for engine mounting. Team Incomplete used the rear ones only, and removed the downtubes. They they fabricated a billet slab to mount the top front of the engine on the timing cover to the frame. I've seen this arrangement in another racing frame picture (made by the master Craig Hanson) taken from Michael Moore's Eurospares site... a veritable godsend to this project.
I'm thinking right now the triangulated space frame will be light enough so that I can keep the downtubes, liight enough so that I can keep the downtubes, like the MKM1000 frame above, thus more effectively isolating engine stresses from the rest of the frame duties (i.e. maintaining steering head relationship to swingarm). But the "only use stock rear mount, fabricate front mount to frame" idea has worked for Team Incomplete, so who am I to say? Another example is from one of Tony Foale's old R69S frames- with leading link front forks, I might add. Check out the picture (again stolen from the Eurospares site. Not an original bone in my body).
In any case, I'll probably keep the steering head and swingarm pivots from the burnt, stock frame.
As far as fabrication, I'll be cutting the tubes on an end-mill. Brazing them together will be done here, or maybe when I get back to California I'll sponge off of Bruce's electricity and MIG weld the thing together.
I've secured a single-sided rear swingarm, driveshaft, and 33/11 final drive from a 95 R100RT. This will bolt right on to the stock frame, with the exception that I need to fabricate/weld a monoshock mount to the frame. Of course, since I'm making my own frame, this shouldn't be an issue. This part is a Monolever, not a Paralever, and for good reasons.
For the front, the easiest thing would be to slap on some upside-down forks from some late-model Japanese racer. However, lest you think my obsessive nature for the absurdly complex and difficult is on the wane, I've also considered a leading link front end (a more modern version of the old /2 Earles Forks), or going all out and making something like Bike God Tony Foale has dubbed the "double-link". They're both trying to isolate braking forces from suspension/bouncing forces, the latter being more pure about the task. Of course, I could always do something like center-hub steering, like this masterpiece of Tony's.
My man Bruce scored a pair of 40mm Del'Lortos (back and side views) from the most recent CityBike swap meet the other weekend. I hear they cast a heavenly, aluminum glow about his garage right now. I am very excited about thout his garage right now. I am very excited about these babies.
Essentially, I am going to singlehandedly make three or four aftermarket BMW parts suppliers very wealthy in the 2000 fiscal year.
Eli has put in his vote for under-seat pipes, a la the BMW R1100S and Ducati 916. I can't really disagree. Though I loved the old R100RS's symmetrical pipe arrangement in their traditional lower locations, the higher locations will make more room for bags, increase clearance, and be another incredible complicated problem to waste my time and money on. What other reasons could one possible want?
More updates coming.
Last updated 12/9/99
