1977 R100S BMW Cafe Racer by Gold Country Cafe Racers
Here’s the tear and build of my latest project –
Oshmo is the supplier of some specialty parts on this exciting build.
I decided to build another cafe bike after I had recently completed an R100/7 into a featured front cover bike for the BMW RA magazine. The tear down process begins on a R100S that i acquired with a bad transmission, as a result it was a real bargain. It already had a lousy re-spray, but was fitted with some really nice bits. It even came with a Staintune stainless exhaust system which I sold along with some of the other parts which covered the cost of the bike itself. I also was fortunate to find a really good fabricator, Artie Cathcart, owner of TCB Fabrication in Chico, CA. Coincidently, he was given a 1990 BMW R100 with a mono shock. He didn’t want the front-end or the rear-end, so I purchased it to build a matching numbers 100S with a Monoshock suspension.
I found some aluminum body parts online for sale in Arizona that I thought would make for a good bike build. Given the cost of these parts I wanted the bike to be noteworthy, not just a /6 or /7 build. Not that there’s anything wrong with those, I happen to have built an sweet R100/7 (Mango Tango) that was featured on the cover of OTL Magazine. However, I was in search of something a bit more desirable like an S model. Fortunately I was able to find a 100S for sale locally. I really think this build will look great with a cobalt blue frame and wheels, to compliment the polished aluminum pieces. In the photo below you see where I painted an outline where I was going to customize the foot pegs bracket by cutting them out, well that was until I saw the wings that Oshmo fabricated while visiting his shop. I ended up with a pair of these wings, their rear-sets top clamp and other bits for the build.
As you can see the tunnel of the tank was definitely built for a wider frame, I believe it was for a Honda CB 750. My enthusiasm got the best of me when I came across these parts online. Regrettably I didn’t ask all the right questions, I didn’t know enough as to which questions to ask. The person selling these had it pictured propped up on a R90/6, making it look like it would be a direct bolt on kit with just a few mods. He was less than forthcoming with his information, it wasn’t a good fit at all.
My fabricator, Artie Cathcart of TCB Fabricators in Chico, CA started by filling in the huge gaps, fore and aft. this is welded inside and out so when it comes to blending it all together by grinding/filing away the weld for polishing later, it will still have strength integrity on the inside. This Toaster Tan top clamp will be switched out with Osh’s Triple Clamp that accepts to Moto Gadget speedo. Scroll down for the finished Top Clamp and MotoGadget Speedo below.
He then went to work on the rebuilding the underside of the tank to give me more volume for fuel and also to copy the stock BMW frame mounts. Here you can see where we added the monoshock mount to the 100S frame. We’ve also designed a new subframe that will be welded into place, and bolts onto Oshmo’s wings for the rear sets that I acquired from Osh.
Artie shaping the underside of the tank. I dropped off a standard tank for Artie to measure and use as a baseline. We’re even planning on using standard BMW bungs for the stock petcocks.
Checking in on the progress over the weekend, looks like the tank is coming along. I gained some more fuel capacity, and we got the traditional BMW frame mounts configured on the tank. Just a little tweaking on fitment and then polishing after the fuel taps are added to accept stock BMW petcocks.
Here the build sits on Artie’s custom frame jig that he designed and built. Installation of Oshmo Wings have taken place. These expertly crafted wings, with the specially fabricated spacer bar provided by Oshmo has really made a difference in the look of this build. I’ve never liked the look of the foot peg supports especially when you switch to rear sets, it just doesn’t look right. These “wings,” as Osh calls them look so much better.
Here’s a closeup before cleanup. As you can see these are much better looking than the stock foot peg supports on the airhead frame.
Today the fabrication of the new sub frame took place. As you can see this 77 R100S was converted to a Monoshock design. People have asked why didn’t I just start with a Monoshock frame? The answer is because I had a matching numbers R100S frame and engine that I wanted to keep together. I had a unique opportunity to grab the rear and from ends of a 1990 R100 and modify this ’77. This will have a better handling rear end, and bigger 4 pot Brembo’s up front.
Because of the mono shock design, special consideration had to take place in the design of the sub-frame. I wanted a sub-frame with a curved shape to compliment the curves of the wings, and the Oshmo rear sets. I think Artie did really well making it all look stock.
I had a chance to check out the sub frame fabrication. I was away traveling on business all last week so it was a real thrill to see it first hand on Saturday. Artie follows direction really well. He gets a sense of what you want then comes up with a way to execute in metal. Here he’s moved away from the straight lines of the standard factory sub frame in favor of the curve I wanted to compliment the Oshmo wings/rear set mounts.
Here you can see the battery box and MotoGadget brain box tray. It also will have a forward tray for the tool roll. As you can see a rear fender/mud guard has been added. You couldn’t see it in the previous photo because he did a good job blending it in with the curve of the sub frame.
Soon he’ll be wrapping up this and moving to the from fender and fairing modifications. I’m getting kind of anxious as it seems like I’m running out of time to get it done in time for the Quail Motorcycle Gathering in Carmel on May 14th. I still have to reassemble the whole bike before I take it in for powder coat to make sure everything is as I want it. Stay tuned for more.
One of the nice touches to the OSHMO Wings is the addition of this steel mesh panel that I dreamed up. Artie took the lead and cut out the pieces and attached them. They’ll either be polished out to contrast against the cobalt blue frame, or powder coated black. If you’re wondering why I’m calling this the Knight Stalker, it’s because the bike with its polished aluminum bits, and the mesh metal, and cobalt blue frame is reminiscent of Sir Galahad, the greatest Knight ever. OK, it’s my fantasy, my bike. 😉
A new custom fender had to be designed for the Knight Stalker to match the rest of the aluminum pieces. Artie banged this out and made it look like it belongs on this bike.
The front fairing came with a universal frame for mounting. It really was hokey, so Artie modified it for better stability and fitment. The overall fit looks fantastic.
Today I drove up to build the bike. I arrived with the motor, swing arm, wheels and swing arm to build it so we could make sure that everything that was fabricated fit as expected. These are not the correct wheels or front end, and rear drive, but it allowed me to make a roller out of it.
The rear wheel appears to be too close to the seat. We didn’t have the mono shock spring configured correctly. As mentioned we just needed it to make it roll.
I decided to shorten the fairing after seeing it on the bike in person. It rode high, although necessary to accommodate the clip-ons for steering (standard bars pictured). Because of this it just didn’t look as good as I had hoped. By shortening it, it will take on more of a bullet cockpit look. Look for updated look soon.
This will be my first build using Magura hand controls and M/C.
I’m also using the MotoGadget components including Micro switches, M-Button, and the keyless M-Switch. All the electrical wiring will be held in the handlebars with only one “configuration” wire going to the M-Unit under the seat.
Today, in L.A. I had an opportunity to pick up the new triple clamp, center nut and custom fork caps from OSHMO. I can’t wait to see it on the finished bike.
Now that I selected a muffler from Akrpopovic, we’ll get started on the custom two into one exhaust headers and pipe. A little modification is needed to this for a left hand mount.