"Tulsa" '85 BMW K100rs Build


 The Start of something special.  
A few years back I built a Cb750 cafe racer for a friend and neighbor of mine.  Long story short, the company he worked for sold and disbanded, so he took a new job and moved to the Seattle area.  Not too long after, he sent me a "head's up text" telling me he might have a guy who wants me to build him a custom bike.  Sho nuff, I got a call from Thomas, and we hashed out what he was looking for, a price, and I got to work.   
I have to admit, there is not a better client to have than one like Thomas.  His requirements were pretty much this,  at least 750cc and it has to turn heads! Music. To. My. Ears!  There were obviously a few requests, and discussions along the way, but there is nothing better than to be given the opportunity to let one's creativity run free (wild).  
 Rolled into the Garage and ready for the teardown.
k100 full fairings
Teardown
Because the rear of this frame drops off after the gas tank, I need to cut it off and weld in a new rear sections (partial).  I didn't want everything to come out of alignment and square on the lower half of the rear, so I welded in some supports and bracing before I got to cutting.
K100rs frame welded and braced

 

 

Chopped! you can see just how much of the frame I removed.  The chain is holding the swingarm, as it shouldn't be allowed to overextend.

K1OOrs cut rear frame

 

I wanted some extra support and material for mounting the new frame rails, this was my solution.

 

 Frame rails and braces mocked up.  All tubes were connected with plugs on the inside, rosette welded, and then fully welded for the strongest possible connection.  

 

Made a little video detailing the process.

 

 

Next came the rear tail section.  Since the BMW is a little brickish and boxy, I thought it'd be cool to accentuate that in the tail.  I decided on an angular look, but this required butt-welds (weak), and therefore required internal support.  

The reinforcement for the tail was achieved with these plugs.  I cut two pieces of tubing, having the same O.D. as the frame tubes I.D., and welded them together at the same angle the tail would be.  This means essentially made the joint about twice as strong, easing and worries of flex caused by the single sided swingarm.

 

I've always hated how bulky turn signals and break lights can be, so I've grown accustomed to inserting them flush in the frame.

 

Ordered some new bearings so I could fit some modern, usd forks on the front.  These were sourced from a '12 hayabusa.  Stem is a little long, but not so long that a couple of spacers can't be safely used to take up the length.

k100 fork swap bearings

 

 

Using some all-thread and large washers, I install the new bearing races into the frame.

 

 

BMW K100rs New forks

 

 Getting started on the rear cowl.  I originally planned to make it out of fiberglass, but considering the tank is aluminum, I figured I should maintain some consistency.  I used 5000 series Al. as it has good weldability and is nice and easy to form.  3000 series also share those properties.  You wouldn't want to try and form 6061, which is the most common and easy to find, mainly because as you manipulate it, it will crack much more readily.

I hope to be able to hide 90% of my electronics here: motogadget m-unit blue ( which will help cut down significantly on the physical wiring), Lithium ion battery, and a couple of the original relays for the ecu.

bmw k100rs rear seat cowl cafeBMW k100rs rear seat cowl cafe

bmw cafe racer rear cowl tail

 

I decided to take a little break from the tail (Aluminum was a f*cking terrible and frustrating decision), and to make some progress on the tank and the frame.  

I was originally going to paint the tank and other body work a blue-metallic, but my wife suggested I switch it up: paint the frame a fancy color and let the aluminum speak for itself...I hid my excitement, said "that's stupid", waited a week, and explained to her my own very similar idea. She didn't buy it.  "You're right, honey, it was a good idea." -NOTHING worse than those words-

 

Frame getting prepped and cleaned for primer.

 

Primed 

 

Mixed up the perfect color. Ford Mediterranean Blue (a little too light and diner seatish) - mixed with a Universal Black until I liked what I saw. 

 

Boom! Now that pops!  You might also notice some other changes that took place when the frame was off getting paint.....

 

 

I've always hated how the stock airbox looks on these bikes, just a giant black plastic turd, not to mention that I rarely see any customization done to this area of the bike.  I knew I was going to weld a Stainless exhaust and air intake, so I should definitely stay with that theme.  I absolutely love the gold and other misc. hues that stainless exhibits once its heated.  No such thing as too much stainless, its like a girl too pretty, or a bike too fast...

I ordered up a couple of  180* mandrel bent SS. from Speedwaymotors.com,  and cut 'em both in half evenly.  These will be my runners.  I then built a box of similar volume as the stock box ( a bit smaller), but i made sure to offset the incoming air inlet below the four runners, so that air flows to each evenly, not giving one runner more available air than another.

 

 

 

If you look closely you can see the welding fixture I used to keep the runners in place.  This was to make sure they stayed in the correct location, as the heat would cause distortion otherwise.

 

I have an Eastwood powder coating gun (inexpensive but good) and an old house oven, so anything I can fit in there gets powder rather than paint.  Here are the side covers I powder coated in Spatter Black.

Powder coated side covers wrinkle spatter black

Time to get to work on the tank.  I'm not the biggest fan of paint stripper, but I do prefer it to the dusty-ass environment created by sanding it off.

BMW stripped bare aluminum tank 

I have good friends, Love em.  Here are the guys helping me get some work done on the bike.  The goal for the aluminum was a brushed look, while not as much sanding and finishing as it would be for a polished look, it was still pretty horrendous.  Here we see my buddy Nick taking one for the team. 

Hit it with the Sander at 120grit, followed by 220, 320 and 600.  Finishing up with a red scotch brite pad, dragged in straight lines down the tank.    600 might have been overkill, but I noticed it was allowing the scotch brite to yield the most consistent results.  I would then follow this up with a 2k urethane clear to prevent oxidation and scratches.

Sanding aluminum tank

 

 

Started work on the seat, I've had some really nice black leather and am super excited to finally get to use it.  Oh and I always get excited to use the old Singer 211G, it makes things so much easier to have a nice piece of equipment. 

In case you were wondering how to make pleats, you sew the leather to a piece of polyscrim.  The scrim foam has fabric on one side (the side not touching the leather), this fabric stops the thread from pulling through the foam, causing the leather to "tuft" where it has been sewn

sew diamond pleated seat

 

I didn't get too many pictures of the process, I was frantically trying to finish the cosmetics for a show...I did not succeed.  Here's how it turned out.