BMW dirt bike ---> cafe bike

This is a story about a bike I finished about five years ago.

The thing about BMW flat twins is, parts are very interchangeable between different years and models. There is a certain combination of those parts that can make a very quick and light bike.

I decided to start with the BMW dirt bike, the 1981 R80G/S:






I found a good donor -





..and dressed it up a little:






Yes, this will do, nicely. Time to strip:





Some better forks can be adapted from their later products. This set came from a 1992 K100RS:






That's what I started with, along with an idea. More to come.


Jon-Lars

I think a cafe bike needs to perform better than the stock version. This means work on all parts of the bike, every category, to make it go, stop, and handle better.

One way to start is to make things lighter. I started gathering parts from specialists around the world.

This aluminum tank came from WBO Racing in Germany, handmade by guys with little hammers:






Mikuni flat slide carbs work well with this engine. I put a velocity stack inside the K&N filter:





Spoked wheels are lightweight and look good. They can be made lighter, by drilling the hub:





I know my limits, and I know when to ask for help. I brought my project to the best engine builder and fabricator I know, and asked him to make the parts come together.

Calling on Dr. Dick Casey:

The next stage of this project took fours years of trying, testing, and re-trying to get it all right. Here are progress shots:

oh man there is something special happening here

The starting point, the mods, the ideas.... This thing stinks of brillance. The unique things you could do with this bike have me all kinds of excited.

This is brilliant, cant wait to see more of this.

That tank is pure sex. I need more pics of this project.

I like the "cow hide" seat in that last set of progress shots, haha. Please let the instant-satisfaction slideshow continue. All the fun, and no wait!

Yep, this is going to be a nice bike when finished fro sure. Signing on to watch.

Very, very cool! Can't wait to see more.

Also liked the gibson bass in the shot. Clever way to show you have taste in guitars as well.

Installment 2:

The heart of a bike is its engine, meaning that an improvement here will make a healthier ride. Flt twins are dead simple designs that can benefit from well-tested modifications that are specific to the BMW 247 as well as general tried and true tweaks.
Most important when doing this kind of makeover is to know how a change in one part of the engine influences every other system of its operation. You can't change the exhaust and expect the carbs to work as before. You have to figure out a plan ahead of time, or plan to spend a LOT of time chasing problems round and round.

This engine is built on the '81 R80 engine case and crank. This is a strong version, stiff, with a light flywheel. To this we added Nikasil cylinders and fitted pistons from the 1000cc parts box. The heads are from a '77 R100RS, which have larger intake valves and a squish band combustion chamber. The heads went in for skimming for a higher CR, flow work, added spark plug per cylinder, valve seat work, spring and bucket changes, and refined rocker arms.This makes the valve train work to a higher RPM. The piston crowns were matched to the squish band in the heads.

The camshaft was changed to the BMW Sport version 336. The exhaust is another story - Hansens Racing ran a program to design the lengths for me, and supplied a kit of straights and u's, along with his skunk work muffler. You have already seen the Mikuni flatslides - the velocity stack inside the air filter does a good job smoothing tairflow to widen the torque band.




The dual plugs are fed by a Silent Hektik ignition, the version that lets you choose from 16 advance curves by turning a rotary switch inside the brain box. This is the slickest improvement, I think. The rest of the electronics are stock, just moved from normal locations to a box mounted on top of the transmission.




Because the engine is raised in the frame, Dick made a special oil pan that keeps the bottom elevation level:





Tarozzi foot controls were the starting point for the foot controls:







All the frame parts and struts were powder coated. I had them painted at a automotive body shop, but they weren't able to get the fram covered in the many nooks. Be careful if you decide to use a pinter for this, making sure they have done a motorcycle frame, and have some past work to show you.

Here are some detail photos of the bike as it is being assembled.

























Next installment will show the finished bike.

Holy smokes, nice job!! Is that a Logan lathe in your garage? Where did you get the headlights?

That is Dr. Dick Casey's shop. the guy in the photo, the builder extraordinaire.

I have skills in some areas, but not others. I want the best possible result of this project, so I brought my ideas to a man who could understand and augment them.

Dick did almost all of the machine and fab work on this one. I did the body work, which will appear in the next installlment.

The headlights are PIAA driving lights for cars.

What an Interesting, well thought out and executed build. Never would have had the vision you had. Great job.

Absolutly awesome. Cant wait to see more.

Here's the bodywork. They are from Airtech, some of their Ducati parts.
I built up the seat quite a bit for strength and shaped the nose to conform to the tank. I also re-shaped the fairing somewhat and reinforced it with epoxy and different glass types from Aircraft Spruce:






Here it is being brought home from Vashon Island. All that is left to finish is to build a seat.




I worked with an upholsterer in Wenatchee to get the foam right, then had them cover it





...and now, we are done.

Looks like your getting a nice cushy seat. Unfortunately I am sitting on 3/4 inch of neoprene. a little stiffer. ehhhh

Here is the finished bike. It is a much better ride than I had expected, quick, fast, and stable. It's better looking than I expected, and has a lot of detail that Dick added on his own. This project took four years to finish and it was worth every minute.