Knight school is a motorcycle specific apprentice style education. In short, we teach the art of the motorcycle... through experience.

Sunday, November 20, 2011

BMW R90 cafe bike

This bike came to me as a rolling basket case. In other words, it was on wheels but many parts had already been removed. The perfect candidate for a cafe bike! BMW R90 1975. 900cc of smooth German engineering. Plenty of power to feel like you are really riding. I took the engine out of the frame and removed swing arm and forks. The picture below is of the engine as I got it. It runs, but needs a cleaning worse then my last dorm room. Those of you who know BMW airhead motors will note the electrics need attention. A custom harness is on the schedule. Usually the last thing I do on a bike of this nature. 

Check out the frame section being blasted. BMW frames are difficult to get all the nooks and crannies but it must be done right to hold paint well. 

Here  is the pile of parts I have to choose from. Wheels are nice, but spokes have rust. Headers are good but mufflers are too big for what I want. forks are nice, rear end is good. Over all this bike needs nothing big replaced. Tanks badges and some oil. 

Half way through paint. Yes it is hanging in the shop. No paint booth. If it were a tank and fenders I would be more careful, but remember we ride the piss out of what we build. Note the blue hue to the paint. This is a low budget black. It does not cover in one coat like some better paints do. I took the picture now because I had run out of paint! A base coat clear coat is being used to lend a little shine to the frame. Please note that this frame has had a number of tabs and mounts removed to make a cleaner final look to the project. 

Here is the swing arm before paint. Yes green oxide primer. In the lower right corner you can just see a bit of the tail section to the frame. In the back ground there are some wooden seat pans I was working on. I build them for all the antique bikes built between 1900 and the mid 1930s when the last wooden pan seats were built by factory seat makers. KNIGHT SCHOOL fabricates everything having to do with motorcycles!

Here is the tank after paint, but before polish...

Here it is after the polished inserts are installed. 

 Heres the tank with "double trouble" the chicken standing on it. Have I mentioned that the school has a mascot named Beep? He is a 12 pound rooster that lives in the shop. 

The frame came out nice and I could not resist putting the tank on it to see what it looked like. Engine gets cleaned and installed next. You can see it dirty and waiting on the floor. Reminds me of my last date...

Yes, Indian decals from a chief on my lift. Leftovers.
 I will clean the engine with some secret stuff that makes aluminum look fairly fresh. I say fairly because I want the bike to look its age, not like a full on restoration, because it is not. It is a custom bike that happens to be old. I want some thing I am not afraid to ride the piss out of. 

I put the engine in, or should I say put the frame on the engine. Install an "R" motor some time and you will know what I am talking about. But all is well, look mom, no scratches! Fitting a BMW engine to a frame without scratching the frame is almost impossible. 

Note the triple tree was on when I put the engine in. The frame likes to fall forward on the head tube when set down alone, so to make it more stable while I am F@#$%ng with it I put the trees on. 

Forks next, just slid them in because the trees were already on. 

On BMWs the trees are very precise so you need to open them with a screwdriver in the slot to widen the clamp so the fork leg will slide up to the top tree. Be cool, this can be an easy place to make a big mistake. Just open it, don't pry it open. I usually just take a flat screwdriver from the top and insert it in the split. Then tap it slightly until it holds itself in place, this should be enough to slip the leg up in place. 

Could not resist, I had to put the tank on to see how it looks. Helps keep me motivated. I mean, I had to put the tank on to make the strap.  Strap, yes it does actually hold the tank on! Nice "Y" shape on this one was a BMW specific thing. You will see in the next few photos that the frame has a gusset up front that lends itself to this set up. 
The red R100 has a straight strap with a gas cap hole in it, check it out. 

Here it is, check out the flat hooks I made for catching the gussets on the frame. Aluminum flat stock bent around to grab the frame and riveted to the leather. Rivets are cool...
Any good industrial builder likes rivets! 

Below is the back latch for the tank strap. As you can see it is spring loaded. This allows removal of the tank with a firm pull. Yes more rivets, Did I mention they are copper. This creates a cool look. Note the strap goes under the spring to cushion it against the paint. The rivets are recessed in the leather from the bottom to miss the paint. I don't know why, Paint scratches from real functional parts are cool. Yes I said it good honest wear is cool. 

Take note of the swing arm, I put it on. Not much to say, except KNOW HOW TO ADJUST A BMW SWING ARM CORRECTLY OR DON'T DO IT. This is one of those jobs I see so many garage guys screw up and the bike handles like crap and is frankly dangerous. Another thing to look at is the cylinders. They will change color here soon. Black cylinders, not heads, cylinders make bikes look older, so black it is!

Below we see the cylinder and head removed from the engine. BMWs are cool for this job because they stick right out in your face. Note all of the carbon build up on the piston. Remove it. Gas and a brass brush or if you are old school and bad ass, use a razor blade. I of course am bad ass. Razor blade for me. While this is open, inspect the inside of the engine the best you can. Note wear marks or metal dust. Look for anything out of order. If you don't know what the order is supposed to be then don't bother looking because you don't know what to look for. 

This is the cylinder after I pulled it off. I put the valve cover back on it to plug a giant hole from sand. Yes sand, I blasted this part as a component to save from having to find other ways to keep the sand out. Smart huh? Of course I had to plug the intake, exhaust and the cylinder hole which you can see here has duct tape and a cardboard plug over it. What you don't see and MUST be done is the head bolt holes. They are still open in this picture. Two of these run oil through them on a BMW. If you do not plug them say good bye to the engine an hour after you start it! 

Below we see the blasted and painted finished product. Every one uses high heat paint on cylinders. If regular paint burns off, your engine is running too hot. High heat paint is for header pipes and mufflers. It will likely burn off the first foot of your header no matter what it is. Don't write and argue with me, just test it for yourself. 

Here we are with the fresh cylinder and head installed on the engine. Is this a thing of beauty or what. Stop looking at the rusty starter, I have not replaced that yet. I will do that after the bike is running. 

Next we started putting controls back on the bike. Fresh paint and loss of some switches that only pansies use make these BMW factory controls actually look good. But the clubman bars and the GRIP TAPE for grips makes them "Rocker". If you don't know what that means, quit reading my blog until you do. Grip tape does some really cool things. It sticks to your hand like shit to a blanket and it does this in the rain too. No oily film feel to it like rubber grips. Did I mention it costs about $1.99 a roll depending where in the world you live. One roll does about four grips depending how thick you make the grips. 

Now look closely at this picture. you done? Note the split in the grip tape in the middle of the hand grip area. WTF? This is My patented half throttle. Only the half toward the controls twists. Why you ask? Because I like it that way. After years of riding fast shit you get tired of hitting a bump and having the throttle twist up and give the engine gas without actually intending to. I developed this for high horse power applications and have a hard time living without it. You throttle the bike up to where you want it and grip the outer half of the bar with your outside two fingers. This prevents the throttle from turning without you wanting it to. After you ride one you will never want to go back. If you make one for your bike, send me $5.00 and your name and I won't come after you for infringement! Unfortunately the grip tape is not a new idea! Try it on your next rat bike you will love it after some of the sticky goes away. 

Finally got to putting the seat together. A single sheet of aluminum cut in two and shaped into a pan. Easy to do if you remember one thing. Materials are cheap! I suggest the first time you try this method you use a paper pattern and some thin aluminum. 

Paper pattern picture here

First come up with the shape you like with a small bit of paper and then transfer the idea to a large, full size piece of paper. Cut, bend and fold this to create a life size portrait of your seat. Trust me the paper is a good idea. After it is done . Unfold it and use it for a pattern for the metal. 

Pattern on aluminium here

Transfer pattern to aluminium and cut out. Bend the 90 degree bends in the side first and then shape the round nacelle at the back. No, nacelle is not just a Star Trek term, it's an aviation term. Read a dictionary. I used a two piece construction method, but notice the patterns were one piece. On the one piece version, you can shape it all at once, with the two piece you will have to shape and then rivet together. Mmmm rivets. Gotta love a fastener that has to be pounded with a hammer. 

Pan half done here

After the pan has been shaped properly. Cut a piece of plywood to match the pan. Laminate some foam to the wood. Remember to leave some over hang for shaping. Thickness depends on your preference. After it dries and you have shaped the edges, cover with leather. Vinyl is for pussies. Can't find small quantities of foam? Steal it from the bottom side of the couch cushions. 

Wood pan with foam. 

Screw the whole thing together and there you have it a cafe seat. I use some heat form plastic on the bottom to rest on frame section for cushion so as not to take paint off. Attach pan to frame however you see fit. 

Picture of bike with seat on it. 

Next we will wire the bike. Just find my magic wand... 
and well poof a wire harness to match my bike. At least thats how most people view electrical work. Don't understand it, must be magic. Very easy if you know exactly what each component does. Just connect the dots. 

1 comment:

  1. Nice project and great colour combo...I have a R60/6 I am working with here in London and I am looking for inspiration...I found your project and I like the polished inserts you have put on the fuel tank. Is this your own work or have you outsourced the knee pads? It would be great if you can share some info.