Friday, May 28, 2010, 07:19 PM ( 946 views ) - BMW Cafe Racer - Posted by Administrator
Sean Harris of Orange County CA has built one of the most beautiful and tasteful BMW café racers I’ve seen in a while -- a short wheelbase R75/5 with clubman bars, café seat, and a striking yellow headlamp lens reminiscent of fog lenses of old!




No stranger to vintage BMW’s, Sean had his eye on a café project for some time. “I've had a Slash 2 that's fully restored for over 10 years and I always wanted a R75/5 SWB. It's still a work in progress as I have yet to really get into the motor, but it runs strong and has been very reliable and much faster than my /2.”

Sean opted for basic black with no pinstripes, a classic and correct look for this generation although pinstripe delete bikes are rarely seen outside Europe. Black valve covers give a custom yet “in-marque” look that compliments the seat and tank, both of which are very well chosen for shape and proportions.






“One of the biggest things to me was the tank. Since I can't afford a Heinrich I opted for a /7 tank because in my opinion anything would be better than the stock /5 touring tank- not my favorite. Once I secured the tank I looked for the right seat I found the current one on Ebay and then had to shorten it about 2.5" to accommodate the SWB as well as the length of the /7 tank. I also wanted to strip off everything that is of no use to me - all the dead weight- turn signals, fender, etc. -it's amazing how much weight that adds up to.” The front fender is bobbed, the rear fender is gone, and he’s fabricated a very tasteful taillight & license plate bracket hanging from the seat. No turn signals means using hand signals, but that adds to the vintage and race-inspired charm.


Sean offers this great tip: “I found the Yellow headlight lens from a place in Burbank, CA called Sticker City- its a really thick sticker that covers the H4 halogen conversion I did- the film was inexpensive -$20 and easy to install but a little tricky because it became a tight fit with the headlight ring and those damn clips on the inside.” I would have sworn he was running a vintage glass foglight lens and this way he keeps the excellent optics of the /5 lens.



Rick is far from done with this project – his plans include clip-ons, front disk brakes, and powder coated rims with stainless spokes, as well as lightened flywheel. “The clubman bars are ok in my opinion - Like I mentioned before I am still on the hunt for the right sized clip ons - its really just to tie it in for a true cafe bike. Rick Monahan of Black Kat Motorwerks in Venice, CA has been very helpful with this project. What's great is that I have built this all on a serious budget and it’s great to see the dramatic change from stock to where it is now.”

Congratulations Sean, that’s one very cool BMW café racer, we can’t wait to see how it progresses in the future!



Monday, February 22, 2010, 09:07 PM ( 13903 views ) - BMW Cafe Racer - Posted by Administrator
Thanks and a tip of the hat to BMWScotter who got me to dig up this post... I guess it's a response I sent to the airheads list. Lots of good ideas here on building a tasteful (and quick) BMW cafe bike.




First, as far as a simple airbox replacement plate, it's a very easy thing
to make. Start with a piece of cardboard and learn where it needs to bend,
then trim it down. Then make the same thing in metal. I made a cool one
for my R60/5 café bike, back when I was running a starter cover, out of an old
WA license plate. It's about the right width, and it gives you some nice
embossed rigidity plus the choice of a nice letter- I had one with 'X',
but I don't seem to have a picture of it.



(you're actually looking at it here, barely, dark triangle between the petcock and side cover, just a bent piece of tin, in this case a license plate, although you can't even really see it. Imagine you're seeing a bent piece of license plate covering the back of the starter cavity, since the airbox is now gone.)



A 'real' racer runs no starter, of course, if that matters. I gather
you're looking omitting at the airbox cover because it looks good, which it does.

But café racers are all about 'feeling' cool and fast, who gives a damn if
you're pegging any more mph on the speedo?

This is why riding position, bars seat and pegs, are so critical to your
experience. I love my café bike because it can literally thrill me as much
as I can stand it at only 45mph. Compare that with a modern sport bike
which can do 100mph effortlessly and you see exactly the reason for a café bike.

It is not about being fast. It is about feeling fast. And it looks fast
and it turns heads. It's fun!



So I have a very different opinion, especially from Danny, who said:


>I vote stock.

Disagree, unless it already is and you like it. There are enough mutt /5's
around that its worth it to either really restore it correctly or modify
it with a vision.


>My philosophy is, if you're going to café something, it ought to be
something that COULD be fast in addition to just looking fast, and that
WAS fast, or at least potentially so, back in the day.


My R60/5 will outrun most R100's, and many oilheads. Not a stock engine,
no, but still only 600cc. For street purposes you can make an airhead very
fast, if you don't mind losing gas mileage.



>(Plus I think most airhead cafes look kinda goofy -- Jon-Lars' Redbike
>excepted, bigtime.)


Here I will agree 100%!!! And I'll except mine too, frankly. I'm biased,
but I'm right:

[/url]

See, I love great airhead café bikes. But I hate ugly ones. I've looked at
a LOT of pictures of them and I'd offer these rules:



Don't mix /5 with /7 era parts, except carefully. I know, I know. That's
half the fun. But realize that the instrument cluster is a really defining
part of the bike, and it makes sense to match that visually to the seat
and tank. Personally, I could never get used to angular /7 covers with a round
/5 tank. I can ignore dual disks though, no problem.

Don't get excited just because you've switched to lower bars and stripped off the RT fairing. Good start. Look around.

Don't overdo the pinstriping. Follow real BMW patterns as much as
possible- there's a right way the lines go over fenders, tanks, and seats. If you make something up, it will look bogus.


Don't use non-BMW colors.There are a lot of good colors to use, if you
want Italian red, why not match an R25 fire bike? If you really want a wider
range, look at BMW car colors, which are where most modern BMW bike colors
come from. Orient Blue is a great deep purple-blue, for instance.

Be really aware that many café seats are really associated with certain
bikes or models, like the John Player Norton. That said, look around and
you'll see that there are some really cool vintage seat repros around for
not a lot of money, including some cool vintage jap stuff. And that said,
realize what a café seat is, and look at its precursors in the Italian
racing 'salami seats'. I personally don't like bobber seats on a BMW at
all, but that's just me.

OK, so enough NO's, let me say something positive here. One of the great
things you can do with a café bike is frankly adopt a full gonzo forward
riding positions. Run clubman bars, to get them down where clipons would
be. (running clipons would mean replacing the headlight brackets)

I mean it. If you have not ridden an airhead with bars this low, try it
first before you comment. It works, I rode mine 5 hours effortlessly to
the Nationals.




The great secret of course is a tank bag which is primarily a pad, and
should be stuffed and adjusted for comfort. Then you're basically lying on
the thing, with your arms outstretched and feet back on the rear pegs.
Just like a normal riding position, you can move your weight to your hands and
feet at will. It's the closest thing to flying.

And this is the big difference. Doubly so if the front end is lowered.

Oh, and get yourself some nice bar-end mirrors, and learn how to adjust
them. Don't settle for stuff that you can't get to work. It's cool in city
riding to be able to flip up the mirrors to squeeze between cars to get to
your turning lane. Gives you nice wide mirrors that fold up for parking.



As far as power, you want some. You want basically a rowdy hot rod, and
the best way to do that is either run stock and shut up, or to install Mikuni
round slide carbs, which you buy pre-jetted from Sudco or Rocky Point for
maybe $300. These give instant kick-your-pants acceleration, great overall
performance, and maybe a third loss in gas mileage. (This too can be
worked, but that's another story) Keep your stock carbs in a box on the shelf in case you 'come to your senses' later.

Another good modification is replacing the heavy stock exhaust pipes with
aftermarket 2-into-1's. They also will make the bike almost as loud as a
Harley, not as loud. Close. BMW folks don't especially like it, but this
is café stuff, sorry. Hey, it's not straight pipes.

Beyond this are other mods which are either debatable (but maybe look
good, like replacing stock airbox setup) or which are a lot more involved, like
a cam swap, or lowering, or medium size, like a lightened flywheel. The
thing is, if you're going that far in you want to be doing it altogether as a
matching package, not upgrading as you go. That's actual race stuff, and
you can do that. For now go with street performance as above and otherwise
keep it simple.

There are a number of upgrades in the form of disk brakes and fork braces
that are very worth doing and which are a good choice for any café bike.


But I think the very first thing is to change the riding position, and
then build the bike to follow. Find out if you really want this full forward
position- it's cool, try it. You can also flip clubman bars upward for a
more normal position, too. The stock motor will give you plenty to play
with this and discover that you love it, or hate it. Most people aren't
lukewarm about it.

Don't forget the tank bag. Lying on a bare tank sucks. Get even the worst
beatup elefantenboy, and find out why they reign supreme:

http://www.x189player.com/r60cafe/image ... eLeft1.jpg


http://www.x189player.com/r60cafe/image ... eLeft2.jpg


If you don't have the position, it's not a café bike, IMHO. And then I
think those are ugly.

-Paul



PS- here are some more hints: study older models and notice what makes
them
look vintage, details like painting the footpegs to match the frame color
make a huge difference.


PPS-

I mentioned the speedo cluster above - this turns out to be nearly the defining element of an airhead cafe bike. Why? Because this decision affects everything else.

What are you going to run the speedo drive from? If it's a /6 or later speedo, you've got to have a /6 or later wiring harness. If it's a /5 speedo, you'll need a /5 front timing cover, even if you're running a late R100 motor - you need the early cover (the timing cover now, the layer the diode board bolts to, not the front cover) witha place for the mechanical tach/speedo cable to fit into... -and- you're going to need a cam with an early style front bearing surface to match that cover... oh, and your oil pump rotor will need to match that cam too...

It's easy to jsut stay stock, then everything matches. If not... you've got to make sure this particular line of dependencies is connected up, or you'll discover at assembly time that something is wrong. (think I got it right the first time...? hah!)

-P

Tuesday, September 9, 2008, 03:34 AM ( 38703 views ) - BMW Cafe Racer - Posted by Administrator
Suggested Reading:



How To Restore Your BMW Twin: 1955-1985
by Mick Walker
view at Amazon



Read my review first!



Clymer Motorcycle Repair: BMW R50/5 Through R100GSPD: 1970-1996
view at Amazon



Not perfect, but most of us have one...(more)



Proficient Motorcycling: The Ultimate Guide to Riding Well
by Ed Hough
view at Amazon



The classic of riding safety, this book could save your life... (more)



Cafe Racer: The Motorcycle: Featherbeds, clip-ons, rear-sets and the making of a ton-up boy
by Mike Seate
view at Amazon





(click images to view as wallpaper size)





1971 BMW short wheelbase r60/5 Cafe Racer with San Jose-built lowered front end, subframe and seat; dual front disk brakes and CC fork brace; 336 cam, aluminum flywheel, Mikuni 32mm VM carbs, and Luftmeister R100 2-into-1 exhaust. Magura clip-ons and a rare Hugon 1/4 fairing complete the package.





This r60 Cafe Racer is very, very quick, and best of all it can scare me happily at 45mph. It handles very well and does very well in traffic. The lowered front end is very trick- there are only about two inches of suspension travel remaining, of which I only use one most of the time. Yet it is never harsh and never bottoms out, even on railroad tracks. This front end was built for nationals racing, and it shows.





The Hugon fairing was hailed as the best fairing in the world especially by long distance riders, in part for its superb aerodynamics and in part for its rugged indestructability. Cut from solid Lexan Citroen windshields and hot shaped, Hugon fairings were actually tested and found to be bulletproof at short ranges. (Actually it is possible to break them, as a friend proved in Central America, but you should have seen what it did to the rest of the bike and rider.)


In use, the Hugon quarter fairing makes a tremendous difference in reducing wind and buffeting. Although full-sized fairings mounted on the handlebars like this are not recommended for SWB airheads, this one has been a positive improvement in stability, especially when buffeted by strong side winds. The full optical visibility is a big advantage to the clear fairing, plus it allows the cool front end hardware to be visible.





The pre-60's era front fender mounted license plate completes the vintage charm. I have to admit it gets me in trouble, though, because it attracts attention from people who always want to ask "what year is it?" I suppose because that's what you ask when you see an unknown old vehicle.


But if I tell the truth and say it's a '71, they're disappointed, maybe they were hoping it was from the 1920's. So I've taken to stretching the truth and saying "well, parts of it are from 1960...". The footpegs, maybe. But that seems to make people a lot happier, and those who continue the conversation at that point understand when I explain that most of it is a 70's period street racer.


The license number is a reference to prewar BMW racing- IIA was the city code for Munich. The first BMW works-built racing engines were marked on the block with WR50 to indicate 500cc racing engines. So I remember these traces of the golden age of prewar racing using 50's style license display on a 70's cafe racer.


Whatever, man. It's a hot rod, and it makes me happy.







Tuesday, September 9, 2008, 02:51 AM ( 2078 views ) - BMW Cafe Racer - Posted by Administrator
"The Isle of Vashon TT is this Sunday," Uncle Phred remarked casually to me Friday night. "If you have something running, bring it down and we'll ride together."


It doesn't take more than that to motivate a last burst of effort to get a motorcycle running. The r60/5 cafe racer was coming along, sure, but not so well. I'd ordered a new range of jets to help with the carb adjustments, and was busy with real life leaving time open to do the work. By my calculations if everything went off well, I could just get it done in time. If not, I was prepared, but I wasn't beaten yet.


When I got to jetting, that went fairly well. It didn't look good to friends and neighbors who dropped by to watch me fiddling with carbs and little brass parts. It seemed like I was doing the same thing over and over, and so I was. They were all puzzled- I thought BMW's ran well? And so they do, especially when you keep them in original stock condition, as I hadn't.





In this case I was essentially adapting an unknown carb to an unknown engine, starting somewhere at random. As it turned out, it was a freak coincidence that it had started so well from the first. I realized this when i noticed I'd installed the carb slides backwards, by switching the right and left cables when I'd routed them. This wasn't really right at all and when i corrected it the jetting was too far off to even run. I had gotten it to idle nicely (the first step, you work upwards) but it wouldn't run at all without the choke on.


If it seems ambitious that I'd expect to jet a carb in a few hours before a ride when it hadn't really run at all yet, well, maybe. But I had taken one precaution this time- in addition to the Twinmax carb sync meter (which is really two rubber hoses that connect to vacuum lines with a gauge to show the balance between the carbs) that makes it so much easier to balance the carbs, in addition to that, I'd ordered a K&N air/fuel meter.


A few nights before, I'd drilled a 3/4" hole in my exhaust collector pipe, yes right through the lovely black ceramic coating of the Lufty 2-into-1 exhaust. Then I'd welded in a threaded fitting, screwed in the oxygen sensor, and mounted the exhaust back on the bike. When it was all done I could remove the sensor and screw in a cap, and get another fitting to weld into another pipe.


That made carb jetting amazingly easy. After revving the motor for 45 seconds or so (hey, I needed to break it in anyway) it would get warm enough and the meter would show a reading. It was often surprising, too. Like, you see belching black smoke and you think it's rich, but I saw it in odd cases when it was really running too lean, too- I think it would 'lope' with richness and blow it out the tailpipe. Well, I guarantee that's sent me off adjusting it the wrong direction in the past.





The sun was down and it was becoming saturday night when I finally finished. I had a good strong idle that was just a little rich, and I had a slightly rich power band and then it would lean out a little bit on cruise, just like it ought to be. Except of course that I hadn't actually ridden it more than a block or so. As it had gotten dark I moved up the street to an empty parking lot away from my neighbors so I wouldn't have to deal with anyone being angry and my incessant revving.


Finally it seemed to be running well enough that I could probably take it out and get it warmed up really and have the next go-around. I wheeled it slowly back toward the garage.





But I wasn't happy, and I wasn't headed out for a test ride. Bad symptoms that had started appearaing the night before were now erupting into full-scale problem. The bike was makign a bad grinding noise, in neutral or in gear. It seemed to be coming from the back of the transmission, and confirmed my worst fears about the output shaft bearing on this junkyard 5-speed.


It was 10:30 at night, and I weighed my options. I could just call it quits and ride the RS the next day, although it wasn't nearly so much a fun old project. But I wasn't beaten yet. I could swap the 5-speed out and put the old 4-speed back in. That would work.


In brief, the next hour or two was spent tearing the rear end apart, unbolting the fneder and battery box and disconnecting hte u-joint and removing the pivot pins and detaching the rear end from the swingarm. In short, taking everything apart so all the puzzle pieces are seperate. OK? REady, go!


And the weird thing was now I really couldn't detect where the horrible grinding noise I'd heard was coming from. I had fully expected the gearbox output shaft to flop around loose in my hand and ooze silver slime on me in troublesome ways, but it didn't. Seemed all pretty normal in fact. Ditto the rear end, and the driveshaft. Through process of elimination I concluded it was a broken U-joint, but you know, it was fine.


(It did help that I'd kinda been through here a couple of times, so I had an idea of what was 'OK'. Like, there's a frightening amount of play in an airhead gearbox. But that's 'OK'.)


So, I aligned everything perfectly and bolted it up and said 'Before, it made grinding noises when I pushed it in neutral. If it doesn't make that noise, maybe it's fixed.' Of course it made the horrible grinding noise again.


Ack. So this time I lie on the bike, rolling slowly back and forth, pressing my hands over the parts, trying to sense where the noise is coming from. It had really felt before like it was coming from the very back of the gearbox... but maybe not...?


Finally I concluded that it sounded like it was coming from inside the swingarm tube. The driveshaft was grinding around in there. But why? I pulled back the rubber boot and noticed that there was a half inch clearance between u-joint and tube on one side, and nearly none on the other. Hm, that's not right. Maybe the swingarm's mis-adjusted? No, and you can't adjsut it far enough to correct this.


OK, so then the gearbox is mis-aligned in the frame. Why? Well... ok, there's a spacer on one side of the engine stud, but not the other. Hmm... I seem to recall that's correct... unless I got it on the wrong side! Duh! So I pulled the stud and removed the spacer and put it on the other side.


Well that was ever stranger, becaue now it was the same problem in the opposite direction- the u-joint would grind against the outside side of the swingarm tube. Weirder and weirder.





So I stopped and followed the adivce of the great Bob Berg, who said 'look at it for a half hour before you call me'. So I looked and thought about it. I felt under the R100RS, sure enough there's a spacer on the right-hand side. Yes, the spacer was supposed to be on the right side all along.


But... the spacer on the RS seemed to be thinner than the one I had. Sure enough, I looked through my parts box and found two more spacers that were half as wide as the one I was trying to use. I installed the correct spacer (about 5mm wide instead of 10mm) and sure enough, the problem went away COMPLETELY.


In this state, I put it to bed for the night and got a few hours of sleep. Would it make it? I would find out. I was planning to raise the needle clip one notch, then go, and I did. And indeed that morning it started and ran and I rode it, fully a couple of miles before the first set of plugs started fouling. I stopped at a local farmer's produce stand, still closed up in the misty dawn light, and raised the clip one more notch.


This time it ran with gusto, and I was away. It made the thiry-mile ride to Uncle Phred's house without incident, and started flawlessly on the way out, though I changed the plugs several times during the day. That night I arrived home safe and sound, sore as hell. And the next day when I fired it up it made all the aches and pains hurt just right.


It has work to do yet, I'm not done refining the jetting for midrange. And then there's the top end main jets that I haven't even touched yet, that will unleash the power.




Meanwhile, a couple hundred miles of riding later, it seems that the cylinders and rings are getting to know each other, and I'm getting power I wasn't before. Now, it's nice and strong at 3-4k rpm, and quite muscular at 4-5k. But between 6 and 7k you really can feel the power of the racing cam getting into teh power band. It revs handily up to 8k rpm, and no doubt more than that. I'm treating it as break-in, and treating it both rough and gently as a result.


This is good news, a new chapter in the r60/5 cafe racer!

Tuesday, September 9, 2008, 01:30 AM ( 4297 views ) - BMW Cafe Racer - Posted by Administrator
At long last the r60/5 cafe racer was coming back together. High on the list of priorities was a swap to dual disk brakes. I'm very familiar with the dual ATE brakes on my R100RS, and I think they're ideal for an airhead.


Surprisingly, even the earliest tiny /5 gas tanks have a cutaway area underneath in front to leave room for mounting the undertank ATE master cylinder. That makes plumbing the brakes a pretty stock operation. The dual disk swap has been well described, it means replacing the sliders with a pair of sliders that hold the ATE calipers.


I opted to paint these black, like the RS did but mainly to continue with the vintage feel. The end result- it feels vintage even though there are disk brakes. I know, to the purist vintage racer this is blasphemy, and it will keep me out of vintage racing. But I don't care, I like to stop well on the highways where I ride. Getting this together was very good news.





Now, it may seem like at this point you could bolt it all together and ride off into the sunset. I thought so too. But I knew too well that there was no guarantee that these parts would work together. I had already proven that it was not adequate to merely rotate the engine through a couple revolutions and conclude it was safe to run.


The documentation with the 336 cam warns that it may be necessary to notch pistons for clearance, and I was pretty sure that with the high-lift cam this would be the case. I planned to use clay to find out how much clearance there was between the valves and piston. But as it turned out, I didn't even get that far.


The problems began when I realized that I couldn't rotate the crank through a full two revolutions (2 crank = 1 cam revolution) At first I thought I was colliding a valve with the piston, but nope. Turns out that the valves were running into each other, and it was serious.


After some thought, it was staring me in the face: the 336 cam wasn't compatable with the large-valve heads. It lifted the valves too high for the large diameter valves to clear each other. So then I was faced with a choice- which one to use?


The regulars on the MC-chassis list were helpful there, pointing out that the larger exhaust valve probably didn't make that big a difference, the size difference was most important with the intake, which wasn't that much larger than stock. And it turns out the stock valve diamters are considered close to optimal for a 600. Both would increase flow, but the cam would also raise the power band, effectively increasing the usable power even more. Oh okay, twist my arm. I was biased- I'd installed the 336 cam already, I didn't want to take it back out. So I was back to stock heads.


All along I was lucky to have the good advice of several friends including Tom Cutter, who was most generous with his knowledge of BMW airhead racing development.


One thing Tom impressed on me right away, when he saw that I couldn't be dissuaded by the fact that racing an airhead is controlled folly in the modern age... that out of the way, he made it very clear that the only way to success was to be prepared to take everything apart and then put it back together again, over and over and over. Every time something changed- valves, cam, valvetrain geometry- it all had to be checked for clearance. Once you were out of stock territory, it was no-man's land, and you had to take precautions.


I had asked him what clearance he recommended- the BMW docs said 1.5mm. "2mm everywhere" was his answer. Everywhere? He meant not only valve-to piston, on the face but also along the sides, and between the valves themselves at overlap- exactly the problem I'd run into.


But how do you measure the clearance between the valves inside the cylinder when you have to assemble it to get all the valvetrain installed and adjusted correctly?





In order to do that, I followed Tom's advice, with some modifications. I cut a set of tubes that were exactly the same length as the cylinders, so they could be bolted up with heads and pushrods and the crank could be turned and the valves could be observed in action. Tom had used aluminum, and replaced the valve springs with lighter springs to prevent the aluminum from being warped out of alignment. I opted for steel tubes with steel washers and aluminum washers on the ends to prevent nicking the heads.







And here we can see the valves in action. As we approach TDC, the exhaust valve is open:






Now we are at TDC, both valves are open briefly (overlap):





And after TDC, the exhaust valve is closed, Elvis has left the building. The intake is open and the next charge is being drawn in:






Here we have a closer look at overlap. This is what I was waiting in suspense for: would there be a 2mm clearance as Tom had advised? Indeed there was, 5mm of clearance, more than enough. I was very glad to have seen it and to know for sure.





It made me think too of the reputation BMW racing engines had all the way back to prewar days: they were bulletproof, indestructable. Now I was beginning to see reasons why- if engineers observed extra-large margin of clearance, it would allow parts to be run way beyond normal tolerances of heat and expansion without catastrophic results.


OK, one hurdle accomplished. Now it was time to notch the pistons.


Now, I don't know how to exactly describe how hair-raising this was, except to say that at times I found it easiest to wait until I was in such a black mood that I didn't care if I did ruin it and grind a hole clear through. I'm nto sure I was really confident until I had a set of backup pistons. But once the grinding began, it was quick to actually do the shaping, but hard to go very deep without wanting to go back and check again with clay. I did this many times.


Install piston on connecting rod, using blowtorch to heat piston so wristpin slides in smoothly. Apply clay to piston, and spray it with WD-40 to keep it from sticking to the valves.






Rotate the crank through two full revolutions, a couple of times, and then disassemble it again (don't put the blowtorch away yet). What you get is a piston with lumps of mashed clay on it.





And if you take a gentle blade (I used a brass feeler gauge instead of a razor blade) you can carve away cross-sections of the clay and measure how much there is, how much gap was left between the valves and the piston.





I must have done this a million times.


When it was finally, finally right, I breathed a BIG sigh of relief and turned to the other piston. With the first one as a model, I got the second one done in maybe a half hour. It figures.


Here's a comparison of a notched piston with the stock piston, which has much smaller notches:





When both pistons were shaped and I'd tested them with clay and smoothed and polished them, it was time for balancing. I weighed them... and was surprised to find that they were both 424.0 grams. Amazing! And a very good sign- time to bolt it together!


It was all picking up momentum now. I got the motor back in the frame, and bolted up the 5-speed I'd been waiting to swap in. It would be a big improvement over the 4-speed, and it was one of the rare early 5-speeds with a kickstart lever, so I could continue to run without a starter.


Now I mostly worked to tie up loose ends. I got the body panels all repainted and pinstriped (more on that some other time) and did some needed repairs on the seat and the subframe fender mounts. There were a lot of little details I ran into- the neutral light didn't work, for instance, because the /6 neutral switch had a seperate ground wire, like the taillights, insted of grounding to the chassis. Ran a new wire, problem solved, next.





Finally when I got it together enough I tried starting it- and on the 3rd try it popped into life! I was delighted, and took it out for several test runs. Things were not right obviously, the carb wasn't jetted right, but it ran.




Thursday, July 3, 2008, 05:32 AM ( 4934 views ) - BMW Cafe Racer - Posted by Administrator
Since the original connecting rod bearings (and most likely the crank) had been well thrashed by their brushes with glory, a bottom end change was in order. Preserving the original r60/5 engine block and crank for possible restoration later, I stripped the bike down.





Note that I'm using an automotive engine hoist, and I recommend it when pulling motors. Not only does it provide 100% positive support that can't fall over even if you lean on it, but since you can't use the centerstand (it comes off with the engine mounting studs) you also don't want to use a motorcycle lift, because that would normally go right under the oil pan- and that's going to get lifted out of the frame.


So an engine hoist works wonders, and a five gallon pail like this one to set the frame on and keep it held steady is just the ticket. You probably can't see in the photo that I pulled the swingarm pivots and unbolted the u-joint and just pulled the whole swingarm and rear end free and left it hanging on the shocks. That's the easiest way.


I began building the new race motor using this good '76 R75/6 bottom end. The changeover from /5 to /6 meant a change in a number of things, including both flywheel (to bigger bolts) and cylinder base size. I could have used an earlier /5 block, but I opted for /6, even though it meant sourcing another pair of cylinders. (r60/6 and r60/7 are not exactly rare, but uncommon, so finding these was not so easy as it would have been for R80, R90, or R100 stuff).






But the tradeoff was worth it, because it allowed the mounting of this lovely flyweight aluminum flywheel (I'm not sure why the light makes one of the flywheel bolts look darker, believe me all five are new bolts):





But that's getting ahead of the story- of course there's a whole lot more three steps forward, two steps back stuff that I'm skipping over but you know it's there. Put it together and take it apart again. Because of course it's the old story: "As long as I'm in there..."


So, yeah. As long as I'm in there, what about another cam? Certainly the stock R60/5 cam could be improved on. But why not a racing cam? As it happens, the famous 336 cam that helped BMW dominate sidecar racing in the 1950's was still available. Whee!


Here we are pressing the timing chain sprocket off the old camshaft.





I'm skipping some ugly steps to get here. What does it take to swap a cam in an airhead motor? Well, besides the front cover you take the alternator and rotor off, and the timing cover, and there's a lot of disconnecting of stuff you want to be sure to reconnect right later. Under that is the timing chain, which on this vintage is a double-row chain running around sprockets on the crank and cam shaft.


And I'm gonna take a stand for being a heretic here. The first time I changed the timing chain on the RS, I cut the old one off, and that was fine, it was worn. This one wasn't worn. So rather than cutting it off and using a new one with a master link, I would rather use the endless timing chain, cause it's cool.


So what I did was used a puller to pull the crank sprocket off the crank -most- of the way but not all the way. If you do this, you can pull the camshaft forward far enough to get the chain loose and off. This is good because when you go to reassemble, the sprocket is correctly aligned on the crank and it's easy to press on- otherwise you have to heat and freeze parts and even then it isn't easy. So to me this is a good trick. I know, I know, the sprocket should be replaced, but if the chain isn't worn and neither is the sprocket, I say run it.


Anyway, here's the 336 cam, compared with a pair of R75 cams. Notice that in addition to the different size lobes, the top R75 cam has a larger lump on the end. That's where the timing cover seal is, and there are two sizes, small (early) and large (late). I chose to use an early small seal, because I wanted to use the original early timing cover that included the speedometer cable for the /5 speedo.





Now a closer look. You can see how much larger the lobes are on the 336 cam, almost 50% more lift and a lot more duration too (wider).






Here we are pressing the cam sprocket onto the 336 cam. Whee!





Every little bit helps when you're riding your cafe racer hard around corners. Years ago I'd come across a BMW police oil pan that included these baffles to prevent windage around corners by keeping the oil from sloshing around. Boy it's fun to pull a part like this out of your special parts stash!





Meanwhile, other changes were in store besides the engine. Having been studying details of 50's as well as prewar BMW's, I decided for fun to detail the cafe racer as though it were from an older era. One of the most striking details of some of the older models was painted rims. I considered all-black but instead opted for the black painted stripe rim of an R51/3. This and a black painted hub would do wonders to give the bike a vintage feel.





And even more important than a faster engine and better paint: dual front disk brakes! Here we see the first mockup with fork brace.





After lying in wait for so long (it seemed) the r60 cafe racer was finally coming back together!




Thursday, July 3, 2008, 04:11 AM ( 11815 views ) - BMW Cafe Racer - Posted by Administrator
In the beginning it was a neglected '71 R60/5. The carbs and exhaust were shot and many little things needed care. I don't have a photo of it in this state but here's a magazine ad showing the model:





The short wheelbase models only appeared for a short time before they were joined and then replaced by a longer wheelbase model with an extra couple inches of spacer welded into the swingarm. This made for better stability which was a real improvement for touring with a luggage or fairing, but the short wheelbase made for a quicker, more nimble ride.


At the time the chrome tank and side panels were disliked, people thought they were gaudy and tasteless. Today of course we love these details, and they add a real beauty to the bike. This particular one was also set up with large front crash bars, a big luggage rack, and it hadn't run in years.


Then I came across parts of a San Jose nationals racer like the one below that had been built in the 70's, at a time when an airhead BMW (an R75/5) was the fastest bike in the world. Most of this vintage race bike was already gone, but I acquired the key parts- the lowered front end, modified subframe, and cafe seat. The rest- engine, etc.- I could build, but an expertly lowered front end was really valuable, and not something I'd want to build myself by trial and error.






I began to disassemble the R60 and installed the front end. The subframe was a stock subframe that had been cut down and braced, and fitted with hardware to mount the cafe seat. Short Koni shocks lowered the rear to match the front, and gave improved handling.











These parts transformed the little short wheelbase R60/5 into a serious cafe racer- low and fast. Most significantly, the San Jose front end lowered it drastically, lowering center of gravity and improving handling. It also made it look really wicked cool.


At first it was very rough, but it began to take shape:








Note the top triple clamp is not the usual stock stamped plate, but a heavy cast unit- actually a lower triple clamp flipped over and machined to fit- a classic period race trick. The next step would be to install an S fairing, and you can see the mounting brackets already installed.





In order to get it to run at all, it would need carburetors. I scored a couple of Mikuni round slide VM's on ebay- not from the same model bike, in fact one was from a two stroke. But Mikunis are tremendously adjustable, and I soon had them jetted, at least for starters.






When it roared to life, and went for its first test ride, it was clear tht this was a good combination- airhead BMW's feel good, but this one felt especially good. Lowering it made it handle better and increased the sensation of speed. I found I could thrill myself as much as I wanted without even going over 45 mph- what a perfect quality!


Looking back, I really prefer the appearance here as a naked bike, without the S fairing, and it was this picture that reminded me to try something different in the next incarnation.

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