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

Monday, October 10, 2011

BMW R100 Airhead cafe racer

Here is a bike we built when I was an instructor at Wyotech in Daytona. Please note the student photos. I coached, they built. Until Wyotech destroyed the bike. 
                                                    But don't worry, happy ending. Love happy endings!

 Will this poor engine ever be the same...
                                 Never fear I checked every part before it was assembled.

                             A girl and a red shirt doing frame work?
What the hell is a red shirt? If you attend Wyotech and get good grades they give you a red shirt. They call it an "eagle tech".  Meant to give you something to shoot for but just pissed everyone off because it was academic not hand skill based.

This was written on the bathroom stall wall at school almost every day. 

Here is the crew that built the original bike. Original you ask? Yes. Original implying there is a copy...

Copy it is! All the way down to finding an actual R100. I of course owned many of the parts from the original bike so there are some things that came directly off of the first one. The seat, carbs, triple tree and so on.

Here is a view of the tank strap that holds the tank in place, very thirties racer. The seat is glove leather over closed cell pad with a wood base bolted to an aluminum pan that has been hand shaped out of one piece of sheet. I am happy to send you a copy of the design of the pan so you too can make one. Just hit my email with a request. Make sure you know what the hell you are asking for. No time for B.S.
 Note the single sided swing arm. 1980 saw the first single sides for BMW on their GS models. I tracked one down, but the wheel proved all but impossible to find. One left in Berlin for a mere $1000! Not gonna pay it so I am building a hub to fit the rear end.

A nice picture of the rear end. The first ones were three bolt hubs. I would not pay for one so the picture below shows the beginning of my solution.

I took a  drum from an earlier bike, actually an R90 I bought came with an extra wheel... Nice. The top picture is the inside of the drum. The bottom picture is of the welds on the outside. I chopped a hole in it and welded in a slug and now I will true it up and drill the three holes in it. Respoke it and there we have it a 1979 single side spoked wheel BMW R100 bad ass cafe bike. Did I mention the engine work? Did you see the deep oil pan? 


  1. Yes, I definitely noticed the deep sump! The BMW aftermarket sumps from "Motoren Israel" are the inspiration for my own DIY mod using sliced up sumps, layered sandwich style, for my DOHC-4 Honda project, "CB900K0 Bol Bomber" - Usually, people upgrade this series with a DRY sump system. But while I'm stuck with the regular wet sump, I figure I've gotta do all I can for it, without spending too much of what budget $$$'s are slated for entirely OTHER "Unobtainium" components.

    As for your HUB mods, I've seen something similar done with the single-sided-swingarm conversion with earlier 4-bolt drum hub, but what they did was make another piece for the pumpkin, the piece with the 3 bolt holes replaced with a 4-bolt version, or perhaps it was a bolt-in section which went inside the hub itself - IIRC, there was much to be done for spacing he hub at the bike's center-line, requiring a spacer to bump the hub to the left, IIRC....

    But IMHO, you'd have to really enjoy the drum hub in question to have gone to this degree of trouble. Plenty of options out there for a rear disc conversion at the same time. Now, I'm one to use a drum wherever I can get away with it. Wish to heck a drum would look better in the extra wide Akront rim for my "CB900K0 Bol Bomber", but it would look like ass - I'd use this here 3.50x18" 'SUPER-AKRONT' rim but that's slated for another DOHC-4 build. To tell the truth, I wish to heck I'd found two of 'em! Anyway yeah, the disc type rear hub might have been just as simple of a conversion, using a "Front Hub Trick" type wheel, as was so often used for rear disc conversion on pre-'75 SOHC CB750K's - or where the heavy-assed CB750F1 rear disc hub was to be avoided - So many rims out there drilled for the Harley rear hubs, it's a mod that shaves costs elsewhere - Of course you'd need an alternative shaft-drive pumpkin, maybe even some of the more bizarre "parallelogram" rear suspension - which doesn't sound like such a bad thing, albeit the frame mods for the monoshock rear end might be a heck of a lot more complicated. ANYWAY yeah, this type of rear drum would make for a great match to another drum up front, or an early style dual-disc front end, maybe even a single disc on a smaller or de-tuned 900 - IMHO, the single-sided-swingarm doesn't necessarily match as "period-correct" to the drum hubs, just as with the wider flat-profile Akront rim and my own drum. There are a lot of folks doing weird inter-generational mix-&-match stuff with the current trend of "STARBUCKS RACER" with USD forks & floating rotors with the gold anodize bedazzled snow-web/spider-flake center carriers, & other such cheesy chachi crap, like the 17" Super-Moto fat wheels - at least on the Beemers it's less common to see 'em in 3-spoke cast/mag rims - and the main reason for which is the Beemer airhead just begs for some classic wire-spoke wheels, 'cause it's such a retro-fried 100yr-old engine type. IMHO the most tasteful thing to do, is shoot for the modern upgrade parts which best emulate the period-correct race type works-spec parts, with oversized outer disc rings on the original 8-rivet carriers (Metalgear Australia and "Robtools" on eBay, both making some cool rebuild kits for fixed composite discs) - Ideally with original calipers spaced differently with alternative caliper hangers - what I'M trying to do here, is use the most period-correct RIMS to go with all that, 'cause a lot of the newer stuff just doesn't have the same look to 'em, they seem like they're just milled from billet with a CNC laser cheese-slicer. I dunno - I suppose there IS a certain something to an early '80s GS-based road racer, with the single-sided swinger AND the drum hub. Perhaps with some added DIY under-bracing to the swinger itself?

  2. It might lend itself well to some type of TONY FOALE style endurance racer or prototype sorta thing, where he was experimenting with mono-shock rear ends right along with the feature's earliest appearance on Superbikes, with the Yam TZ750's, so you'd see his frames for the SOHC-4 & DOHC-4 Honda utilizing mono-shock rear end with his leading-link forks etc. And so often, the Honda rear disc hubs were so heavy AND the concurrent cast/mag aftermarket wheels had so much weight out in their periphery, that it made sense to use a rear drum on those odd-ball Tony Foale kit-frame bikes. So something like THAT makes sense to have the single-sided-swingarm with a drum. Perhaps some type of quick-change front end, with calipers that don't get in the way of a front wheel removal, maybe even the quick-release axle clamps or spindle etc. Probably the most radical version of which would be the Honda RS1000 & subsequent DARVILL-racing aftermarket chassis which used a more simplified lightweight version of those same pentagonal hub locks etc. THAT might pair well with the single-sided-swinger. Then again, I dunno about using an early version of which especially the more spindly versions of which, on a '70s-'80s Endurance racer, when even those street-bikes which used the tech didn't race with it - plenty of first-gen VFR series (as opposed to VF-R) Honda V-fours, went with a conventional swinger for their Superbike racers.... MEH. I'm all for a "retro-fried" version of more modern stuff. As opposed to a "modernized classic", if you know what I mean.

    Just make sure you lace it to a decent period-correct racing rim. The "Super-Akront" 3.50" rims (16" & 18" only) don't have a bead-retention ridge, ergo they can't be sealed up tube-less using aquarium silicone, and would require an inner-tube no matter what - But they're still THAT light a weight in this particular profile - deemed "D" profile when stamped as simply "AKRONT" or "SUPER-AKRONT" more commonly - they've got a high triangular drop-section, giving the whole profile a rather domed appearance, and they seem to use a higher domed dimple for the spoke nipples, too - besides this, they're also often drilled for a side-valve type inner-tube. I don't know whether there was ever a tube like that for 18" rims, though it would certainly be cool - might limit one's choices for a lightweight racing tube though, leaving you with only heavy-weight tubes? But yeah, they're not only VERY light for their size, they're mondo cool for mid-'70s race-bikes, some very rare Unobtainium stuff - Far more common in 16" though. I'm planning to use a 16"-er up FRONT on my 985cc Honda, for more of a "Freddie Spencer Replica" vibe. And an 18"-er on my next DOHC-4, a 736cc stock-tuned bike "featherweight" for my daughter. I friggin' LOVE these rims - They've got such a beautiful look with a big drum hub, the drop-center profile giving even shorter spokes than otherwise.... They're easily 2/3rds the weight of an "equivalent" Morad/Borrani in 3.00" width, and the Borrani version needs an inner-tube too - The Akront "TR" profile is almost as light, but lacks it's vintage aesthetic, while the "TC" profile is much more thick walled and rather heavy thereby. There's really NOTHING which compares to the "D" profile - it's just too bad about the lack of bead ridges. If only one could ADD something in there?

    As for finding a decent vintage style TIRE in the appropriate size, you're on your own!