Guest Post: Alan Lapp's Dirtbag Challenge DR650

Innovation is a scarce resource in today's motorcycle industry, despite what the OEMs might lead you to believe. Behind every supposed leap forward in electronic trickery aimed at keeping your untalented ass out of the weeds is several decades of stagnant design and engineering tarted up with fancy new plastics. We haven't seen a real revolution in motorcycle design in a long while, at least one that didn't deviate far from the accepted formula of oversized bicycle with a big horny engine stuck in the middle.

The people who truly innovate are not found at major manufacturers. They aren't listening to focus groups or making clay mockups in well-lit design studios with Instagram accounts vomited all over "inspiration boards" on the wall. The people who are driving innovation are doing so in their garages and their homes, building their dreams without the constrictions of tradition and bean counter interference compromising their vision of perfection. They build the future the way they envision it, everyone else be damned. Their work is pure. Their genius is only recognized by the few who can appreciate the iconoclastic vision.  

This is not the story of one of those machines. This is the story of a Dirtbag bike.

This is not the result of years of engineering and testing. This machine is an example of the beauty of the hack. It is the result of a fever dream put into metal with hacksaws, angle grinders and barely-adequate welds. It is terrifying in more ways than one and rides far worse than it looks. This is Alan Lapp's Dirtbag DR650, and like all good Dirtbag bikes it is awesome because it is the result of a perfect storm of creativity, innovation, and terrible decisions made under the pressure of a ridiculous deadline and an absurd budget.   

For the uninitiated, the Dirtbag Challenge Low Rent Chopper Build Off is one of California's finest events for the slightly deranged tinkerer who desires the opportunity to exercise their moto-hacking skills. The premise is simple - build something cool in 30 days for a budget of no more than 1000$ including the cost of the donor machine. You are allowed as much pre-planning and drafting as you desire, but you aren't allowed to put hacksaw to metal until the specified build period is underway. Then it's a mad rush to get the thing built, running and rideable: static hipster art pieces won't do, as part of the challenge is completing a ride aboard your deathtrap. Burnouts are optional, but encouraged.

This is the story of Al's Dirtbag DR650, in his own words.

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 My wife and I moved to the Bay Area about 7 years ago. I got introduced to the guys that ran CityBike Magazine a few months after we moved and I became the Art Director for them until recently, when the magazine changed hands. I was introduced to many aspects of Bay Area Moto-Culture by association with CB. Great people, great local history. I used to be a bit of a hard-drinking, hard-riding maniac. When I experienced the Dirtbag Challenge, I thought “this is my tribe.” We didn’t have anything even remotely like this on the East Coast. The police attitude is very different in Maryland - they’d have arrested everyone and charged them with everything from littering to speeding to thinking about anarchy.

When I quit drinking 20 year ago I started road racing a Honda Hawk, which happened to be what I was riding at the time. I didn’t have any money, and when I needed stuff I built it instead of buying it. When I needed an exhaust, I read Smith & Morrison’s Scientific Design of Intake and Exhaust Systems cover to cover until I understood it (mostly) and built one in my shop. I also have participated on Michael Moore’s Motorcycle Chassis Design List for probably close to 25 years, and felt a bit like a poseur since I’d never built a chassis completely from scratch.

So, in my opinion, it was pretty much inevitable that I’d build a DBC bike.

My first attempt at a DBC bike was based on a Ducati ST2 which had been in a garage fire.  I did a bunch of suspension mods, basically turning it into an ADV Ducati with 12” of suspension travel.  Turned out that the ignition module was DOA and couldn’t be revived within budget.  So, it got shelved to, perhaps, someday, revisit for a future DBC bike.

The DR650 donor has an interesting story: it belonged to Wade Boyd’s girlfriend, Christina, and when we bought it for my wife, it had a purple fringed saddle with alien skull tattoos. Everywhere we went, people asked “isn’t that Christina’s bike”? I still have the seat.

At some point, the bike had been swamped under water and not rinsed out properly, and at about 40,000 miles all the bearings in the bottom end were totally hammered. It was making sickening noises. The piston rocked in the bore, the valve stems wallowed about in their guides, the big end of the rod wobbled like a freshly reformed drunk, the clutch basket rattled on its bearing like castanets and the transmission was having a mid-life crisis.

So I did what any good husband would do: I set about to rebuild my wife’s bike. I bought new bearings, and went to eBay for a crank and rod assembly and clutch basket. I chose a high-compression JE piston in the stock bore which was miraculously unscathed. To hell with the valve stems, I had Kenny Augustine lap the seats for an outrageous sum of money. Rest in peace, Kenny.

Anyway, long story short, I got it reassembled and it wouldn’t shift into 5th. After much tinkering I got it shifting correctly on the workbench, but the motor languished; since beginning the project my wife had bought a much better, newer Versys 650. The motor kept my workbench from blowing away in a strong wind for 5 years in this freshly rebuilt state.

I’ve been thoroughly impressed with the ideas of Norman Hossack. I saw a glossy photo thumbtacked to the bulletin board of my local MC accessory shop (The Dirt Shop, College Park, MD) of an early prototype based on an XR500 and thought “this is the future!”.

Image Source

If Norman Hossack was a teen crush, John Britten was my first true love. You can see in this photo that the V1000 also used a type of Hossack front end, only with vastly improved materials and design.

As a result, I’ve always wanted to build a bike with a Hossack front end. They neatly sidestep all the engineering shortcomings of tubular fork front ends.

So, about the build, there are a couple of facts that stand in direct opposition to my participation in the DBC. First, I’m a graphic designer and my biggest client is a boutique political advertising agency on the East Coast of the US. Elections are normally the first week of November, and all printing & mailing is done during the month of October… precisely in the middle of the build window for DBC.

Second, I have end stage renal failure. I’m on dialysis, which is basically, a part time job on top of the regular business interests. Plus, I wasn’t sure I’d have the energy or fitness to do it in subsequent years.

Not that I’m complaining: is what it is. Everyone has challenges to work around.

Anyway, Julian Farnam, multi-award winning Dirtbag and all around nice guy, and I had become good friends and dirt riding buddies, and I mentioned an interest in trying another DBC bike. He encouraged me to plan ahead, and work to the plan. He also catalyzed the process by volunteering a pair of R6 shocks which were excess to his needs and perfect for mine.

I spent time designing the DBC bike in Adobe Illustrator at actual size — I literally have a 9’ wide 4’ high drawing of my bike. Why not CAD? Because Illustrator has been my daily tool for twenty years and it is so deeply ingrained in my psyche that CAD doesn’t make sense because it’s not Illustrator.

I had originally planned to build around a mid-1970s Honda XL350 motor, with a set of CRF forks from a previous year’s attempt. When I realized I’d have to have the most ridiculously offset triple clamps to get the kind of trail I’d need, given the rake I’d designed, I switched to the Hossack front end. I actually got as far as building the frame loop for that motor, but Julian suggested I start with something which has a title and can be registered on the street if so desired. That’s what shifted the build to the DR650.

I consulted Julian about my proposed steering geometry, which he rubber-stamped as unlikely to kill me, and helped me figure out where to put the lower shock mounts so that the spring rates would be in the ball park, based on a few assumptions about how much the finished DBC bike would weigh, and the stock R6 spring rate. The spring rates actually worked out pretty well: the front is spot on, the rear could use a slightly stiffer spring or different shock mounting location.

I spent about a month prior to the GO date gathering bits and pieces, supplies and consumables (it would SUCK to get 20 days into the build and break your only bandsaw blade, right?). The funny thing is that there is less than $150 in steel in this build — the main spine frame is made from 3” steel tubing, and a 20’ stick of it is $46, which is enough to build 2 frames with plenty left over!

One of the major technologies in this build was figuring out how to miter the round tubes so that when they were all welded together, they formed a closed circle, not a helix and not an open C shape. So getting the angles right and clocking the second cut to be in plane with the first cut was a challenge. A digital protractor was used to set a woodworking bevel gauge, and that was used to set the angle of the vice on the bandsaw. To clock the second cut, after the first cut was made, a digital level was zeroed on the freshly-cut miter. The bandsaw vice was then reset to the angle for the other end, and the digital level used on the opposite end to rotate the tube into the same relationship to the blade as the first cut to ensure that the miters would work right. I came up with this process, and as far as I know it is novel. It worked out fantastically well - on the DR650 frame, the gap between the first and last tubes was less than 1/16 of an inch!

My ecstasy was short-lived: the very moment the frame loop was cool enough to touch after welding, I tried to slide it over the motor. Much to my dismay, I discovered that it DIDN’T slide over the motor. After some head scratching and diagnostic work I discovered that the ruler I’d used in my original photograph of the engine, upon which I based all my design work, was not perpendicular to the camera, causing some foreshortening and a ~3% scaling error.

Because I’d already wasted one entire frame's worth of tubing on the aborted XL350 build, I didn’t quite have enough left over to build a third. I suppose in retrospect I could have, and perhaps should have, just bought more tubing but I didn’t. Instead I pinned the frame down to my milling machine table and cut away all the areas where the motor and frame were interfering, then welded in covers for the new holes. It’s worth mentioning at this point that the frame is actually the gas tank, taking a page from Erik Buell - another inspirational out-of-the-box thinker. Fuel drains out of the bottom of the tank, and is lifted to the carb via a surge tank by a $35 vacuum-operated Mikuni pulse pump from a watercraft.

The build of the suspension pieces actually went very smoothly: as Julian repeatedly told me, plan the build, build to the plan. The only fussy bit was what I refer to as the steering head: the part which the handle bars bolt to, and houses the cross-shaft for the Middleton link. I’d have been much better off building this as a bolt-together assembly rather than a weld-together assembly, which distorted the only point of critical alignment on the piece. And being stubborn, I tried to fix it while the clock was ticking rather than discard it and design a better piece. It eventually got whipped into shape, but it was horribly time consuming. There’s a lesson in there somewhere if you care to look for it.

The operation of a Hossack front end probably needs some discussion for those readers who may not have seen one. A Hossack FE (front end) belongs to a category of non-telescopic front ends called FFEs — funny front ends. It operates just like an automotive “twin A-arm suspension” as one might see on a road racing car, Trophy Truck, Quad, or side-by-side. It’s basically an automotive front end turned 90°. The wheel is held by an upright, which also houses upper and lower pivots which located at the pointy end end of the A-arms. This is also what differentiates it from a Girder front end. First off, Girder front ends are designed to interchange with telescopic forks, which inescapably means that all of the suspension links and shock absorber are part of the steered mass, as they are on a telescopic fork front end. The Hossack arrangement relocates the linkage and shock absorber to the non-steered part of the suspension.

In addition to the reduced steered mass, the Hossack also has much less friction than a telescopic fork: it doesn’t contain oil, therefore it doesn’t need to have seals. A very nerdy benefit of a Hossack front end is that lateral (side-to-side) stiffness can be tuned independently of longitudinal (fore-and-aft) stiffness, something that cannot be done with cylindrical fork tubes. MotoGP designers have been chasing lateral grip for decades, gaining the understanding that a chassis needs to be stiff longitudinally so it can transmit horsepower to the rear wheel and braking force into the chassis in a well-behaved and predictable manner. However, the lateral stiffness has to be different than — in fact significantly less than — longitudinal stiffness. Excess lateral stiffness can lead to front-end chatter.

One of the downsides to the Hossack is that direct steering linkage is prone to bump steer. It’s easy to get all of the steering linkage pivot points and suspension pivot points to line up perfectly when the wheel is pointed straight ahead. When the pivots are lined up, the wheel can go over a bump without creating a steering input, i.e. zero bump steer. However, when the front wheel is steered to one side or the other, the steering pivots and suspension pivots necessarily cease to line up, which isn’t a problem unless a bump or dip is encountered. Unfortunately, the real world is full of bumps and dips. When the steering & suspension pivots are NOT aligned and the suspension compresses or rebounds, there is a steering input created by this misalignment. A good link design can minimize this effect, but not eliminate it.

Enter the Middleton Link. Designed by a fellow MC_Chassis_List-er, the link is put in between the steering mechanism and the steering links. The Middleton Link axis is horizontal and lateral. There are tabs at each end of the link. The steering links attach to the tabs. When the handlebars are turned, one steering link is in tension, the other in compression, and these forces balance out: the Middleton Link doesn’t move. However if the suspension is compressed or extended while the steering is turned, the necessary misalignment between the suspension pivots and steering link pivots is resolved by causing the Middleton link to rotate, bringing forces at the steering links back into balance instead of causing unwanted steering input. It also allows a great deal of freedom in the location of the handlebars.

Clear as mud?

I had a lot of friends help with the build - motorcycle photographer Bob Stokstad was a reliable and enthusiastic helper - but it was terribly ambitious. I achieved a rolling chassis, but couldn’t finish the build in time for the event. One of those friends showed Pol Brown, the organizer of the Dirtbag Challenge, cellphone pics of the current progress. Pol made it known to me that he wanted the bike entered in the 2015 Challenge, so I had a goal.

I was also invited to be in the non-Harley custom section of the Bay Area Motorcycle SuperShow, where it got a lot of curiosity and misguided praise from The Motor Company Doodz; many of them called it a “badass hill climb bike” which sort of left me puzzled.

Fast forward a year, and the 2015 GO date rolls around. I had never been much of a list guy, but there are some real benefits of a list. It’s a little bit like an analog tachometer; you know not only what RPM, but also the instantaneous relationship to redline. With the list, I could observe progress, and judge my pace. 2014 was all heavy lifting, which I’m good at. 2015 was all about details, which I’m not good at. The list was instrumental in getting the “I”s dotted and “T”s crossed. I’m only semi-literate with electrical stuff, so Julian came over and worked with me to get the old harness reattached to the bike.

I have to say that I so deeply prefer the look of the bike in the BAMS state - just as a bare frame - than with it all cluttered up with all the stuff that it takes to actually make it work. It’s so elemental and spare, you can see and understand all the moving bits.

On the day before the ride, Julian came over again to help. We got it started and I got to test ride it for the first time. No surprise that it ran terribly. The jetting was entirely off because I’d removed the air box entirely and reconfigured the stock header using a 2-stroke stinger as a muffler. We managed to get it “close enough”, or so I thought.

The day of the ride, Julian showed up at my house with his DBC Ducati chopper from 2014 on a trailer, and we loaded up to head into San Francisco. It’s worth nothing that at this point I managed to get only 3 hours of sleep due to the political advertising work load. My client had a full on panic attack when he realized out I’d be out all day Sunday, despite my numerous warnings ahead of time.

We pulled into Hunters Point about 7:30, a bit early (I may have preferred another hour of sleep) and hung around for 2 hours, watching the other Dirtbags pull in and show off their handiwork. Some kind soul brought coffee and donuts, even though I could really seriously have used a big fat shot of caffeine, I had to abstain because of my kidneys (all you craven Red Bull drinkers, think about what you’re doing to your bodies!). The ride is supposed to leave at 9:00, but I think we left closer to 10. The local MC Club (that’s club with a capital C if you understand my meaning) ran interference, blocking the cross streets so we had a thunderous straight shot out to the highway, where it became apparent that Houston, we have a problem.

After a few short miles, the transmission started dropping abruptly out of 5th back into 4th, then eventually not going into 5th at all. To compound the problem the carb wasn’t jetted well enough to run smoothly at a cruise, but would function acceptably with my thumb on the choke lever. I rode about 90 miles of the 120 mile route with the choke on.

Jake, on his absolutely adorable XL125, and I were partners in the slow lane on the highway, both of us wringing the necks off our respective rides just to average about 55 mph. The handling was surprisingly mild: very stable, not very quick to change directions at all, the only downside was that the vintage DOT-legal trials tire didn’t like pavement grooves and would wander a bit. It didn’t even try to kill me once. Jake, however, got the worst of it: the DR motor had developed a nasty oil leak on the left side, and the 2-stroke muffler was blowing fiberglass packing onto his faceshield. His helmet looked like it had been tarred and feathered. Sorry Jake.

We got to the famous Alice's Restaurant where we socialized and bought gas. The rear of the bike felt squirrelly on the twisty bits, but I couldn’t tell if it was the oil on the tire, the knobby tread, swing arm flex, or if some critical weld was about to pop, so I didn’t push it hard. I put a couple of wraps of safety wire under the carb needle to richen the midrange.

On the next leg — Alice's to Pescadero via Stage Road — the pavement is quite choppy upon which I discovered much to my dismay that the R6 shocks, which were designed for rising-rate rocker linkage, have grossly too much compression damping when mounted directly to the swing arm without any linkage — Julian experienced this with his DBC Ducati as well. By the time we arrived at Pescadero, my jaw hurt from clenching to keep my teeth from clacking together. My thighs and lower back were screaming in pain from the forward controls. On the plus side the revised "jetting" was working pretty well. Halfway to Pescadero the rickety 2-stroke stinger lost all its packing and the end cap vibrated off, changing the back pressure and causing it to run like shit again.

On the way out of Pescadero the carb popped off the extended manifold, but that was a pretty quick easy repair — I didn’t even take off my helmet to do it.

I was considering taking secondary roads back to the party, but decided to tough it out and follow the route which went uphill on Higgins Creek Rd, back out Skyline to 92, then back onto the highway and into the city. I don’t know what I was thinking (perhaps only of the pain in my legs and back) but I passed up buying gas at Pescadero. As a result, I ran out of gas at Daly City, a mere 10 minutes from the end of the ride. I walked to the nearest exit and bought a jerry can and gas. In the meantime the DBC sweep truck came by, found the vicinity of my bike swarming with California Highway Patrol due to an auto accident, and wisely didn’t stop. I’m glad I wasn’t around for questioning.

Once refueled I made it back into the city for the party. When I rolled into the gate, I was vigorously cheered by my fellow Dirtbags, and I did a big smoky burnout: a burnout that I’d earned by working like a madman, jamming workshop time in between paid work and doctor visits for two Octobers in a row.

This year was an unusual year for voting at the DBC. As Pol says “Only a Dirtbag can judge a Dirtbag”. There are about 6 awards, the names of which I can’t remember. This year, aside from “Cleverest Award”, one guy on a screaming purple KTM 500 2-stroke MX chopper swept them all. I nabbed the Cleverest, which was a great honour.

I want to close by offering my most sincere thanks to both Julian Farnam and Bob Stokstad for their support and facilitation of this build. It’s been a real pleasure.

Maybe next year I’ll build a Britten tribute bike…

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POSTSCRIPT: On May 27th 2016, I received a kidney transplant. It’s a modern miracle of science, but it only works when people are willing to donate. Please consider being an organ donor. With any luck, I’ll build a bunch more DBC bikes.

Interesting Links
Alan Lapp's Level Five Graphics Site
Alan Lapp's Zenfolio
Norman Hossack Design
Dirtbag Challenge Website
Dirtbag Documentary Page
MC Chassis Design Mailing List
Julian Farnam's FFE 350
Julian Farnam's CHOPPRD
OddBike Brittens at Barber
US Organ Donor Website
Canadian Transplant Society Website