DR650 Cafe. Scratch Built Amelioration

Hurco550

Keep er' Between the Ditches
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Just over 11 years ago in October of 2012, I joined this forum. I had been bitten by the Cafe Racer Craze that was sweeping the vintage motorcycle world. I was 22 years old, working full time as a Tool and Die Maker by day and an Adult Education Adjunct Welding Instructor by night. (I still teach at the school, but in a full time capacity, which will come into play in this build.) At the time, "Cafe Racer TV" was in full swing, and one of my night class students happened to mention that he had a cb550 that he would let go "cheap". A deal was struck and I became the proud owner. I messed with the bike for a few years. As it goes with so many projects from such an era of a mans life, kids, home buying, marriage etc. all got in the way and the project left as well.
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Over the next decade, I have owned, modified, restored and built multiple other bikes and have remained a fairly active member here on do the ton. Yet the fact remains.... I still have never built a "cafe racer". I know.... the horror... the humanity...

I have decided that its time to remedy that, and hopefully in a spectacular enough fashion to atone for me sins.

A little over a year ago, I finished up my first bike with a frame that I had built from scratch. It was a simple piece as frames go. A Hardtail bobber designed around a 96+ Suzuki DR650 engine. I really enjoyed the build and have also really enjoyed putting several thousand miles on a bike that I assembled from a pile of steel that I measured, bent, cut and fitted by hand.
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This led me to decide that it was time to build my next scratch built frame around another venerable dual sport engine. In this case it will be a (guessing to be) 1978 Honda XL500 engine. I wanted to build something that was on the same basic idea of the bobber. Bare bones, no frills machine with lots of torque. But on this one will be built in the cafe style with a real focus on an ability to eat up the twisties and handle like its on rails. It will end up with a set of GSXR forks, laced 17" supermoto wheels, and a hand built chromoly frame.

The engine came to me by way of a $100 swap meet score from Mid Ohio AMA Vintage Days. A quick side cover disassembly shows that the cam chain tensioner gave up the ghost at some point. I am hoping that it didn't end up bending a valve, but the engine will likely end up with a pretty full on top end refresh regardless.

As aforementioned in this post, my full time gig is at a vocational school as a welding and fabrication instructor. I talked to a few of my level 2 students who have a real knack for CAD and higher end fabrication work, and they are interested in being part of this project. If were being honest, it would be way easier just to do this solo, but man does it make me smile to see a group of young folks as jazzed up about a project, so I decided that we would do at least parts of it as a class project. The first part of the job was to set up the engine on a layout table with a few data points and lay out the engine mount locations. At home, this would've been done in a bit more rudimentary fashion, but doing it in here we decided to go less "hacky" with it than my normal style.
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Ill keep posting as I go. Fair warning, the dr650 bobber was right at 3 years from first post to first ride, and there's a good possibility that this one goes the same way.
 
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I'm on board. That fixture table is sweet, looks brand new! Tony Foal sells software for analyzing bike geometry. Might be worth looking into if you want something that handles well.
 
The DR650 Bobber stands as an example of your keen eye for "Bike Beauty Follows Function"- so this should be one slick Cafe Racer!
 
I'm on board. That fixture table is sweet, looks brand new! Tony Foal sells software for analyzing bike geometry. Might be worth looking into if you want something that handles well.
I will look into it. I am doing as much research as possible, and will likely do much to copy some known geometry from later model sport bikes, but that calculator could prove invaluable as well, especially when figuring up rear shock rate etc. Thanks for the link!
 
I haven't been shy about my admiration for the "Bobberer" end result; with or without side hack. If this one, (Caférer? :) ) is even close to as successful it'll be a real masterwork. You might even get me to donate that gray seat I've got if that fits your café bike motif!
 
I have more than a little experience building these motors, if you need any free advice. I have built them in a variety of configurations, some of which I liked better than others. I do have some spare engine parts laying around.
 
A neat little aside on this project... When I started to build my first aforementioned "cafe racer" from a cb550, I fell in love with the Dime City Cycles "Wrapped Cafe" seat. I bought one back then, but when the project got somewhat "dissolved" the seat got sold to fund other projects as well. When I started mulling over this project again, I decided that it needed to have several things as a homage to the original build that was left unfinished. One of said things was a DCC tuck and fold wrapped cafe seat. I hopped DCC a few months ago, and to my surprise, they no longer carried the seats. BOO. I decided to go ahead and see if Facebook marketplace had any on the used market, and to my surprise, I came upon a listing from the guy who originally made the seats for them, and had 5 assorted seats left over. One of which being the black tuck and fold one that I originally swooned over. We made a deal and he shipped me two seats (one non pleated black one as well, that may just sit on the shelf until another use comes along) for $175 shipped. DCC used to get $260 + shipping a piece for them, so I'm happy as can be. (shown on the cognito moto cb550, which is the bike that made me want it to begin with)
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I also got some of the basic CAD drawings done. Most of the process to this point is tedious and boring but it is nice once you get a solid base point it is nice to be able to see some thing come together. In this current setup, we are sitting at:
24.5 deg rake
3.73" trail
52" Wheelbase
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And here is a very quick first sketch of a possible layout of frame and body work. It will obviously end up much more refined.
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That's a short wheelbase! Is there a reason you are going this short?

Are you taking center of gravity into consideration? I also have been working on a custom chassis design and this is one thing I am having a hard time factoring in. Its easy enough to figure it out once the bike is complete but I haven't wrapped my head around a way to calculate the hypothetical CG.
 
That's a short wheelbase! Is there a reason you are going this short?

Are you taking center of gravity into consideration? I also have been working on a custom chassis design and this is one thing I am having a hard time factoring in. Its easy enough to figure it out once the bike is complete but I haven't wrapped my head around a way to calculate the hypothetical CG.
It is a hair short. Same as a buell XB12s. Rake is stolen from the gsxr750 of the same year as the forks came from.

The short answer is that I am not factoring COG into the equation. The engine height is based off of the angle of the swingarm and pivot compared to the countershaft. This whole thing will be my first dive into building a frame from scratch that isnt a hardtail, and have little doubt that it wont be my last. Its the first step in a trial and error experiment, but starting from the best initial specs that I could come up with.
 
Trial and error is how we ended up with most "standard" geometry numbers from manufacturers anyhow so I guess I'll have to settle that for myself as well. I recently played around with raising and lowering the seat height on my SV650 at the track and was surprised how much it affected tip-in. I'm probably overly fixated on CG but A/B tests are always eye opening.

I'm designing as much adjustablilty in my chassis as possible - adjustable fork offset, swingarm pivot, extra long chain adjusters for additional wheelbase, rear shock mounts, using the headstock bearings off an R1 so I can use rake cup bearings if I need to...etc. Maybe overkill for me but with so many variables present I like the idea of fine tuning the geometry instead of being locked in to my potentially poor design.

Your project is inspiring, and its interesting to see how others are tackling the same issues!
 
Since you've ridden my FT/XR and you should have a decent feel for it's setup with a common engine, I figure I'll throw a couple numbers in here. Also assuming you went with my engine height, so the COG conversation may get a few more data points. With my DR350 front end, I surely dive more in the turns than the GSXR will, but it's super balanced and manages tight hairpins incredibley well. Curious how big of a difference being 5.5" shorter on the wheel base will be, coupled with the shorter trail.

Wheel base- 57.5"
Seat height- 32.5" w/o sag
Rake- 27"
Trail- 4.5"
 
The engine came to me by way of a $100 swap meet score from Mid Ohio AMA Vintage Days. A quick side cover disassembly shows that the cam chain tensioner gave up the ghost at some point. I am hoping that it didn't end up bending a valve, but the engine will likely end up with a pretty full on top end refresh regardless.
I think I have spare cam chain tensioners if you want them. I also have a brand new still in the box Megacycle 144x21 cam. I have had it for about 35 years and don't think I will be using it since I haven't built that kind of engine again. To run that cam it needs valve springs and retainers, shortened valve guides, hardwelded and reshaped rockers and a piston with relieved valve pockets. To make best use, the head should be ported along with a big carb and good pipe. Since you are taking your time on this build, making an awesome motor for it makes some sense. I can let this cam go for a very good price, including a trade out for future considerations or a donation to my favorite charity, Raceline Ministry.
 
I think I have spare cam chain tensioners if you want them. I also have a brand new still in the box Megacycle 144x21 cam. I have had it for about 35 years and don't think I will be using it since I haven't built that kind of engine again. To run that cam it needs valve springs and retainers, shortened valve guides, hardwelded and reshaped rockers and a piston with relieved valve pockets. To make best use, the head should be ported along with a big carb and good pipe. Since you are taking your time on this build, making an awesome motor for it makes some sense. I can let this cam go for a very good price, including a trade out for future considerations or a donation to my favorite charity, Raceline Ministry.
Hey man, I would absolutely be interested in the tensioners. Not sure if you have any other bits laying around, but I do know that the little piece for the auto decomp is broken as well and I need to track another one down. Its number 6 in this picture I think. If you had any of that around I'd be happy to buy it off of you.
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As far as the cam goes, that is VERY interesting and I would absolutely be interested. I have a local guy that does engine work for me and is an old flat track guy with a good familiarity with these motors. Ill pick his brain and see if he may have the valve train parts or a source for them. Since you have experience with these motors, what do you think of the longevity of one with that setup. I think it would be a hoot on the twisties with that work done, but I do also want it to hold together with more or less Honda like reliability.

Found this info sheet on the cam that I will take with me to the engine guy.
 
I probably have #6 but it is still in the motor. When I pull the clutch cover, I'll pull it out. I don't use the automatic decompression, I just learned how to kick start these beasts. I know where the tensioner and slipper is, so I can box them up. I have not had any problem running the 144-21 cam as long as the rockers are hard welded up and reradiused. I don't know what Megacycle does as far as the specific measurements are, but the principle is to move the contact point onto the radius of the rocker pad rather than the edge due to the lift of the cam, so it doesn't lose all of the lubrication. The high lift also neccesitates using shortened valve guides and high perf springs. I have a spare head with 2 bent intake valves your motor guy could look at. I wonder if stock guides could be machined shorter while still in the head? Lastly, you have to make sure that the piston has enough depth to the valve pockets to accommodate the lift. Stock pistons don't, the Wiseco pistons do. The 12.5:1 Wiseco piston requires the used of race gas to prevent detonation or they will break at the wrist pin boss. That will totally destroy the entire top end and crank. I was able to reuse the cases and transmission.
Does your engine guy do porting? At least to match the manifolds? Do you have a carb? I don't think I will be using the 38mm flatslide that I have. I will make you an excellent package deal on a bunch of this stuff.
 
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