CB desert sled

[Luke]

Originally Posted by azcagiva

Looks good. Dad is in the process of building a cafe racer of his four.

I have an extra set of those forks if you need any parts or anything. I might even still have a set of heavy springs for those too. I will dig through my stuff and see if I can find them if you want.


The husky style shocks are going to be awesome.

-John

Thanks! I think these are in pretty good shape, but haven't pulled them apart yet. I'll look into spring rates, but I'm sure I'll need heavier ones.

[oregoncoast]

Originally Posted by Luke

See picture 2. We needed to line up the rear wheel with the frame, and couldn't find your laser alignment rack. Was it out for calibration?

Wow, all highfalutin and stuff with your fancy-pants rear-wheel/frame alignment tool aren't you??

[TwinDuro]

Originally Posted by Luke

Flood

When I started riding, it took a couple of exciting corners to learn that 'countersteering' wasn't 'applying a little pressure to the inside bar' like everyone said. It was holding the grips tight and twisting the bar like you're loosening a rusty lug nut. An experienced rider friend insisted I was doing it all wrong until he rode my bike.

I hope this bike will steer a little easier than that one.

Oh man, the 'sled is looking great thus far Luke and Alex; keep up the good work!

Seriously, that's no joke about "twisting the bar like you're loosening a rusty lug nut." It's a good thing Honda put wide bars on the CB500/550/650 because just as mentioned, the leverage was needed and appreciated!

With an underwhelming front disk, a strong rear drum, worn out TT bearings and lots of fork dive, a typical-condition stock CB does give you a workout when pushed. I understand why the steering stops were broken off on mine... There's nothing like a good tank-slapper to get your attention!

Can't wait to see the new subframe!

[Luke]

A little swingarm work today. In order to get the back wheel to match the front - both in travel and in weight - the swingarm needs to be about 4" longer than stock. The bike will eventually get either a heavily reenforced swingarm or a totally custom one but I wanted something now for mocking up locations for everything. Shock mounts, chain roller, etc.

Start by marking and cutting up the wrong swingarm. Oops. Good thing they're only $20.


Move on to the right swingarm.




Rick supervised










Results

[TwinDuro]

I can't say it enough, the CB is looking great Luke, Alex and Rick, keep up the good work!

Your mock-up swingarm is looking good (pretty arc welding BTW) as well! The stance of the bike looks killer and I can't wait to see the new rear shocks! When you put 'em on, make sure to charge the beer can reservoirs with plenty of nitrogen!

I just got the joke about the KTM seat in your previous post! When you get to the point where you need a permanent seat, PM me...

[YOUNZ]

Pittsburgh beer?

[Luke]

Originally Posted by YOUNZ

Pittsburgh beer?

Yup.


The local fancy grocery store carries it.


I have absolutely no idea what possessed them to do this. I've never seen it anywhere but there and West PA.

[LC Garage]

Here's what I saw when I came home from work last night;



Luke (and the ever elusive Doc Sprocket) had two motors scattered about and Luke was testing to see "what fits what".

[Luke]

So, a little explanation about the motor. The plan is a 550/650 hybrid , a 650 motor with a 550 transmission. There's a good write-up on this type of build by Paulages at SOHC4.net

Alex and I took apart most of one of the 650 motors on Tuesday, I finished up disassembly today and even got a little re-assembly started.

Starting on the motor. This had spent years as a spare motor for someone else's project, so it was a bit of a mess on the outside.




The inside looked much better than the outside. A bit of crust on the pistons, but it was oily crust.


We took pictures of the clockwork. Nothing special, but it helps with putting it back together.



Stupidity of the Day: we started disassembling the motor before draining the oil. Mess was made.




We did this without a manual. This was fine until we tried to split the cases. The primary chain was holding the crank in place, which was holding the cases together. On the up side, the manual says that it was possible to split the cases without removing the alternator rotor, which is not true. So we pulled it. Not having a proper puller, we improvised. Who would have guessed that the front axle of a DRZ400 is a perfect fit?



We got the top case off, but couldn't take the crank out because we couldn't figure out how to get the primary shaft out.


This was the end of disassembly for the day. We finished up by cleaning a lot of parts.



Mmmmmm, journals.











It turns out that the primary shaft just slides out if you hit it with a hammer. There's a thread cut into it for attaching a slide hammer too. And one of the motor mount bolts is just the right size. Beats waiting 4 weeks for the Honda special tool.


Today there was more disassembly and cleaning. Pistons, valves, everything, was separated. Plastic tubs are handy.




I did a little assembly too. The 550 clutch cover has to be sanded to let the 650 drive gear fit. The 550 cover has to be used because it fits the kickstarter.





The 550 case has to be modified to fit the 650 chain guide, so I mounted it to my mini-mill and cut a new slot. Definite scale issues here.



Typical machining (for me anyway). An hour to set up and 5 minutes to cut. The clamps that came with the mill were made for tiny little model steam engine parts, not real engine parts.





A final moral shot of the bike. I also put new throttle cables and carb jets in.






The rear suspension design is coming along as well. If it fails, it won't be for lack of theory.


It's some Matlab/Octave code that figures out the leverage of the rear wheel on the shocks based on the geometry.

And yes, if you squint at the code on the right you can see that I was trying to do a linkage system. It probably won't happen, but was an interesting mental exercise.

[jesusgatos]

Let's see some napkin sketches. What kind of linkage are you thinking about using?

[LC Garage]

Originally Posted by Luke

The rear suspension design is coming along as well. If it fails, it won't be for lack of theory.

String Theory?

[Luke]

Originally Posted by jesusgatos

Let's see some napkin sketches. What kind of linkage are you thinking about using?

Worse than napkin sketches. I'm learning to use Sketchup.



Frame on the left, not drawn. The shock is in gold, the popsicle stick is the link. Almost all the wheel travel is in the downward direction.



The linkages I've seen use an 'opening scissors' type of action to get the progressive movement. They give the shock an extra push at the end of the travel. This does the same, but indirectly. The rotation of the triangle moves the shock out to where it has more leverage on the wheel.

By the numbers, it should have good action. Fabrication looks like trouble, though. Keeping the shock/triangle joint from buckling sideways would be the big trick.

There are a few other ways, but that's one.

[TwinDuro]

A dual-shock, dual-linkage setup? That's cool and very different; I like it!

As far as keeping the shock/triangle joint from buckling... how about an inch-or-so thick piece of 7075-T6 for the triangle, with some structural webbing created by milling out some of the material to keep the unsprung weight down and a supported roller bearing on the end closest to the axle? That bearing could ride on a stub welded into a gusset in the swingarm, with the bearing half supported by the swing-arm structure itself...

I need a napkin!

[DOCsprocket]

I think in the spirit of vintage motorcycle racing, that no computers should be used in the fabrication of this bike. You should only use a vintage-correct Texas Instruments calculator (the kind with the red numbers).

[DOCsprocket]

NORRA sanctions the use of any of these during the design and fabrication of this bike: http://www.vintagecalculators.com/ht...lculators.html

Any use of a computer (Commodore Vic-20 through present) is in clear violation of regulations.