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PostPosted: Thu Feb 16, 2012 5:58 am 
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Joined: Wed Feb 01, 2012 12:33 pm
Posts: 453
pretty impressive break on you s-bike there, think its a design flaw rather than being a few pounds heavy.
The shock mount on the front triangle looks as though it has no pivot.
Bet if it had a regular eye to eye pivot shock you wouldn't have any problems.
A small coil shock would really look the part on that frame.
look forward to seeing this beast come to life!


Last edited by 13 on Thu Feb 16, 2012 9:16 am, edited 1 time in total.

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PostPosted: Thu Feb 16, 2012 9:05 am 
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I think this is the most interesting project on RB at the moment, I can really sense your passion and dedication. Good luck and count me in! :D


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PostPosted: Fri Mar 09, 2012 12:55 am 
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Joined: Sun Aug 21, 2011 11:57 pm
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Location: Antwerp, Belgium
I guess it's time for a small update. Not that I have any new info or progress, but still ...

I've been searching for the frame's place of birth, but no luck so far.
The people at Verlicchi don't recognize it, which lead me to believe it might have been a Yeti frame after all. I mailed FTW, but he doesn't recognize it either.

I just sent another mail to a different section of Verlicchi. If that doesn't help, I'll mail Yeti themselves.
My 503 has an "SBIKE by Fabio Cavalli" decal on the seat tube, so I'm actually considering mailing every Fabio Cavalli I can find on the internet.

-----

Basically the only good news is that the broken 828 has donated its cable stops and rear suspension unit. Once I can detach its core element from the 828's swingarm, I'll post pictures of the internals.
It contains several springs, but no dampers whatsoever. So it'll be a boing-boing ride.
I'm not sure which full suspension models of other brands were available in the 1990-1992 period, but I doubt any of them will have an advanced rear suspension either.


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PostPosted: Thu Mar 22, 2012 10:29 am 
Dirt Disciple

Joined: Fri Feb 10, 2006 6:53 pm
Posts: 31
Location: sotteville les rouen france
Some news about origins?
Have you contact the sbike boss ?
I'm interesting by all informations ,i would like to try learning informations :wink:
thanks raging bulls


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PostPosted: Thu Mar 22, 2012 12:06 pm 
Old School Grand Master
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Location: Antwerp, Belgium
Mike,

I know which Fabio Cavalli to contact, but am still looking for his contact info.
He was on the board of directors for a large pharmaceutical company, but left that recently in order to pursue another goal. So his email address there isn't valid anymore.
I'll just have to wait and see where he pops up next.

As for the frame's origins, I recently received a scan from an article in a Belgian magazine. It says Francesco Quinn built all the Sbike prototypes in the USA, after which they get shipped to Switzerland to be finalized for production by the Sbike engineers there.
There's lots of other info in there, but it's all in Dutch. I'm planning to translate the entire article to English and put it on my site soon.

I have no idea whether Francesco Quinn welded the frames himself or had Yeti do it, but Yeti is often credited for building the original Quinn prototypes and is widely rumoured to have built the Sbike prototypes as well.
I'm tempted to say that Quinn himself didn't weld and that the frame was probably built by Yeti. For me that's enough to ask FTW to finish it, but I'm giving myself a few months to get some definite answers.
Contacting Quinn would have provided the correct answer for sure, but unfortunately he died last august.

I need to save up some money for finishing the frame anyway, because I suspect it won't be cheap.
Having it done by FTW means that I need to ship both the prototype and the 828 (for reference and measurements) to the US, and I'm not just going to use a cardboard box for shipping such an important frame.


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PostPosted: Thu May 31, 2012 2:18 pm 
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Location: Antwerp, Belgium
Time for another post.

I've contacted Fabio Cavalli, so now I'm hoping he does reply.
If not, I'm completely stuck and will have to build the bike to the best of my knowledge.

I've been able to get some more info by examining the parts.

Image

The picture above is where I tried to fit an original 31.8 Sbike handlebar into the custom stems. They're obviously intended for a 25.4 handlebar.

All aluminium Sbikes built in 1992 or later had 31.8mm handlebars, and even the original 729 prototype (built in 1991) had a 31.8 handlebar.
That leads me to believe that this particular frame was built in 1990 or early 1991, which means it would predate all the production full suspension Sbikes.
We can now exclude the option of this being a later evolution or a downhill special. The 25.4 stem wouldn't be used on one of those.
Could this really be the first attempt at a full suspension Sbike? Unicorns don't get any better than this, at least not if you're into Sbikes.

If Mr. Cavalli replies and knows more about this frame, so much the better. If not, I'll go with 1991 as a guideline.
The high-end 1991 Sbikes sported a full '91 XT set and Ritchey WCS Pro rims. I know all the correct code numbers for the XT parts and should be able to find all that NOS if I spend enough time on eBay.

Regarding the welding that still needs to be done : I know FTW welded the first prototype that Francesco Quinn designed, so IMO he's the only man for the job.
While I'm waiting for Mr. Cavalli's response, I'll be taking the necessary pictures for FTW, so he knows what to do. I plan to ship it to Vermont somewhere in July or August.
So it looks like the actual build itself will only start during the winter months ... if I can get all the parts by then.




Anyway, by lack of new material, I'll show a bit more about the rear shock.
People have been wondering and asking me how these things work, so I was due to explain it anyway.


Image
All the parts in the right order. I used the swingarm and broken top triangle of the (deceased) 828 to show where everything goes.


Image
Putting the adjuster ring over the main shaft.


Image
Sliding the bottom spring into the adjuster.


Image
This washer fits nicely onto the main shaft.
Basically this washer supports the main spring. The bottom spring is merely used to hold the adjuster ring against the bottom of the main shaft at all times.


Image
Main spring going onto the bottom assembly.


Image
The spring cover sliding into place.
This part acts both as protection against dirt and as a bump stop. There's a rubber ring in there which will hit the adjuster ring if the shock compresses too far.
Pretty clever stuff really.


Image
Putting the shock onto the frame. Top end first due to the length of thread sticking out.


Image
Yet another spring.
This one seems to enable the top cap to tilt a bit when necessary, eliminating the need for a proper pivot. Basically the entire shock can tilt a few degrees around the top mounting plate, which is enough for proper operation.



Image
Sliding the top cap over the top spring. This is a snug fit. In fact it touches the side plates of the mount.
This'll only get worse if I have the frame painted, so I might have to sand the cap down a bit or have a new one made.
Plenty of thickness, so there'll be no effect on integrity. Besides, this part is mainly cosmetic.


Image
The top adjuster nut being screwed on. I read reports that mention this nut can apparently be tensioned up to the point where the suspension can be locked out.
Theoretically, that's possible indeed. However it means turning it so much that the bump stops engage.
This particular nut won't take that much thread because it's closed at the top, so at best it allows some control of the spring tension.


Image
And there you have it, the frame with the shock installed.
The rear section will be polished to match the shock's finish, and then clearcoated (powder coat, of course).
The front will probably be red. It's a good thing I have a proper red Sbike already, so I can let the paintshop select the correct matching colour.



Those of you who paid attention, will probably notice that there's no damping whatsoever in this shock. Yes, it's a boing-boing affair indeed.
You probably noticed the lack of grease as well. That's because this is just a dry assembly for the pictures. I'll do it properly when the time comes to build the bike.


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PostPosted: Thu May 31, 2012 2:31 pm 
retrobike rider
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Location: Nth Somerset, UK
Fascinating build.

Is it possible to add some friction to the pivot point, in order to add some very rudimentary damping? This is how the earliest motorcycle suspension worked.


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PostPosted: Thu May 31, 2012 8:10 pm 
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Location: Antwerp, Belgium
Adding friction to the pivot should be possible, but it'll increase the load on the bearings and will require a much greater spring preload.
The latter will increase the pressure on the top mount because the shock won't pivot there as easily, and that could lead to fracture of the seat tube (as seen on the 828 that donated this shock in the first place).

So while it's perfectly possible, I'd prefer to avoid that.


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PostPosted: Thu May 31, 2012 8:23 pm 
retrobike rider
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Fair enough.

Best left as it is then :wink:


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