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PostPosted: Fri Feb 17, 2012 6:18 pm 
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Joined: Mon Oct 13, 2008 11:14 pm
Posts: 2817
Location: London
My only gripe with this kind of build would be the White Bros UD forks, they were a hell in maintaining!


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PostPosted: Fri Feb 17, 2012 7:03 pm 
Dirt Disciple

Joined: Fri Dec 09, 2011 12:01 am
Posts: 61
Location: USA
13 wrote:
Nice 8) look forward to seeing this build!
the 1st gen rotec was one of my dream bikes of the late 90's. Always wanted one built up with an internal geared hub to eliminate having a derailuer.
what were they like to pedal? word bitd was they were pretty wild


Concentric pivot bikes have a reputation for not pedaling well, but out of the three I have owned, I never had any complaints. A smooth, round pedal stroke helps. A shock with an adjustable platform or separate high and low speed adjustments is also beneficial. I think about 6" travel is the limit for a good concentric setup also. As with all bikes, it is best to adjust your riding style to suit the bikes strengths and avoid its weaknesses.

I am also a fan of internally geared bikes. My Rotec saw a few races with a Rohloff fitted. I had to make an adapter to widen the Rohloff to 150mm spacing. The main problem was the chain would not clear the bottom of the swingarm, necessitating the use of a tensioner and guide. Adding those parts back in eliminated the advantage of simplicity. I think I could have made it work with a custom made moto style chain slider underneath the swingarm, but retired the bike before I got around to it.

I still have the adapter:
Image


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PostPosted: Fri Feb 17, 2012 7:51 pm 
Dirt Disciple

Joined: Fri Dec 09, 2011 12:01 am
Posts: 61
Location: USA
Here is a look at my collection of small parts for the frame:
Image


I will be using Big'Un hubs. A MkII front and a Mk1 rear to match the proportions of typical Dirt Bike hubs. I looked for 32H hubs in black or silver because those colors tend to not fade and are typical on moto's.

Levers will be Hope Mono's because I think they look the most moto like. I found some with red reservoir caps for that 'factory' look

Calipers will be Hope Mini #8 rear (found a NOS one!) and DH4 #3 front. I would like to use a DH4 #8 front, but have not been able to find one....

I found a black front hub, but the axle caps are chewed up bad and I am trying to find better ones.

The black rear hub is over in England at a new friends house. I bought some brake parts from him and he has been helping me source some other items since. Thanks Steve! The rear hub got a 12mm axle conversion and will soon have a 185 rotor to match the 205 front. I'm guessing that will all be here in 2-3 weeks.

The White Brothers fork that came on the MkII frame was too tatty for my liking. Lots of scrapes and scratches that would show through even with polishing and fresh anodizing. So it's going away and I'm working on the purchase of a cleaner one. White Brothers still use the same chassis, so they can be updated with the latest parts, making for nice modern, reliable fork.

That's about all for now. These projects move at glacial speed...

If anyone has a lead on old Rotec parts, Big'Un hubs/parts or a Hope DH4 #8 caliper, please let me know. Thanks!

-Alan


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PostPosted: Fri Feb 17, 2012 8:31 pm 
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Joined: Tue Oct 21, 2008 4:18 pm
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You've hooked me! Looks amazing. I've a chair pulled up for this build.


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PostPosted: Sat Feb 18, 2012 10:44 am 
retrobike rider / Gold Trader
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Joined: Sun Jun 06, 2010 4:21 pm
Posts: 1051
Location: Gateway to the Lake District
And another drawn in for the build, I've just stuck the kettle on.


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PostPosted: Sun Feb 19, 2012 1:14 pm 
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Joined: Thu Jun 30, 2011 2:54 pm
Posts: 905
Location: Heathfield
This is fantastic, I've never heard of Rotec before today, but I'll be following this thread with interest. The top bike is truly a thing of beauty and I usually hate bouncers.


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PostPosted: Sun Feb 19, 2012 8:09 pm 
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Joined: Sat Jul 18, 2009 8:52 pm
Posts: 793
Location: Costa-del-Oldham
Brilliant start already

I cant wait to see the build continue :D


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PostPosted: Mon Feb 20, 2012 10:11 pm 
Dirt Disciple

Joined: Fri Dec 09, 2011 12:01 am
Posts: 61
Location: USA
Just a small update:

The main swingarm bearings used on these bikes was pulled out of an aviation catalog. They are airplane flap bearings. As you can imagine, there's not nearly the dirt, dust, and grime up at 30,000 feet as there is on a downhill race course. The stock bearings have no more than a "fiber shield" (upper left in pic) to protect the bearings from contamination. It is almost no use at all, and made for frequent re-packing of the bearings. Pulling off the crank, chain guide, linkage etc. being required...

I have looked for better sealed bearings, but could not find any with the right specifications. So I turned to looking at other bearings to harvest there seals. Everything I found was too wide. But then I had a light bulb go on and remembered the tapered bearings in 1.5" headsets. They had a narrow seal... So I dug some up in my shop and sure enough - they fit!

The diameter was slightly large, but carefully snipping out just enough material allowed the seals to snap into the race grooves like a C-clip.

Photographic evidence:
Image


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PostPosted: Mon Feb 20, 2012 11:52 pm 
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Joined: Mon Oct 13, 2008 11:14 pm
Posts: 2817
Location: London
Clever! :wink:


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PostPosted: Tue Feb 21, 2012 12:08 pm 
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Joined: Wed Feb 01, 2012 12:33 pm
Posts: 453
smart work.
will save some labour in the future. don't you love it when something like that just, works!


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