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Old December 6th, 2010, 8:43 PM   #1
rmp
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Default Wicked unicrown fork - dropouts or other?

Just pulled the old unicrown off my Wicked and cleaning it up for sale/auction (honesty, right?).



I'm 99.5% sure it's the original Fat Wicked unicrown fork that came on this frameset when I bought it NOS in 1992, but is there anything distinctive to look for? It appears to have SHIMANO stamped into the dropouts, but it's hard to read.









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Old December 7th, 2010, 11:48 AM   #2
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Sure looks like a Somerville unicrown. We built lots of them but there wasn't any serial numbering or any other permanent marking to distinguish them (a mistake in my mind but not in my control at the time)
We did use lots of Shimano dropouts - they were relatively cheap and plentiful. I don't remember any breaking but I'm sure one or two have failed along the way.
One way to tell is to see if the dropout is welded to the fork blade. We always TIG welded them and ground the weld face flat just like it looks in the photo. If you remove the paint and the metal looks nice and silvery, then it is welded and most likely a genuine FAT fork. If the metal appears slightly yellowish and is a different shade than the fork blade, then it is silver brazed and is not a FAT unicrown. If the metal is a bronze color, then it has been brazed with a copper alloy and is definitely not a FAT unicrown.
The brake mounts look pretty familiar and they look like they are TIG welded, so my guess is that it is a FAT unicrown.
Enjoy
Scott
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Old December 7th, 2010, 12:15 PM   #3
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Thanks Scott. I was 99% sure it was, as the bike/fork has been in either my or my bro's possession for the vast vast majority of it's existence, but these forks are relatively unheralded compared to the segmented units and the earlier box crown forks.

Thanks again for the input.
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Old December 8th, 2010, 8:19 AM   #4
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Looks just like my Wicked unicrown fork (S dropouts, tig'ed bosses). Mine doesn't have the fender hole drilled in the crown though.
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Old January 25th, 2011, 4:31 PM   #5
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Default Scott any help?

Scott - Just wondering if you could enlighten me on the history of the FCC box crown fork and what the main differences are compared to the Yo and unicrown?

Thanks
AB
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Old January 31st, 2011, 11:43 AM   #6
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Hey AB - saw your PM but will address your question here - Just got back from a whirlwind tour of Korea and China and saw a cool velodrome in Changwon, Korea

OK the unicrown gets its name from the fact that the fork tubes are drawn and then bent into such a shape that the top of each blade forms the crown of the fork. Traditionally, steel bicycle forks have been built by brazing fork blades to a cast part called the "crown" with also is brazed to the steerer tube.

The FCC "box crown" fork has a crown that was simply made from a piece of 1" square 4130 tube that was machined to accept the steerer tube and the fork blades which were TIG welded to the crown. We used Columbus road bike steerer tubes which had rifling in the inside at the crown area to provide extra torsional rigidity. We used Tange Prestige road bike fork blades which were very light. The Tange blades presented a challenge for TIG welding since the chrome-moly was not optimized for welding and tended to undercut if the proper techniques were not followed by the welder. These forks were very light compared to the unicrown, but not as durable. After receiving some back that had developed cracks at the back of the blade / crown junction, we added gussets to improve the strength of that area.

The FCC YO fork was made from mitered tubes which formed the "crown" of the fork. The "blades" were 4130 tubes and I don't remember if those tubes were True Temper butted tubes or if they were just straight-gauge aircraft tube. A flat cap was cut from sheet stock and was welded to each blade which was fitted to the crown tubes and steerer tube, clamped in a jig, and then TIG welded. Fatigue testing of the first few prototypes revealed a potential for failure at the back of the fork so we added silver-brazed "tear-drop" gussets which were laser-cut from 4130 tube. I believe the silver brazing heat cycle helped to stress-relieve the TIG welds, but I have no conclusive engineering data to back that up. I always believed that the YO forks should have been heat-treated but that step was cost-prohibitive since we had no heat treating equipment and would have had to send them to a local shop.

The original YO fork used 1.125" OD tubes for the crown and blades (or legs) and the BOI (Big One Inch) Yo fork used 1" OD tubes for the crown and blades.

Overall, the YO fork is superior to both the box crown and the unicrown for strength-to-weight ratio, torsional rigidity, and fatigue life performance. It just looks cool too.

To the best of my knowledge, FCC Somerville only produced forks with cantilever brake mounts. There may have been some customs or one-offs that had disc brake mounts but I don't believe we had any production forks with DB mounts.

Hope that answers your question
ENOUGH SNOW ALREADY!!
Scott
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Old February 2nd, 2011, 10:38 AM   #7
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Thanks Scott,

That definitely answers my question and curiousity on FCC fork evolution.

I hear yah on the whole snow issue - bring on Spring!

AB
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