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Framebuilders Thinking about a custom frame? Lugged vs Fillet Brazed. Different Frame materials? Newvex or Pacenti Lugs? why get a custom Road, Mountain, or Track Frame? Got a question about framebuilding? Lets discuss framebuilding at it's finest.

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Old 01-10-12, 10:38 PM   #1
balindamood 
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1-inch Tandem Fork crown

In about a week, I expect to take posession of a very early Santana tandem. While gathering whatever data I could about the bike, I checked in with Santana to see if they had any infomration regarding year built/model etc. I got the following response:

Quote:
VERY IMPORTANT:
Santana recommends for safety that the old fork that it is on this
bike be replaced before ANY RIDING is done on this machine; DO NOT
ride the bike with the fork that you purchased the bike with. While the
original 1" steer tube fork that your bike has was the strongest fork available
back in the 1980s it is only good for a maximum of 15 years of average usage.
Please contact our customer service for information about the purchase of a replacement fork for your bike.
After an extensive search of the internet, I have found no reference anywhere to fork failures for this model. I further had a discussion with Santana who would only vaguely reference "their engineer," and the person on the phone could not pin-point the failure point/mechanism, only that "it is the entire fork". He also rambled a bit about brinnelled headsets. I found another forum post (another forum) where they recently gave the same warning to someone lse with a Tandem of similar vintage. They are happy to sell me a chrome unicrown replacement fork for $300-400.

As an engineer and impresario frame technician, all I can say bu#@sh%$.

The bike appears to have low miles, and I do intend to fully inspect it and monitor it for any issues. However, the possibility exists that at some point I may have to replace the fork, and I am certainly not going to used anything chromed or incorporating a unicrown. The issue is, after perusing the usual frame-building supply houses, that I cannot find any cast crowns that would seem to be suitible for tandems, fork blades, or heavy-duty steerer tubes.

Any ideas for possible sources??

Picture or the existing fork:

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Old 01-10-12, 11:04 PM   #2
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If that was blue, it would look a lot like the tandem I built for myself. I'm not too worried about that fork, although I have wondered about it a little
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Old 01-11-12, 06:33 AM   #3
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I would say that a Pacenti Paris-Brest crown would be plenty strong. Use the heaviest gage that you can find; I think there are 1.2 blades out there.

Pete
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Old 01-11-12, 01:20 PM   #4
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as far as 1" tandem fork parts, that ship has sailed. If I was building a tandem fork for a replacement, I probably would have some plates machined and make a double or triple plate crown. i would also sleeve the lower part of the steerer. Contrary to the assertions of some people that have posted on here recently, steerer failure is a concern, particularly on a tandem.
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Old 01-11-12, 03:54 PM   #5
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It seems to me that the failure mechanism is the prying/bending force between the fork crown and immediately above the lower headset bearing on the steerer tube. Strengthening the lower steerer tube is easily done by inserting a smaller diameter tube within it (this is in fact what Santana has done). The problem in my opinion is likely the crown, itself, with not enough insertion of the steerer into the crown to properly transmit the load. This would result in either a broken crown, or a seperation as the forces try to wallow out the hole. While I may be able to get away with MTB fork legs and a reinforced steerer tube, some inf is needed regarding the amound of steerer tube that should be inserted into the crown, and if there are any cast crowns available that can provide this.
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Old 01-11-12, 05:55 PM   #6
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Seriously, I think the Pacenti crown would do the trick:


Fork crown by pruckelshaus, on Flickr

I've not seen a "taller" crown from bottom of crown to crown race perspective.

Also, the current fork is steel. It's not going to explode. Personally, judging by the picture, I would ride it but perform a regular pre-ride inspection. Looks like a beautiful bike.
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Old 04-12-13, 08:54 AM   #7
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Sorry to resurrect this post from the archives, but I was wondering how things have gone with your Santana?

I just bought an early 80's Élan, and got the same recommendation from Santana.

I thnk they're covering their butts in case a failure occurs, but the likelihood of it actually happening is questionable.
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Old 04-12-13, 12:00 PM   #8
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making a twin plate fork crown from scratch , is not too tough, though I did get some pretty substantial round blades.
drill press .. one plate is drilled through, the steerer or the fork blades butt against the other..

The one made got an offset between the Steerer and the fork blades for part of the trail,
and bent the blades for the rest.
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Old 04-12-13, 12:28 PM   #9
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OP; That is a beautiful bike and so is the fork. Condition looks outstanding as well.

However I would say that anytime the OEM says "be careful with that old gal, she has a weak hip", then I would recommend indeed to be real careful. But as stated, putting on some generic chome part would be a crime, so to speak. If you are under 150 pounds each and aren't doing panniers... then the risk is probably not to high, but that is another discussion (are you a religious man?).

My best recommendation would be to flip her over, pull the front wheel, and run an inside micrometer up the steerer from the bottom edge of the crown up to about a 1/4" of the bottom of the stem. What you want to confirm is that the ID of the steerer is consistent top to bottom; Basically that it is not tapered on the inside and that there aren't ridges or other 'features' to complicate things.

Assuming the ID is consistant, look for a stick of good Chromoly seamless tubing (think Aircraft Spruce) with an OD that is a good match to the steerer ID. Look for about 0.125 wall, or a bit thicker if it looks like you will have to machine off a bit of the tubes OD to get it to fit within a 1/1000 or so of the steerer ID.

If the ID of the steerer is tapered; bummer, but a sleeve can be machined from bar stock to match. If it is and there isn't chomoly tube stock available with thick enough wall to cover the range, you aren't yet completely screwed. A decent maching shop can chuck a piece of solid bar in the lathe and take its OD down to match the tapered ID of the steerer and then bore out the center. Would be very smart to take the fork with you so the lathe operator can make his own measurements. Machine work is not dirt cheap, but its not grossly expensive either. I have had such a sleeve made for a different purpose in the past (circa 2002) for about $80.

Either way, when you have the "repair part" and its the right OD and length; Pull the fork, remove and save the crown race. Then arrange with a real builder who has experience using silver solder for lugged frame construction and pay him well to sweat in the reinforcing sleeve. Have him leave about 1/8" hanging out the bottom so it can be dressed down to a 1/16" with a file before sending it in for prime and paint.

Santana might be able to provide matching original paint (or the paint codes) if you provide the SN. They have been able to send me a couple of ounces of touchup paint before for $10. Won't hurt to ask...and beg a little.

Hope that helps. (PM me if you just want to just start over with a different bike (it would be understandable) as I sometimes buy the older 2bikes just because I like the way they look).

/K
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