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Builder's Corner Restoration and preservation. Keep them running in perfect shape. What size is your bottom bracket?

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Old March 13th, 2010, 2:56 PM   #1
d3f3nd3r
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Default Cracked seat tube in Fat Chance Trials frame, seat tube frozen

OK, it's been a long time since I've posted anything, but I finally got around to my next project a 1985 Fat Trials bike. Sweet I know until I got to the seat tube. eBay strikes again!!



Any suggestions? I am guessing someone put the wrong sized seat tube in it and clamped it to high hell cracking it on both sides (other side looks same as pictured). I suppose given the condition I will just do a single speed cruiser build so I am not against fixing the the seat height.

What would you do? cut the seat tube at the crack and cut a slot into the remainder and hope a clamp takes? Weld a seat tube to the frame? Wall art? And any suggestions on getting it unstuck? It's a shame as it's a cool piece of Fat and biking history.

thanks for any help and suggestions.

Matt
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Old March 14th, 2010, 2:19 AM   #2
bonsaii
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Default Short seat post

I belive this is a result of a too short seat post. Get it welded and fit a seat post with sufficient lenght. I would certainly try that before cutting of the original pipe stub.

Good luck!

-bns

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Originally Posted by d3f3nd3r View Post
OK, it's been a long time since I've posted anything, but I finally got around to my next project a 1985 Fat Trials bike. Sweet I know until I got to the seat tube. eBay strikes again!!



Any suggestions? I am guessing someone put the wrong sized seat tube in it and clamped it to high hell cracking it on both sides (other side looks same as pictured). I suppose given the condition I will just do a single speed cruiser build so I am not against fixing the the seat height.

What would you do? cut the seat tube at the crack and cut a slot into the remainder and hope a clamp takes? Weld a seat tube to the frame? Wall art? And any suggestions on getting it unstuck? It's a shame as it's a cool piece of Fat and biking history.

thanks for any help and suggestions.

Matt
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Old March 14th, 2010, 12:20 PM   #3
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I don't think there's any easy or cheap way to fix this.

What about having someone straighten it out as best as possible, then turn a 26.4 bar stock seat post with a 22.2 clamp end section on a lathe.

A little heavy, but I don't imagine anything could ever bend again.

The person who could do the above could also likely machine you an insert that could be brazed into the straightened seat tube with an internal dimension of 25.0 or 22.2 (something smaller than 26.4 that could get seatposts in).

Good luck!
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Old March 16th, 2010, 7:58 PM   #4
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That seat tube can be repaired. The old post needs to be removed. It can be cut out or frozen out if you have access to liquid argon (too much fun) or nitrogen. Once the post is out, the area needs to be cleaned thoroughly. The crack can be stop-drilled right at the end and then you take a small file and carefully file the crack along its length to prep it to be welded. Make a copper backing by getting a small length of 1.25" copper tube (standard plumbing size and then cut a slot in it. Use a hose clamp to squeeze it together and slide into the seat tube far enough to be behind the crack. Release the hose clamp enough so the copper springs out and butts up tightly to the crack. Have the crack welded using a TIG welder and ER80S-D2 filler wire if your local welder can get it. If not then regular ER70S-2 or -6 will suffice. After the weld is completed, the seat tube slot needs to be reinforced by brazing a washer over the hole at the bottom of the slot. Use a carbon steel or a stainless steel washer. I do not recommended using a plated or galvanized washer. It is best if the washer can be rounded to fit the contour of the tube. Carefully position the washer and braze it to the seat tube using silver alloy. 56% is recommended. Once the braze is completed, wash off the remaining flux and then carefully cut through the washer where it covers the slot. Clean the area and paint it. If you can afford a good paint job, then go for it. if not just try to match the existing with some good spray paint. The Trials bike is EXTREMELY rare and is worth fixing.

good luck
Scott
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Old March 17th, 2010, 3:38 AM   #5
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Scott! I'm your biggest fan in Norway, if not Europe..! Biggest fan, period.

Nice procedure!

- arne


Quote:
Originally Posted by I-ROBOT View Post
That seat tube can be repaired. The old post needs to be removed. It can be cut out or frozen out if you have access to liquid argon (too much fun) or nitrogen. Once the post is out, the area needs to be cleaned thoroughly. The crack can be stop-drilled right at the end and then you take a small file and carefully file the crack along its length to prep it to be welded. Make a copper backing by getting a small length of 1.25" copper tube (standard plumbing size and then cut a slot in it. Use a hose clamp to squeeze it together and slide into the seat tube far enough to be behind the crack. Release the hose clamp enough so the copper springs out and butts up tightly to the crack. Have the crack welded using a TIG welder and ER80S-D2 filler wire if your local welder can get it. If not then regular ER70S-2 or -6 will suffice. After the weld is completed, the seat tube slot needs to be reinforced by brazing a washer over the hole at the bottom of the slot. Use a carbon steel or a stainless steel washer. I do not recommended using a plated or galvanized washer. It is best if the washer can be rounded to fit the contour of the tube. Carefully position the washer and braze it to the seat tube using silver alloy. 56% is recommended. Once the braze is completed, wash off the remaining flux and then carefully cut through the washer where it covers the slot. Clean the area and paint it. If you can afford a good paint job, then go for it. if not just try to match the existing with some good spray paint. The Trials bike is EXTREMELY rare and is worth fixing.

good luck
Scott
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Old March 17th, 2010, 11:47 AM   #6
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Thanks Arne
I appreciate the support. I fixed several cracked seat tubes that way over the years. I forget whose idea it was to make the washer reinforcement but eventually we did all of the seat tubes that way.

If you spot an early Fat with a washer on the seat tube slot, chances are (all puns intended) that it was repaired.

Scott
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Old March 17th, 2010, 5:22 PM   #7
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Default Thanks for the help

Yeah I agree I picked this thing up because it was so rare so I want to make it right as best I can.

Scott, one question though. I am not following the washer suggestion. If you braze the washer at the bottom of the slit contoured to the tub how does the seat clamp fit over it? I must be wrong as to where you put the washer.

I guess the next step is finding a welder who can do such a job, anything in the Chicago area? Or someone I can send the frame to?

Matt
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Old March 18th, 2010, 2:29 AM   #8
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The washer shall be placed at the down side of the slot, so that the inner radius of the washer coincide with the "stadium" shape in the slot . The seat clamp will me mounted higher than this point...?
That's how I understand Scotts procedure.

Keep up the good work! Good luck!
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Old March 18th, 2010, 11:53 AM   #9
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Here's a quick sketch to show what I mean


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File Type: jpg seat tube repair.jpg (40.4 KB, 33 views)
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Old March 19th, 2010, 6:33 PM   #10
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Default Thanks *UPDATE*

Ah I see, makes sense.

Sadly the post that was in there was wrenched pretty good and after letter a bunch of liquid wrench sit in and freezing the seat tube it split apart and broke at the top the seat tube and has butterflied out the crack on one side. I wouldn't say I went at it like an angry monkey but after few turns to break it free it cracked and then failure.

I didnt think I could have a bigger problem but seat tube is broke flush with the top of the seat tube!

I SUCK! I tried the last resort I could think of which was a hacksaw blade and roll in the tube but I cant get a good purchase on the tube to roll it. I am sure there is a lot of eye rolling by the experts in metal here. Sorry. But really I went at it with love not hate I swear.

Matt
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Old April 2nd, 2010, 4:23 AM   #11
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Hi.

Post some pics on this. I bet Scott has a procedure for reapir! Never give up!
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