Cycling and bicycle discussion forums. 
   Click here to join our community Log in to access your Control Panel  


Go Back   > >

Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

User Tag List

Reply
 
Thread Tools Search this Thread
Old 10-11-11, 09:22 AM   #1
dabee1106
Member
Thread Starter
 
Join Date: Jun 2009
Bikes:
Posts: 30
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Broken frame

The chainstays broke on my full suspension mountain bike broke this weekend. I can get a replacement chainstay but it will cost alot more than paying someone to weld it for me. It broke the tube next to the weld but not at the weld. If I get it repaired will it foreber be weaker were it broke?
Attached Images
File Type: jpg Broken Frame.jpg (81.9 KB, 96 views)
dabee1106 is offline   Reply With Quote
Old 10-11-11, 09:43 AM   #2
mikezs
Noob
 
mikezs's Avatar
 
Join Date: Sep 2011
Location: Essex, UK
Bikes: Specialized Rockhopper Expert Disc 2009, Giant Boulder 510 Sports 1999, Olympic Competitor 1978
Posts: 71
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by dabee1106 View Post
If I get it repaired will it foreber be weaker were it broke?
If it's a good quality weld, it should be stronger than before as there's extra reinforcing material added.
mikezs is offline   Reply With Quote
Old 10-11-11, 11:10 AM   #3
demoncyclist 
Senior Member
 
demoncyclist's Avatar
 
Join Date: Oct 2002
Location: Medway, MA
Bikes: 2011 Lynskey Sportive, 1988 Cannondale SM400
Posts: 2,694
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 8 Post(s)
If that is an aluminum frame, it is probably impossible for the average welder to repair. You should take it to the shop where it was purchased. There may be a warranty on the frame.
__________________
DEMON

Satanic Mechanic
STAR 3 Spinning Instructor

2011 Lynskey Sportive (Shimano Ultegra 10s)
1988 Cannondale SM400 (Suntour XC-M 7s)
demoncyclist is offline   Reply With Quote
Old 10-11-11, 12:16 PM   #4
jimn
Junior Mint
 
jimn's Avatar
 
Join Date: Mar 2006
Location: Brooklyn, NY
Bikes: http://nachlin.com/bicycles/
Posts: 100
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
I don't know about suspension swing-arms, but aluminum frames are heat-treated after welding. If you have a welder fix the break, the properties of the aluminum may be so changed that it breaks again fairly easily. So, unless you can get someone to weld it for really cheap, and don't mind being the crash test pilot, you will need to replace the part.
jimn is offline   Reply With Quote
Old 10-11-11, 04:43 PM   #5
arceye
Junior Member
 
Join Date: Sep 2011
Bikes:
Posts: 6
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
I agree with jimn
I was taught that the weekest part of the weld is the heat effected zone next to the weld, thats why most fractures are right next to the weld line. "stress is reduced by heat treatment, weld prep design and weld proceedure"
If you look at the original weld it is designed so as not to create a:- direct virtical shear stress line.
p.s. There are also different grades of filler rod /wire with different tensile strenghts so make sure the right one is used
sorry I can't be more helpfull but it's been years since I last welded aluminum.
Paul
arceye is offline   Reply With Quote
Old 10-11-11, 08:08 PM   #6
JohnDThompson 
Old fart
 
JohnDThompson's Avatar
 
Join Date: Nov 2004
Location: Appleton WI
Bikes: Several, mostly not name brands.
Posts: 16,529
Mentioned: 4 Post(s)
Tagged: 0 Thread(s)
Quoted: 127 Post(s)
Don't bother welding it; it will break again in short order.

If you're the original owner of the frame, I'd look into getting warranty replacement or at least a discount on repair.
JohnDThompson is offline   Reply With Quote
Old 10-12-11, 09:08 AM   #7
reddog3
Senior Member
 
Join Date: Nov 2010
Location: River City, OR
Bikes:
Posts: 650
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 3 Post(s)
The pic isn't clear- but it almost looks as if this is a solid insert rather than a tube. Either way... if properly welded and heat treated a break here shouldn't occur unless it's a design flaw, or some outside factor- like a little help from gouging caused by chain derailment, etc. Then of course we don't know if the alloy is the best choice to resist breakage.

I'd be inclined to go for a new swingarm so I had some recourse in the event it happens again. Then wrap it with some sort of protecter to resist damage from thrown chains.
reddog3 is offline   Reply With Quote
Old 10-12-11, 09:14 AM   #8
himespau 
Senior Member
 
himespau's Avatar
 
Join Date: Jun 2008
Location: Louisville, KY
Bikes:
Posts: 9,598
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 117 Post(s)
Yeah, definitely if you're the first owner go to the lbs to see about a warranty.
himespau is offline   Reply With Quote
Old 10-12-11, 12:16 PM   #9
gyozadude
Senior Member
 
gyozadude's Avatar
 
Join Date: Jun 2011
Location: Sunnyvale, California
Bikes: Bridgestone RB-1, 600, T700, MB-6 w/ Dirt Drops, MB-Zip, Bianchi Limited, Nashbar Hounder
Posts: 1,180
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Aluminum frames in general can't be re-welded or reformed without a significant process of heat treatment. So, yes, a really good welder might be able to get in there and weld, but unless he has the ovens to bake the frame (and this takes hours/a day) the joint will never be that strong, and unless he has superbe atmospheric conditions in his fab, re-welding aluminum is very difficult on jagged breaks. You need to start with very clean aluminum which is rapidly welded right after cleaning to prevent oxide from forming on the exterior which I here creates micro-fracture sites in the weld that will fail again.

Hope you're okay and didn't suffer physically. Let us hear about the warranty.
gyozadude is offline   Reply With Quote
Old 10-12-11, 02:37 PM   #10
cbchess
Map maker
 
cbchess's Avatar
 
Join Date: Feb 2008
Location: Richmond,VA
Bikes: Ventana El Ciclon, Walt Works 29er, Specialized Enduro (fixed up for my son).
Posts: 728
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
replacement swing arm is the best way to go IMHO
cbchess is offline   Reply With Quote
Old 10-14-11, 09:36 PM   #11
76Crescent
Member
 
76Crescent's Avatar
 
Join Date: Mar 2008
Location: Atlanta, GA
Bikes: Too many!
Posts: 26
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by arceye View Post
I agree with jimn
I was taught that the weekest part of the weld is the heat effected zone next to the weld, thats why most fractures are right next to the weld line. "stress is reduced by heat treatment, weld prep design and weld proceedure"
If you look at the original weld it is designed so as not to create a:- direct virtical shear stress line.
p.s. There are also different grades of filler rod /wire with different tensile strenghts so make sure the right one is used
sorry I can't be more helpfull but it's been years since I last welded aluminum.
Paul
Ding Ding Ding. We have a winner!

I'm a certified welder. I've done a good bit of TIG welding which is how your frame was made. Like others have said aluminum frames are heat treated, and this is not possible/practical for most people even with really nice welding setups. Also like others have said aluminum is weakest around the weld not at it, so it would likely break next to the weld very soon. It's not worth your money to pay anybody to weld it. Sorry. Try and get a warranty or buy a new swing arm.
76Crescent is offline   Reply With Quote
Old 10-17-11, 08:03 AM   #12
dabee1106
Member
Thread Starter
 
Join Date: Jun 2009
Bikes:
Posts: 30
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
It was not covered under warrant because I bought the bike used. My buddy welded it for me for free but it broke again first ride after being repaired so now a new swingarm is on the way. I was not hurt in any way but chainstay was rubbing on tire when sitting on the bike so the tire took most of the abuse. Thanks for the help everyone.
dabee1106 is offline   Reply With Quote
Old 10-17-11, 10:20 AM   #13
cobba
B A N N E D
 
Join Date: Aug 2006
Bikes:
Posts: 1,417
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 10 Post(s)
How to fix it if you really need to fix it.
Photo 1
Photo 2
Photo 3
Photo 4
cobba is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off



All times are GMT -6. The time now is 06:07 AM.