Non-welder looking for repair advice on 4130 chromoly bike

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Hello,I apologize in advance if this post is in the wrong place/not applicable for this forum. I am not a welder, but am looking for opinions from welders as to damage that has occurred to a mountain bike that I have, made of 4130 chromoly steel. A couple of the joints have small cracks appearing from what appears to be stress (this is a known problem for this model/manufacturer of the bike, and the cracks are on the drive-side of the bike where the gears/chain are). The bike just passed the warranty deadline of 3 years, so at this point I have to look into repair options myself.Others with this bike model have experienced much worse cracking - mine appears to be minor. I am looking for opinions as to if:1. Can this damage be repaired?2. Is this damage enough to warrant a repair, or should I just monitor the damage at this time?Please see attached for photos. What the photos show are the drive side of the bike, and the big hole is where the cranks would go. The first photo is the damage found on the outside of the bike, the second photo is the bike frame flipped upside down, looking at the inside from where the tire would fit in between (the other side of the tubing in the first photo).Thank you in advance for your opinions/expertise!



Reply:Everything can be repaired.  The question in your case is going to be, if you are going to hire somebody, is the cost of the repair more than a new frame.If you want a better answer to your question you should at least remove the paint so people can see a better picture of the crack.  What is this frame worth if you were to buy it?You should definitely replace or repair the frame, unless you are okay with the assumed risk of having a failure while you are riding it.
Reply:It is simple job less than 1 hour plus cost of welding rod.Dave

Originally Posted by pedalharder

Hello,I apologize in advance if this post is in the wrong place/not applicable for this forum. I am not a welder, but am looking for opinions from welders as to damage that has occurred to a mountain bike that I have, made of 4130 chromoly steel. A couple of the joints have small cracks appearing from what appears to be stress (this is a known problem for this model/manufacturer of the bike, and the cracks are on the drive-side of the bike where the gears/chain are). The bike just passed the warranty deadline of 3 years, so at this point I have to look into repair options myself.Others with this bike model have experienced much worse cracking - mine appears to be minor. I am looking for opinions as to if:1. Can this damage be repaired?2. Is this damage enough to warrant a repair, or should I just monitor the damage at this time?Please see attached for photos. What the photos show are the drive side of the bike, and the big hole is where the cranks would go. The first photo is the damage found on the outside of the bike, the second photo is the bike frame flipped upside down, looking at the inside from where the tire would fit in between (the other side of the tubing in the first photo).Thank you in advance for your opinions/expertise!



Reply:I would only do the repair if you allowed me to add suitable gussets,, which would add a few ounces of weight,,depending on the type of bike, a few ounces might matter to the frame owner,,,BUT,, with gussets, you would not need to worry about that part breaking again.Simply weld what you have, it will be broken again in 3 years,,
Reply:Quality Used Mt bike prices are crazy high.So at the current values of used mt bikes it may be worth repairing.  You will lose paint doing a repair.  If you have space, then reinforcement could be added to the chain stay on both sides.  It will make the bike noticeably stiffer. As suggested remove some paint.  To confirm weld or braze.  I assume welded?  If welded the a weld repair will be fairly easy to make it just safe and rideable.  Really concerned about cosmetics or brazed, then it will cost more.What type riding do you do?
Reply:If look closely to photo it like it was not fully welded. So was metal tubing fail just beyond the weld.Dave

Originally Posted by tapwelder

Quality Used Mt bike prices are crazy high.So at the current values of used mt bikes it may be worth repairing.  You will lose paint doing a repair.  If you have space, then reinforcement could be added to the chain stay on both sides.  It will make the bike noticeably stiffer. As suggested remove some paint.  To confirm weld or braze.  I assume welded?  If welded the a weld repair will be fairly easy to make it just safe and rideable.  Really concerned about cosmetics or brazed, then it will cost more.What type riding do you do?
Reply:Yup, drive side chain stay cracks. The constant pedaling stresses fatigued it. And yes new bikes or even frames are expensive and hard to get. A repair would entail removing the paint, and welding with ER80S-D2 tig rod. Better yet add reinforcement but you may warp the bottom bracket shell requiring chasing with a tap. What I do when so inclined is load with a sacrificial BB, weld gently, and remove. Chasing with a tap is still a good idea.But I would do the simple repair and stop mashing the pedals favoring spinning. If it cracks again, repair again.Weld like a "WELDOR", not a wel-"DERR"

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