i have found a large crack in a load bearing my bike frame !

[monster]

hi

i have recently found some cracks in my bike frame which is very worrying to me. the first was on the part of the fram that supports the battery. it had not broken all the way through only about 80% through that tube which was one of three supporting the battery weight. i welded it closed and was willing to ride it again. now i have noticed a crack in the part of the frame that supports the rider! the crack goes half way through the chain-stay. you can see it in the picture. this was a cheap chinese bike that i converted and i've only had about 8 months use out of it! i only weigh 10stone and my batteries + motor weight 20Kg. do you think i should weld it and hope for the best?

 

[John in CR]

...do you think i should weld it and hope for the best?

Between that or risking your battery falling off or your wheel falling off, it seems like a pretty obvious choice. Yes, of course with steel you fix it stronger than new quite easily.

I heard a new squeak up front on my bike Saturday. A quick inspection revealed a crack in the connection of my headset to the bike frame. Needless to say that problem got fixed by welding immediately.

John

 

[LI-ghtcycle]

Wow! That's with a steel frame too! Makes me all the more curious about A squeak my front-end has developed since I have an aluminum frame!

I have already had a "mishap" with my nephew riding a "chaser" (half bike for kids that attaches to the seat post) cracking my frame at the seat post, and that was before I had it electric!

I got it welded up cheap, but ugly, I think the weld is sound but it's got a huge bead because his welder wasn't really designed to weld such thin aluminum, and he made the mistake of offering to just let me pay with what cash I had atm, $20 :wink: (or rather I just think he was trying to be nice ) but now I am really paranoid about my frame cracking again.

 

[Malcolm]

It's hard to see clearly from your photo, but I'd probably repair the lower crack with a rectangular patch of 1mm plate or scrap tube. Make a plate that extends either side of the crack about one inch. Shape it as close as you can to match the tube, then weld round it. You could also cut a slot about 3mm wide in the patch and weld over the crack, to lessen the risk of burn-through and give a stronger repair. To be really sure you could weld triangular gusset plates either side of the suspension mounting between the chainstays and battery supports.

Was it a MIG welder you got for Christmas? You might want to practice first on some scrap of the same thickness, or slightly thinnner, just to get the settings dialled in.

 

[biohazardman]

I'm sure the weld would be stronger, if properly done, than the thin material the frame is made from so you could weld it. Likely it will just break again next to the weld though as it looks to be a stress point. Malcolm has some good info on making it stronger and if you are going to keep the frame it would be best to do as he recommends. Lighter batteries might help. Simply spreading out the battery weight could help too but a frame of a different design might be a better idea. Even then, some thought on battery placement and weight is necessary for your safety and long frame life. Good that you caught it when you did could have been a nasty failure at speed.

 

[John in CR]

Wow! That's with a steel frame too! Makes me all the more curious about A squeak my front-end has developed since I have an aluminum frame!

I have already had a "mishap" with my nephew riding a "chaser" (half bike for kids that attaches to the seat post) cracking my frame at the seat post, and that was before I had it electric!

I got it welded up cheap, but ugly, I think the weld is sound but it's got a huge bead because his welder wasn't really designed to weld such thin aluminum, and he made the mistake of offering to just let me pay with what cash I had atm, $20 :wink: (or rather I just think he was trying to be nice ) but now I am really paranoid about my frame cracking again.

Li-ghtcycle,
Be careful with that repaired seat post. Aluminum frames have to be heat treated to make them stronger, so when you weld on it afterward, the surrounding aluminum is much weaker than it was before. Absolutely thoroughly check that headset. I don't know if aluminum cracks squeak like they do with steel. The telltale on mine before inspection was increasing/decreasing weight on the seat made it squeak, so I just had someone track down the source by ear while I created the sound. I ride daily in the 40-50mph range, so I'm paranoid about the possibility of any problem, especially up front.

 

[AussieJester]

If it was me i would brace the area using a 3-4mm steel plate that joined the left and right chainstay...i would also sleeve
both sides of the chainstays in that area as it is obviously a fail point of the frame...

Best of luck..

KiM

 

[ejonesss]

i would say stop using that bike and either get a new bike or a new frame and try to salvage the good parts.

if that crack goes all the way through then the frame is going to fail or be weak and may fail at the wrong time.

 

[gogo]

That is a really poor design and needs some triangles. I'd strengthen that area and then weld in some tubing something like I have added on your picture.

 

[monster]

yes its a crappy design, but i've never had a bike break before so i din't antisipate the problem. i want to get my moneys worth out of it tho. i'll start looking for new frames. im not so keen to shell out $150 for a whole new bike when i only want the frame and its difficult to get just frames for folding bikes.

cheers for all the welding advice, what do you think of my repair? i welded the crack on both sides. then grinded it flat on one side, and then welded this 4mm strip across it. i blew a small hole through the chainstay on the left of the picture but was able to weld it back up by sticking a welding rod in the hole and welding round it.

 

[monster]

i added this to the frame too. its a suspension guide rail. its to prevent sideways rotational movement about the suspension pivot. its not load bearing.

 

[biohazardman]

Big heavy motor and lots of amps for a little folding bike. Probly why it keeps cracking. I would expect it will continue to do so. I doubt there are to many folding frames that will hold up to that kind of weight and power but if anyone knows about one it's a good chance they are around here. I wish you luck with finding one and hope you can do so before things get bad again. Keep a close eye on it and be safe.

 

[monster]

i normally use a 400series i only have the big X5 in at the moment because i had a problem with the usualy motor.

 

[Drunkskunk]

I'd agree with gogo. that thing needs some triangles. At the very least, I'd run a piece of that angle iron along the bottom of the chain stays to stiffen them both up.

 

[etard]

Dude, was that rim built with a hammer?!!??

Put that welder to work!! have you thought about just building your own ebike specific rear end? you could use alot of the same parts just overbuild it all.

 

[gogo]

Ya etard, I noticed that rim too. That lip looks dangerously short.

I guess the chain clearance would make triangulation bits difficult to fit. Since there's nothing wrong with the rest of the frame, etard's suggestion of a complete rebuild of the rear swingarm seems like a good idea.