Some Cracked Metal on my E-bike!

SniperGaulois

SniperGaulois

10 kW
Joined
Jan 31, 2008
Messages
797
Location
Rhone-Alpes
My derailleur fell off the other day, it was cracked by the hub axis. Upon inspection the metal of the fork is also cracked where the torque of the axis has forced it after 3-4 years of use.

What is my best option for it, how should i deal with it?
the fork end is made of steel?

I was going to just put a torque arm on that side as a reinforcement, there's already a steel torque arm on the hub side.

rvfrbl.jpg
 
My guess would be that the TA on the other side is not adequate.

If it's not an expensive bike, I'd just replace it. But since it's steel, you can weld a repair on it. I don't have the link handy, but there are places you can buy an entire replacement dropout. They sell to people who make their own bike frames.

Either way, you need a better torque control device.
 
I figured that it was steel and i had to file a tiny bit to get the new hanger on and it's aluminium, i though all the fork ends were made of steel.

You can find special welding sticks on ebay that are for welding aluminium easily. i have some except i'd need a proper flame.

I made a new torque arm from a spanner , so it will stop it spinning, i hope it is ok for another year. Yes Dogman, the old TA was indeed not great, the axis can move in it by 1-2 mm, it was ok for a couple of bikes and then this happened.

When i make the next bike i'll get all the best handcrafted gear from the forums.
 
I hate to say it, but that frame is done. Those "welding rods" for aluminum can't do structural welds, and the heat needed to melt them anneals the aluminum, making it soft. too soft to hold an axle. its possible to weld aluminum, but it has to be heat treated in a kiln afterwords, and that means ... a hell of a lot of work an expense by professionals.

Try for a steel frame on your next bike if you can find a suitable one. Certainly get better torque arms, especially if you're going to be using regen braking, as they puts extra stress on the axle.
 
"I made a new torque arm from a spanner"

Now that is a brilliant idea! I have a bike that the torque arm I got won't fit. And a spanner is going to be a lot cheaper than the £22 I pay for torque arms.
 
Drunkskunk said:
I hate to say it, but that frame is done. Those "welding rods" for aluminum can't do structural welds, and the heat needed to melt them anneals the aluminum, making it soft. too soft to hold an axle. its possible to weld aluminum, but it has to be heat treated in a kiln afterwords, and that means ... a hell of a lot of work an expense by professionals.

Try for a steel frame on your next bike if you can find a suitable one. Certainly get better torque arms, especially if you're going to be using regen braking, as they puts extra stress on the axle.
Click to expand...


Have to agree, it looks like that frame is finished...

That said, if it were a frame of particularly high value, financially or sentimentally, then a repair could be possible...

If its 6061 alloy, the welding will anneal it, but heat treatment will bring it back to its proper T6 level of hardness. Problem is that heat treatment is very expensive, and you'll need a new paint job afterwards. 7005 is the other commonly used alloy, which also anneals when heated. But it can be welded, and will then age harden. Leave it in a cupboard for a couple of months and it will harden over time. I'm not sure I'd be bolting a motor back into it, welds in such high stress areas are reliant upon the skill of the welder to a degree where confidence in the weld would be questionable, but it should be a serviceable frame for human power alone...
 
I would make an integrated torque plate and derailleur hanger and just use a solid method to fasten it to the old dropouts. That will get the bike back to working and solve the torque arm issue with something much less likely to fail.

Welding is nice if you have the facilities and skill, and if you absolutely need a factory finished look. Otherwise, just do it ugly and strong. Like Chyna:

220px-Chyna.jpg
 
drsolly said:
"I made a new torque arm from a spanner"

Now that is a brilliant idea! I have a bike that the torque arm I got won't fit. And a spanner is going to be a lot cheaper than the £22 I pay for torque arms.
Click to expand...
Keep in mind the spanner may not take the load as well as you'd like, depending on it's quality. I've snapped more than a couple of them even with only 1200W peak, on DayGlo Avenger on a "350W" front geared Fusin hubmotor, and a "500W" 9C front DD hubmotor on Crazybike2 at only 1500-2KW peak.
 
Your rear flang is broke and front fork. T he thread keep going back and forth don't know which end we are talking about.
It time to get new used bike.
I use an old comly M.B. bike Diamond back under a 100usd. Craigslist.
 
What would cost you less money and less time without an e-bike? Would getting another frame and modifying for your motor be faster? Or, would a strong and ugly repair be faster and cost less money then another frame?

in the sand.JPG

huummmm......I bet she could carry my e-bike up the stairs... :shock:

I say go with what is faster which probably is getting another frame because a repair would take time and effort by a welder to get it good.

:D
 
999zip999 said:
What bike is it ? Pic ?
Click to expand...

I forgot to add...."With me on it!!!" :oops: :lol:

@zzoing... Also, a magnet will be helpful in finding a steel frame if you are going to get another frame.

:D
 
Move any good components you have on that bike to the next one.

Your frame is toast, it's done, it's over. Get another bike, and this time put a decent TA on it. Two is pretty standard for alloy frames. You had one, and it clearly had some slop in it.

FWIW, I have a very good alloy frame sitting around doing nothing. I am told it is a specialized frame, but after it was stolen somebody powder coated it. Kinda ugly now, since I let it sit outside too long.
 
Inspired by this thread, I've done this:

ta.jpg


It's a short 10mm spanner, and a jubilee clip.
 
Oh no i need a new bike! it's a checker pig, same frame as this www.fahrrad-fachmarkt.com/race-pig.html, alivio gears, it's pretty nice. i think that if they fixed planes with rubber bands and sticks in the old days, i can find a way to shore up the bike for a while!

I want a new dual suspension one as soon as possible. the front fork is ok, the time i bought some aluminium welding rods was for some front suspension forks... and they werent made of aluminium... Magnesium! arg. For the moment i'll have the derailer hanger, half the fork ends and a torque arm holding the wheel on that side on the old bike, i'd be tempted to make a steel thing with some rivets on the wheel side as well until i have a nice frame for a dual suspension one.
 
I just ordered half a dozen more spanner and jubilee clips; I'm planning to put two torque arms on each bike. It'll only cost about one beer token per bike.
 
You're talking about the part of your bike that holds the motor wheel on the bike, and a failure could easily be catastrophic. Imagine a small bump at top speed and the wheel comes off.

While aluminum can be welded it would require heat treatment just to get back to the original strength, that was inadequate and heat treatment of a piece the size of a bike frame is likely to cost more than a new one. The forget the aluminum brazing rods you've seen on infomercials, because the resulting alloy is fragile. That's why they say not to use them on structural joints, and an ebike dropout is about as stressful a structural part as there is.

Definitely get another frame.
 
Unlike what a material datasheet may lead you to believe, after you weld aluminum, you never get full strength back, and you never can reach T6 again in the HAZ area near the weld.

I see a strong machined boss in the dropout above the axle slot with a nice tapped hole. I would design a piece to be CNC machined out of steel, that fits over and is constrained tightly by all those large strong physical features remaining on the drop-out, then slather it with some excellent epoxy after throughly prepping the surfaces to maximize adhesion, and screw it into place using that threaded boss.

My hunch is that it would yield a stronger end result than would be possible through any welding process.
 
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