Bent Chainring
 

So I was racing my bike today and my drivetrain kept seizing up. I would bacakpedal a couple rotations and then kick it forward again, and I'd be fine. But then I looked down when chain obviously came and much to my surprise, I find my chainring totally bent, maybe a 30 degree angle form the original plane to the new one. They are old square-taper suginos, steel, I think. with the chainring attached to the crank. Could I just bend it back? How could I prevent this from happening again?
thanks

Riveted?
Not- unbolt, match bcd -replace.
Rivited, the crank arm\spyder needs replacing I think.
Square taper is the spyder mount onto the bb rotating spindle -you just need a real crank\spyder to mount the rings onto the spindle.
BB's fine, [o] tapers fine.

Yeah, it's a spider-type crank, but I'm not sure that it can be removed. I actually think I checked, and it can't. It's not the bolt-on type of crankset.

Sucks but real cranks\spyder and you can push down HARD!


quick..gut a bike for the cranks\spyder, have a mech match the axle to the cranks.
Doubles\triples space out different =chain line to the rear.

May mean a new bb, axle is maybe 20$, new cartridge bb, 30$.
The chainrings and chains etc are replaced as you ride.
Cheap bike, ....not sure.

take an adjustable wrench or a hammer to it and see what you can do, it's already broken, yeah?

Steel yes, alu weakens bent.

yes steel real, alu gobi good!

Not for chainrings........alu.
Not bent.
Steel rims suck, steel frames ROCK!

I'm sorry, I know I'm totally being a grammar dick but can you please answer in sentences, rather than fragments, I totally can't understand a thing you're saying, and it's not like I'm clueless about bicycle anatomy. and for the record the bb is fine, I switched out the spindle and repacked the bearings a couple of weeks ago, it's all crank spider. I guess I'd be worried about catastrophic failure assosiated with bending it back.

I think what I would say, primarily, is that you couldn't hurt anything by trying to bend it back. Use an adjustable monkey wrench to get some leverage, adjust the jaws to the thinness of the ring and give it a go, slowly. It may be a lost cause, you may have to replace the ring. I suppose the ring should have bent before any BB damage. I am guessing that 30 deg. is a bit of an over statement, because it would probably throw your chain and wouldn’t fit through your derailleur (if you have one?). The force applied to the ring parallels the drive train, so what I’m thinking is a little weakness in a side-to-side won’t make that much difference.
Adam

Steel yes, bend back.
Alu, not. Simple.

Nature of the latticing? (sp) of the metals structure, steel is a grain, alu more a lattice like crystal -cracks when flexed.
Steel can be bent\flexed. Alu suffers under this =metal fatique.

I second Mr. You...who are you, and WTH are you talking about? Why can't you write in even half-complete sentences? Reads like you've just come down from another star system or something.

I hereby declare this thread useless.

O.P. >"I'm sorry, I know I'm totally being a grammar dick but can you please answer in sentences, rather than fragments, I totally can't understand a thing you're saying, and it's not like I'm clueless about bicycle anatomy. and for the record the bb is fine, I switched out the spindle and repacked the bearings a couple of weeks ago, it's all crank spider. I guess I'd be worried about catastrophic failure assosiated with bending it back."

? Use the search function to locate threads about metallurgy.

Crystal structure :The regular, repeating pattern of atoms in a metal. Crystal structures develop as a metal solidifies.

Grain structure: The relationship between the small, individual crystals in a metal or alloy.

Tensile strength The ability of a metal to resist forces that attempt to pull apart or stretch it.

Ductility A metal's ability to be drawn, stretched, or formed without breaking.

"When a stress is applied to the atomic lattice it will "slip" along certain geometrical planes that vary in size, number and importance, depending if the alignment is HCP, FCC or BCC. The lattice will also contain flaws (missing atoms, misaligned rows) that will travel freely through the lattice when stress is applied, which explains metal ductility. However, continual stress will rid the lattice of flaws (by pushing them to the grain boundary) to produce a more rigid/strong metal, which explains another metal property - work-hardening.

The outer electrons of metallic atoms are loosely held by the nucleus and exist in a fluid-like state shared by all the atoms of the metal. This "migration" of electrons explains the high thermal and electrical conductivity properties of metals.

Common furniture metals can be grouped into two main classifications - ferrous and non-ferrous, from the Greek word ferro, which means iron. Steel and stainless steel are typical ferrous iron alloys; aluminium is a typical non-ferrous metal."

"With steel, there is a stress level below which fatigue failures do not occur: the fatigue limit. A part loaded below the fatigue limit may eventually develop fatigue cracks, but they won't grow to the point of fracture. Therefore, a steel part (such as a crankshaft) can theoretically remain in service forever, provided it doesn't corrode or wear beyond service limits.

In sharp contrast, aluminum and other nonferrous metals have no fatigue limit. No matter how low the stress level, eventually the metal will suffer a fatigue failure if it is subjected to enough cycles. This means that aluminum parts are inherently life-limited."

http://www.avweb.com/news/maint/184271-1.html

The lattices or 'structure' of Aluminum do not have the same tensile property of steels in that they are fractured along the lattices when bent where steel being tensile can have the grain re-align without fracture.

A bent piece of ALU will be WEAKEn when bent back.
I will point to the abandonment of aluminum affixed derailer hangers in Alu frame bike design.
If bent, then bent back, they often fail.
A better fix is to remove and use a replaceable hanger.
A steel hanger affixed to the frame, bent, simply re-align. Can be done several times without it breaking.
From my limited knowledge of the star called 'earth' metallurgy.

Quote:

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Originally Posted by peripatetic

I second Mr. You...who are you, and WITH are you talking about? Why can't you write in even half-complete sentences? Reads like you've just come down from another star system or something.
I hereby declare this thread useless.

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I declare your post moot, but not obtuse.
Is all this easier to understand? Do whatever you feel is safe.
You know what I think. Bother, lack of research skills, me again posting and I type with 2 fingers.

http://sheldonbrown.com/bbsize.html

If you wanted to run cranks\spyder with removeable rings, this chart can help you mate -say a used crankset to the current bb.
Usually you would HAVE the new cranks and use the chart to select the correct axle length or that's what I did.
Determine the axle length, what ring amount, then copy the possible cranksets compatable with your current BB axle.?

An idea anyway.
I like old frames but prefer newer drive components.
We just removed a loose ball bb and cottered crank system off a Peugeot PX-10 and replaced it with a cartridge bb, Shimano 600 crankset and new rings.

-What a difference, my friend weighs 200+ and now he has a drive that is totally solid.
The new parts were 2 rings and the cartridge bb, the cranks were salvaged.
The rings were the most costly as we bought in a lbs instead of online.

This is perhaps only something to consider if the bike is quality enought to spend on an upgraded crankset.
Or bike that is intended to run many miles\chains -this is a good idea as the single rings can be replaced easily as they wear.