Bending an alloy chainring

[Christopher]

The fixed commuter has a 42t single alloy ring, it is so bent that the chain tension varies to an unsafe degree. I want to try and bend it back a bit straighter, options are:

1) Leave ring on spider, use adjustable spanner with some care to try and bend ring?

2) Take off bike and use a big flat stone and a light lumphammer to show it who's boss?

TBH I don't much care if I break it, it only cost £10 and if I can't bend it back I will break it to bits and chuck it in the scrap bin.

 

[Christopher]

No.
I assume trying to bend it cold will break it? Will soon find out...

 

[Christopher]

Thanks Lee, I may also drag the vice out from under the bed and use that...

 

[gbb]

I straightened a chainring with an adjustable spanner...not brilliantly, but it was better.
I'd lay it on a slab, with a piece of timber or similar on it and give it some with a hammer. Theyre not that brittle..or that strong.....certainly a Suntour hybrid one wasnt.

 

[llllllll]

I've bent a steel chainring back into shape with the adjustable spanner/mole grips method in the past. It was reletively successfull - I never got it perfect but it was usable. Vice sounds like the best bet though.

 

[02GF74]

how did you manage to bend it!!??!

anyways, you say you have a vice. I would remove it from the crank, place it in a vie and straighten it by doing up the jaw - some bits of wood or aluminium against the jawsto avoid makring the ring. If that is not possible, then grip part of the ring in the vice and gnetly push by hand the rest to strighten it.

you can then refit it to the crank, spin the crank, marking the section(s) where it is still out of straight, then repeating the process.

Note that aluminium allloy does not like being bent repeatedly so bend it a little at a time so as not to overdo it.

 

[Joe]

I did mine on the bike with an adjustable spanner. Probably not idea but it's still going strong!

 

[Amanda P]

Try applying a bit of heat, know anyone with an oxyacelytane torch?

NO NO NO! Not on an alloy ring.

The trouble is that alloy doesn't change colour as it gets hotter. One minute it's a hot chain ring, the next moment you've melted a hole in it. Terribly easy to do with oxyacetylene, which can be hot enough to melt steel, let alone aluminium alloy.

If it's not pringled, cold bending should do it.

 

[cheadle hulme]

You keep a vice under your bed?

 

[zzpza]

You keep a vice under your bed?

i was just thinking that too....

 

[jpembroke]

I would happily bend teeth back in to position (with a pair of pliers) but an entire chain ring???? I think it's time for a new one.

 

[Christopher]

Well, that was interesting! I took the chainring off and bent it in all sorts of directions, it was all too easy to do, but could not get it straight no matter what I did. Eventually I realised that I have bent two of the 5 arms on the spider so that is the end of that - have now stipped the fixie and most of it is in a cardboard box in the bedroom and am using the Dave Yates tourer to commute on, don't want to do that permanently but will hopefully get a bike on the cycle-to-work scheme if they run it again this year.

I like riding fixed for sure but don't want to just get another spider and wreck that. I read about this sort of thing on the singlespeed part of a MTB forum and the way to wreck a SS transmission is to go up a steep hill very slowly under maximum force and be a fat swine, all of which applies to me, I have to get up a 1 in 7 somehow to get home and a short 1 in 10 or so on the way to work. Am amazed though that the rear wheel is undamaged, I must have built it okay.

The vice is under the bed because I trip over it when it's in the living room. Honestly!

 

[Chuffy]

I'm sorry, but....oops!

I did wonder how it was bent exactly, because I can imagine the chainline being out on account of the bent ring but not the tension...

Having read your description of how to wreck your transmission I'm starting to wonder about my ongoing single-speed woez (documented on a couple of other threads) since I am a fat bast who grunts up hills in an unsuitable ratio....

 

[byegad]

If it's badly bent a new one is cheap enough. Unless you fancy spending money on elastoplasts and dental work when it chucks the chain!

 

[DJ]

You keep a vice under your bed?

Maybe the bed is the only vice he has?

I tryed straightening a chain ring too once - it went to the scrappy in the end.