Chain too taught then too slack - help?!

I took my wheel off yesterday but after I put it back the chain is now acting insane.

It goes from being too tight to too slack in one rotation. How is that even possible? Has anyone ever experience that?

I think it's the chain but the four bike shops I took it to today weren't convinced of that but then they didn't have a better solution.

other info:

• I did not have this problem before having removed the wheel
  
• the chain, cog and chainring are all only two months old
  
• I think my frame might be slightly bent as recently I spend ages unsuccessfully trying to align my wheel correctly but it it always looks like its leaning no matter what I do (but this didn't seem to have this affect on the chain before)
  
• the wheel however is true
  
  

Apparently this is somewhat normal that it will be more taught in one position than in another but the is exTREME! All the bike shop people were really confused by it,

Has anyone experienced this? Is it possible to stretch a chain in one part and not another?

got an oval chainring?

try taking off the chain, loosening the chainring bolts, wiggle chain ring, then retighten/put back chain

nope, perfectly round.

Singlespeed? Only thing I can think is your wheel nuts are slipping and the wheel is tracking within the dropouts.

@Bruced no, fixed, plus I've got chain tensioners...

@31t®um thanks, will give that a go, though not until tomorrow when I can hijack my mates tools...

nope, perfectly round.

Who is it made by?

token

but when I say perfectly I don't mean like I had it measured by NASA, just that its round not oval :)

The problem is the chainring though and since removing and refitting the wheel, you have increased the chain tension highlighting this problem.

Why do you suspect a bent frame anyway? Did you crash it? Although a bent frame wouldnt explain the variation in chain tension.

if you had a mate with the same chain length try a swap and see if your problem transfers,
loan chain ?
does it streth on his bike ?
try his chain on your bike has the problem gone then its the wheel or chainset.

Check for something loose?

Check the chain for any tight spots. I would look at the alighnment.

Why do you suspect a bent frame anyway? Did you crash it? Although a bent frame wouldnt explain the variation in chain tension.

just cos I can't get my wheel straight any longer, thought that could then alter the axis thereby moving the cog with it...? My logic is so poor, please bare with me...made sense in my head though?

if you had a mate with the same chain length try a swap and see if your problem transfers,
loan chain ?
does it streth on his bike ?
try his chain on your bike has the problem gone then its the wheel or chainset.

I just tried my old chain and it seemed better, but now I'm even more confused cos I took that off cos it was stretched. Unfortunately it's a quick release and I've lost the actual part to close it so I can't use it... makes me question why I kept it...

The problem is the chainring though and since removing and refitting the wheel, you have increased the chain tension highlighting this problem.

So you think the chainring has been damaged? Or that it's just always been wrong? So the solution would be a new chainring?

it could be a bent axle.

So you think the chainring has been damaged? Or that it's just always been wrong? So the solution would be a new chainring?

Damaged? Probably not, but it's very likely that it's not centred exactly on it's bolts. If you loosen them off you'll probably see it move slightly as the chain pulls it back. I expect pulling your wheel further back has just exacerbated an issue that was already there. It's a common problem as chainrings are never perfectly round and/or centred.

I think Sheldon explains it all via this thread...?

http://www.lfgss.com/thread23972.html

amazing... I see the logic in it. Will give this a try tomorrow. I'm still not 100% convinced though (not to question Sheldon) purely cos of the huge difference between tight and slack. It's literally going from binding to the point where it looks like it could actually come off, it's so extreme. Will see how it goes though...
thanks!

spin the wheel by hand and mark/make a point of when it tightens. if it is happening in a pattern or predictable place in each rotation, then you know its the wheel ie a bent axle.

then spin the cranks by hand and make a point of where it tightens.

whichever of the two has a pattern in when the chain tightens will indicate which will have the fault

as mumbles says, your chainring is not centred on your cranks. My left nut is on the fact that you're using a cheap chainset, sugino messengers or the like which are notorious for this.

My advice is take it to a LBS that knows what they're doing. or do what 31trum says. or buy some decent cranks and a chainring.

^you only have a right nut :)

...so I ended up taking the bike into Bon Vélo, all I said was 'chain' and he knew exactly what it was and sorted it exactly as you all recommended, with the bolts.
They totally know what they're doing in Bon Vélo, it's running so smoothly now, none of the other shops had a clue.
Thanks everyone for your help, I really thought it was the chain not the chainring, let alone the bolts on the chainring!

I've just removed an 18T sprocket from the wheel I bought last week.

Same thing. The rear cog was bent.

Damaged? Probably not, but it's very likely that it's not centred exactly on it's bolts. If you loosen them off you'll probably see it move slightly as the chain pulls it back. I expect pulling your wheel further back has just exacerbated an issue that was already there. It's a common problem as chainrings are never perfectly round and/or centred.

I think Sheldon explains it all via this thread...?

http://www.lfgss.com/thread23972.html

Pretty much this and what Murtle said.

I had similar problems and it did the trick nicely. Just loosen your chain ring bolts a little, to the point where you chain is tight you whack it carefully it will sort itself out. gently turn the rear wheel and keep doing same thing until your just tapping the chain gently and it's even tension all the way round. Then tighten chainring bolts. Should do the job and yes, don't over tighten your chain. Easy done with all slack chain remarks on'ere ;-]

Oooops, complete timing and advice fail :P