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Discussion Starter · #1 ·
Awhile ago I had the bike setup with XTR m970 cranks, Salsa SS ring, and a surly cog. At this time, I noticed that the chain tension changed while pedaling through a full cycle each time. I searched on mtbr and read that it's common so I went ahead and rode for awhile. Last week I was riding and heard a big 'plink' and figured my chain just dropped, but I noticed my chainring bent and two of the bolts even popped off. The other two remaining bolts were loose as well. I figured that was my fault for not making sure all the bolts were tight.

So now I've got a new Chris King cog, chain, and a blackspire ring. After installing everything, I'm still getting that incosistent chain tension, but this time, it's a bit more severe. At one point, it's way too loose and could drop easily, but at another point, the chain just gets way too tight.

Am I missing something here?
 

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Did you try centering your chainring? I doubt this is your problem though, can't imagine it being so far off that you could drop the chain.

Anyway, install the ring with the bolts handtight and find the spot where the tension is highest. Then slap the chain, so that the ring will move a little. Find the new tightest spot, and repeat until tension is acceptable all the way round. Don't forget to bolt up the ring properly when you're done.

Here's the info on Sheldon Brown's site: http://www.sheldonbrown.com/singlespeed.html#tension
 

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flexbaba said:
Did you try centering your chainring? I doubt this is your problem though, can't imagine it being so far off that you could drop the chain.

Anyway, install the ring with the bolts handtight and find the spot where the tension is highest. Then slap the chain, so that the ring will move a little. Find the new tightest spot, and repeat until tension is acceptable all the way round. Don't forget to bolt up the ring properly when you're done.

Here's the info on Sheldon Brown's site: http://www.sheldonbrown.com/singlespeed.html#tension
i did this to my vagrant earlier today, works like a charm!!!
 

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sounds like an out of round cog or chainring, which suprises me because both blackspire and CK are good stuff. I have seen cases where the crank's bolt pattern is out a little bit, so if you can get access to an indicator, i'd check that.
Try centering it first, but if it's out as much as you're describing, i doubt you'll have enough play in the bolt holes.
 

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Sounds like either a) bent crank shaft b) angularly installed spider arm or c) off centered chain ring bolt holes? Since you can install a ring, all 4 holes are bored with accurate spacing – but if it was done off centered, then you would have that consistent wobbly ring no matter what ring you use. It so, that’s a warranty issue. Take it back to the shop.
 

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Discussion Starter · #7 · (Edited)
Centering the chain ring via Sheldon Brown's method seemed to help a little bit but I'm still getting that sound where something is slightly off but have no idea where it's coming from and how to fix it. The chain ring and cog are brand new and seem pretty damn straight. Rear wheel is centered in the drop outs.

I appreciate the help so far.
 

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JHANguyen said:
Centering the chain ring via Sheldon Brown's method seemed to help a little bit but I'm still getting that sound where something is slightly off but have no idea where it's coming from and how to fix it. The chain ring and cog are brand new and seem pretty damn straight. Rear wheel is centered in the drop outs.

I appreciate the help so far.
most likely you wouldnt see the runout by eye, it only takes it being off a hair to cause issues. If the bolt pattern was off position .005" (.01" total indicator runout), your chain would go crazy. If centering your chainring helped, then it might be a chainring/crank issue. Any chance you can try the chainring on a different crank? It's just a 104bcd, so most 4 bolt cranks will work. That will help narrow it down. Have you tried what was mentioned before; checking to see if it only has 1 tight spot and one loose spot per revolution of the crank, or is it nearly twice per rev?
I'd be suprised if the chainring was out, but if it is, contact them, i'm sure they'll take care of you. Every once in a while, a non-conforming part might make it's way out the door by accident, no matter who the manufacturer is. But like i said, we gotta narrow it down first.
Bike shops should carry a "master ring" that is known to be perfectly round to help narrow these problems down. I think singlespeeding has taken off enough to justify the cost :)

Also, how old is the chain? an old chain will make noise on new gears because the pitch doesnt match.
 
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