Bicycle Mechanics - Tell me whats wrong with this picture...

I just got done putting this bike together. Everything is great except for the rear derailluer when trying to shift onto the largest cog. Goes from this on the second to last:
http://webpages.charter.net/cierrecart/DSCF3453.JPG

to this when it shifts onto the last cog:
http://webpages.charter.net/cierrecart/DSCF3454.JPG

It binds up and makes a bunch of racket and the only way to release it is to shift back down while reverse pedaling.



Is the chain too short? It's brand new and I sized it by wrapping it over the two largest cogs (the front only has the two smaller because of the bash guard taking up the space of the third (I just realized that might be the problem, duh!) and then adding 2 rivets (or one inch) per the instructions.



Any help here?

Thanks!

Chain length is big big plus 2 links.

easiest way to get the right chain length: small chainring/small cog fed through both derailleurs, with enough tension so the chain doesn't rub on the rear derailleur pulley cage. usually, i'll shoot for 2cm clearance between the chain and the derailleur cage.

big/big plus two links works as well, but it's faster to just thread everything through once, cut, then connect the chain.

So, in other words, chain is too short.

oops...yeah.

looks like a KMC Z-chain on there, too.

try a SRAM chain, or a decent shimano chain instead. the bike will shift buttery smooth.

And make sure that the upper pulley doesn't make contact with the largest cog (by adjusting the b-limit screw on the derailleur).

Bob

I'm surprised something didn't explode when you shifted it while riding. Lucky?

oops...yeah.

looks like a KMC Z-chain on there, too.

try a SRAM chain, or a decent shimano chain instead. the bike will shift buttery smooth.


Shifting is pretty smooth other than that last cog, and i was working on a tight budget so a $6 chain was right up my alley.



So......how many links should I be adding here? Is the problem because I used the largest rear cog and the middle front chainring when I sized it?






AS for things exploding.....I checked it all out before even stepping foot on the bike. Once on a test ride, I shifted gently and listened carefully.

since you don't have a big ring, add two links.

Two links to what I already have or should I just try to resize it and add two links?