Chain running along teeth in biggest chain ring

NickPsy

pretty much finished building my first bike however when setting up the front derailleur I came across a problem when the chain moves up onto the biggest ring its fine but then after pedalling a little more the chain rides on the left side as if it wants to move back down but isnt quite able to. Also if its not doing that it seems to slant to the side. As in if the chain runs flat such as - it sometimes goes like / on a slant. Thats the best I can describe it

is it simply a case of messing with the tension and h/l screw until its sorted or something else ?

Anonymous

Is the chain and chainring new, or second hand?
Is the front mech touching the chain when it's in gear?

nicklouse

what gear combo does it happen in?

what is your chainline measurement?

NickPsy

both the chain and chain ring are from my old bike - i should have said its my first build not first bike ever.

no the mech isnt touching the chain and it seems to happen in all gears on the back when trying to get up to the biggest front chainring

Anonymous

So does it happen when shifting, or after shifting?

Sounds like it might be a chainring/chain mismatch, as though one has worn more than the other.

NickPsy

it will shift onto the chainring fine but then after a few pedals it flicks up so its not sat properly as if it wants to move back down to second but cant get there

Anonymous

then I stick with my guess/diagnosis of worn chain and/or chainring

The Rookie

+1, sounds like the chain rolling up the worn teeth on the ring.....

New chainring times!

Simon