chainring

cat hunter

Regular
Hi there . I'm after a bit of advice. I've just replaced a chainring on my tern link p 9 because my old one was bent. But now I've put the new one on it still looks a little bit bent when I rotate the crank . I've checked the chainring on a flat surface and its fine and checked the mating surfaces of the chainring and the crank . I've tightened the chainring bolts all opposite to each other to 7 nm .but I can't see why when I look down at the chain on the chainring it goes slightly left to right as I turn the pedal. But when I turn the crank with chainring and chain guard removed it all looks straight Any help to tell me where I have gone wrong would be cool
 

raleighnut

Legendary Member
It could be the way the entire crank sits on the bottom bracket, what type of BB is it.
 
OP
C

cat hunter

Regular
Don't know what type of BB it has. Been looking online but no luck . The chain guard has a little bit of a bend but its definitely not that .i will have to take it off again tomorrow and see if I can find the problem.cheer dudes
 

silva

Senior Member
Location
Belgium
The first test is executed while pedaling and looking down.
The next test is turning without chainring, which suggests turning cranks with hand.
The force difference is big.
It could be that the perceived as bent is due to a chainring whose mount has some wiggle room, for ex due to worn bearings in the bottom bracket. Another explanation might be a frame that flexes enough (due to the forces it undergoes) to make it noticable.
 

Ajax Bay

Guru
Location
East Devon
grease the bolts too
Personally I would not grease the bolts. Apply a dab of threadlock to each one before assembly.
To quantify this 'bent' issue, rig up a transparent ruler across the top of the chainring (may need a second pair of hands) and see if the teeth move from side to side during a revolution.
 
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