Chain ring rubbing on frame

hedzup · #1 03-31.-2008

Hi all,

My chain ring has started to rub on the frame of my bike (see photo). I suspect the problem is a worn bottom bracket but can't feel any roughness or stiffness when I turn the cranks by hand. There seems to be a small amount of play in the bottom bracket but it doesn't seem to be excessive (but I'm not sure what is excessive). Does anyone have advice on how I can check whether it is the BB or a bent chain ring.

The chain ring is a shimano biopace which is why the area of rubbing extends beyond the visible portion of the inner chain ring.

The rubing is not constant but seems to come and go.

Thanks

AB

Insaneclimber · #2 03-31.-2008

Hey man
Any play in the bottom bracket is too much, so i would guess that your problem lies there. as for checking straightness of chainrings, just drop the chain off and give the cranks a spinn. While there spinning eyeball the teeth from above you will easily see if its warped. PS a couple of mm either way don't matter too much.

I would suggest at least dissassembling your bb to check the bearings and the tightness of the cups.

Powerful Pete · #3 03-31.-2008

Yup, there should be no play that you can feel in your BB. Disassemble and re-assemble. If you are not comfortable doing this at home do take it to your local shop and have them do it.

And please do clean that chain and those chainrings!

Peter@vecchios · #4 03-31.-2008

Quote:

Originally Posted by hedzup

Hi all,

My chain ring has started to rub on the frame of my bike (see photo). I suspect the problem is a worn bottom bracket but can't feel any roughness or stiffness when I turn the cranks by hand. There seems to be a small amount of play in the bottom bracket but it doesn't seem to be excessive (but I'm not sure what is excessive). Does anyone have advice on how I can check whether it is the BB or a bent chain ring.

The chain ring is a shimano biopace which is why the area of rubbing extends beyond the visible portion of the inner chain ring.

The rubing is not constant but seems to come and go.

Thanks

I would pull the cranks and OVH or replace the BB. I would suggest using a slightly longer BB spindle if you replace. That ring is really close to the frame.

AB

I would pull the cranks and OVH or replace the BB. I would suggest using a slightly longer BB spindle if you replace. That ring is really close to the frame.

oldbobcat · #5 04-01.-2008

Quote:

Originally Posted by Peter@vecchios

I would pull the cranks and OVH or replace the BB. I would suggest using a slightly longer BB spindle if you replace. That ring is really close to the frame.

Or, if the BB is otherwise OK and there is extra spindle on the other side, re-install the RH cup with a spacer ring or two.

hedzup · #6 04-01.-2008

Hi all,

Thanks for the replies. I went into a fantastic bike shop yesterday and they replaced BB with a version with a slightly longer spindle and gave me lots of useful advice (including replacing the biopace with something a bit rounder when the chain rings wear out

).

Cheers

AB

alfeng · #7 04-01.-2008

Quote:

Originally Posted by hedzup

My chain ring has started to rub on the frame of my bike (see photo). I suspect the problem is a worn bottom bracket but can't feel any roughness or stiffness when I turn the cranks by hand. There seems to be a small amount of play in the bottom bracket but it doesn't seem to be excessive (but I'm not sure what is excessive). Does anyone have advice on how I can check whether it is the BB or a bent chain ring.

The rubing is not constant but seems to come and go.

This is after-the-fact because the BB was just replaced ...

If pressng the non-driveside of the crank toward the frame had moved your inner chainring AWAY from the chainstay & pulling the non-driveside crankarm away from the frame made the chainring rub against the chainstay then you probably needed to adjust the adjustable cup which must have loosened from the frame.

Usually (for those who might encounter a similar problem in the future), you would need to remove the non-driveside crankarm ... then loosen the lockring (which is probably loose), tighten/adjust the cup (which you would have done if you had overhauled the BB), tighten the lockring ...

OR, installing a cartridge-type BB (probably 113mm -- but, who knows what size your shop installed?!?) will preclude the problem of left-right play in the spindle.

hedzup · #8 04-02.-2008

Quote:

Originally Posted by alfeng

This is after-the-fact because the BB was just replaced ...

If pressng the non-driveside of the crank toward the frame had moved your inner chainring AWAY from the chainstay & pulling the non-driveside crankarm away from the frame made the chainring rub against the chainstay then you probably needed to adjust the adjustable cup which must have loosened from the frame.

Usually (for those who might encounter a similar problem in the future), you would need to remove the non-driveside crankarm ... then loosen the lockring (which is probably loose), tighten/adjust the cup (which you would have done if you had overhauled the BB), tighten the lockring ...

OR, installing a cartridge-type BB (probably 113mm -- but, who knows what size your shop installed?!?) will preclude the problem of left-right play in the spindle.

I should have mentioned that the existing BB was a sealed bearing type.

RedRider2009 · #9 04-02.-2008

That is the bike to bring if you go on a camping trip and need a fire! Good Luck

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