Chainring out of true?

alomac

I seem to have a problem with the outer ring of my Shimano M442 crankset, in that it allows the chain to rub against the outer plate of the front mech through part of its travel. It basicallyseems to be out of true, unless this warping is some sort of deliberate device to aid shifting.
I've tried winding out the H limiter screw, but I'm at or near the end of its travel. I'll try rotating the mech on its band (seat-post mount) later, but are there anyother ideas? The mech and shifters are Deore. The chainring bolts have all been equally torqued (15 Nm).

supersonic

You can definitely see a warp as it spins? Do all three rings do it in the same place?

zaris

take the chainring off and see what happens, maybe its bent which i doubt unless you crashed it badly. Best guess at the moment, might be the front mech needing a full checkover.

/zaris

alomac

I took the chain off and gave it a spin, and though it was much harder to eyeball than I expected, there appears to be a small but definite warp outwards across all three rings at the point where the crankarm crosses over them.

I don't ever recall taking a serious hit to the chainrings, but I do belt the pedals quite badly, quite often. The front does mech need adjusting btw, which is how I began taking an interest in this whole area to begin with.

Cheers,
Adam.

supersonic

Also when pedalling hard flex can cause a little bit of rub.

All three rings that go in the same place can be a badly aligned crank to the axle, or spider.

I'd adjust the front mech, and be aware that some gear combos will cause rub.

zaris

Look at the park tool website for info on how to adjust your front mech, also check this youtube videos out kinda dated but does the job, it's how i learnt

youtube
http://www.youtube.com/watch?v=ngm6dr-1 ... re=related

parktool
http://www.parktool.com/repair/readhowto.asp?id=75

hope it helps
/zaris

mediamonkey

If it's across all three chainrings, are you sure it's not play in the bottom bracket? The first thing that alerted me to the fact my BB was knackered was the chain rubbing against the front mech once per pedal revolution. There was enough play in the crank axle that the chainrings would wobble out slightly and cause the rubbing.

Grab your crank arm and try to rock it "in and out" (i.e. towards the frame of the bike). If it wobbles, your BB needs adjusting (or, more likely, replacing, as they're usually sealed cartridge jobs these days)