jlam

I have a 2005 Giant OCR 3 that I bought second hand just over a year ago, and I've put about 3000 km since then. The bike looked quite unused when I got it off Craigslist, so I thought it was a steal at $300. It's a triple and 8sp with Sora components. I use it as a commuter for a 40 km round trip through main roads and about 8 km on the shoulder of a highway (where most of the dirt comes from). I'm no expert in bike mechanics, but I've been maintaining and replacing components myself (derailleurs, cables, etc).

Everything has been fine until about a few weeks ago when I started noticing a subtle skipping sound coming from my drive train. After a bit of troubleshooting, I saw that the chain wasn't mating perfectly with the cassette. If I pedaled slowly, there would be times where the links would "fall into place" after 1/8 of a revolution from leaving the jockey wheel, instead of going seamlessly from the derailleur to the cassette. Turns out my chain was stretched just over 1/16", so I bought a new one to replace it in hopes that the skipping would stop. Unfortunately, it didn't solve the problem. There's still a subtle skipping that occurs when I pedal (using all cogs and all chain rings), and now there's a significant skipping in the 2nd, 3rd and 4th highest/smallest cogs where the chain would momentarily disengage from the cog when I'm pedaling out of my seat.

Additionally, I noticed that the sound occurs when I'm pedaling hard whenever the pedals are at peak positions (either when my right or left leg is in full extension), which might suggest that my applied pedaling load is causing some misalignment somewhere. However, when I pedal the bike when it's on the stand, I can't recreate the noise and the chain shifts through all the cogs smoothly.

Things I've done already:
1) Rear derailleur adjustment (limit screws, b-screw, cable* tension)
2) No kinks in shifting cable - just replaced them a few months ago
3) Front derailleur adjustment
4) Chain replacement
5) Checked cassette for looseness
6) Checked BB and pedals for play and any grittiness in bearings, but all seems to be smooth
7) Chain rings look fine

I took a closer look at the cassette and it appears as though some teeth are misaligned and/or worn out. I'm thinking that a new cassette would fix the problem, but I'm just wondering if I should be looking at anything else? Or anything that I've missed?

I can't wait to ride a silent bike again... This hunting for noise has been driving me nuts (pun intended)!

zacster

Two things. First, possibly your cassette is worn out as you suspect. A worn chain will cause a worn cassette. Second, your derailleur is mis-aligned. The first picture makes it look bent in, and this will cause all kinds of problems. There is a tool to check this, the Park DAG-2, but you don't necessarily want to buy it. Take the bike to a shop and have them do it for you. Once it is aligned everything else can be adjusted.

dsbrantjr

A new chain on a used cassette often does not play well. It is difficult to judge the state of wear of a cassette visually; some of the "misaligned or worn-out" teeth may be that way by design to aid in shifting. A replacement cassette may be what is needed.

AnkleWork

zacster +1, and your chain looks dry. Actually your cassette does not *look* too bad in the photo. Worry about it only after correcting any other faults.

TallRider

since you recently replaced the chain, I suspect this is a new chain on somewhat-worn cassette issue. as others are primarily thinking, too. Symptoms you report are consistent with this, as the chain will "jump" most under peak load.
If your cassette is worn, then the chain will "jump" more on some gears than others (the gears that got used the most with a worn-out chain are the gears that will have the most-worn teeth). So: does the chain jump more on some gears than others?

I can't tell from the picture if your rear derailer hanger is misaligned, but it's worth checking as zacster suggests.

Retro Grouch 

I doubt it's a "new chain on an old cassette" issue because you were having the problem before you replaced the chain.

I doubt your cassette teeth are worn out. What you are seeing are probably "shift gates" built into the cassette cogs. Look at the cog exactly opposite the worn teeth and see if you find another set that looks just like them.

The first thing that I do when I have a rear shifting issue that doesn't respond to normal tuneing is to check derailleur hanger alignment:
1. Shift into a gear combination that makes your derailleur arm point straight down.
2. Prop your bike up vertically and look at it from the back.
3. Does your derailleur arm seem to angle toward the rear wheel? If it does, even a tiny bit, that's it.

You can try to straighten it yourself (leave the derailleur in place while you try to bend it back) but it's probably a better idea to take it to a shop that has the proper gauge for realigning the hanger. It's only about a $15.00 or $20.00 job.

ursle

Got the correct replacement chain?
(looks wide)

Retro Grouch 

It's 8-speed. 6/7/8-speed take the same chain.

FBinNY 

The OP may try a poor man's hanger alignment using tools he probably already owns.

Place a 6mm hex key into the mounting bolt, and grabbing the whole derailleur and levering the key upward, pull the RD out until the cage appears vertical, forming a straight line from the sprocket, along the chain to the lower pulley. If you have a poor eye of this kind of stuff, place a yardstick vertically against the wheel as a reference, and set the RD cage parallel to that.

This method isn't ultra precise, but is good enough for government work (and 8s systems) and will eliminate RD cage alignment as the issue.

Important - aligning the hanger moves the RD and changes both limit screw settings along with cable trim adjustment for index shifters. Make sure yo readjust the limits before riding.

If you're lucky the bike will be fine, but IME skipping under load is classic for worn sprockets, especially when it happens mainly on the most used sprockets, and even more likely if a new chain was fitted.

sreten

Hi, my money is on a overused single rear sprocket, rgds, sreten.

jlam

Thanks for the input!

I took a closer look at my rear derailleur and it appears that the hangar is slightly bent. When I compared the derailleur cage to a straight edge, the top and bottom of the cage were off by ~1-2 mm, with the bottom being bent toward the spokes. I did what FBinNY suggested and was able to get it straight, but the problem still exists. I took it for a spin and found that the creaking sound went away if I pedaled as if I was sprinting (off the saddle and rocking bike side to side). I rechecked my pedals (Keo Classics), and there's a tiny bit of side-to-side play. However, I switched pedals to some MTB ones I had and the sound was still there...

I ordered a new cassette since the chain only skips under load when I'm in the higher cogs (which happen to be the ones I use most), and shifting is fine in the lower ones. I'll try and drop by my LBS this week to have my hangar checked out.

jlam

Turns out that the bearings in my BB were shot. When I disassembled, greased, and reassembled my headset, pedals and seatpost, the sound was still there! So I took a closer look at it while my bike was on the ground and pressed my foot against one of the pedals and voila, the creaking noise made its appearance. I went out to buy a new BB to install, and as soon as I got back on my bike, I heard nothing... Music to my ears

cny-bikeman

Well, it's a good thing to overhaul the BB, but that's not necessarily what caused the creak. Bearings most often make noise when rotating rather than in one place. It's more likely the problem was with the crank/spindle interface, and by overhauling the BB when you reinstalled the cranks they were tightened down better.