Bicycle Mechanics - Derailler flange hitting chain. Which screw to adjust?

Question #1: Hopefully, I have the terminology right. But the links to the photos (http://mytruealterego.blogspot.com/2008/04/rear-derailleur-problems.html) will explain in pictures. The first photo shows the part that I am talking about (circled in red). When I am on the smallest chainring and the smallest rear cog (as shown in the second picture) the little flange is touching the top of the chain. I was wondering if anyone knew what to adjust. I just changed the rear cassette (only).

Question #2: While testing the derailleur on the stand after changing the cassette, I was turning the crank with my hands and noticed that when I am on the largest chainring and smallest rear cog, I feel a little bit of roughness (like bearing grinding or something like that). It goes away once the chain is moved away. Any idea what this is about?

Question #1: Hopefully, I have the terminology right. But the links to the photos (http://mytruealterego.blogspot.com/2008/04/rear-derailleur-problems.html) will explain in pictures. The first photo shows the part that I am talking about (circled in red). When I am on the smallest chainring and the smallest rear cog (as shown in the second picture) the little flange is touching the top of the chain. I was wondering if anyone knew what to adjust. I just changed the rear cassette (only).

You shouldn't be using those gears anyway, but if you changed the Cassette, and not the chain, it will get destroyed pretty quickly by a worn chain.

some links to help you:

http://sheldonbrown.com/derailer-adjustment.html#chain
http://sheldonbrown.com/chains.html

you chain is to long and need to be shorten. to do so you need to break the chain ,remove a link or two so it doesn't hit the cage guide . i take it your new cassette have small gears ?

for you 2nd question check your dérailleur adjustment , the high gear need to be adjusted in or out ?

04jtb: I am confused by your response. Why should I not use those gears e.g. on a decline? I am going to change the chain as well, just waiting for it to get in.

bikeman715: For Q1, why should the chain length matter now? I only replaced the rear cassette with the same kind...and it wasn't doing this on my old cassette.

You should not use the small to small or the big to big combinations (cross-chaining).
And your chain is too long. There are several methods to check for correct chain length. One check is that when in the small to small combination the rear derailleur should not "bottom out". There should always be some tension on the chain. If you'll do some searching there are several instructions available for sizing the chain. Try http://www.parktool.com and http://www.sheldonbrown.com.

Al

Cross chaining causes excess friction in the moving parts due to the chain angle. This makes you work harder and causes excess wear in the drive train over a long period of time.
What kind of cassette change did you make?

Al

I replaced a Shimano Ultegra 6600 with the same kind because it was worn out. So I guess what's the extent to which you can cross-chain..upto last-but-one OK?

04jtb: I am confused by your response. Why should I not use those gears e.g. on a decline? I am going to change the chain as well, just waiting for it to get in.


Try to avoid the gears that make the chain cross over at an extreme angle. These "criss-cross" gears are bad for the chain and sprockets. Especially bad is to combine the inside (small) front sprocket with the outside (small) rear sprocket. This noisy, inefficient gear causes the chain to wear out prematurely.

hope this helps

I replaced a Shimano Ultegra 6600 with the same kind because it was worn out. So I guess what's the extent to which you can cross-chain..upto last-but-one OK?

Was the tooth count on the smallest cog the same on both cassettes? I guess you've already answered that.
Was the chain also replaced? Maybe you've already answered that.
If the new cassette is exactly the same as the old then there should be no reason for new chain slack.
Has the chain been measured for elongation (stretch)?
A new chain will measure exactly 12 inches over a 24 pin interval. By the time that interval reaches 12 1/16th inches it should be replaced. But from the posted photo it appears that you have more slack than could be accounted for with normal stretch. If the chain now measures OK then it seems you may need to remove one link (that's a full inch). Or at least enough so that the derailleur is putting the chain in tension.
Edit: Just noticed that you plan to replace the chain.

Al

I just checked and I realized that the cassette I ordered is 12-27 instead of 12-25. So the answer is that the number of teeth on the smallest cog is the same on both cassettes.

The chain is worn but not so much that it should cause this issue. Sheldonbrown.com says that chains last for few thousand miles and mine must be a thousand at the most.

I replaced a Shimano Ultegra 6600 with the same kind because it was worn out. So I guess what's the extent to which you can cross-chain..upto last-but-one OK?There really isn't a correct answer to this. Everyone will say never go big-big or small-small. It has to do with the number of cogs and the length of the chainstays. If you have ever noticed, a chain does not angle to the side very easily. If you have very long chainstays, then the angle of the chain will be less than if you had short chainstays.

What you want to do is try to have as straight of a chain as possible. If moving from the small chainring to the large and moving to a larger rear cog will give you a better chain line, then you should use that and vice versa. On my 24 speed, I will never go to to the second biggest or second smallest cogs with my smallest and largest chainrings. The middle chainring will never go to the biggest or the smallest cog. Basically, I will only use 6 of the 8 cogs with each chainring.

Depending on your set up, you most likely have some overlap in gearing. Use Sheldon's (pbuh) Gear Calculator (http://www.sheldonbrown.com/gears/) to discover your gear inches. You can print out a small cheat sheet to tape to your stem. Once you know what gear inches, gain ratio, etc. you want, determine which chainring and cog will give you the least angle.

If you want, you could even black out the combinations that you don't want to use. For example if you have two options that will give you a gear inch of 40.8, black out the one that has the worse chain angle. I haven't done it yet, but I want to set my cheat sheet with blacked out combinations that I never want to use, highlight combinations in orange ok combinations and yellow for best combinations.