Bicycle Mechanics - ready to change out chainring, but...

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jackb
09-28-10, 11:54 AM
Based on advice given here, I decided to change a 30t chainring for a 24t to get some lower gears. I just received the chainring, but before I dive into removing the crank and chainring, I have a few questions concerning this Octalink bottom bracket and crank.

1. Do I need any special tools? I can see an allen bolt which looks like 10mm. i can get a wrench at the local hardware store. Anything I should be aware of?

2. I have an old crank removal tool from twenty years ago. will that work or will I have to buy something new? If the latter, what?

3. After the crank is off, I will unbolt the inner chainring and replace with 24t. anything I should be aware of?

4. Will I have to move/adjust the front derailleur or replace it?

5. Anything else I should know about.

Thanks for the help.

fietsbob
09-28-10, 12:25 PM
Hardware stores have Metric allen wrenches I have an 8mm allen as my crank arm fixing bolt,
but I cannot see yours.

The Octalink is a bigger tube than the square taper , you need a new crank arm extractor tool.

IF there are 2 little pin spanner holes in a ring around the bolt head

you may have a self extracting bolt . the ring screws into the place where the extractor may
be threaded into , It should come out with out another tool..

[carefull I've had a self extractor strip the crankarm and not budge ]

If there is a black plastic ring around the bolt Its not self extracting..

You should not have to remove the FD.
if you are not changing the big ring..

you will need a 5mm allen to take off the third ring mounting bolts.
nhluhr
09-28-10, 07:40 PM
There is a tool made by shimano that is used to screw in those self-extractor nuts AND to hold chainring nuts. It makes it a lot easier to work on cranks but you can get by without it.

Shimano TL-FC21
http://www.starbike.com/images/Shimano/werkzeug/TL-FC21.jpg

Self-Extractor Crank Bolt:
http://images.jensonusa.com/large/cr/cr408z24_____15___aloy.jpg

Non-self-extracting bolt:
http://www.jejamescycles.co.uk/product-images-large/truvativ-crank-arm-bolt-m15-m22-alloy-self-extracting-gxp-1-pc-58376.jpg

If you have and will use the self-extractor function, make sure the nut is screwed all the way into the crank-arm before you start unscrewing the bolt, or else the lack of thread engagement in the arm may strip the self-extractor out of the arm and damage threads on one or the other. When you put it back together, clean and re-grease all the surfaces that will touch inside. Make sure you tighten the self-extractor down all the way (with the washer in between) after you tighten the crank bolt.