What size bottom bracket for Giant Alias

[willsmother]

The BB in my new Giant Alias is making a 'clunk' when I power up hills. My friends are going to help me tighten or regrease/re seat it but I thought I may get a spare one when I go to Darwin just in case it needs replacing. It has only just started doing it. I have put about 1500 km on the bike since I got it end April, with some pretty long/hilly rides in the mix. It is of course under warranty but I am in Dili, East Timor and I bought it from a bike shop in Melbourne so that's all a bit hard. I know it is a Shimano Octalink ES25 but they come in different lengths and diameters and I don't know which is the right size. Thanks for advice. Helen

[mitzikatzi]

How did the fork spring swap go?

Grab the crank arms and try to move them. There should be no movement of the cranks on the axle. If so tighten the mounting bolts.

[mitzikatzi]

Jonny Watson from United Kingdom asks
how do i measure the size of a BB from the frame - if i havent got an old BB to measure????
CRC Replies:

To get the correct BB size you will need to measure the Width of the bottom bracket on the frame. It will be 68mm or 73mm on a Mountain Bike. The axle length depends on the cranks, as a guide, most modern ISIS cranks use a 113mm but there are exceptions

Shimano ES25 Octalink Bottom Bracket
or
some might say a better quality one
Shimano ES51 Octalink Bottom Bracket

Ring and ask the shop that sold you the bike?

[willsmother]

Have been too gutless to do fork spring swap yet even though the spring has arrived. Have tried ringing bike shop, they said they thought 68*113. Cranks seem tight enough, have swapped pedals to see if it was pedal bearings, not difference with other pedals which is a shame, pedals would have been easy option.
Dili bike shop has ONE BB (as in their entire stock of BB is one BB) , seems to be someone's order they did not pick up, but it is a Shimano ES51, no size specified, I could get lucky. Equivalent of 140000 IDR so around $30
But it may just need the existing one tightening since it is only 2 months old

[mitzikatzi]

It is easy enough to measure you frame to see if it is 68 or 73mm.
You can also remove the cranks and measure the spindle length.
The easiest way is to remove the bottom bracket and read what is written on it. This also allows you to grease the threads and reinstall useful to do this to get rid of noises.