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Replacing a Bottom Bracket

Recently the bottom bracket on my Mountain Bike broke, I thought it had gotten very loud and graty when I pedalled and when I looked at it you could move the pedals and cranks sideways at least 5mm. Apparentley this is a dead giveaway of a broken one, still it had lasted 4 years in the mud and grit of the Yorkshire Dales!!

So using my trusty Zinn and the Art of Mountain Bike Maintenance book, I decided to have a go at fixing it myself instead of finding a new bike shop to goto, as Kudu Bikes in Hawes has recently closed it doors.

So my Iron Horse Azure Sport has an ISIS Cartridge type Bottom Bracket (BB)

So having figured out I needed a Shimano ISIS tool to remove it, I found one cheap at  a LifeLine Shimano Cartridge Bottom Bracket Tool and as I was not sure what bottom bracket I needed I decided to pull it apart first and then order one, luckily for me as I almost wasted some money there, having almost purchased a Shimano MB-530 one.

So first of all you must remove the Crank-set, that’s the chain-rings and the pedal arms.

To do this you need at least in my case:

1. 8mm  hex key (Allen key)

2. Crank Puller (in my case it has an integral wrench arm)

3. Bottom Bracket Socket tool. (ISIS/Octalink)


Removing the Bottom Bracket

So using an 8mm Allen key I removed the dust cap covering the  on both sides of the bike. (These can get very stiff and I found I needed to stand on the pedal and on the Allen key in order to move them)

Then using a crank puller tool I removed the cranks from the bike on the chain-ring side. The outer threads of the Crank Tool are screwed into the threads on the crank, making sure its tight otherwise you can damage the threads and then the crank tool handle is rotated anticlockwise, this pushed the centre thread of the crank tool into the bike and the Crank is slowly pushed off the bike. I then unscrewed the crank puller from the Cranks.

Now using the ISIS BB tool I unscrewed, remembering that is clockwise to unfasten the drive side of the Bottom Bracket which pulled it out of the bottom of the bike, the non-drive side is just a cover the hold it in place and can be unscrewed using the BB tool afterwards (anticlockwise).

I found that the BB was a Truvativ PowerSpline which apparently cannot be substituted for a Shimano ISIS BB as the Crank-set on my Iron Horse was also a Truvativ one that only works with Powerspline BB`s. So not wanting to replace the whole lot I sourced the correct size BB from Chain Reaction Cycles, in this case a 73 x 113mm.

The 73mm denotes the width of the BB and 113mm is the spindle length. You must get the correct size. some bikes also have to have the correct thread type, there being British, Italian and others.

Installing the Bottom Bracket.

First I put some grease onto the threads of the new bottom bracket, then left hand side (non drive side can be removed as this is installed first.

I threaded the left cup non drive side (clockwise) in three to four turns, this helps to align the BB from the other side.

I then slide the BB Cartridge into the right (Drive-side) bottom-bracket shell, as I had all of the correct size parts I did not need any spacers. So now I tightened it up clockwise using the BB Installation tool that I`d used to remove it. Until the lip seats against the face of the Bottom-Bracket Shell, which was pretty much as tight as it would go.

I then tightened the left and side up with the same tool.

Now I put some more grease on the crank spindle and pushed the drive side back on (the 3 chain-rings and pedal (crank) arm) making sure to put the chain back around the outside of the chainrings. Next I put back the Cap (new ones came with the BB) and tighten it up with the 8mm Allen key.

Next I put back the crank on the left (non-drive) side of the bike remembering that it must have the pedal opposite to the drive side and screwed the cap back on.

Then it was time for a ride!!

after my first ride I check the covers were still tight with the 8mm Allen key (hex key) and all was great!!

Sorry there are no pictures maybe next time, but I was so worried I’d get it wrong that I never thought about photos!

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