Square Taper Bottom Bracket Question?

[Cletus Van Damme]

I removed the bottom bracket from Marin Mill Valley 2004 hybrid bike as it felt a bit rough. I cannot read most of the printed text on it as it has worn off but it is a Truvativ BB same as the chainset manufacturer. I know that the spindle length is 113mm and I am guessing that the thread will be 68mm? I am going to take it to work to get it measured properly. The bike is a triple and the BB has a metal spacer fitted to the drive side cup/thread. I was wondering do I have to buy a Truvativ BB or can I buy a cheap Shimano one? Just wondered if the crank bolts were a standard thread that is all. I am guessing that I will have to use the spacer on whichever BB that I buy to maintain the correct chain line?

Thanks for any help.

 

[RecordAceFromNew]

I removed the bottom bracket from Marin Mill Valley 2004 hybrid bike as it felt a bit rough. I cannot read most of the printed text on it as it has worn off but it is a Truvativ BB same as the chainset manufacturer. I know that the spindle length is 113mm and I am guessing that the thread will be 68mm? I am going to take it to work to get it measured properly. The bike is a triple and the BB has a metal spacer fitted to the drive side cup/thread. I was wondering do I have to buy a Truvativ BB or can I buy a cheap Shimano one? Just wondered if the crank bolts were a standard thread that is all. I am guessing that I will have to use the spacer on whichever BB that I buy to maintain the correct chain line?

Thanks for any help.

If it is a Truvativ square taper bb then it is JIS, so you should be able to replace it with an equivalent sized Shimano square tapered BB. If in doubt you can check the chainline before and after and use this as your reference (and it probably also confirms why the spacer is there). The chainline outcome shouldn't vary by more than 1mm.

The only other possible bb shell (of the frame) width is 73mm in this case, so you shouldn't need anything more than a simple ruler to find out whether it is 68mm.

Square tapered crank bolts have M8 fine (1mm) thread.

 

[Cletus Van Damme]

If it is a Truvativ square taper bb then it is JIS, so you should be able to replace it with an equivalent sized Shimano square tapered BB. If in doubt you can check the chainline before and after and use this as your reference (and it probably also confirms why the spacer is there). The chainline outcome shouldn't vary by more than 1mm.

The only other possible bb shell (of the frame) width is 73mm in this case, so you shouldn't need anything more than a simple ruler to find out whether it is 68mm.

Square tapered crank bolts have M8 fine (1mm) thread.

Thanks very much for taking the time to write such a detailed explanation again mate. I will have to measure the BB shell when I get home where the bike is. I got my wires crossed a little about what I am measuring, I just thought 68mm as I was sure that I could just make this out on the BB. Thanks again

 

[Cletus Van Damme]

If in doubt you can check the chainline before and after and use this as your reference (and it probably also confirms why the spacer is there). The chainline outcome shouldn't vary by more than 1mm..

Thanks for the help, great as usual. Bought a cheap as chips Shimano BB-UN26 for £8 delivered. No need to use a spacer with this item and the chain line is superb, hopefully this will last another 9 years