gt bottom bracket
- Thread starter rigbob
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Measure the BB shell. GT's from around then usually had a 73mm BB shell.
weeman_mtb
Retrobike Rider
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It depends also on what crankset you got as to what bottom bracket you need.
What chainline are you getting on the drive side? This is measured from the centre of the middle chainring to the centre of the frame if you are running a triple on the front. Around 48/50mm is normal, if you're getting a lot less then you are going to need one with a longer spindle and the other side should hopefully come right then too.
What chainline are you getting on the drive side? This is measured from the centre of the middle chainring to the centre of the frame if you are running a triple on the front. Around 48/50mm is normal, if you're getting a lot less then you are going to need one with a longer spindle and the other side should hopefully come right then too.
SeeingisBelievingGTMuseum
Old School Grand Master
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Please tell us what crank set you are trying to mount on the 113 spindle. BB vs. frame has little to do with it. BB spindle length needs to match what the crank manufacturer recommends.
weeman_mtb
Retrobike Rider
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stevetait":vpb2rhfm said:Drystone has the answer....you can still fit a smaller 68mm BB into it but it needs to be a 73mm shell. The result would be crank arms very close or catching.
This does make a lot of sense, a quick ruler across the bottom bracket tube or whatever you call it (
) will soon tell if that's the case.SeeingisBelievingGTMuseum
Old School Grand Master
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stevetait":2qprld6p said:Drystone has the answer....you can still fit a smaller 68mm BB into it but it needs to be a 73mm shell. The result would be crank arms very close or catching.
Even if the cups go in the spindle is still 113mm in length regardless whether it's a 73 or 68mm wide BB shell. How will that solve anything. If it hits on a 113 width doesn't matter now does it. Bottom line is it will need to be longer to clear and work properly.
Threading a 68mm BB into a 73mm BB shell is not the right thing to do either and hugely poor advice. If it's a 68mm BB with a shoulder on one side it will throw the hole thing off one direction once installed....bad, bad advice. Is this to be a wall hanger or a rider?
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gm1230126":1ld1j2ar said:stevetait":1ld1j2ar said:Drystone has the answer....you can still fit a smaller 68mm BB into it but it needs to be a 73mm shell. The result would be crank arms very close or catching.
Even if the cups go in the spindle is still 113mm in length regardless whether it's a 73 or 68mm wide BB shell. How will that solve anything. If it hits on a 113 width doesn't matter now does it. Bottom line is it will need to be longer to clear and work properly.
Threading a 68mm BB into a 73mm BB shell is not the right thing to do either and hugely poor advice. If it's a 68mm BB with a shoulder on one side it will throw the hole thing off one direction once installed....bad, bad advice. Is this to be a wall hanger or a rider?
Just to clarify on this. When I suggested measuring the BB shell, I suspected that it would be a 73mm BB tube as was usual for GT frames back then.
Attempting to install a 68mm BB into a frame designed for a 73mm BB is a bad idea and certainly not something I'd ever or have ever recommended.
I think the fact that the OP stated that the non drive side crank was closer/too close to the stay gives away at least that part of the problem.
A 68mm BB in a 73mm BB tube will not centre the BB spindle correctly as the spindle will be about 5mm off centre due to the difference in BB shell widths. ie 73 - 68 = 5mm.
Now it may be that the BB spindle is also too short. Octalink BBs commonly come in 113mm, 118mm and 121mm lengths. You can also find them in 126mm too. However 113mm and 118mm do appear to be the most popular.
Next time I'll be try to be less succinct and put more detail in my first response...
