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Discussion Starter · #1 ·
I have a GT 1991 with a Ti BB. One of the 6903-RS bearings went bad 3 months ago and I changed it with some cheap bearings I found on amazon. The squeaking started again not long after and has gotten worse ever since. It won't be long before it fails again. I ride 7-10 miles a day or so with half of it uphill, a chunk of it fairly steep. So there is some stress on the bottom bracket but I was not expecting it to be that bad. Should I go with higher quality bearings?
 

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Hi lb1R,
Others here know much more about bikes than I do, but as an industrial plant maintenance buyer, I can assure you there's a stunning quality range on bearings. The difference between a bottom tier bearing and a top tier bearing is like the difference between dollar tree and space shuttle. So my initial inclination is, yes, buy a better bearing. However, it bears noting (see what I did there?) that a bike's bottom bracket sustains negligible stress, as bearings go. The strongest most aggressive rider will put very little stress on that bearing compared to a powered application. So I can't help wondering if something else is going on. Although it seems unlikely, the first thought is maybe something isn't quite straight. Are your bearings parallel to each other, and thus perpendicular to the spindle? When new and freshly installed, is there any binding? Have you owned this bike since 1991?
 

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Magically Delicious
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Cheap bearings and cheap seals permitting water and dirt/dust leading to bearing contamination and a gritty tactile feel and sound. The situation can easily be further compromised by failing to incorporate some standard practices to add additional barriers to prevent contaminates from ever reaching those budget seals. Practices not commonly found in industrial settings.
 

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Discussion Starter · #4 ·
Have you owned this bike since 1991?
I have owned the bike for a little over a year. I built it starting with a 1991 GT Xizang used frame. When I first installed the bottom bracket, I made the mistake of over tightening the cup on one side, which messed up one of the bearing. I replaced the bearing and things were ok for a few months. Then a squeaking under harder pedaling developed, and the replaced bearing eventually completely fell apart. I replaced it and the exact same is going on. Out of the two bearings I got with the bottom bracket I got, the remaining one is still ok and the two bearings that failed are the new ones I got. So maybe I need to upgrade. I replaced the second failed one this evening with a cheap one. I'll see how long it lasts.

I am not 100% clear as to what is the proper way to install this kind of bottom bracket, that has the Ti spindle, a press fit bearing on each side, and aluminium cups. Even the slightest over tightening leads to the spindle not turning properly. I ended up very gently tightening it up by hand.

1943251
 

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The bearing is seated in aluminum cups? Could be squeak is coming from that interface?

My 91 ti bike needed plumber tape on cup threads to stop the squeak, it was aluminum ti interface that was problem.

Do the bearings you remove feel rough? Did you pop the seals and see that they’re greased?

Those super light custom bb are cool in the “I can’t believe they got that bad design to work” sort of way.

I’m with jbweld - if it’s actually the bearing I’d try a un51/un71.
 
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Evolutionsverlierer
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The bearing is seated in aluminum cups? Could be squeak is coming from that interface?

My 91 ti bike needed plumber tape on cup threads to stop the squeak, it was aluminum ti interface that was problem.

Do the bearings you remove feel rough? Did you pop the seals and see that they're greased?

Those super light custom bb are cool in the "I can't believe they got that bad design to work" sort of way.

I'm with jbweld - if it's actually the bearing I'd try a un51/un71.
Very good point there and you made me remember that with an old titanium bottom bracket from tune* they said to wrap the threads in a similar fashion.

*from a time when I had more money than sense.
 

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Discussion Starter · #10 ·
Does it look like this when it's out? (nevermind the numbers)
XiZang is a very cool bike!


-F
It kind of looks like that except that both cups have two pieces. The advantage is that this allowed me to adjust where the spindle sits laterally which I had to do. I went with a 73x112.5 but it seems a little wide and when centered, the shifting to the largest ring chain was not working. I ended up moving the spindle left by 2-3 mm and that solved the shifting problem. The big disadvantage is that it opens the door for over tightening and messing up the bearings. The large aluminum ring that sits on top of the black plastic cup in your picture is not easy to install and adjust. On my BB, there are very few threads to work with. I ended up just not using them.

I'd just get a Shimano un51 bb and be done with it. I think they're less than 30 bucks.
That's what I started with but the squeaking was immediate. I did not try the teflon tape though and moved to the Ti spindle and bearings which are very light.
As it is the bike weights a bit under 21lbs.

The bearing is seated in aluminum cups? Could be squeak is coming from that interface?

My 91 ti bike needed plumber tape on cup threads to stop the squeak, it was aluminum ti interface that was problem.

Do the bearings you remove feel rough? Did you pop the seals and see that they're greased?

Those super light custom bb are cool in the "I can't believe they got that bad design to work" sort of way.

I'm with jbweld - if it's actually the bearing I'd try a un51/un71.
The bearings are definitely the problem. The one I removed and changed yesterday felt very rough. I popped the seal and they were not greased. I don't think they were greased to start with. They were very cheap. I ordered some more expensive ones.
 

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EAT MORE GRIME
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It's Hambini time again

you first need to check how aligned the bottom bracket shell actually is. if it is off by the slightest, it can eat bearings.

go visit hambini site and dig into everything about bottom brackets

 

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Discussion Starter · #13 ·
If the Shimano bb was new and properly installed and you heard a squeak right away then I don't think the noise had anything to do with the bb.
It did not. It was the Ti / Al interface. I moved on to the Ti BB right away for the weight savings.

It's Hambini time again

you first need to check how aligned the bottom bracket shell actually is. if it is off by the slightest, it can eat bearings.

go visit hambini site and dig into everything about bottom brackets

Great channel. Thanks for the pointer.
 

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Professional Crastinator
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It kind of looks like that except that both cups have two pieces. The advantage is that this allowed me to adjust where the spindle sits laterally which I had to do. I went with a 73x112.5 but it seems a little wide and when centered, the shifting to the largest ring chain was not working. I ended up moving the spindle left by 2-3 mm and that solved the shifting problem. The big disadvantage is that it opens the door for over tightening and messing up the bearings. The large aluminum ring that sits on top of the black plastic cup in your picture is not easy to install and adjust. On my BB, there are very few threads to work with. I ended up just not using them.
...
So each side has a cup and a lock ring, and you left the lock ring(s) off? That would allow the cup to spin/move/loosen/tighten. Is there a chance that the spindle is in backwards? I think I remember ones that were 2-3mm shorter on one side. That would leave room for the lock ring(s).

-F
 

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Discussion Starter · #15 ·
So each side has a cup and a lock ring, and you left the lock ring(s) off? That would allow the cup to spin/move/loosen/tighten. Is there a chance that the spindle is in backwards? I think I remember ones that were 2-3mm shorter on one side. That would leave room for the lock ring(s).

-F
Here is a picture of the set up minus one of the two lockings. The locking here is broken which is why I took it off. It's made out of aluminium and it is not strong enough. Without the lockring, you are spot on, the cup tightened on its own and pushed on the bearing on the drive side, which created the noise and the rubbing. I am looking for a steel replacement lockring but so far no luck. The cups are the same size on both side.

Meanwhile, I changed to a standard Shimano sealed cartridge. I used some teflon tape but unfortunately, it wasn't long before the bottom bracket started squeaking. However, this time, the squeaking in not under hard pedaling but under normal pedaling. I'll try some agin-seize lubricant and see if this helps.

1943733
 

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... it wasn't long before the bottom bracket started squeaking.
Are you sure it's the bottom bracket?

Seat, Seatpost, Pedals, etc, etc?

My latest suspicious noise turned out to be the hanger for my Ortleib seat bag that creaked as it rocked in the saddle rails as I pedaled.

But if it's really the bearings moving in their housing, I've had good luck with Loctite 641.
 

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Discussion Starter · #18 ·
Are you sure it's the bottom bracket?

Seat, Seatpost, Pedals, etc, etc?

My latest suspicious noise turned out to be the hanger for my Ortleib seat bag that creaked as it rocked in the saddle rails as I pedaled.

But if it's really the bearings moving in their housing, I've had good luck with Loctite 641.
The seat creaks a bit too but sounds different. The seat bag creaked before I removed it. It is the BB for sure. Not sure yet if it is the internal Al/Ti threads contact or the cup lip against the BB shell or the bearing external shell against the cups' inner surface.
 

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Here is a picture of the set up minus one of the two lockings. The locking here is broken which is why I took it off. It's made out of aluminium and it is not strong enough. Without the lockring, you are spot on, the cup tightened on its own and pushed on the bearing on the drive side, which created the noise and the rubbing. I am looking for a steel replacement lockring but so far no luck. The cups are the same size on both side.

Meanwhile, I changed to a standard Shimano sealed cartridge. I used some teflon tape but unfortunately, it wasn't long before the bottom bracket started squeaking. However, this time, the squeaking in not under hard pedaling but under normal pedaling. I'll try some agin-seize lubricant and see if this helps.

View attachment 1943733
You can measure each end of the spindle to see if one is slightly longer. If it has a short end, I think it will work better on the drive side.
BOTH cups require a lock ring, or it will not maintain correct adjustment. "Correct adjustment" is pretty much hand tighten the cups, then hold them in place using the lock rings. That's it. If it's any tighter, then your bearings have an undue side load on them and will fail quickly since they are probably not intended for side loads. Some bearing are intended for side loads.

-F
 
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