Which bottom bracket length is right?

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NoIdea
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Which bottom bracket length is right?

Post by NoIdea »

I've just had mine taken out and so I'm shopping for a replacement...
No markings are engraved on mine, it looks like there might once have been a sticker so I have no idea of brand or model, though I suspect it is an old Shimano.

This is the old one,

Image

It's 68mm width and English thread.

I have measured the spindle width with a digital caliper and I get a length of 111.5mm :?

My LBS stocks VP brand VP-BC73 BB's and looking at the range online the nearest sizes are either 110.5mm or 113mm.

So which should go for, the 110.5 or the 113mm?
I'm guessing/hoping that either are close enough that they won't really affect the shifting?

JFYI
Crankset is Shimano FC-4400 175mm 440014403 S2
Front Derailleur is Shimano 105 FD-5501
The bike has twin front chain ring.
2006 Specialized Allez Sport 18 speed with various upgrades.
Samuel D
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Re: Which bottom bracket length is right?

Post by Samuel D »

Shimano says to go with a 110 mm bottom bracket for the double. See specifications in this PDF.
nsew
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Re: Which bottom bracket length is right?

Post by nsew »

It’s a Shimano crank so go with the recommended Shimano bottom bracket. Source the 110mm UN54. Have you got those bottom bracket shell threads thoroughly cleaned up and a good anti seize paste in there? PS, enjoyed the removal thread! Congrats.
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cycleruk
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Re: Which bottom bracket length is right?

Post by cycleruk »

Would it not be as simple as just measuring over the ends of the spindle. ?
You'll never know if you don't try it.
Samuel D
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Re: Which bottom bracket length is right?

Post by Samuel D »

cycleruk wrote:Would it not be as simple as just measuring over the ends of the spindle. ?

As he explains, he did that and got 111.5 mm: smack in the middle of the two closest sizes.

Nominal length and actual length can vary a little. Often actual variations of a millimetre or two don’t make much difference anyway, but you need to check clearances with the frame, etc.
nsew
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Re: Which bottom bracket length is right?

Post by nsew »

All things being equal the difference is effectively half. 3mm difference = 1.5mm on each side. So the effective inward movement of the cranks between a 111.5mm spindle and 110mm spindle is 0.75mm each side. Not enough to throw your previous chain line off. Use the your new bb to chase the bb shell threads a few times without fully tightening, you’ll know when the threads are cleaned up enough.
Samuel D
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Re: Which bottom bracket length is right?

Post by Samuel D »

Many spindles aren’t symmetrical. From memory, there is barely any difference on the right-hand side between the Shimano 110 mm and 113 mm models: something like half a millimetre. The rest is on the left side.

I think a wire brush would do a better job of cleaning the threads in the shell.
Brucey
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Re: Which bottom bracket length is right?

Post by Brucey »

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nsew
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Re: Which bottom bracket length is right?

Post by nsew »

Samuel D wrote:Many spindles aren’t symmetrical. From memory, there is barely any difference on the right-hand side between the Shimano 110 mm and 113 mm models: something like half a millimetre. The rest is on the left side.

I think a wire brush would do a better job of cleaning the threads in the shell.


You’re correct I’ve only been messing around with 122.5 and 127 for years now. however the OP should not be considering a 113mm bb unless something is off. I use rags and degreaser and don’t stop until the shell is spotless and dry. Then grease/anti seize the shell and “chase” a few times with the new greased bb to confirm all is as it should be.
nsew
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Re: Which bottom bracket length is right?

Post by nsew »

There is variance in measured spindle lengths with Shimano bottom brackets. Of the five I have here they measure .50 - 1.0mm over what is stated. I don’t have the 110mm but the 113mm measures 114mm. A 118mm measures 118.6mm. The Stronglights I have come in pretty close but always above. So I imagine a 110mm will measure up between 110.5 and 111.0mm. Saturday night fun and games.
nsew
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Re: Which bottom bracket length is right?

Post by nsew »

The Shimano 110mm bottom bracket is asymmetric and shares the same drive side length as the symmetric 107mm. The 113mm is symmetric and would therefore push out each crank by 1.5mm over the Shimano recommended 110mm. Assuming the cranks haven’t been off and on multiple times and the tapers deformed then UN5X 110mm is the way to go.
nsew
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Re: Which bottom bracket length is right?

Post by nsew »

Samuel D wrote:Many spindles aren’t symmetrical. From memory, there is barely any difference on the right-hand side between the Shimano 110 mm and 113 mm models: something like half a millimetre. The rest is on the left side.

I think a wire brush would do a better job of cleaning the threads in the shell.


Taking a break from the mauling down under. A wire brush to clean out aluminium bb threads? After more thought, the symmetric 113mm bottom bracket would add all of the 3mm difference onto the drive side - totally throwing out the OP’s chainline.
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Gattonero
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Re: Which bottom bracket length is right?

Post by Gattonero »

Samuel D wrote:
cycleruk wrote:Would it not be as simple as just measuring over the ends of the spindle. ?

As he explains, he did that and got 111.5 mm: smack in the middle of the two closest sizes.

Nominal length and actual length can vary a little. Often actual variations of a millimetre or two don’t make much difference anyway, but you need to check clearances with the frame, etc.


I can't see him saying that has actually measured the protruding spindle of both sides. He only says he's got 111.5mm and nothing much.
To check the measurements on both sides of the spindle is the easiest way, assuming you can get a correct measuring point.
In fact, this measurement should have been done before removing the bb unit from the frame. Right now, I'd clean the threads and screw back in (without tightening much at all!) the Bb unit then measure again the protruding spindle on both sides, using the edges of the BB shell as reference.
Also worth checking again the chainline and clearance of the rings to the frame: on small tubing frames you often go for the smaller size, on oversize tubing you go for the next size up (as you may have the FD touching the frame when shifting to the smallest ring)
It is by riding a bicycle that you learn the contours of a country best,
since you have to sweat up the hills and coast down them.
Thus you remember them as they actually are...
Brucey
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Re: Which bottom bracket length is right?

Post by Brucey »

see

https://forum.cyclinguk.org/viewtopic.php?f=5&t=105385

for actual measurements of UN55 bottom brackets.

BTW 113mm length not listed; I think I didn't have one to hand at the time.

cheers
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NoIdea
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Re: Which bottom bracket length is right?

Post by NoIdea »

Thanks for all the replies, I'm constantly amazed by how active this form is and how helpful everyone is! :D

Yes, I will clean the frame BB very well. My plan was to use WD40 and an old toothbrush. The shop has said that once I've cleaned it, if the threads need clearing then just to bring it back as he has a tap that will do it. The threads are in surprisingly good/clean shape though.
I will clean and test with the new BB before applying anti seize and torquing up.

I do have some proper anti-seize but I could just use silicon grease instead as I'm not sure what metals are present in my anti-seize paste. It's in a sample pot rather than the original container so I don't know what brand it is. It is a "Pure Nickel" type grease anit-seize so it has nickel, graphite and maybe even aluminium in it - would that be better, I have some copper slip spray also?

So you would all recommend staying with Shimano for the replacement BB?
My LBS said he once stocked the lower level Shimano BB's but had too many returns so has switch to VP for that level.

Just had a look on fleabay and can see there are UN25's, UN26's which I guess is as the original, and the ones the LBS had a high return rate on.
I have also found the UN55 110mm's on fleabay to, which is what I'll go with then. :D
2006 Specialized Allez Sport 18 speed with various upgrades.
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