Author Topic: Bottom bracket replacement - 118 vs 110  (Read 2959 times)

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Offline esassaman

Bottom bracket replacement - 118 vs 110
« on: May 20, 2012, 10:35:26 pm »
Got a bad bottom bracket (now that I have it out), an old square-taper Shimano LP20, 118mm wide. I happen to have an old LP26 (from a double chainring RSX setup insted of a triple RSX like mine) that is 110mm wide and I just wanted to confirm that this will not work. I think the pedals may actually scrape against the bottom bracket if I put them back on, I'm not sure. Darn it! Yet another trip to the LBS. I assume it's pretty darn important to replace your BB with one the same exact spindle width, right?

Offline DaveB

Re: Bottom bracket replacement - 118 vs 110
« Reply #1 on: May 21, 2012, 07:55:53 am »
While an exact length match may not be necessary (you could probably use a 120 mm or possibly a 116 mm spindle for example) the 8 mm mismatch in your case is very likely to have the chainrings hitting the chainstays.  Also, not all spindles are symetrical so an overall length change may not be evenly distributed on both sides.   

Offline dkoloko

Re: Bottom bracket replacement - 118 vs 110
« Reply #2 on: May 21, 2012, 02:13:53 pm »
Gear Guru Berto advises that a double BB will work 80 percent of time for triple crankset. You must try to see. If anything hits frame, I suspect it will be inner chainring, not pedals.

Offline RussSeaton

Re: Bottom bracket replacement - 118 vs 110
« Reply #3 on: May 21, 2012, 03:18:33 pm »
When replacing bottom brackets I try to get one as short as possible while not having the inner chainring hit the chainstays.  And another thing to consider is whether the inner cage of the front derailleur will hit the seattube if you adjust it to shift onto the inner chainring.  If the bottom bracket is too short the front derailleur just won't be able to shift to the inner chainring.  Several things to worry about.  Really the only thing you can do is try the shorter bottom bracket to see if it will work.

Offline esassaman

Re: Bottom bracket replacement - 118 vs 110
« Reply #4 on: May 21, 2012, 08:27:41 pm »
Thanks everyone. After further research I realized the spare BB I have is really old and pretty low quality, so I decided to stick with the exact same size and upgrade to a new Shimano UN55. Turns out that bottom brackets in my size are still common, so I picked one up at my LBS, it's installed, and awaiting a new chain, we'll see how it goes! Got three shiny new TA chainrings on the front and a new cassette, everything's lookin' good so far! Kinda wish I had a torque wrench after installing the cranks, I understand you don't want to torque them down too hard or the aluminum may split on the cranks. Ever hear of that happening?

Offline DaveB

Re: Bottom bracket replacement - 118 vs 110
« Reply #5 on: May 22, 2012, 08:01:44 pm »
Kinda wish I had a torque wrench after installing the cranks, I understand you don't want to torque them down too hard or the aluminum may split on the cranks. Ever hear of that happening?
The main problem with square taper cranks isn't torquing them too much, it's not torquing them enough.  Too little torque and they loosen on the spindle, the square hole gets distorted and they are ruined. 

The recommended torque is 300 - 400 inch-pounds which is WAY more than you think and well beyond what is done with the usual short ratchet.  If you can borrow a torque wrench or get to a bike shop that has one it's well worth the bother.   

BTW, once they are torqued to spec DO NOT retorque them periodically.  Set them once and leave them alone until you have to remove them completely.  Periodically retorquing will "chase" the crank up the taper and that's what eventually can split them.   

Offline esassaman

Re: Bottom bracket replacement - 118 vs 110
« Reply #6 on: May 22, 2012, 10:00:40 pm »
Hey any excuse for new tools! I need a torque wrench now! Woohoo! Thanks for the advice :)