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shimming tapered BBs? (the tapers, not cups)
 

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walter
Joined: 11 Jan 2004
Posts: 4391
Location: metro-motown-area

8/6/13 7:40 AM

shimming tapered BBs? (the tapers, not cups)

have a set of older campy cranks that are coming in a bit far and hitting chainstays on a bike i'm building using a 115mm spindle. the crank tapers are in good shape, but it's a combination of old cranks with narrow Q and newer chainstays that are a bit phatter.

i need the cranks to sit ~3mm out further on each side to clear the chainstays. i could get a 120mm ISO taper phil BB, but that'll set me back close to $200 all in (including spindle, cups, and tool).

i've heard that shimming the BB tapers with thin aluminum stock, like coke-can stuff, is an option. wondering if anyone on the forum as tried that successfully and can share your experience.

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Sparky
Joined: 08 Dec 2003
Posts: 19068
Location: PDX

8/6/13 9:34 AM

Yes, done the soda can shim, just do not over tighten it. You may think in your mind it needs to be tighter with the shim, it is not true.

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walter
Joined: 11 Jan 2004
Posts: 4391
Location: metro-motown-area

8/6/13 9:58 AM

my impulse is to just torque to spec and leave it

regardless of shimmed or not. ~35nm i think is the normal spec for tapered cranks.

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ErikS
Joined: 19 May 2005
Posts: 8337
Location: Slowing boiling over in the steamy south, Global Warming is real

8/6/13 10:25 AM

it won't last.

The shim will be soft and wear very fast.

What BB is it, you may be able to order just a different spindle. The odd option is to look at the clearance on the non-drive side. You might be able to just flip the spindle around and gain the clearance you need on the drive side. Just some ideas to try, though I suspect you have tried and/or already thought of those tricks.

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Sparky
Joined: 08 Dec 2003
Posts: 19068
Location: PDX

8/6/13 10:32 AM

"The shim will be soft and wear very fast. "


You'd be surprised, but you should check for that frequently to be sure.

Sometimes an off centered situation will have the arm closer on the non drive side, but works in function.
I have used spacers on the drive side of the BB if shouldered. [cast shoulder like Shimano Sq taper BB] Or even used a non shouldered old style that allows you to float the BB in the shell. I have a Ti sealed bearing BB like this for 20 years in use. Lock rings on both cups.

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walter
Joined: 11 Jan 2004
Posts: 4391
Location: metro-motown-area

8/6/13 11:27 AM

interesting

the spacer is in compression between the BB and crank...what would cause any wear, assuming it's installed and torqued to spec?

longer BB is available from phil wood, but priced for royalty...$200 bones for spindle, cups, and proprietary tool.

if this doesnt work out, i'll be fitting a sugino super-mighty crank with same ISO taper as campy but fits better with respect to the chainstay clearance. but i gotta give the campy option an honest try...it's for a steel merckx for chrissake! ;-)

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Sparky
Joined: 08 Dec 2003
Posts: 19068
Location: PDX

8/6/13 1:03 PM

"the spacer is in compression between the BB and crank...what would cause any wear, assuming it's installed and torqued to spec? "


Soft metal, compression, gets thinner, it can get loose.
Not overnight IMO. 2-3 times a season, maybe...

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walter
Joined: 11 Jan 2004
Posts: 4391
Location: metro-motown-area

8/6/13 1:05 PM

so a harder alloy, no issues

maybe a call to mcmaster is in order!

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Anthony Smith
Joined: 12 Jan 2004
Posts: 848
Location: Ohio

8/7/13 2:41 PM

shims

I have shimmed tapers with pop can stock and red lock tite to make damaged/rounded out arms work--without difficulty and the repair seems to last for years and years.

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