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Old 04-05-13, 05:34 PM   #1
jenrick
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Worth going to another shop? GXP BB question

I'm in the process of upgrading my road bike, and I ran into some great deals on SRAM stuff lately. I was able to get a Red GXP crank for a good price, but to put it in I'd needed to swap out the through spindle type my bike currently had for a GXP BB. I don't have a GXP BB tool, so I figured I'd take it to the LBS to have the old one removed, the threads chased, frame faced, and the new BB installed.

The old BB was frozen in place and took the mech about 30 minutes to get free, which IMO was worth the $18 I paid for the BB install all by itself. The new GXP BB was installed with just a dab of grease on the frame threads. The threads were not chased or the frame faced. Now in their defense I just asked for the new BB to be installed, I assumed that this would be included. Anyway the new BB was installed, along with the cranks. Watching him install the cranks he also didn't grease the shaft SRAM recommends, and torque wrench was never involved in the installation of the BB or cranks. The cranks now have a noticeable (at least when turning by hand) stiff spot at about 12 oclock on the drive side. Trying to spin the cranks by hand results in about 1-1.25 revolutions before they stop. My old cranks would do quiet a few more, and were butter smooth throughout the whole revolution.

I can easily pull the crank and grease it, and I've can torque the cranks per spec no problem. Assuming that pulling the crank and greasing it solves the problem, would it be worth it to take the bike into another shop that I know will thread and face the BB to have this done, and have the BB re-installed and torqued to spec?

-Jenrick
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Old 04-05-13, 07:00 PM   #2
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Well, *something's* going on with it, if it's got a stiff spot in it's rotation, and these external cup jobbies *are* sensitive to the BB surfaces (and threads) being as parallel as possible, so I probably would bother to have the threads chased and the surfaces faced.
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Old 04-05-13, 07:38 PM   #3
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Most frames these days are faced as part of the manufacturing process.
You didn't say what exact frame it was, but unless it's one where a tapped, faced bottom bracket shell is subsequently heated very hot, there should be no expectation of misalignment.

The spindle should have had a wipe of grease, and to the extent that the bb threads were seriously under-greased, you could just shorten the service interval before the next R&R comes around, particularly if the cups were to actually start creaking from being under-torqued.

Also, is there an aluminum-against-steel interface involved with the bb theads? That would argue for using a good grease or possibly some anti-seize in the mix, but even a very simple grease will prevent corrosion for some time.

You'd think the mechanic would be more conscientious when customers were watching, but I've also probably missed lubing some spindles over the years.

I would re-visit the spin-test after 100 miles. Seals in particular can take some time to break in.
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Old 04-09-13, 09:00 AM   #4
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Quick update, after taking it out for about 20-30 miles on a couple of short rides to test the shifting, brakes, etc. they spin fine now. I'm guessing there was a spot of grease or a high spot in the bearing. Either way they work great now.

-Jenrick
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