Bicycle Mechanics - Barnett's got it wrong on BB installs? (long)

Well, probably not since I'm sure they know more about wrenching on bikes than a relative newbie like myself, but I just can't understand their thinking on installing Shimano cartridge BB's. I'll get to my Barnett's question in a bit, but first some background on why I'm messing with the BB on my MTB in the first place.

I've been having a problem with something knocking and creaking in the front of the drivetrain, which I can barely feel in the pedals and which happens in exactly the same spot in the pedal stroke. I repacked and readjusted the pedal bearings but that didn't fix it. I swapped to an old spare set of pedals that originally came on my roadie and which probably didn't have more than 20 miles on them (cheap pair of toe clip pedals), but that didn't fix it either. I tried pulling and reinstalling the cranks, but no luck with that either. Tried the same but this time greasing the tapers (I know, I know...), but no joy. The cranks looked fine and the holes where the taper mates to the cranks looked okay.

So this left me with the bottom bracket. The reason I didn't look at that sooner is that I had it replaced about 300 miles ago by a good shop and it should be okay. The spindle turns smoothly and there's no slop. Nonetheless, I decided to remove the BB and reinstall it with some Teflon tape to maybe stop the creaking, and this is where my Barnett's question comes in.

If you look at Chapter 10 of Barnett's (Cartridge-Bearing Bottom Brackets) in the section that deals with installing Shimano cartridge BB, it says to "Install the main body fully in the correct side and snug gently" and then to "Secure the adapter ring to 260-350 in-lbs." WTF?! The BB body in my case threads in from the drive side and the adapter ring installs on the left side. The BB body threads in on the drive side of the crank, and if I just "snug gently" then isn't that going to cause lots of creaking since that's the side that's under the most load and shouldn't it be torqued down pretty well? And just how in the world am I supposed to torque the flimsy plastic adapter ring on the non-drive side to 260-350 in-lbs (22-29 ft-lbs)? If these instructions were reversed it would make perfect sense to me, but as it is I am confused and now have to go to the LBS and hope they have another adapter ring to replace the one I broke the flange off of trying to torque it to the spec given by Barnett's. The manual even says you can back the BB body out of the shell by about 1 mm to correct the chainline and then tighten the adapter ring -- again I ask; WTF?!

:confused:

You encountered the same thing I did when I was installing a Shimano UN-73 BB on my Kirk. The UN-73 has a plastic adapter ring that cannot possibly stand up under 25~35 ft Lbs of torque. What I did was install the drive side moderately snug, install the adapter ring until snug, tightened the drive side very snug, tightened the adapter ring until very snug, then torqued the driveside to recommended specs.

I did use grease and teflon tape on both sides. No problems after 500 miles. I cannot understand the directions in Barnett's as accomplishing what's needed to keep the BB in place and doing it's job. I wish someone could enlighten me on why the BB is installed in this manner.

However, I'm through screwing around with cheap-s**t BB's and have a Phil Wood on order.

I think the reason it's threaded that way is to keep the BB from coming loose during normal riding. By making one side right hand threads and the other left hand threads, it'll always "tighten" when the cranks are turned forward....make sense?

As far as the torque specs, it just sounds like someone overlooked a mistake. Has anyone tried contacting Barnett's about this?

This is a very good question, BTW.

My question wasn't about the threading, as it was about the 'method' of installing and securing the BB. I can't see how the BB can really be secure if one side is merely "snugged gently", and the other side tightned. I wonder if they are talking about a different type of BB?

I guess if you tighten the body without the adapter ring on the other side, it would never reach those torque specs because there is nothing on the other side the load the "fastener." By having an adapter ring, both sides would load against each other and create an interference fit on the threads, allowing for the torque spec.

However, I do agree with you ... the plastic cap should not be torqued to such high forces, and since your method works proves that there may have been an editting error on the part of Barnett's.

On the third paragraph, it mentions that you should install the main body completely before securing the lockring. :confused:

I guess it makes a difference whether or not your BB has the 'shoulders' on the outside that tighten against the BB shell or are the ones that are designed to thread completely into the shell and tighten against itself. In my case, the Shimano UN-53 BB has the shoulders and tightens against the BB shell. Regardless of that, it's unlikely that a plastic retainer or adapter rings of whatever design could be tightened to the spec given by Barnett's without being damaged. Luckily my LBS had a replacement part in the spare parts box, so this learning experience didn't end up costing me a new BB.

I have to admit that I do not usually torque the BB cups.
I install the drive side cartridge most of the way and then install the nondrive cup for about half of its threads. This is because I have found if you insert the cartridge all the way the non drive cup does not want to thread in. Once I have the non drive cup started, I tighten the drive side cart, TIGHT. Then I tighten up the non drive cup. I use grease and teflon and also grease the inside of the nondrive cup.

My installation procedure is identical to the Rev's. There's really no other practical way of installing these things.....

Shimano, rather than Barnett's, may be the eye of the storm on this technical glitch. I'll have to check a cut-sheet at home for the UN-72, but I seem to recall the the UN-52 also uses the plastic adjusting ring and if you look at Shimano's cut-sheet you'll see they call for even higher torque values than what you'll find in Barnett's...

http://bike.shimano.com/product_images/BB/si_images/BB_UN52_SI.pdf

Although it doesn't excuse Barnett's for not coming up with tailored guidance, for some strange reason Park Tool's instructions for installation of Shimano's plastic BB adjusting ring/cup also calls for 360in lbs of torque.

http://www.parktool.com/repair_help/FAQcartdg.shtml

When I've encountered them my installation methods are consistent with what other mechanics have already mentioned -- tribal knowledge rules when manuals and tech data fails.

Regards,
Mark

As far as torquing B/B cups......I've always tightened them by feel, using my tribal instinct. Over the years, never encountered any problems. I use a torque wrench on crank bolts only.

Using the proper tools and techniques those plastic rings can be torqued to the factory spec. I have torqued them in the past but most just tighten them 'till they are tight.

Originally posted by miamijim
Using the proper tools and techniques those plastic rings can be torqued to the factory spec. I have torqued them in the past but most just tighten them 'till they are tight.

What tools would that be? I've got the Park Shimano BB tool, 3/8" ratchet, torque wrench and still can't the get the plastic adapter rings to specs with them starting to deform.

I thing the Barnett manual installation instructions refer to BB's that have adjustable cups on both sides. Not cups with shoulders.