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Thread: How smooth rolling should newly installed crankset/BB be?

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    Default How smooth rolling should newly installed crankset/BB be?

    Just installed a new BB (Shimano DA9100 BSA) and new crankset (DA9100), greased and tightened according to specs etc.

    I tightened the cap by hand and stopped at pretty much the first resistance (specs says 0.7-1.5nm). Now when I spin the cranks by hand I can hear mild "resisting sound" and the sound is more noticeable if I spin it harder. By hand feel, I don't feel any obvious point of resistance during rotations, but the whole revolution is not exactly silent and free spinning.

    Another detail I notice is that the preload cap is barely flush with the left crank arm, protrudes a little from the opening. Is this normal?
     

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    Default Re: How smooth rolling should newly installed crankset/BB be?

    Although I don't understand all the details, resistance under load is very different than resistance while cranking by hand in the work stand. Just puttering around in the back of my LBS and hand spinning cranks (no chain on) that have been properly installed by an expert mechanic (all three major brands), I'm surprised how much resistance there is. On the other hand, my beaten to death SRAM GXP bottom bracket spins relatively easily by hand after the end of a gritty cross season.
    Lou D'Amelio
    Bucks County PA

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    Default Re: How smooth rolling should newly installed crankset/BB be?

    Not a bike mechanic, but I would judge the resistance after one ride and not in the stand.
    The better the seals, the higher the resistance it seems sometimes.
    I have the same with the cap not being flush, but mix and match parts often.
    When I once lost the cap I just preloaded with wood clamps, just don't overdo it.
     

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    Default Re: How smooth rolling should newly installed crankset/BB be?

    Lots of questions. Is it a press in or threaded bb. Has the frame been faced, all paint removed. If pressed in did you use cup guides of correct size. If threaded were cups torques to spec. Are all o-rings or seals on drive and non-drive side of crankset. Can you use a torque wrench for the preload cap.My procedure is to over tighten the cap by hand, losen the cap to where play in the left crank arm can be felt. Then if it is a new bb set torque wrench to 1nm. and tighten. It is my experience that Shimano bb will spin significantly better after 5-10 hours of use.
     

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    Default Re: How smooth rolling should newly installed crankset/BB be?

    Here's my empirical data set = 1 observation:

    I just recently had the Campy BB replaced on my Sachs for the first time since I received it new in 2016. Something had been starting to make a conspicuous and palpable clicking noise within the past ~3-4 months, and I brought it to the LBS for diagnosis/cure. I has suspected it was an issue w/ the cups/bearings, so wasn't at all surprised when they said replacement was their prescription.

    What did surprise me was how much of a difference it made to the experience of riding the bike!
    Slick sweet super-smooth spinny-spinny goodness, OMG! Why did I wait so long?


    Quote Originally Posted by amaro View Post
    Another detail I notice is that the preload cap is barely flush with the left crank arm, protrudes a little from the opening. Is this normal?
    When I had a Shimano Ultegra 6700 crankset on my Strong, I would pull it and re-install it regularly (S&S-coupled bike, so packed and traveled with several times a year). In all that time it never protruded from the opening, was always flush if not countersunk.
     

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    Default Re: How smooth rolling should newly installed crankset/BB be?

    I have an Ultegra bb in a bike that is like new after at least 7-8 years.
    Those things are bombproof.
     

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    Default Re: How smooth rolling should newly installed crankset/BB be?

    Quote Originally Posted by SteveP View Post
    I have an Ultegra bb in a bike that is like new after at least 7-8 years.
    Those things are bombproof.
    Have you ridden the bike?
     

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    Default Re: How smooth rolling should newly installed crankset/BB be?

    Quick experiment:

    Let's say your "rough" BB is causing you to have to continuously exert 50 grams at the pedal spindle to move the 175mm crank around at 90 rpm. Unless you have a horribly bad BB, 50 g is IMO a huge amount - e.g. the Cilf bar I happen to have on hand "weighs" 68 g.

    HP = Torque x RPM / 5252 TQ = ft lbs

    1 HP = 745.7 Watts

    Power (Watts) = TQ x (90 x 745.7 / 5252 )

    TQ = 50 g x 175 mm x ( 1 in / 25.4mm ) x ( 1 ft / 12 in ) x ( 1 lb / 453.6 g ) = 0.0633 ft lbs

    Power used due to bad BB = ( 90 x 745.7 x 0.0633 ) / 5252 = 0.81 Watts

    It's up to you do decide if this is a significant loss or not. I don't think it is.

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    Default Re: How smooth rolling should newly installed crankset/BB be?

    Yeah, they donít spin like youíd expect - but as others have said it doesnít matter.

    One thing to watch for though is how you look for movement. I realised recently that I think Iíve been over tightening them for a decade+. My procedure was to tighten the cap and wiggle the crank until play was gone - but obviously the NDS crank doesnít have its bolts tightened so you are going to get a little movement if you grab the pedal and shake it - what you are looking for is lateral movement at the BB end. If you stop the crank moving at all youíve made it a little tight.

    They spin a little more freely if you stop at the no horizontal movement point.
     

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    Default Re: How smooth rolling should newly installed crankset/BB be?

    Quote Originally Posted by twowheels View Post
    Have you ridden the bike?
    If I rode the bike stuff would wear out and I would have to replace.. makes no sense really.

    Both Times have them.. every year or 2 I take the crank arms off and they are really spot on.
    Note ... The white Time has been my gravel bike until recently... has gotten pretty gravelly from time to time..
    After one notable gravel ride ( with TT and BeWheels ) 100 k in pouring rain I have to replace everything on the bike except the bb...
    chain, cassette, headset, rear der... cables of course... the bike was hatcheted.
    TT refused to cover my repairs to show what a mean man he really is...
    Funny day... we started the ride under ominous skies... it literally started pouring 5 minutes in...
    I'm looking at Josh... with a " What do you think ? The cars are right there .. like right there...it's going to pour all day you know?" look on my face.
    His look back was... It's only 62 miles so shut up you baby? Still he refused to cover my repairs!

    BB perfect.
     

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    Default Re: How smooth rolling should newly installed crankset/BB be?

    Thanks everyone for your input. The cranks do turn lighter now with more spins, the only potential concern is that whether the preload cap will stay in place as it does protrudes a tiny little bit from the axle opening.
     

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