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  1. #1
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    Shimano BB shell fail...causes?

    Few weeks ago I swapped out the shot stock bearings in my Shimano cups with Enduro bearings. Installation was straight forward and up until yesterday I had about 4 or so hours of ride time on the setup. During a ride yesterday I heard a little creaking coming from the crank area. Nothing crazy. No play in the cranks or anything obviously out of place. About half way through the ride I was attempting a steep/short climb when the chain popped twice under power. Initial inspection showed the chain had lost quite a bit of tension. At first I thought maybe my tensioners or axle loosened up and the wheel slid forward in the dropouts but that wasn't the case. I could wiggle the crankarms and see the drive side cup moving enough to cause the chain to lose tension.

    Finally got home for the tear down. Removed the crankset and the cup came off with the driveside crankarm/spindle. Left side cup was no longer snug either but it came out in one piece.

    So what went wrong here? Installation of the cups into the frame was done the same way I have done it many many times before...make sure threads are clean, apply a lube of some sort to the threads, and tighten until snug. The only difference this time around was I used anti-seize instead of my usual Park lube. At first I thought it was the move to anti-seize caused the cups to loosen but after some research it looks like that is a common thread lube for the bb. I'm baffled as to what happened...and still working on getting what is left of the shell out of the frame without damaging the threads.

    Second spacer fell on floor before I took pic:


    Both spacers that were on there before:
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  2. #2
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    ... and if we just ...

    Quote Originally Posted by A1an View Post
    Few weeks ago I swapped out the shot stock bearings in my Shimano cups with Enduro bearings. Installation was straight forward and up until yesterday I had about 4 or so hours of ride time on the setup. During a ride yesterday I heard a little creaking coming from the crank area. Nothing crazy. No play in the cranks or anything obviously out of place. About half way through the ride I was attempting a steep/short climb when the chain popped twice under power. Initial inspection showed the chain had lost quite a bit of tension. At first I thought maybe my tensioners or axle loosened up and the wheel slid forward in the dropouts but that wasn't the case. I could wiggle the crankarms and see the drive side cup moving enough to cause the chain to lose tension.

    Finally got home for the tear down. Removed the crankset and the cup came off with the driveside crankarm/spindle. Left side cup was no longer snug either but it came out in one piece.

    So what went wrong here? Installation of the cups into the frame was done the same way I have done it many many times before...make sure threads are clean, apply a lube of some sort to the threads, and tighten until snug. The only difference this time around was I used anti-seize instead of my usual Park lube. At first I thought it was the move to anti-seize caused the cups to loosen but after some research it looks like that is a common thread lube for the bb. I'm baffled as to what happened...and still working on getting what is left of the shell out of the frame without damaging the threads.

    Second spacer fell on floor before I took pic:


    Both spacers that were on there before:
    man thats horrible....that nobody responded

  3. #3
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  4. #4
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    you baked it in the oven too long...... you is stupid

  5. #5
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    Quote Originally Posted by darrinw2001 View Post
    you baked it in the oven too long...... you is stupid
    What the hell?

    Not much to say about it. Never heard of it happening before. From the looks of the grease and clean spot, assuming it didn't get dirty after the fact, it was already cracked and the small spot left finally gave up. I suppose a 68mm bottom bracket shell is worst case for thread engagement.
    When you say you tightened them snug - they should be quite tight - over 30 lbs on a 1 ft bar. I'm always surprised how tight they go on my torque wrench. The torque will help spread the load over more threads, less shearing action.

  6. #6
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    I can't type a response. I'm picking up my eyeballs off the desk.


    On a serious side
    I thought the Shim bb bearings were not supposed to be replaceable? I know you can do it, but I wonder if there's a reason like yours? Shim is notorious for being overly picky on how well things work. I just wonder if the stresses from the bearing replacement were just enough to cause a failure?

    Now, as for getting that thing our of your BB, I wish I had a great idea. The only thing I can come up with is a large type screw extractor.
    Lead by my Lefty............... right down the trail, no brakes.

  7. #7
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    Use a (very large) blind bearing puller (expandable type) to remove it. You should be able to rent something appropriate from an auto parts store. The idea would be to get it wedged in the broken portion of the cup, and turn it out. Since it's broken, it shouldn't have much hold in the bottom bracket shell.

  8. #8
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    The rest of the cup came out pretty easily. Sprayed it down with an upside down can of compressed air to cool it then went at it with a screw driver to unthread it.

    I don't think the bearing replacement itself caused this. Maybe if I over heated the cups to get them out it could have caused some issues with the alloy, but I didn't go that route. Bearings were removed using a socket and hammer then the Enduro bearings were pressed back in.
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  9. #9
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    How big are those spacers? Might just be an illusion but they look huge.

    Never seen that happen before and probably never will again. How did you install the bearings? How tight when you installed the cups?

  10. #10
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    Those are the normal spacers that come with the bb from Shimano. Two on the drive side and one on the other for 68mm.

    Old bearing on the drive side came out fairly easily with a socket and couple smacks from a hammer. Left side was a little more challenging du to the shape of the cup. New bearings pressed in with a bench vice using the old bearing to keep the load on the outside race of the new one. Pretty straight forward procedure.

    Some folks have heated the cups to remove the old bearings then tap in new Enduro bearings after they have been in the freezer a while. Enduro also sells a tool.
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  11. #11
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    I've pressed Enduro bearings into several different Shimano BBs with lots of miles and zero issues. I don't think the problem is with the use of the bearings.

  12. #12
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    I had one of the Shimano cups crack like that due to my bottom bracket shell face being really out of square, the LBS tech just cranked down on it to close up the uneven gap rather than get out the facing tool and do it right. Mine cracked a bit closer to where the cup meets the face of the bb shell, about in the middle of the spacer(73mm shell). The entire crankset was brand new and still had the original Shimano bearings.

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