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Bottom Bracket Replacement - Wrong Size?

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Bottom Bracket Replacement - Wrong Size?

Old 10-03-20, 04:42 AM
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Bottom Bracket Replacement - Wrong Size?

Hi Guys,

Just replacing my bottom bracket, had a Chain Haur CH52, and I'm trying to replace it with a Shimano BBUN55 (can't post pics or URLs so description below) but the Shimano feels WAY too tight... I've greased all the threads, but the originals I can pretty much hand tighten most of the way, but the Shimano I have to get a spanner on to get anywhere, to the point where it feels like I'm cross threading them. Is that normal or have I ordered the wrong size?

The CH52:
68x113L EN

The BBUN55:
<- LL113 ->
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Old 10-03-20, 05:57 AM
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The "BC" in each description says you have the same threading standard on each.

I assume you cleaned the shell out with a wire brush and rag before you greased it.

Sometimes a slight misalignment in the shell or cartridge will make tightening very difficult, but only at the end of the process. Are you having difficulty installing the cartridge before the "adjustable" ring goes in? Sometimes I see the opposite, where the cartridge goes in fine, then the ring is very tight. In that case, I'll loosen the cartridge a turn, see if that helps.

A well-equipped shop will have the taps to clean out the threads, and face the shell, if the problem persists.
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Old 10-03-20, 07:20 AM
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Yeah, gave the shell a clean out with a wire brush and some degreaser first, shame I have got a tap that big otherwise I would have given it a run through with that as well... The lefthand cup/adjuster went in fine after a bit of alignment, but the cartridge it's self turned a half to a full crank or so before tighting right up
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Old 10-03-20, 07:31 AM
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Make sure something like the screw holding the cable guide on the bottom of the shell isn't causing misalignment. I had a similar problem on a Koga with internal light wiring.

Does the DS cup have factory thread locker on it? Being such fine thread they have to be indexed and aligned closely. Did you try turning backward and feeling for the "drop" as the threads line up?
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Old 10-03-20, 08:23 AM
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Ive used a clean rag to try to pick up grit that can accumulate in the fine threads , I'd make super sure that the threads are as clean as you can. Don't forget to liberally grease everything after its nice and clean and hope you havent forced it when it shouldnt have been forced (cross threaded)
Don't know what to say more than the others have said.
good point on watching for the head of the cable guide sometimes being in the way.
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Old 10-04-20, 06:39 AM
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I encountered the same situation a few years ago. Old cups went in fine, another set of cups went in fine, but the Shimano cartridge tightened up quickly after a few threads. Re-tapping the shell solved the problem nicely.

Since you have removed the old one, you probably know that the cartridge has left-hand threads and are screwing it in CCW, right?.
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