UN70 problems

Had the same issue recently, and as I hate anything which is "threaded plastic" on my bikes I removed the cup (putting a big washer next to the inner (closer to the center of BB) lip of the cup and tapping it gently freed it), and replaced it with a steel one from the UN51-52-53 series (UN54 NDS cup is also plastic I think) which fits tightly and nicely.

DISCLAIMER: I did try UN55 alu cups and they are a loose, bad fit. I'm also not sure that any newly made plastic cup from Shimano budget BBs as UN26 and the likes, would fit, never did that. Earlier UN5x series can be had for cheap monies too, even a used/dead one will do as you only need the quite strong steel NDS cup which will (if not rusted/damaged) serve you for ages again for sure.

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Thanks

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Not sure a un70 should have a plastic cup anyway, maybe it was an ill fitting replacement and was threadlocked on? As mentioned, keep your eye out in the sale threads for a shot BB, maybe even ask in your lbs?

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ishaw":2ai533zb said:

Not sure a un70 should have a plastic cup anyway, maybe it was an ill fitting replacement and was threadlocked on? As mentioned, keep your eye out in the sale threads for a shot BB, maybe even ask in your lbs?

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UN70 BBs as far as I know used solid axles and plastic NDS cups, the DS cup was alu. Both cups became alloy in the UN71 series as well as the axle turned hollow making it the best Shimano sq. taper BB ever in my opinion, given the so many sizes it was offered in, and was piped only by the UN90 ones which were made in limited (for low profile cranks) sizes anyway.

UN73 was a presumably manufacturing-cost effective part- made of as a steel (forged from the housing or rather it seemed)/plastic cup hybrid (hollow axle still present, though), then it all went downhill as it was stopped and replaced by the UN55 BBs (nothing fancy anymore).

Got 2 silky smooth UN70s, at least 25 or more years old, definitely worth saving them. They don't make them like they did anymore, built to last and very durable.

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Yeah it's still silky smooth which is why I don't want to write it off just yet. Just need to get that plastic cup off somehow without destroying it!
Kes

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I had a simiar issue once. Stick the BB back in the frame using the stuck cup only. Then you'll need the applince of science, namely a hammer. Somewhere between a tap and a wallop on the spindle will be required to shoot the BB out of the stuck cup. If you feel happier, bit of a squirting/soaking of plusgas before hand will ease matters along.

I think I have a spare cup that you can have, I'll go digging.

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I'll try the hammer method tomorrow thanks for that
Kes

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How did this end?

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Sorry Tad I've been too busy to have a go at it yet but I've been dripping penetrating oil into the gap between the bb and cup every night.
Hopefully it'll shift when I do give it a whack!
Kes

A big basin of hot and very soapy water.

Being plastic nothing likely rusted to itself so it must be something else holding it on and given its a bb, thats got to be oily gunk.
Solution, clean the gunk away

Hold the bb cup and wiggle the main body while pulling at it.