When to Replace a Worn BB?

It's a Shimano cartridge BB installed in a 1992 Panasonic MTB Deore Lx, it still pedals smoothly, doesn't "grind" or click, and the gears shift seamlessly front and back. (Not sure of the model BB, but it's lasted 17 years. Shimano sure don't make them like they used to!)

I'm replacing the rest of the drive-chain with new parts, but I'm wary of fitting a new Shimano BB because of the rotten quality control plaguing their Singapore factory. One recent example I came across was a chap in the UK who had two brand new Shimano UN54 BBs go wonky. The shop fitted and replaced them both. Dodgy Shimano BBs are well known over here in SE Asia. Ask Trek about them. The problem is the Singapore factory QC. It may include the Japan factory too, I don't know. The parts we have to buy are made in Sg.

Why don't Shimano fire the Sg staff, this problem is not new, and it's time it was fixed, it's ruining their reputation.

The alternative BB is a VP made in Taiwan, which is gaining a better reputation than Shimano over here. And you find them factory fitted in many new quality bikes.

http://www.vpcomponents.com

Similar story with Shimano chains:
KMC are better http://www.kmcchain.com

And axles too:
"Tank" are better. http://www.tankcycle.com.tw/product_29.asp

However, my basic question:

How much play in a cartridge BB is too much?

My friendly LBS tested mine today, and said it was "okay really", but when he tested it on the granny ring he conceded it might be better changed.

Waggling the cranks with your hands you can both see and feel play in the yaw axis.

I measured it with the chain on the granny, and the left crank parallel to the chain-stay; the pedal end tip of the left crank moves 1.0 mm from side to side as you waggle the cranks. (It is wear on the bearings btw, not loose cups.)

Is this tolerable or too much in your opinion?

Please try this test on your BB and post the result here.
(You may be surprised. Often there's more play than you might imagine.)

did i honestly just read all that to come to the conclusion of replacing the worn bottom bracket when its worn :roll:

Why not do this test.

Take the worn Bottom bracket out, chop the casing open and see if the bearing are buggered. Conclude that they probably are and that since the casing keeping it all together is now buggered up you need to buy a new one.

Buy yourself a UN7x or 91 from ebay and be done with it.

Are you a politician? That's the most round about way of asking if your BB is knackered.

Any play in a cartridge BB means it's time for a new one.

How many people stand around talking about square taper BB's? :shock:

I'd have thought that the end of the market UN-54 is pitched at is not exactly in to caring, so how do they get a 'reputation'?

I'm hardly suprised that modern square taper BB's don't last 17 years, there must be a bean counter at Shimano that is simply furious the original ones were designed so well

I would agree that any play in the axle is too much play, but I for one thought your information was very interesting. I've always been pleased with Shimano bbs, but maybe they all came from Japan and I didn't know that the Singapore factory had a bad reputation.

I've never had an early 90s shimano bb, but if it has cartridge bearings then I'm not clear why you can't just fit new bearings and keep using it. Alternatively if it's not bothering you at the moment, you could just keep on with it, as it's not going to damage anything other than itself. Sooner or later it'll grind to a halt, but I expect it'll give you plenty of audible warning before it does.

But then again if you need to fit new cranks, you'll struggle to find any to fit onto that square taper axle!

Anthony":2rq5o53s said:

I've never had an early 90s shimano bb, but if it has cartridge bearings then I'm not clear why you can't just fit new bearings and keep using it.

Click to expand...

You can't replace the bearings in any of the early Shimano BBs. I think you can in some of the XTR and Dura Ace BBs in recent years though.

Anthony":2rq5o53s said:

But then again if you need to fit new cranks, you'll struggle to find any to fit onto that square taper axle!

Click to expand...

Middleburn still do square taper compatible cranks.

Well, in answer to the OP, if you are renewing the drive train, why not renew the BB as well. I have just done it on a '93 Saracen, one of the new UN54's, if it goes wonky, then I will replace it, it isn't exactly a hard or time consuming job.

My BB felt ok with the cranks on, but with the cranks off, the bearing state was obvious and after much deliberation about other types of BB, semi sealed and open types, I eventually plumbed for a UN54, and at £9 it hardly broke the bank and it was an upgrade from a knackered lower quality bracket, which to be fair had lasted this far, the cranks still turned and there was no discernable play, it was just that I had it stripped down and found the bearings 'notchy' indicating dry bearings, I flushed it through and a load of orangey fluid came out, that's it BB buggered, internal rust.

But I am seeing VP BB's and I did think about the them, as their pedals are pretty good, but with me, I stuck with what I knew, the big 's'.

Now, if I could have found a better upgrade, a semi sealed unit I would have gone for it, as replacing bearing races when they are worn appeals, and it is a compromise between sealed and the serviceability of open. But, square taper axles, there are not a lot of options around now, so for simplicity's sake bung in a Shimano or VP unit, just make sure the cycle BB shell has clean threads, and screw in the plastic cup first, it makes a guide for the BB to go in squarely, as metal threads if they cross thread will provide you with more problems.

Have fun.

BTW, I got into my old BB, a Shimano LC something or other, hardly a good quality bearing unit, but anyway you can get in, it is possible, but the things that have to come off first, get buggered up in the process, as there are things in there that are designed to go in one direction and stay there.

But to the OP, I do agree, it is good to find out what is going on in cycling in Asia, the home of all the shiny bits we all put trust in. Most over here just believe the hype and advertising and go for what is popular, the trade names being on everyone's lips, so good that name has become, but if there is cause for concern, it is good to know and maybe if the big 'S' finds out we know, it may make them sort out their problems, as reputation is the most important thing in any company, just look what happened to Saracen Cycles of Warwick.

If there is any sideways play I replace the BB immediately

REKIBorter":3js6u1y3 said:

If there is any sideways play I replace the BB immediately

Click to expand...

Exactly... BBs are meant to rotate, not move laterally. If theres any play its on its way out so replace it now before it explodes 20 miles away from nowhere.

I ignored a bit of lateral play on a BB about a year ago and it stopped turning halfway up a climb, ending the ride. Boo!