robertlabrie

I ride a Pacific Cycles road bike, about 150 miles a week (30+ miles a day, 5 days) in the hills around metro Atlanta. Anyway I destroyed the factory bottom bracket, and the Sunlite SL-26 68mm bottom bracket the local shop put in (It's a Shimano BB-26 clone I think). Ok, so I since bought the tools and put a third cheap bottom bracket in this bike, I expect to also destroy. I'm looking for some tips on what to look for when selecting the inevitable fourth BB. Bearing material? Shaft material? On this journey I've already learned there is a lot I don't know about this component. I can say that I know it's not a competition bike, maybe my best option is to just keep popping cheap BBs on it? Thoughts?

Thanks,
Rob

GrainBrain

How many miles are you getting between BBs? I'd try out an actual Shimano unit next. You could always try to get a Paul BB but that's $$$

Fwiw I've got 3k miles on a sunlight un-26 clone, still going strong. Maybe your BB threads aren't perfectly aligned, factory defect in frame?

fietsbob

yea the whole Idea of fit and forget BB is they're easy to replace quickly
and cheap to do so..

A past thread showed how to tear them down,
but Id not bother except for modifying the cartridge
with a Zirk fitting drilled in and through the BB shell..

and being able to load a lot of grease in it..
My hand made touring bike got a treatment like that.
but it's Unique.. BB shell a closed tube..


..there the taking it apart , would include clearing out the chips from the drilling, and threading..

may be too much expense and bother, so plan to remove and discard
as you find them past their prime..



...

robertlabrie

I don't know exactly how long it lasted, based on my average, maybe 1500 to 2000 miles. I think the shop over-torqued it when they put it on. It's also possible that it's a defective frame, being a Pacific Cycles Target bike. Any way to check that without a micrometer?

Playing with the old BB, the left side (not crank) bearing ring is offset from the cartridge, and spinning it around it feels rough and make a bit of a crunching sound. I understand it's hard to judge without holding it, but you think it's more likely that I warped the shaft or ground out the bearing?

I can do a Shimano next, UN26 or UN55? Seems to be hard to find specs, but more expensive is always more better right?

fietsbob

big differenc the left sleeve is aluminum on the 55, plastic on the 26,
but t he plastic wont corrode galvanically like the aluminum can,

in steel frames,,

(see the 1001 stuck seat post threads...)





...

nfmisso

It sounds like a frame problem. BB cartridges have very stiff shafts and relatively thin shells. If the BB shell in the frame is not square thru and the axes of both threaded sections not concentric, the shell of the cartridge will be distorted, destroying the bearings in short order.

Suggestions:
First take the bike to a well equipped shop, and have them face the BB and chase the threads. See: https://www.parktool.com/blog/repair...ing-and-facing
The person doing this should be able to tell you if they are able to repair the situation or not.

If they are successful, use grease on the threads when the BB cartridge and make sure that it is properly torqued (BB cartridges are supposed to have relatively high torque, check the specifications for the particular BB you install - use a torque wrench).

If the face & chase is unsuccessful, one option is to take it to a machine shop, and have them make the bore square with the frame, a use a threadless BB, like this one: https://www.amazon.com/Sunlite-Threa.../dp/B002K2IG66 NOTE: they are available in various sizes.

robertlabrie

The frame is 6061 aluminum, should be ok? I hadn't thought about galvanic corrosion, a seized BB sounds unpleasant. I'm thinking to splurge on the 55 next time, any tips on keeping it from getting locked into the frame?

fietsbob

anti seize grease ..

rosefarts

I've destroyed 1 in my lifetime. It wasn't all the way tightened up and I rode it many miles until the bearings fell out.

Something is wrong with the bike or the installation. I am not sure a higher price bb would have better luck.

Andrew R Stewart 

I can think of at least one reason why a BB or otherwise decent construction would wear out well before it "ought to" and has nothing to do with the frame or install. Load or water exposure (gee... that's two reasons). I suspect that the OP is a commuter given his miles/days a week of use. I wouldn't be surprised if this bike sees a lot of exposure, both when ridden as well as when parked. Commuting can be about the most abusive type of use one can give a bike. Add in lot's of weight and hills and this low life of the BBs isn't too surprising to me. Not saying that I would expect this low mileage or that I, too, wouldn't be frustrated by it. Just that I've seen this kind of thing before with high mileage and all condition riders, especially if there's a lot of weight involved.

I will say that the situation I describe often has other wear issues going on too, like wheel bearings, spokes, brake pads, chains.

I'm not accusing the OP of anything, just offering more experiences that do happen to, thankfully few, others. Andy

I should add that the OP might think about having a service focused and motivated shop (and with a very low cost bike many shops don't go that extra step of thoughtful assessment beyond the flat rate repair) do the next install with a UN-55 BB. I do wonder what the old BBs looked like on removal. Andy

robertlabrie

Thanks to everyone for your replies. I'm not a commuter, but I do laps at Stone Mountain park for cardio health. I weight around 190 and my 30 mile ride gains 1600 feet, I am up on the pedals a lot. Maybe it's load. Or maybe it's a frame issue like nfmisso suggests, but I don't think this bike isn't worth the kind of professional treatment he recommends (machining a $400 frame?). I did install my last BB using a torque wrench to the spec on the package, we'll see how long it lasts, but if it doesn't hang on, I'll try a UN55 once (it doesn't cost that much more) and maybe start shopping for a better ride.

AndrewRStewart I tried to upload some pics but the forum is saying I'm not allowed to post URLs?

Again, thanks to everyone for being so welcoming, I certainly didn't expect a magic bullet fix and I've got some good info to think on.

deacon mark

I would get a new set of Shimano Hollowtech cranks with external bearings and be done with for years. Swapping BB every 1500-2000 is crazy. I have never wore a external BB out that I know but granted the most mileage I have on one is about 15000 miles.

rosefarts

With a low end frame and sloppy tolerances, an external BB is likely to wear out much much faster than an old style square taper. On a higher end bike worth getting faced, they sure ride nice. They weren't introduced for durability.

Andrew R Stewart 

+1. Andy