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ovalized bb shell(6 posts)

ovalized bb shelljason in nh
Jul 24, 2001 3:54 PM
I got a bummed frame here. The bb shell is ovalized and i was wondering if anyone had any solutions on how to use this frame. Is there a product that will fill it? any help would be great.
Oh boy, that's a toughy...grzy mnky
Jul 24, 2001 4:36 PM
Guess we'd need to know the frame material, make/model and degree of damage. If it's high-end ti or steel then a custom shop could replace the BB shell, but it won't be cheap. If it's aluminum you're screwed b/c heat treating issues. If it's carbon forget it.

I kinda wonder how it became ovalized and how someone managed to keep riding it in such a degraded state. Shifting and keeping the chain on must've been a real challenge.

Ultimately it depends upon the degree of ovalization - any chance you can measure it with good calipers and get the max./min.? There's also a chance you could "chase the threads" with a BB tap and jig and face the ends with a BB ream. The idea being if it isn't too bad you can clean up the mating surfaces and get a good cartridge BB to fit. The other thought is to go to an outfit like Phil Wood & Co. and get a set of custom machined cups that will match a new bore and set of threads in the BB. Or maybe you just get the BB bored and go for a set of pressed in over sized sealed bearings ala early Klein bikes.

A picture is worth a zillion words so I'd track down a good local frame builder and see what they suggest. Of course you're going to have to be careful that any material removal doesn't compromise the structural integrity and make the frame dangerous to ride. There's no way a volume manaufacturer would even touch this b/c of the liability, but maybe they'll set you up with a sweet "crash replacement" deal. It doesn't hurt to ask.
Hmmm....possible solutions...alansutton
Jul 24, 2001 6:13 PM
I've had to deal with this a few times. First of all, make sure it's the BB shell that's damaged and not bad cups. I've tried a few different solutions-, none of which are easy. If the frame in steel and the BB is English threaded, I'd try to have to re-tapped to Italian threads, which use a slightly a larger diameter bore. This is very difficult and you will end up with threads of poor quality, but it will work. If the frame is aluminum, due to it's softness you can't re-tap it to a larger bore without destroying it. I've seen people try- with horrible results. You can install a Mavic threadless BB, but these are increasingly harder to find and don't work it the frame is badly ovalized.
The last resort is to reinstall a BB using Loctite RC680. This has worked for where other solutions have failed. This Loctite is hard enough to fill the gap. However this installation is permanent, so use new BB, and once it's worn out- you throw your frame away. The good news is that bottom brackets last a long time these days and unless it's a Dura Ace, you may be able to ride a couple of years on it.
Good Luck.
Thread lockers and retaining compounds.Calvin Jones-Park Tool
Jul 25, 2001 4:43 AM
A small amount of ovalization occurs in many bikes. The shell becomes deformed during welding.

Have you attempted to thread in a bottom bracket? If it installs, I would recommend a thread locking compound such as Loctite #242. It has some ability to fill gaps and will help hold it secure. If the bb will secure to proper torque, it should be rideable, and without creaking or moving.

The #242 is service removeable, meaning normal procedures can get it out. If you step up to the retaining compounds, such as RC609, the gap filling ability is greater, and it is stronger. It can be removed with mild heat, such as from a heat gun, which will weaken it enough to allow removal.

If the bb will threads in, I would not recommned tapping, as that will remove more material. If possible, give us an accurate ID across the oval, which will be two numbers.
go to a frame builderRusty McNasty
Jul 25, 2001 6:43 AM
they can replace your BB shell, but it ain't gonna be cheap.
re: ovalized bb shellixiz
Jul 25, 2001 11:09 AM
depends on how much you really want to spend.
You can rethread it but if its really ovalized then there will be a thin section and may crack

Or if you can find a helicoil (probably custom because ive never sen one that large.)