flangehead

I have a low-end 1990 Fuji steel road bike which hadn't seen much use in 25 years until COVID hit. I replaced bad rubber/plastic and started riding it for exercise. It has a cup and cone bottom bracket, and I noticed a bit of play so I opened it up. In addition to some very slight pitting on the non-drive side cup, I saw an internal crack at 6:00 beginning on the NDS running 3/4 of the way to the DS. No sign of the crack externally, though the bike has unusually thick paint. My initial decision was that the frame is now scrap but I could run it to failure being alert to crack growth. I buttoned it back up.

However, I got to thinking that I might be able to increase time to failure by:

a) drilling end of crack to arrest it.
b) install cartridge BB bearing/spindle to replace cup and cone, on the logic that I'd get more circumferential metal to reduce the load on the crack. (This assumes I can get all the right dimensions, which I have not yet confirmed.)

I think I can get away with $30-$40 for the cartridge and the tool. That's probably more $ than I ought to be putting into it, but gives me a little project to do.

Thoughts on this run-to-failure strategy? Any practical experience?


Crack is very similar to the photo (not mine; I buttoned it back up after cleaning/greasing). My crack is NOT intersecting any penetrations.


Not my photo, but the crack in my BB is very similar.. at 6:00 position, starting on NDS.

Bill Kapaun

Is there room for a skinny hose clamp?

Amt0571

I have a Dahon which developed a couple of cracks coming from the clamp area on the seat tube. I drilled the end of both cracks and it has held up for 3 years. I would try it.

andrewclaus

I'm not sure I completely agree that a cartridge adds stability, but it may be incremental. The joint between the sides is often just a tight plastic sleeve. Good luck with it. And the cost of the tool may pay off on another bike sometime. If there's a co-op near you, they'll have a bin full of salvaged cartridges. And a tool you can rent.

If the shell fails, you'll have warning and it shouldn't cause harm if you heed obvious warnings. I don't know this from experience with a total failure, but it's hard to ignore BB noises.

Be aware that the cable guide screw may interfere with a cartridge BB. At minimum, loosen the screw when installing the cartridge. Sometimes the "screw" is just a plastic knob that can be cut off.

pdlamb

Color me confused. The picture looks like you're showing us a cup. If that's the case, as long as you can screw it in without boogering it up, I'd think it would run for a long time (or until you break it trying to remove it again).

If it's the shell on the bike frame itself, you might see if a good welder can weld the crack back up. You'll have to fix the paint around the BB, and perhaps get your LBS to run taps into the shell to clean up from the weld.

lubloi

I wouldn't be so sure it's a crack. Many bottom bracket shells were/are welded from sheet metal. The weld was made at 6 o'clock on the outside of the shell and then ground down. On the inside of the shell, a line remains visible in the steel where the two sides meet.

It does not hurt to switch to a cartridge bottom bracket and to take a look at the shell every couple of months, but I wouldn't be surprised if this frame had a few more decades of life left in it. By the way, the fact that the crack is only visible in the steel, not in the paint is also a giveaway: paint typically shows a visible crack earlier than steel does.

Bill Kapaun

I would stick with cup & cone.
DS will take similar force/stress from either type.
Torquing down the NDS on a cartridge is going to have a "wedging" effect spreading the shell, like a pipe fitting.
A cup w/ lock ring isn't.

3alarmer 

...+1. That central bottom area of the BB shell is often partially removed in some higher end Italian bikes. It's not impossible it's cracked, but I've never seen that myself. Certainly your proposed repair will do no harm.

Iride01 

Drilling does help to stop cracks, but I've seen a lot of people that drill cracks fail to find the actual end of the crack and the drilled hole does nothing. Probably won't hurt though to try even if you do miss the end of the crack. Use a strong magnifier to look before you drill.

What Bill Kapaun said makes sense. And if you happen to have a two piece crank with external cups, that too, I think, will be better than a cartridge.

Brazing is an option too. For certain the more than 800°F heat is going to mess up some paint on the seat and down tube too. But if you want it to last longer, that's what to do. Doing nothing it still might last long enough.

blamester

Same opinion.

delbiker1 

You state the picture is not of your bb shell, but it is similar to what yous looks like. Without an actual picture of yours, everything is just speculation. Just going by your description, not so sure it is a crack. You have actually seen it, hence, you have a better idea of that than anyone commenting here. I would not do anything, including riding the bike, until I got confirmation from someone knowledgeable about such things, and has actually had eyes on it.

Iride01 

Good catch... in my speed reading ADHD (without the H) world, I missed that. And if they are just seeing the mark going through the threads shown in that picture, then that looks like a seam or other artifact of the manufacturing process.

Moe Zhoost

Picture does not convince me that it's a crack. To me it looks like a scratch. It's common to see a welded seam at 6 o-clock so that's a possibility as others have said.

Why not post a pic of yours. Any opinions based on that "similar" picture are low value.

xiaoman1 

To my old eyes, it looks like a crack on both sides of the BB shell....Drill it and see what happens,
Best, Ben

Just saw that it appears to have migrated completely out on side....possible toast to me.

flangehead

First off, thank you everyone for your advice. It helped me overcome my rush to judgment.

Short story is I ground on the defect and it was only superficial. No evidence of crack through body on either end or on outside. Problem solved.

Excess details: I opened it back up to make measurements and inspect more closely. I hadn't removed the drive side cup the first time. Ended up I had the same surface defect on the DS. Interestingly, the defect curves; I'd expect a tube weld to be straight. It is very similar to the defect in the previous internet photo I posted. Here is picture of mine:


Photo from DS. Surface defect does not touch cable guide screw hole.

I decided to splurge and get a cartridge instead of a cone/cup rebuild kit. I'll have to use a short screw for the cable guide.

Thanks everyone!

Moe Zhoost

That's a weld line. It looks like it curves a bit because of the machining for the threading, which widens the inside diameter.

Hang on to the spindle and cups if the bearing surfaces are good.

delbiker1 

Not sure of this, you may not have to replace the screw. Just back it out before installation of the new BB, screw it back in after installation. I have a couple of bikes that I have to backout the screw before pulling the BB, both cartridge type, and back in after reinstalling. That is not unusual and it does not affect anything afterward.

I am glad you figured it out and there is no crack in the shell.

JohnDThompson 

+1 this. The OP's picture shows what I would identify as the weld seam. But the OP says the picture isn't his bike. A picture of the actual area of concern on the actual bike would probably help.

grizzly59

Sand the outside and remove the paint. Turn the bike upside down. Find a magnifier. Using something like a syringe and needle, drip a bit of coleman fuel, paint thinner, something like it onto the "crack" and watch it. See if the drip keeps disappearing into the crack. Look at the inside and see if it's making that area wet. If the liquid is getting through to the other side, it's a crack and not a weld. Someone who is a pro at steel frame repair will give you the next step.