eugew23

Hello all,
I noticed something was off with my '78 Centurion LeMans when the non-drive side crank arm started to feel loose when I pedaled. I took it off today to find out that the threads on the spindle (?) of the bb (correct me if I'm wrong please, I'm not exactly sure what this part is called) is chipped. Is this salvageable, or do I need to replace it? Any information regarding what my issue is, or how I can resolve this would be helpful!

Andrew R Stewart 

I've seen this more then a few times. The axle is hardened and as such tends to not deform like most abused threads do at first. It chips instead. Try threading a nut back on. How does it seem to fit. This is all judgement based so we can't give other then opinions. Most of the time I've dealt with this the axle's threads were in good enough condition so the nut went on and off easily and with a lot of remaining contact surface. Only a very few times did I feel the reusing the axle would not be the right thing to do to a customer. I have to admit I don't remember any of these, when I left the axle as is, coming back with further issues. Of course some of that is also about the crank arm condition and how you torque down the nut (and test ride then re torque). Andy

dsbrantjr

If the nut cannot be secured satisfactorily a replacement spindle can be obtained, or a cartridge-type bottom bracket installed.

cpach

It's had to tell from the photos but it also looks like the actual taper interface may be slightly messed up as well. I'd just replace it with a cheap cartridge BB and call it a day.

bldegle2

The threads do look damaged. Basically you need to chase it with an threading die. You can see lots of material in the thread valley's and some of the thread ridges themselves are gone on the top side. After chasing to fix whats is left and the nut goes on properly (I would get a new nut), reassemble and see what is...

sweeks

If the nut doesn't thread on easily, you can get a "THREAD FILE" to restore the threads. Chances are when you removed the nut, the threads were set more-or-less right. The chip, unless you somehow impacted the left-side crank, might well have been there since the bike was new.
Of more concern, IMO, is the possibility that riding the bike with a loose crank has damaged the square taper on the crank since it's aluminum (softer than the crank axle). If this is the case, a new BB cartridge will not be the final solution.
I'd recommend re-installing the crank, torquing it properly, then riding it. Check the torque after a few miles, then after a couple of longer intervals. If it doesn't loosen up again, you're home free.

eugew23

Thanks for everyone's input.
I have already tried threading the original nut back in, but it will not secure properly and cannot be torqued properly. I can't really tell if the nut is any good, but I'll try a different one and see how it goes. Hopefully, I didn't already screw up the threading on the axle already while removing the nut the first time...

Retro Grouch 

Nobody's mentioned the crank arm but my bet is the square hole is, since it was loose, the square hole is buggered badly enough to be un-fixable too.

Andrew R Stewart 

My ending sentence in post 2 alluded to this. Andy

sweeks

See also the middle paragraph in post 6.

JohnDThompson 

BB spindles are hardened steel, and resist reforming with dies or thread files. If the retaining nut does not engage securely, the best solution is to replace the spindle (remove from the bike; the spindle should be marked with an arcane code you can use to match with a suitable replacement) or install a modern cartridge bottom bracket, although that may take some experimentation to get the right spindle length.

sweeks

Yes, I'm aware of this. The files are also hardened, and though it's not as effective as it should be small defects in the threads can be removed with some effort (in my limited experience). It's probably hard on the file. I sure wouldn't use a die unless I were willing to throw it away. Your recommendation to replace the spindle is the most reasonable.

70sSanO

So, what are your plans? About 15 years ago the woman next door moved and left a couple of bikes half rusted in her back yard. One was an 80’s Lemans. I stripped off what wasn’t rusted/frozen. Included was a 116mm threaded spindle.

Those cranks are probably 144bcd, which limits you to a minimum 41t inside chainring.

Personally, I would go with a more versatile crank and a cartridge bb, but PM me if you want the spindle. I probably have the GLP cranks somewhere around here.

John