I have a Trek 6700 with an outboard bearing LX bottom bracket two piece crankset. The original Shimano bb bearings are shot and I noticed that the threads on one of the cups threaded rather roughly when I removed it and the bearing cup looked a little cross-threaded. Now, I'm wondering if I should have the lbs chase the threads on the frame or whether the cups are designed with softer metal than the aluminum of the frame so they won't strip the frame threads. Does anyone know the answer to this?

Also, what about the spacers that come with the bearings? How does one know how many to use and on which side? I'm not sure if the frame is designed for 68mm or 73mm.

Thanx in advance for any advice.

$20 at your LBS. Good investment if you want to lengthen the life of the frame. Once the threads are totally shot it is a tough fix. Good luck.

Yes, getting the threads tapped and faced at a good LBS is a good idea. See this thread. The threads on the cups likely got gummed up from poor BB shell threading and the shell threads may have some galled aluminum from the cups stuck in them.

The shell on that bike should be 68mm. For Shimano external BB, 2 spacers go on the right side and one on the left side if you have a 68mm shell and aren't using an E-type FD or chainguide.

I just replaced the outboard bottom bracket bearings on my LX crankset with new Race Face bearings. The only way it would work was with no spacers. Otherwise, the length of splined crank spindle coming through the cup would not be long enough to bolt the non-drive side crank on. This is with a 73mm shell on a Trek 6700. That goes against the instructions but there was no other option and hopefully it still works. At least there is no play in the bb now.

if your theads "get totally shot" the fix isn't that tough to do. The tough part is finding someone with Italian thread cutters. Italian bottom brackets are little wider- 70mm vs 68mm for English and have a little larger diameter how much I can't remember. Here' show to do it cut Italian threads in your bb and, ( if you can can find), use Italain cups and an English Spindle, tricky bearing adj., or all Italin- if your system doesn't mind the slight difference in chainline. Don't forget Italian bbs are right hand thread on BOTH sides

Press-in BB's are also a worst-case-scenario option.

If you have an old BB around, you can cut 3 or 4 wide slots in each with a dremel tool to make a thread chasing tool.

He's got a Trek. Theres no way its Italian. Its a 73mm english shell.

I don't think he was saying they were Italian threads. He was saying that a "fix" of destroyed English threads is to cut new Italian threads in that are slightly larger than an English.

Just like my suggestion of pressed BB, it's not ideal, but it's better than a new frame . . .

I just can't figure out why the LX crankset won't fit with one 5 mm spacer on the drive side, as per the instructions that come with the bearings. It works okay, although one of the plastic covers that goes between the bearing and the crank spindle got slightly spindled and mutilated during the installation process of pushing the spindle through it. The outside part that covers the bearing is intact but the inside part between the spindle and the inside of the bearing is somewhat mangled. I suppose it is nothing to worry about but there must be an easier way to get the spindle through the non-drive side bearing besides whacking it with a hammer...Doing it tool-less with my hands was not enough force to get the job done.