I picked up a well abused Trek 830 a few weeks back for a parts bike. I was mainly interested in the drivetrain and shifters, however, any additional good parts are always good to save for some future project. In trying to get the bike apart, the stem was stuck. I loosened the stem bolt and gave it a few more wacks with carpenters hammer. Then hit the stem bolt harder but not hard enough to damage the bolt. The stem wedge loosened. It turned out that the shop that assembled the bike greased the seat post but not the stem wedge. Or maybe that was Trek's job.
The threads in the wedge were damaged from the beating. My fault, maybe.
Well, usually that would be the end of the stem wedge, but I thought I could at least try to repair it by drilling and tapping in a larger bolt, cutting this bolt to fit in the wedge and then drilling and tapping it M6. This is one of those "nothing to loose" propositions. If the repair fails, the part was going to get tossed anyway and I would learn something from the experience.
I should have drilled and tapped a 7/16" - 20 nf, but I didn't have that size screw. So I went for 3/8" - 16 coarse thread. That would not have left enough steel for the M6, but that wasn't the issue. I was able to drill and tap the wedge pretty well. In the process of tightening the vise to hold the wedge while I deformed teh screw threads, I clamped the wedge hard enough to crack it. The crack is easier to see with MarkerfFlux, a crude version of MagnaFlux.
What I learned:
- Stem wedges are cast iron (I knew this already, but had it reinforced)
- Not all stem wedges are the same hardness (softness)
- This wedge was on the softer side
- Don't use a 3/8" bolt to repair an M6 tapped hole
- Don't use a grade 5 bolt to repair a stem wedge because it is too hard
- Use Loctite high strength threadlocker or CA glue to hold the threaded insert in
- Don't try to tighten the wedge in a vise so tight
- Just forget about trying to repair a stem wedge
- I'm an idiot