I have a Schwinn hybrid circuit 27" bike that is about 3 years old. It has an older style bottom bracket set with regular ball bearings. I bought a newer style shimano bottom bracket set to replace what I have, but it will not fully seat. About halfway with threading, it becomes too tight to turn and won't thread any further. I bought the correct 68mm set, but it seems the threads on the left and right side within the bikes bottom bracket are not aligned. With the new bottom bracket set, I can screw in each side separately by itself fully, i just can't screw both sides together. When one side is screwed in all the way, and I look inside the bottom bracket, the spindle definitely looks crooked and not centered. This is the only plausible explanation to me that the left and right threads are not aligned with each other. Is there anything I can do to make this conversion work?
by jakal_x
2 Comments
It sounds like it’s been cross threaded, either by you or in assembly. Because it’s an entry-level bike, there is a chance that the bottom bracket shell is misaligned, but that would probably be due to a bad batch of shells making it through QC, so way up the supply chain.
When you initially tried to start screwing in the BB, did you use a tool, or start by hand? I always screw it in by hand, and only use a tool for final tightening, to avoid cross-threading. When you screw one side in all the way, which side are you screwing in? A cartridge BB of this type is designed to be anchored by the drive side (left hand threaded). The non-drive side merely supports the bearing on that side, and in earlier versions was often plastic. If you can thread it in from the drive side all the way, is the raised shoulder flush against the bottom bracket shell face? If not, or if the spindle is off center when fully threaded in, then it sounds like cross threading. Is there uneven wear on the bearing surfaces of the old bottom bracket? That would indicate longer term misalignment.
I would take it to a shop and ask them to check and potentially chase the bottom bracket threads. Because it’s already an inexpensive bike, it’s possible they’ll say it’s toast or not worth trying to fix, so be prepared for this. However, they may be able to chase the threads with a thread cutting tool and restore them. Expect to pay around $50 or so for this. Hope this is helpful.
Correct me if I’m wrong in my methodology here, but I’d install the drive side fully. Grease the inside of the retaining sleeve and put that in till it stops. The retraining is probably hitting the edge of the bearing body. Put the crank arm on the drive side and use it as leverage to flex the bracketing slightly to get it into the center while you’re screwing the sleeve in.
Again any other options? This is what I’ve done to get past this issue. I only say this because you said you can put both parts on all the way without issue on their own so it’s not a cross thread problem