I'm doing my first build from the frame up and Im having some questions/issues on the bottom bracket install. My frame has a 73mm english threaded bottom bracket. I'm trying to install a corresponding wheels mfg bottom bracket [threaded mtb abec-3 bb]. Ive cleaned and greased the bb shell and am able to smoothly hand hand threaded both sides of the bb bracket into the frame some distance. Since it's a 73mm shell and shimano compatible bb I'm using a 5mm spacer on the drive side.
When handed threading I encounter hard resistance at the point shown in the first two photos. As shown there is still a sizeable gap between the bb outer shell and the frame. When I start to use a wrench to titen down the bb more to required torque there is a grinding rough feel and I'm worried I'm going to damage the threads in the frame if I try to torque anymore. When I back out the bb it looks like there is slight marring on the bb shell threads.
Is this just an issue of needing to add more spacers? The bb only came with another 1.8mm and .7mm spacer which I assume is for the non drive side for a 68mm bb shell (not needed for my case). Alternatively could it just be marred threads from the frame mfg? It feels like there are rough spots around the edge of the holes within the bb shell shown in the last two photos. Is this grinding type resistance something I should just power through?
Appreciate any input! Just dont want to mess up anything on my new frame!
by vaderstungun
5 Comments
Is this* the BB you bought?
[https://wheelsmfg.com/bottom-brackets/threaded-bb/standard-mtb-bottom-bracket-with-steel-bearings-for-24mm-cranks-shimano.html](https://wheelsmfg.com/bottom-brackets/threaded-bb/standard-mtb-bottom-bracket-with-steel-bearings-for-24mm-cranks-shimano.html)
[* or the copper version thereof]
I would take the frame to a shop and have them chase the BB threads
*Waaaaay* back in the day, it was standard practice to face and chase *all* frames to prepare them for building. It was once an essential part of building a bicycle. Thoughtful builders and frame makers still go through these processes, but unfortunately, it seems to be lost on the industry as a whole at the moment. Which, is a bummer.
The threads need chased. Its as simple as that. I’m of the mind set this should be one of the first things you do with any new frame. If you are going to go through the trouble of chasing the frame, you might as well face it too, why not?
Also, that spacer does not go between the frame and the BB. The bottom bracket shell must sit flush against the frame, this is why we face, after all. If you need to space/shim your crankset, do it between the crank and the bottom bracket, not the bottom bracket and the frame.
What frame? I think it’s crazy that frame builders don’t chase their threads by default.
You would add a spacer to a 68mm shell. 73mm would be the default width.