sq taper bb question

Strange play has developed in the drive side crank arm of my converted-to-ss commuter in the last couple of days. Bolt wasn’t moving so wasn’t immediately concerned. Tonight I’ve removed the arm, getting the bolt out was hard but didn’t need the puller to get the arm off, just wiggled and pulled. BB looks ok in itself (had visions of slightly bent axle) but after cleaning everything and sticking it back on, the bolt now won’t tighten.

If I’ve threaded the bb, guess i need to replace it (bolt looks ok) but could the square hole in the crank arm be damaged?

you could have tightened the crank all the way to the end of the taper, have a look inside the square hole inside the crank-arm and you should see a little ‘ridge mark’ where it’s stopped tightening onto the taper, if you can’t see one, it might be that it’s tightened all the way to the end

alternately if it’s a Shimano BB with a ‘shoulder’ at the bearing end then the crank could be merely tightening onto that rather than tightening fully on the axle

If its a shimano then it might have a sleeve on the driveside.It could be butting up against it.it it looks like theres one there you could try removing it. this will allow the arm to pull on a little more once torqued.i removed one on one of my bikes and torqued it to 55nm and threadlocked the fixing bolt. never had a problem with it.