I have an issue with my recently built steel fixed gear bike. When tightening the crankarms on the BB, I can easily over-tighten them to the point they can't turn anymore because the crankset makes contact with the BB. I thought that might be normal to not tighten it too much, so I went as far as I could without making contact and called it a day, but after a 10km ride, the non-drive side arm was coming loose. I didn't use thread locker but still, that doesn't feel right.

My gear:

• frame: 68mm english-threaded BB shell
• crankset: Miche Primato Advansed Pista 165mm (recommended BB size: 107mm)
• BB: Tange - LN-3922 68mm Bottom Bracket - BSA 107 mm

Any idea what is wrong here? Do I need to get a longer BB (e.g. 113mm) despite having the recommended size?

Thanks for your help!