So, I'm trying to install a shimano un-54 cartridge bottom bracket into a raleigh super grand prix from about 79/80. It does not have a raleigh proprietary bottom bracket, nor a thread pitch of 26 tpi. The problem is that the cartridge bb doesn't seem to want to thread in easily all the way. It goes in like butter for about half the threads, then starts to give some resistance, and, by the time I'm down to the last two or three threads on the cartridge, I need to turn the spline tool pretty hard (which I haven't actually done all the way yet). I anticipate I'll really have to hanker down to get the lip of the bb flush with the shell. I stopped and removed the cartridge once to check the bb threads, which seem fine, no sheering, cross threading, or bits of newly spun steel wool in them, and then attempted to reinstall, with a little more progress. So, right now, there are still one or two threads exposed on the drive side of the bottom bracket, and 3-4 on the plastic left side, with both sides offering resistance. It almost feels as though the bb is bottoming out, or that there aren't enough threads in the shell or something, if this is even possible or makes sense. I threaded in an old tange bottom bracket cup before attempting the cartridge to check the thread pitch, and it went in fine, although i didn't fully install it...has anyone else had this problem? Does it have to do with the difference between modern ISO and early BSC threading? Also, the bottom bracket is a funky width, measuring 69.5-70mm (though definitely not italian). Any solutions? Should I just go against good mechanical sense and apply the extra pressure to get the bb in? I tried this when mating a new shimano freewheel to a zeus hub...sheered the threads on the hub a little, but the wheel's still running strong, haven't stripped anything after two years...still kind of regret it though. Could I possibly thread a track lock ring onto the cartridge to take up the exposed threads and have the crank a little more outboard? Would a track lock ring even fit a cartridge bb? Anyway, any advice would be very welcome. Also, yes, I'm using copious amounts of grease.