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.

Maybe not the same, but the BB in my Raleigh USA Marathon got "tight" as it went in further, but didn't have any problems seating it all the way in on both sides. Just spun the wrench with more force

You don't still have a rivet protruding into the BB area from the cable guide on the bottom? I had to grind mine off from the inside with a dremel so the Shimano BB would fit.

Are there enough threads in the bottom bracket shell?
I've noticed some older bikes don't have as many threads cut into the shell as others.
Get a ruler, or better yet, some vernier calipers, and measure the threads on the shell and on the cartridge and compare.

An LBS will have a bb tap to reface the threads(clean them up real good). Takes a few minutes.

Sometimes the inner threads, especially if the previous cup was "short", can get rusty or filled with gunk, making it hard to thread newer cups on.

Had a similar issue once, I used some course steel wool to clean the threads inside the bottom bracket resulting in loads of rust and paint being removed from the threads deep inside where the old cups hadn't sat. A bit of oil on the threads and the new cups spun in no problem.

FWIW. I have a '80 Nottingham G.P. (I have more than one Raleigh G.P.) And my '80 uses a Raleigh BB. It's not standard thread.

But if the OP is threading the BB more than half way, it sure sounds like his is standard.

True, But a english thread BB will thread partway into a Raleigh shell. Or it might have been re-tapped in the past. Hard to say without looking at it.

This is what I did (third post down) and it works like a charm- no binding, and I can still use the original cups if I want:

https://www.bikeforums.net/showthread...958&highlight=

Your BB is binding because the shell is 26 TPI and the BB is 24 TPI. Plus your shell width is likely 70-71 mm and the BB is made for 68 mm shell width.

I figured if the shell was 26tpi the BB would bind after a couple turns. The OP seems to be saying that it's threading easily almost all the way in. But anyway, your technique is pretty inspired. I'm going to wind up doing that on an old Grand Prix, I'm sure.

When you ground out the shell 3mm, did you ground out the left or right side of the frame's shell or both?