I haven't been home to measure them yet but I've just found a note I scribbled ages ago which tells me the handlebar stem od is 25.4mm, so it looks like the forks are 1 1/8" .
I bought this Bear Valley from new, around 1992 but a few years of being stored unused in the shed has taken its toll and it does look a bit sorry for itself.
It has a fair bit of surface rust around the bottom bracket and stays, so I intended to strip the frame down and repaint it, but...