Just wondering what tool exactly I need to chase / clean my bb threads.

I had an issue where I was swapping BBs between two bikes. One of hte cups threaded completely in no problem, one went half way then got tough to turn, and none of the cups will thread at all on the other bike without being forced, which leads me to believe perhaps I just need to chase the threads.

If anyone knows the tool name and size needed.

84-85 raleigh olympian is the problem bb.

Go to a bike shop and get them to do it, the cost of the tools are $500+, if you want to buy one, it's a Park BTS-1 https://www.parktool.com/product/bott...cing-set-BTS-1

The professional tools for this are quite expensive and not likely to be cost-effective for a home mechanic. If the threads aren't too badly buggered, use a wire brush to remove rust and debris -- that's often sufficient. If it doesn't work, you can make a light-duty thread chaser out of an old cup by grinding some slots across the threads to catch chips: