How can I replace the belt on my 8mm projector?

I have a Keystone 8mm Automatic movie projector with the auto-thread feature that needs the projector belt replaced as it was completely missing when I bought it. I purchased belt and went to put it on. But, it looks like I'd have to remove the steel rod that goes through armature and I certainly don't want to damage anything internally. Please help and I thank you in advance.
Diane, August 2017