Very difficult to help you without a photograph. Spinner is the company name of a Taiwanese fork maker/supplier. All the catalog specs tell us is the fork was made/supplied by Spinner, is built with cro-moly steel and has a unicrown design.
If the fork is unicrown and if the paint matches the rest of the bike, it is probably original. We can't do much more without photos.
Have you removed the fork from the frame and weighed it, and compared it to other forks, or are you just thinking the fork is light because the headset adjustment allows it to turn easily? You can not judge the weight, strength and material/build quality of a fork by how easily it spins in the frame.
In general, better-quality frames/forks are lighter than cheaper frames/forks. Cheap steel forks are heavy because they use cheaper steel, which is heavier. So if the fork in your frame is lighter than the original, it very well may be an upgraded fork of better quality. Usually you'd be unhappy if somebody substituted a cheaper, heavier fork, not a better/lighter fork.
So if the fork is unicrown and the paint matches, there's little reason to think it's not original. If you want to know for sure, you'll need to remove the fork, see if there are any identifying stamps on the steer tube (I have no idea whether or how Spinner stamped their forks), then weigh it, then find out if anyone else knows the weight of a known original fork for the same model, same size and same year as yours. Sounds like a lot of trouble, but if you just have to know if the fork is original that's the only way to know fer sure.
Originally Posted by shuru421
i am in help of finding out whether or not my 1989 Fuji Roubaix has original forks.
refers the fork to be "Spinner SPT 829 Aero Unicrown Cromoly Tubing". what does that mean? i realized that it should be chromoly, but whats the spinner spt 829 aero unicrown talk?
i know i cant judge the weight of the fork compared to the frame, but the fork seems very light. swivels easily. like i said, cant compare it to the frame but the fork seems wayy too light, doesnt feel as sturdy as the frames chromoly. thanks.