Oscillating Roller Knocking and Changing Spin Direction

The oscillating roller in the top frame assembly of my SP 15-21 has a funny habit of knocking about halfway through its oscillation and briefly changing its direction of spin. It lasts for about 5 seconds then corrects itself, but the whole thing doesn’t sound good and it adds resistance if it happens right before I’m pulling a print. Any thougthts on why this is caused? My colleague thought it might be because of overly sticky ink and she recommended I add some plate oil…but that doesn’t seem to do the trick at the moment.

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Sounds like something wrong with either the worm crescent or the worm gear. Do you know how to take the oscillating roller apart to check?

I agree with Bowerbox- you likely need a new crescent. NA Graphics and Paul Moxon have them available.