I've been using a chain driven kv beet drill and for some reason the main drive chain keeps coming off. I believe it's because something is making the seeder units run tight. If I take all the plastic covers off by the meeting wheels the drive wheel runs smoothly. But it gets tight as I go into drilling with everything back on. I've noticed some seeds getting between this plastic cover and the metering disc which it think is acting like a break. But I can't see why it's doing this. Any advice please?