A Tight 2nd Operation Roll setting is when the roll is set too tight (too close to the chuck) for the particular can and end in use. This puts unnecessary stress on the seamer, the seamer tooling and bearings and most importantly, on the seam itself.
Above: These are the 2nd operation rolls from two heads of the same seamer as measured by the Clearance Gauge. You can see that the roll on the left is set too tight (less than 0.025″ from the chuck) vs the roll on the right, set to about 0.030″, tight enough to form a good finished seam.
A Tight 2nd Operation Roll can cause: