Honda sold (or gave away) that Protector in 1970 and 1971 as a warranty-aversion device. The Artfrombama incident was pretty common back then, at the chains were not yet up to modern strength. The first sprockets were smaller, too: the front was 16 and the rear 45. All 750s were recalled and a 17 front and 48 rear was fitted, along with an endless drive chain, and the Protector. But, as soon as the chain developed some slack, it would hook into the back edge of the cheesy sheet metal Protector and fold it up and cause another kind of damage, so these were discontinued before 1971 was over. The ultimate solution was to run 18 front sprocket and 48 rear, with endless chains. This effectively overgeared the lower 2 gears so the torque could not exceed the chain strength of the day, and it stopped the damage, although it slowed the bikes down from too tall gearing.
And, mechanics like me HATED the endless chain, as it meant that a simple chain replacement involved removing the rear wheel, shocks, and swingarm. Diamond sprang to the rescue first, with the press-fit master links that were stronger than the chains themselves. Then Reynolds came into the fray with their (ultimate ever) incredibly strong ( and expensive!) chains. Then, Honda tapered their sprocket teeth on the 18/48 sprockets and increased the base circle an extra 0.5mm below the teeth, just when Diamond came out with the chains that had extra hard pins and extra clearance in the rollers, along with case-hardened (Rockwell 65 minimum) rollers. This combination proved to be the best, longest-lasting, smoothest, quietest drive ever on these bikes. I've ridden this combination as far as 40,000 miles on a single set of chain & sprockets.
