These just became available for purchase about a week ago. I bought one about 5 minutes after it first went on sale. People running heavier valve springs and cams have been stretching their stock chains out a lot lately. This is the first double roller set made for the 3100, 3400, and 3500. It has multiple keyways on the crankshaft gear for + or - 6 degrees of advance. Part of the crank has to be clearanced .025 for the larger gear, and the timing cover needs some grinding as well. Im sure you guys dont have much to say, but I was pretty excited to see it came in the mail today. "Cheap" insurance against putting a valve through some custom pistons, and Im able to move the powerband of my cam around as well.