Technician A says flat tappet lifters require a break-in period. Technician B says flat tappet lifters should be checked for bleed-down using a special tool. Who is correct?

Flat tappet lifters indeed require a break-in period because they operate under high friction and load conditions during the initial use. This period allows the lifters to properly seat against the camshaft, ensuring optimal contact and performance. If a proper break-in is not followed, there can be accelerated wear or failure of the lifters and camshaft, leading to potential engine issues.

On the other hand, the mention of checking flat tappet lifters for bleed-down using a special tool pertains more to hydraulic lifters rather than flat tappet lifters specifically. Hydraulic lifters are designed to self-adjust for wear and maintain a certain amount of oil within them to function correctly. They can experience bleed-down issues if they are faulty or if the oil passage is blocked.

By focusing on the characteristics of flat tappet lifters, it is clear that Technician A is right about the requirement for a break-in period, ensuring their longevity and performance, while Technician B's statement does not accurately apply to flat tappet lifters in the same context.