What type of engines have valves and springs that can be removed without the use of tools?

The correct answer is that OHV (Overhead Valve) engines have a design feature that allows their valves and springs to be removed without the need for specialized tools. This is primarily due to the engine's construction, where the valve train is designed for easier maintenance and assembly. In many OHV engines, the rocker arms can often be removed by hand, allowing access to the valvetrain without needing to disassemble other components, which is convenient for tasks such as replacement or adjustment of the springs and valves.

Other types of engines, such as DOHC (Double Overhead Camshaft) and SOHC (Single Overhead Camshaft) engines, generally require specific tools for the removal of their valve components due to their design complexity. Turbo engines, on the other hand, refer to those equipped with a turbocharger and don't specifically relate to the ease of valve removal. Therefore, focusing on the utility and workability of the OHV engine design highlights why it is more user-friendly for maintenance tasks related to the valve and spring assembly.