Technician A says that umbrella valve seals are installed in their operating position during cylinder head assembly. Technician B says that positive valve seals are positioned by the valve. Who is right?

In this scenario, both technicians misrepresent the installation and function of the valve seals.

Umbrella valve seals, which are designed to prevent oil from entering the combustion chamber, are not installed in their operating position by default during cylinder head assembly. Instead, they usually need to be positioned correctly once the valve springs and retainers are in place to ensure they seal effectively.

Positive valve seals, on the other hand, are typically installed directly onto the valve stems themselves before the valve springs are installed. This helps to create a tight fit and prevents oil from leaking into the cylinder. They are designed to work as a component of the valve assembly and are not simply positioned by the valve but rather need to be placed accurately for effective sealing.

Given the inaccuracies in both technicians' statements regarding the installation and positioning of these valve seals, the correct choice is that neither technician is accurate in their understanding of these components' roles and assembly practices.