FAA Powerplant Written Practice Test

What is a likely result of grinding the valves of a reciprocating engine to a feather head edge?

1. Increased power output

2. Sticking valves

3. Preecognition and burned valves

4. Improved fuel efficiency

The correct answer is: Preecognition and burned valves

Grinding the valves of a reciprocating engine to a feather head edge is likely to lead to preignition and burned valves. When the valve faces are excessively ground down, the shape and mass of the valves can be altered to a point where they don't dissipate heat effectively. This can cause the valves to operate at higher temperatures, increasing the likelihood of preignition, which occurs when the fuel-air mixture ignites prematurely. This intense heat can result in burned valves, ultimately affecting engine performance and reliability. Other choices may suggest positive outcomes, such as increased power output or improved fuel efficiency, but these are not the direct results of improperly modified valves. Sticking valves, while a concern, are generally associated with other issues such as inadequate lubrication or contamination, rather than the grinding of the valves themselves to an excessively thin profile.