Q: My 2005 Honda Pilot just passed 100,000 miles, and it looks like I need to have the timing belt replaced and valves adjusted soon. My repair shop is offering a special deal on the timing belt replacement, and I understand why that’s needed. It’s the valve adjustment I don’t understand. I haven’t owned a car or truck before that needed a valve adjustment. Why is this needed? Is it something that needs to be taken seriously, like the timing belt, or could it be deferred for a while?

A: Good question, Dave. An engine’s valves are driven by the camshafts, which contain many egg-shaped lobes. The cam may act directly upon the valves or through a seesaw-like rocker arm, depending on the manufacturer’s design. This needs to be a precise connection, so the valves are accurately controlled, in order to provide optimum engine performance, quiet operation and long valve life.

As with any mechanical connection, temperature, wear and metal distortion can cause changes over time in the clearance between the parts. For quiet and precise operation, you want very little clearance (slop) in the connection. But if the clearance were to become zero, and a valve should remain propped open, the engine would misfire or shake, and the valve would be damaged. Valves need to close fully to transfer their heat to the cylinder head, or they’ll overheat and fail.

Most modern car and truck engines use hydraulic valve lifters, while some employ a mechanical connection between the cam and valves. Hydraulic valve lifters use the engine’s oil, within a very precise mechanism, to absorb valve train clearance and push the valves open. Mechanically operated valves require a small clearance to be maintained between the cam lobe and following device, and require periodic inspection/adjustment.

Which is better? Hydraulic lifters are quieter and maintenance-free, but are fussy about having clean oil of the correct viscosity. A mechanically operated valve train is simpler, lighter — which is important for rapidly moving parts — and is better suited to high-revving engine operation. A mechanical system should be less problematic from a repair standpoint, but will require occasional maintenance.

Honda employs a highly sophisticated valve-operating strategy know as V-TEC, which, depending on the version, can switch between differing cam lobes in order to optimize engine performance or shut down cylinders to save fuel. I assume that there simply isn’t room to squeeze in hydraulic lifters among all this mechanical wizardry, and trouble-free, high-rpm operation is a priority. The bottom line is that you may pay slightly more over the long haul for occasional valve adjustments to enjoy exemplary engine performance.

Can you defer the valve adjustment for a while? Perhaps. The valves went 100,000 miles without any trouble, and unlike the timing belt, there’s nothing to break. What’s a few more miles? Keep in mind the consequences of a tight valve could be an expensive engine repair. The book time for a valve adjustment is three hours on your Pilot.