What Causes Engine Valves to Break?

Let's explore some theory, which is always interesting: why do the valves in our engine, whether intake or exhaust, break? Consider the cold adjustment (where applicable) that has a tolerance. If the "clearance"—the distance between the tip and the top of the valve—is not respected, "tipping" occurs, meaning the valve remains slightly open.

If it's an intake valve, power is lost. If it's an exhaust valve, it risks burning out. This also happens with hydraulic tappets; instead of clearance, there will be an oil-filled cup. The spring can also negatively affect operation: if installed incorrectly, the tip will inevitably break.

Let's see what happens during machining. If the valve seat is not properly mounted, it will wear unevenly, causing severe damage.

Alternatively, poor grinding where the valve guide is too wide can allow oil to leak into the valve. On the other hand, if it's too tight, it will seize.

Let's examine the damage from wear. If the tappets are worn, they will damage the valve head, breaking the valve's interlocking part.

If the valve head is worn, the rocker arm pressing down will also break it. Excessive pressures in the combustion chamber will cause wear at the sealing area. High temperatures in the combustion chamber also stress the valves, especially the exhaust ones.