Car detailing and valeting

Each of your engine’s cylinders are equipped with at least two valves. An intake valve allows fuel to enter the combustion chamber. An exhaust valve lets gases produced during the combustion process to escape into the exhaust system. Both open and close thousands of times per minute. They play a key role in the efficiency and performance of your engine.

The valves can fail for a number of reasons, some of which are external to the engine. This article will describe a few of them. The following details are important since merely replacing a valve once it fails, and failing to fix the underlying problem, will eventually result in a subsequent failure.

High Combustion Temperatures

When the air-fuel mixture in the combustion chamber is ignited, the temperature can climb to over 2,500 degrees Fahrenheit. The intake and exhaust valves (IV and EV, respectively) are exposed to this heat. Most of it hits the EV since exhaust gases pass by it on the way to the exhaust manifold. Some also hits the IV.

Normally, both valves retain much of the heat produced during operation. But the EV’s operating temperature is higher than that of the IV due to greater exposure to the combustion gases. The part may erode over time. When this happens, holes can develop in its face. This allows compression to leak from the combustion chamber, which affects the engine’s performance.

Accumulation Of Deposits

The valves, as well as other valvetrain components, are designed to allow most of the combustion heat to dissipate. One of the ways in which this occurs is through the interface between the valve seat and the valve face. As long as the contact between them is good, the former will draw most of the heat away from the latter. When the interface is poor, the valve will retain more heat than normal, and eventually fail.

One of the reasons the contact between the seat and the valve suffers is because of deposits that accumulate on both parts. When this happens, the seat cannot properly draw heat away from the valve.

Insufficient Valve Lash

Valve lash (VL) is the space between the valve stem and the rocker arm. The latter pushes against the former, which pushes the valve to open it. When the space is inadequate, the valve absorbs too much heat, which eventually leads to failure.

Other Problems That Increase The Engine’s Temperature

Thus far, we have discussed issues that directly involve components of the engine and valvetrain. But problems elsewhere can cause the temperature inside the combustion chambers to rise, thus exposing the intake and exhaust valves to excess heat.

For example, if there is insufficient coolant in the cooling system, the engine will become hotter than normal during operation. This is also the case if the radiator becomes clogged, preventing the coolant from releasing the heat it absorbs from the engine. A failure or malfunction of any component in the cooling system (e.g. water pump, cooling fan, etc.) can contribute to valve failure.

The temperature inside the combustion chambers can also be affected by spark knock, pre-ignition, and poor ignition timing from the PCM (powertrain control module). Each of these issues may not, in itself, cause valve failure, but can contribute to it over time.

The Cost Of A Valve Job

A valve job may cost as little as a few hundred dollars or a thousand dollars (or more). Much depends on the parts used to replace those that are defective. Cheap replacements are less expensive, but will be more susceptible to failure down the road. It’s also necessary to determine and fix the problem that led to the valve’s failure in the first place. Here, costs vary widely. For example, replacing a clogged radiator will likely be less expensive than resolving the cause of pre-ignition.

It is often unclear that an engine valve has failed or become severely compromised by heat. If you notice your engine behaving strangely, have a mechanic inspect it.

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