What causes bent engine valves?
1) Timing belt/chain failure
The most common cause of bent valves is a timing chain or belt failure. Of course, this depends on whether the engine in question is of interference design or not. Interference design refers to engines where improper timing can cause piston-valve contact. Engines without interference, on the other hand, will not suffer this type of damage.
2) Engine overspeeding
Engine overspeeding is also a possible cause of valve damage. When an engine is over-revved even for a short time, it can cause a condition known as “valve floating.” The term “valve floating” refers to a situation where an engine’s valves do not cycle (open and close) fully as intended, which can lead to contact between the valves and pistons.
3) Lack of lubrication
In extreme cases, lack of proper lubrication can cause an engine’s valves to drag in their guides, eventually causing contact between the valves and pistons. This can also occur when engine oil deteriorates due to repeated neglect of prescribed maintenance.
4) Engine overheating
Valve failure has also been known to occur when an engine is allowed to overheat excessively or for extended periods of time. This overheating can deform internal engine parts such as the intake and exhaust valves.
How to tell if a valve is bent
Valve damage can be detected in several ways, including a careful physical examination. The engine’s valve covers may be removed before starting the affected engine and checking to see if the valves operate smoothly.
Alternatively, the engine’s intake and exhaust manifolds may be removed. At this point, inspection through the exposed intake and exhaust ports is possible.
Valve damage can also be identified using specialized equipment designed to identify compression loss. This equipment can be used to perform leak tests to determine if the engine’s intake and exhaust valves are sealing properly.
How much does it cost to repair?
The only “right” way to repair a bent or damaged valve is to replace it. This is a fairly involved repair, as it requires removing the engine’s cylinder head.
Because of this, labor costs are usually quite high. In most cases, it will cost you around $800 to $1,500 to properly replace a damaged valve head.
However, this price can be significantly reduced if you remove and reinstall the affected cylinder head yourself. In these circumstances, the cost of replacing the valves can be closer to $400 to $600.
There are also many valve repair methods that can be used without removing the affected cylinder head. In most cases, you will need to pressurize the cylinder with compressed air before attempting to manually straighten the bent valves.
Although such repairs are significantly more cost-effective, such attempts are still not recommended, as the “repaired” valve will be weakened, and the corresponding valve guide and valve seat may also be damaged.
