Bent Valves
Burnt valves
The other common type of valve failure is valve burn, or burnt valves. Essentially this is caused by combustion gases escaping between the valve and valve seat when they are not sealing correctly. The hot combustion gases are forced past the valve which starts to burn away the edge of the valve, progressively getting worse the longer it is left without being rectified. Normally this type of failure affects the exhaust valves only, but it can also damage the intake valves.
Possible causes of burnt valves are:
- Excessive localized heat
- Burnt Exhaust Valve
- Combustion gases escaping past the valve and concentrated at only one point
- Irregular valve sealing with cylinder head valve seat. Carbon residues generated by irregular combustion (poor mixture) will appear at the seat region and will jeopardize the sealing between the valve and its seats
- Deficient refrigeration is another factor, due to partial obstruction of the cylinder head cooling. As a consequence, the valve is cooled inadequately
- Incorrect valve clearance can jeopardize the valve sealing and also cause this type of failure
- Running a dry fuel such as L.P.G resulting in inadequate lubrication of the valve seat, causing the valve seat to fail and consequently, the valves
To help prevent this type of failure, there are a few things you can do. Maintain a clean, efficient cooling system so the engine does not run too hot, use good quality fuels to help prevent carbon build up on the valve seats, and have your mechanic regularly check the valve clearances are within specifications.
If your vehicle is using an aftermarket L.P.G fuel system, you must check that the engine is L.P.G compatible (most are NOT). In the event your engine is running L.P.G but is not L.P.G compatible, valve failure is imminent. It will generally be less costly to have your cylinder head removed and modified for L.P.G before the valves start to burn, rather than wait until the damage is done. Once the L.P.G modifications are complete, it will be safe to use the L.P.G without damaging your engine.