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A Basic Guide to Engine Valve Failure

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Engine Valves

The valves in your cylinder head are a vital component of your engine and undergo enormous stresses, opening and closing up to 2500 times every minute under normal operating conditions. When one or more of these valves are damaged, the result can be anything from reduced power and poor fuel consumption, to complete engine failure.  The two most common types of valve failure are bent/broken valves and burnt valves.

Bent Valves

The most common failure of valves is bending or breaking as a result of contact with the pistons. The valves contacting the top of a piston is due to incorrect engine synchronization caused by timing chain/belt breakage and incorrect fitting of new belts and chains. If you suspect your engine may have bent or broken valves, it is crucial not to attempt to start the engine as this may result in more costly damage being caused to the cylinder head, pistons and cylinder bores.

The bent valves above are a result of a fatigued timing belt that has broken. Your timing belt doesn’t last forever and needs to be replaced according to the manufacturer’s service guidelines. Replacing your timing belt is cheap insurance against costly engine damage.

Burnt valvesValve-Piston-Diagram

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.

A burnt valve will cause issues with your vehicle’s performance and fuel consumption. Rough idle, reduced power, backfiring, and misfire are all symptoms of valve burn. If your engine is showing symptoms like these, we recommend you get your car checked by a trusted mechanic, as continual driving with a burnt valve will cause more damage to your engine, and will in turn cost more to repair in the long run.


Possible causes of burnt valves are:

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Bent valves caused by broken timing belt

  • Excessive localized heat
  • 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 seat
  • 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 valv
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    A Valve Starting To Burn

    e 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

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Burnt Exhaust Valve

the L.P.G without damaging your engine.

The Damage That A Lack Of Servicing Can Cause

You may think that having your vehicle regularly serviced is not essential however the following situation that one of our customers found themselves in may cause you to reconsider!

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The piston rings are full of carbon deposits which caused low engine compression

The customer came to us earlier in the year wanting a service on his Hyundai Getz – it had done 51,000 kms & its last service was 30,000 kms ago. While carrying out the service we found that it had low compression due to the rings on the pistons being full of carbon deposits as highlighted in the picture below.

This damage was a direct result of the vehicle not having had an oil change in 30,000 kms. As a result, the engine had to be fully dismantled, cleaned and rectified costing the customer in excess of $4,000.00. Had more regular servicing been carried out on the vehicle this damage would not have occurred and the customer would only have been up for the cost of a service – a much less costly exercise!

Has it been a while since your last service? Even though you might not have experienced any repercussions yet it is most often the case that damage is already being done to your vehicle’s essential components. Don’t keep putting it off until it’s too late!