Valves


Does your engine misfire or have a running problem? Is there excessive smoke coming from the exhaust?

Low compression or a tapping noise, could mean that you have a burnt out valve or the valve seats may be suffering with tarnish deposits. Auto Experts Medway in Chatham near Rochester MedwayAuto Experts Medway in Chatham near Rochester in the centre of Medway

What is a Valve?

A poppet valve (also called mushroom valve) is a valve typically used to control the timing and quantity of gas or vapour flow into the cylinder head of an engine. Valves are usually either round or oval and are tapered and are a disk shape on the end of a shaft called a valve stem. The portion of the hole in the cylinder head where the valve sits is referred as the ‘valve seat’. The shaft guides the valve stem portion by sliding through a valve guide.

How is a Valve operated?

The engine normally operates the valves by pushing on the stems with cams and cam followers. The shape and position of the cam determines the valve lift and when and how quickly (or slowly) the valve is opened. The cams are normally placed on a fixed camshaft which is then geared to the crankshaft, running at half crankshaft speed in a four-stroke engine.

Valve wear:

In the early days of engine building, the poppet valve was a major problem. Valves needed to be re-ground every two years or so by a process known as a valve job. In more modern vehicles valve seats may be made of improved alloys and the valves themselves may be made of stainless steel. These improvements have generally made this problem disappear completely and made leaded fuel unnecessary.

Common faults:

Valve burn is generally due to overheating and can be a major problem. Poor maintenance is a key factor, low oil level or incorrect oil grade can cause excessive valve and indeed general engine wear. This can lead to defective sealing around the valve seating and can cause engine knock or tapping sound. Another major cause of burnt valves is a lack of valve clearance at the tappet, meaning the valve cannot completely close.  This can cause extremely hot combustion gases to leak between the valve and the seat. This can cause the engine to burn oil, this burnt oil may be visible from the vehicles exhaust and will look like blue smoke.

Over time a valve can get a build up of tarnish deposits around the valve stem and can cause the valve to lag. This can cause an engine to have a tapping noise on first start up or in extreme cases your engine may develop a running problem, may misfire or have low compression.

Why Choose Auto Experts Medway?

We at Auto Experts Medway in Medway have established a superb reputation for high quality replacement services, refer to our testimonials from our customers from Chatham, Gillingham and Rochester on our testimonial page.
On many occasions when carrying out a diagnosis a partial strip down is necessary. Should you agree to have any necessary work completed at this time, this initial diagnosis becomes free due to the fact that your vehicle has been partially stripped down already.
So if your vehicle has a misfire, or a tapping noise or running problem, or if it appears that there is smoke coming from the exhaust. It may be due to poor valve seats or a valve may be burnt out. Come to Auto Experts Medway in Chatham we are close to both Gillingham and Rochester in Medway making us the idea garage for shoppers and commuters.

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