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Owing to the fact that the inlet valve is not subjected to the temperatures which the exhaust valve reaches, it is very rarely necessary to grind it in. The period at which valve grinding becomes necessary varies with different engines and the care of driving, etc. Roughly, with a water-cooled engine, the exhaust valve should be ground in after 3,000 miles and the inlet after 6,000. No harm can be done by grinding in a valve, so that if an engine loses power before it has run this distance it is well to examine the valves and give them a slight grinding. After the valve is replaced the cotter should be readjusted, and locked by means of the nut. If a valve is badly burnt examination will show whether it is better to fit a new valve rather than grind in the old one. Very often a badly burnt valve can be recut and trued, and to replace the whole process of valve grinding, a process of valve truing and an apparatus for carrying it out has been evolved by the Southern Automobiles, Ltd. The apparatus consists of a pair of cutters, one of which recuts the valve face after it has been removed, whilst the other has the same effect on the valve seating. Into the respective merits of the two processes it is not proposed to enter, but valve grinding is the more common practice, and it can be applied not only to the main engine valves, but to other valves when the need arises. Thus a petrol or water tap sometimes leaks slightly, when it should be removed and the removable part ground in with some fine emery powder. It will have been gathered that grinding-in of valves is done to restore loss of compression, but this weakness is sometimes due to other causes. For instance, any one of the cylinder joints may be leaking. The sparking plug washer and that upon the valve cap which screws into the opening sometimes leak, and to ascertain if this is the case some paraffin should be squirted round these washers and the engine turned round just to come on to the compression stroke. When pulled slowly over the compression stroke the presence of bubbles will indicate if there is any leakage at these points. If there is leakage new washers must be used. On no account should any adhesive mixture, such as boiled oil or gold size, be put on the screw threads. This is sometimes done to obtain good compression, but it is inadvisable, on account of the extreme difficulty in separating the parts later.
Article Source: http://www.new.citynewslive.com
Peter Salmonford is a keen fan of cars, and likes to write about antique and modern vehcles. Take a look at his other articles on hydrogen conversion, the benefits of an electric car kit and using browns gas in your own car.
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