The Performance of (car paint protection) Antique Car Engines

October 29th, 2008 admin Posted in automotive |

By Peter Salmonford

It is often assumed that when an engine is new it gives its maximum power, but in actuality this is not the case. At the outset the bearings are tight and the bearing surfaces comparatively rough, and it is not until the engine has run some months that the highest power is developed. It is not to be assumed that up to this period the engine gradually increases in power, but that a higher power can be obtained from an engine after being well run in than when it is new.

In actual practice the engine gradually gives less and less power unless it receives the necessary small amount of attention to keep it up to its best pitch. The cause of this is a gradual loss of compression, chiefly owing to the burning away or pitting of the valves and their seats, the remedy for which is regrinding. Valve-grinding is a somewhat laborious process, but it is one which generally effects considerable improvement in the engine’s running, and it should be made a periodic practice, and not be left till the engine is running very badly, as the necessary grinding will then be somewhat difficult.

If a valve is examined it will be found that it has a flat angular surface on the underside of the head, and this surface rests upon a similar conical surface, called the valve seat, formed in the cylinder head. These two surfaces must be absolutely true and smooth so as to prevent any gas leakages when the valve is closed by the valve spring.

When the exhaust valve is opened the exhaust gas, which is an intensely hot flame, passes between these two conical surfaces, making them practically red hot, which is their normal condition during running of the engine. It is hardly surprising, therefore, that in course of time the surfaces deteriorate, and the necessity for regrinding can be ascertained from an inspection of the valve and its seat. If smooth and bright all round, the valve is in good order. If dirty and rough, it requires regrinding. When loss of power is experienced, to ascertain if it is due to loss of compression, the engine should be turned round slowly, with the switch off, and if the resistance on the compression stroke is not what it was when the engine was new, it is clear that there is a leakage somewhere, and the exhaust valve should then be examined as mentioned. Possibly only one or two of the valves are at fault, so the compression in each cylinder in turn should be tested in this way.

Before a valve is ground in it is, of course, necessary to remove it, and this, with its replacement, forms probably the most difficult part of valve grinding, on account of the stiffness of the valve spring, coupled with the fact that the parts are generally difficult of access, on account of the presence of the piping, etc.

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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Grinding Valves in Antique Cars
By Peter Salmonford

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.

Handling Soot in Antique Car Engines
By Peter Salmonford

In the course of running soot is formed in the engine, the quantity varying with the richness of the mixture and the facility for the lubricating oil to get past the piston. This carbonaceous deposit, combined with the non-inflammable constituents of road dust which are sucked through the carburetter, adheres to the cylinder walls and combustion head, causing falling off of power, and in time preignition. When the valve cap is removed it will be found that its underside is coated with soot, and sometimes even with a hard deposit, an indication of the state of the interior of the cylinder. To remove this carbon deposit, the usual procedure is to take off the cylinder so as to expose the parts and scratch off the deposit with a screwdriver or some similar instrument. From the tops of the piston the deposit can be cut away with a knife, and when removed the surfaces should be polished with fine emery cloth, as deposit adheres less easily to a polished surface. The deposit must be completely removed from all parts of the cylinder as well as the piston, a matter of some difficulty.

There have been one or two inventions evolved from time to time to remove the deposit without necessitating the dismantling of the engine. One of these is to insert a steel ball of about 5 inch diameter into the cylinder and then to run the engine, its action being to hammer the carbon deposit and so chip it off the surface. Another, and more promising, process consists in passing a stream of oxygen into the cylinder, lighting it, and so causing a chemical combination to take place between the carbon and the oxygen. As soon as all the carbon has combined the flame goes out, and it is known that the cylinder is clean. The writer has not tried either of these schemes, but mentions them as matters of interest. The ball process, however, would seem rather risky.

To keep an engine in good running order the valves, apart from grinding-in, require careful attention. In the olden days silence of running was not of great importance, but nowadays it is an essential, and to obtain it one of the most important points is to see that the clearance between the valve tappet and the bottom of the valve stem is small. As the engine runs it will be understood that the tappet rises rapidly and strikes the foot of the valve. If there is a large clearance between these two the impact between the tappet and the valve causes a clicking noise, which should be stopped by adjusting the tappet head close up to the valve stem. The usual distance or clearance is about 5 inches. The top of the tappet head is inlaid with fibre to reduce the noise, and in course of time this fibre becomes dented or recessed. The tappet should then be removed and its head filed flush so as to remove the indentation.

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