Defects in Cylinders
After the cylinders have been removed and stripped of all fittings, they should be thoroughly cleaned and then carefully examined for defects. The interior or bore should be looked at with a view of finding score marks, grooves, cuts or scratches in the interior, because there are many faults that may be ascribed to depreciation at this point. The cylinder bore may be worn out of round, which can only be determined by measuring with an internal caliper or dial indicator even if the cylinder bore shows no sign of wear. The flange at the bottom of the cylinder by which it is held to the engine base may be cracked. The water jacket wall may have opened up due to freezing of the jacket water at some time or other or it may be filled with scale and sediment due to the use of impure cooling water. The valve seat may be scored or pitted, while the threads holding the valve chamber cap may be worn so that the cap will not be a tight fit. The detachable head construction makes it possible to remove that member and obtain ready access to the piston tops for scraping out carbon without taking the main cylinder portion from the crank-case. When the valves need grinding the head may be removed and carried to the bench where the work may be performed with absolute assurance that none of the valve grinding compound will penetrate into the interior of the cylinder as is sometimes unavoidable with the I-head cylinder. If the cylinder should be scored, the water jacket and combustion head may be saved and a new cylinder casting purchased at considerably less cost than that of the complete unit cylinder.
The detachable head construction has only recently been applied on airplane engines, though it was one of the earliest forms of automobile engine construction. In the early days it was difficult to procure gaskets or packings that would be both gas and water tight. The sheet asbestos commonly used was too soft and blew out readily. Besides a new gasket had to be made every time the cylinder head was removed. Woven wire and asbestos packings impregnated with rubber, red lead, graphite and other filling materials were more satisfactory than the soft sheet asbestos, but were prone to burn out if the water supply became low. Materials such as sheet copper or brass proved to be too hard to form a sufficiently yielding packing medium that would allow for the inevitable slight inaccuracies in machining the cylinder head and cylinder. The invention of the copper-asbestos gasket, which is composed of two sheets of very thin, soft copper bound together by a thin edging of the same material and having a piece of sheet asbestos interposed solved this problem. Copper-asbestos packings form an effective seal against leakage of water and a positive retention means for keeping the explosion pressure in the cylinder. The great advantage of the detachable head is that it permits of very easy inspection of the piston tops and combustion chamber and ready removal of carbon deposits.