Many instances of scored cylinders can be attributed to the faulty design of cylinder and piston. The temperature of the exhaust gases is high, and, as they pass through the exhaust ports, they raise the temperature of the exhaust port bridges to at least 800°. There is, at best, but a poor cooling effect around the ports, and often this high temperature causes the bridges to elongate. Since the ends of the bridges are held from movement by the rest of the cylinder casting, the bridge must bend and warp to accommodate this growth of the iron. This will, of course, score the piston on• the underside. The rough piston then continues the damage by cutting the cylinder surface. When the cylinder and piston are inspected, and the piston has a bright streak on the bottom, it is safe to assume that the bridges have warped. This distortion must be corrected by bringing the bridge back to its original position. To smooth up the bridge, a file should have its end ground square with the edges sharp. This scraper can then be used to remove the excess metal. If the damage be severe, a roughing cut can be made with a flat file or a block of emery stone.
In some engines the piston is made very light; the walls and head are not able to resist the high pressures. The piston walls tend to bend into an elliptical shape. Once the piston gets out of true, it is only a question of time until the cylinder is badly scored. The only remedy in this event is the purchase of a piston with heavier walls and top.
There exists on some cylinders, especially those on vertical engines, a grooving or cutting of the wall surface into ridges and valleys, these ridges extending about the girth of the cylinder. Just what causes this manner of cutting is unknown, though it occurs more often where the piston has considerable play. Smoothing with a scraper provides the only relief, which unfor tunately is but temporary, as secondary grooves soon begin to appear between the old cuts.
Fractured Cylinders.—Fractured cylinders, due to a poor cooling effect of the circulating water, is Often encountered. It might be stated as an axiom that a fractured cylinder is indicative of a lack of attention on the part of the. engineer. The jackets of practically all engines provide enough water storage space to absorb sufficient heat to prevent the engine from fracturing due to heat stresses. The great trouble that must be overcome is the lack of that careful attention that the engineer should give the machinery under his care. It is absolutely imperative that the flow of cooling water should be uninterrupted. It should
not be necessary to state that the water rhust begin to flow as soon as the engine starts firing. If an engineer lets the entire jacket run dry when starting, he should not blame the manufac turer if a fracture develops in the cylinder.
When the water is bad, carrying much sediment, the deposits, which will always occur on the cylinder walls, must be removed. It is far better to remove the mineral or vegetable matter before the water enters the jacket. • Unfortunately this demands an expensive purification system which is out of question in the average plant. It follows that the jackets must be cleaned periodically. If the scale is bad, an acid solution will allow it to be washed out. Graphite, pumped into the circulating water pipe at frequent intervals, will cause the scale to break loose from the iron walls and prevent new scale from forming. Care should be observed in using graphite. The scale will drop off the hot cylinder walls, allowing water to strike the fresh portion of the wall while it is at a very high temperature: The best plan is to cut the scale with acid and use the graphite to prevent any further scaling. Due to the low temprature of the cooling water, commercial boiler compounds do not prove successful as a scale solvent.
In journeying among oil engine plants, one is struck by the great number of fractured cylinders laying around. It would appear that practically no effort is ever made to repair a cylinder where a crack extends through the wall to the interior. Oil engine cylinders are always high priced (in fact, entirely out of proportion to the factory cost) and more study should be spent on the question of welding the fracture. On engines of less than 10-inch diameter, the expense of welding, with the risk of it being unsatisfactory, is too high for such a procedure to be recommended. On the larger cylinders, if the services of an ex perienced oxyacetylene welder can be secured, the saving is well worth the trouble of welding. In welding ordinary cast-iron parts, the usual method is to cut out a V of the metal, this cut extending through the entire fracture. This allows the welding iron or steel to be deposited in layers, building up from the bottom of the fracture. If this is done in a cylinder, there is a strong tendency for the cylinder to warp out of shape. A small V, to open up the top of the fracture, should be cut, and the welding iron should be kept almost to the burning point to allow it, when deposited, to flow as deep as.possible into the fracture.