Reboring Cylinders.—The natural course of wear in the liner increases the clearances to such an extent as to require reboring. The liner, as an average, will need replacement or reboring every three to five years, dependent on the hours of service and the attention it has received.
When the engineer is confronted with the problem of cylinder reboring, it is well for him to shift the work to the shoulders of some machine shop that makes a specialty of such work. The actual reboring is not hard, neither is the setting up of the boring machine; however, it requires a boring bar that will cost around :00, and few shops are willing to place their machine on a rental basis. A shop that does much of this work charges $15 per inch of cylinder diameter—a 16X24 in. cylinder would cost $240 to be rebored and fitted with a new piston. This represents a fair charge and is far less costly than the entire replacement of the liner.
Liner Replacement.—All cylinders are of a thickness that will allow at least one reboring. If the liner becomes worn, after it has had one reboring, or if it is fractured, the withdrawal of the damaged liner is easily effected by the use of the draw-bolt, as outlined in Fig. 74. The spider may be made with either two or three fingers; the two fingers are as serviceable as the three fingers. The bolt is of cold rolled shafting, the thread having a 1M-inch diameter. The spiders are placed over the cylinder flange and the front end of the liner as indicated. A part turn of the nut will bring the rod under tension; a few sharp blows on the inner surface of the liner at the head end will, in most cases, loosen it so that the bolt can pull it out with ease. If the liner resists, additional bolt tension, followed with hammer blows along the liner supports, will expedite the removal.
In inserting a new liner the oil passages must check, as also must the dowels. After the casting has been driven into place by the use of a sledge and hardwood block, the bolt and spiders used in removing the discarded part can be reversed to press the liner into the recess.
Cylinder and Head Joints.—While a few engineers depend on a metal-to-metal joint at the head to withstand the cylinder pressures, some form of gasketing is now well-nigh universal. The gasket may be either a flat copper ring, a copper wire, or a round rubber ring.
The flat copper ring is very successful as a gas check and is not difficult to make. Its objectionable feature is the large
amount of sheet copper that is wasted in cutting the ring. Ex perience proves that the thinner copper sheet makes the best gaskets; thickness of metal is ample and enables the gasket to conform to the flange face. The gasket is best cut scant so that it fits easily into the gasket recess. If it is so wide as to require driving, the edges will bend and the gasket will not prove gas-tight. If a gasket cutter is not at hand, a pair of tin ner's shears will be very satisfactory. A wooden mallet is handy to hammer the gasket to a flat surface.
In case sheet copper cannot be procured, an equally service able ring can be made of No. 10 gage soft copper wire; when the bare copper is not available, water-proofed electrical wire of No. 10 gage may have its insulation burned off and the bare wire used. The wire is formed into a circle of the proper diameter and the ends sol dered together. If the cyl inder flange is not provided with a recess to receive the ring, the latter should be placed inside the bolt circle, touching each stud. This allows the leverage to be a minimum. The wire must be free from kinks or bends.
Round rubber gaskets are often used on vertical engines, particularly on the McIntosh & Seymour engines. The rubber tubing is shaped into a ring of the proper diameter and the ends united by rubber glue. In engines where the cooling compartment of the head communicates with the cylinder jacket by cored openings at the flange the openings are surrounded with like tubes. These gaskets of rubber tubing can always be obtained from the engine builder, but any mill supply house will furnish the tubing in coils at a far less cost.
Drawing Up Cylinder Stud Nuts.—In tightening up the cyl inder-head nuts, many engineers draw up one nut as snugly as possible before drawing up any of the other nuts. Such handi work is evidence of a lack of mechanical knowledge and is to be shunned. If the top of the studs are numbered in pairs, similar to Fig. 75, and tightened in rotation, the head can. be drawn down quite evenly. As example, all the nuts are run down against the head, then the No. 1 nuts are given an eighth turn, followed by a similar performance on No. 2 nuts, etc. Re turning to the No. 1 they are given another eighth turn, etc. When giving the nuts the final movement, a workman can strike the wrench handle several sharp blows with a sledge.