Chapter XXVIII: Erecting (4)

FITTING ENGINE CYLINDERS.[35]--When engine cylinders are made in quantities, as in locomotive building shops, a great deal of the fitting work is saved by the machine work; but when a single cylinder or a pair of cylinders only are to be fitted up it will not pay to make jigs and appliances; hence, they are usually fitted up entirely by hand. The first thing to do is to mark off all the holes requiring to be drilled, and have the drilling done.

[35] From the "Complete Practical Machinist."

In marking the holes in the cylinder covers it is to be noted whether that part of the cylinder cover which fits into the cylinder has a portion cut away to give room for the steam to enter (as is usually the case), and if so, first mark a line across the inside flange of the cover, parallel to the part cut away, and then scribe each end of the line across the edge of the flange. Then mark a similar line across the cylinder end, parallel to the steam port where it enters the cylinder, and scribe each end of this line across the cylinder flange, so that, when the cylinder cover is placed into the cylinder and the lines on the flanges of the cylinder and the cover are placed parallel to each other, the piece cut away on the cover will stand exactly opposite to the steam port, as it is intended to do. The cover may then be clamped to the cylinder, and holes of the requisite size for the tap (the tapping holes, as they are commonly called) may be drilled through the cover and the requisite depth into the cylinder at the same time.

The cylinder covers must, after being drilled, as above, be taken from the cylinder, and the clearing drill put through the holes already drilled so that they will admit the bolts or studs, the clearing holes being made 1/16 inch larger than the diameter of the bolts or studs. The steam chest may be either clamped to the cylinder, and tapping holes drilled through it and the cylinder (the same as done in the case of the covers), or it may have its clearing holes drilled in it while so clamped, care being taken to let the point of the drill enter deep enough to pass completely through the steam chest, and into the cylinder deep enough to cut or drill a countersink nearly or quite equal to the diameter of the drill. If, however, the steam chest is already drilled, it may be set upon the cylinder, and the holes marked on the cylinder face by a scriber or by the end of a piece of wood or of a bolt, which end may be made either conical or flat for the purpose, marking being placed upon it; so that, by putting it through the hole of the chest, permitting it to rest upon the cylinder face (which may be chalked so as to show the marks plainly), and then revolving it with the hand, it will mark the cylinder face. This plan is generally resorted to when the holes in the chest are too deep to permit of being scribed. To true the back face, round a hole against which face the bolt head or the face of the nut may bed, in cases where such facing cannot be done by a pin countersink or a cutter used in a machine, the tool shown in Fig. 2510 may be employed, _a_ being a pin provided with a slot at one end to admit the cutter B, which is held fast by the key C, and is also provided with a square end _f_, by which it may be turned or revolved by means of a wrench, and with a thread to receive the nut E, _d_ being a washer; so that, by screwing up the nut E, the cutting-edges of the cutter are forced against the cylinder _g_, and will, when revolved, cut the face, against which they are forced, true with the hole in the cylinder through which the pin _a_ is passed.

After the drilling the cylinder should be placed on end and all the holes that can be got at should be tapped. Then the cover joint, supposing it to be a ground joint, should be made according to the directions given for making ground joints, when the cylinder may be turned upside down and the other cover fitted. Then the holes for the cylinder cocks and for the steam and exhaust pipe should be tapped, and the faces for these pipe joints fitted as required.

The steam-chest holes should then be tapped and the ports marked out and chipped and filed to the lines, such lines being marked as described in the remarks on lining out work.

The face for the steam-chest seat and the steam-chest cover may then be prepared by filing, scraping, or grinding, as may be required, and simultaneously the valve seat and valve face may be fitted. If the cylinders are to be bolted together as in a locomotive, the holes for holding them together should be drilled about 1/64 inch smaller than the bolts, so that they may be reamed out together after the cylinder bores are aligned.

One cylinder face should be marked and drilled first, and the two cylinder bores being set to align true the other cylinder should be marked from the other, or if there is a saddle between the two cylinders both cylinders may be marked and drilled, and also the holes on one side of the saddle. Temporary bolts may then be put through the holes that are drilled in the cylinder and saddle and clamps used to hold the undrilled cylinder to the saddle, when the cylinder bores may be set true one to the other, and the holes on the remaining side of the saddle marked through those already drilled in the cylinder. These latter holes being drilled, temporary bolts of smaller diameter than the holes (so as to give room to move the cylinders to align their bores) may be used to bolt the cylinders together while their bores are accurately aligned, which alignment may be effected as follows:--

The bores should be set as near true as possible, tested by a spirit-level rested on the bore and placed as near true as can be judged with the length of the bore, and a plumb rule may be applied to the end faces where the cover joint comes. Then a straight-edge should be applied, as in Fig. 2511, in which S is the straight-edge, and C and D the two cylinder ends.

The method of testing is shown in Fig. 2511, where the straight-edge S is shown in three positions, marked respectively 1, 2, and 3 at one end, and F, G, and H at the other.

The first test should be made by simply placing the straight-edge across the two cylinder faces, as at G 3; and when the cylinders are set apparently true and the spirit-level applied to the respective bores shows them true, greater accuracy may be secured by placing the straight-edge in position 1 H, being pressed firmly to its cylinder face with end 1 above the other cylinder face. Then, while end H is held firmly to its cylinder, let end 1 lower until it passes entirely over the face of cylinder C, whose face it should just touch; if on meeting C the straight-edge strikes it or does not meet it, further adjustment of the cylinder positions is necessary. Next place the straight-edge in position 2, pressing end F firmly against cylinder D, and passing the other end entirely over the end of cylinder C, which it should just touch, and no more. It will then be necessary to repeat this process, pressing the straight-edge against cylinder C and testing the other end with cylinder D, and the cylinders thus set will be (if the end faces are true, as they should be, and usually are) more truly aligned than is possible by the use of the spirit-level. This method also brings the end faces of the cylinders in the same plane, so that each piston head will travel central in the length of the cylinder bore, approaching the cylinder covers equally, and therefore keeps the clearance equal. Incidentally, also, this secures accuracy in the cross-head traverse on the guide bars (supposing these bars to be bolted to the cylinder cover). The holes for bolting the cylinders together may then be reamed and the bolts driven in and screwed up.

To guide the tap when tapping the cylinder cover and steam-chest holes the guide stand S, shown in Fig. 2512, should be employed. It is bolted to the cylinder face by the bolt B, which passes through a slot in the stand.

The tap T is inserted through the two arms of the stand and its end inserted in the hole to be tapped when bolt B is tightened up.

The stem of the tap should be of slightly larger diameter than the tap thread, so as to fit in the holes of the guide or stand.

When, however, one end of the guide bars is carried on the cylinder cover, it is necessary when setting that cover to be marked for the drilling, to so set it that the seats for the guide bar ends shall be horizontally level when the cylinder is on the engine; and when setting the bores of the cylinder in line to mark the holes for bolting the cylinders together or to the saddle, this point should also be looked to, as if these seats are not in line the faces of the guide bars will not be in line, and will not, therefore, bed fair to the cross-head guide unless the error is in some way corrected.

It is desirable that these seatings be quite true and in line one with the other on both cylinders, so that if liners require to be made, or if the ends of the bars require to be filed to let the bars together at any time, the surfaces may be filed true to the face of the bar, and thus be set true and to fit the cross-head guides without requiring to put the bars on and off to fit them true by trial.

REBORING CYLINDERS IN THEIR PLACES ON THE ENGINE.--When a cylinder bore becomes so worn out of cylindrical truth, or becomes grooved or cut, as it is termed, as to require to be rebored, it may be done with the class of boring bar shown in Fig. 2513. It consists of a bar having journal bearing in castings which bolt on to the two ends of the cylinder in place of the cylinder covers. On the bar is fitted a sliding head carrying the cutting tool and fed by a screw passing within the bar. To operate the bar and simultaneously the feed screw, the hand-wheel and worm-wheel is employed, giving rotary motion to the worm-wheel which is fast upon the bar. Fast also upon the bar is the inside one of the two small gears shown, which operates the inner of the two small gears shown above it. The outer of the upper gears engages with the outer of the lower ones, the latter being fast upon the feed screw. In the inner pair the lower is of largest diameter, but in the outer pair the upper is the largest, and as a result the outer of the lower rotates the fastest, and hence rotates the feed screw, causing the tool to feed to its cut.

The proportions of these wheels are, first or inside pair, lower wheel 36, upper 37; outside pair, upper 37, lower 36, so that the feed per bar rotation is in amount that produced by moving the outer lower gear a part of a rotation equal to twice the pitch of the teeth, the cutting tool motion depending upon the pitch of the feed screw.

To enable the rapid traverse of the head from end to end of the bar, the upper pair of gears are mounted on an eccentric stud, so that by operating the small handle shown they may be disengaged from the lower feed gears and the feed screw operated direct by means of the handle shown.

In setting such a bar to a cylinder bore it is to be remembered that two methods may be employed. First, the bar may be set to accommodate the cylinder bore, truing it out with as light a cut as possible. In this case the bore of the cylinder may be made out of line with the guide bars and with the centre of the length of the crank-pin journal.

In the second the bar may be set with a view to bore it out in line with the guide bars and crank pin, and then taking as much cut as will be necessary to true the bore.

The latter plan is the preferable of the two, unless the repairs are so extensive as to require the guide bars to be redressed and the main bearing renewed, in which case those parts requiring to be re-aligned, the cylinder may be rebored with a view to take out as little metal as possible, and the other parts set to suit the new bore.

To set the bar true to the guide bars and crank pin, and thus retain the axis of the new bore true with that of the original bore, the bar should be set true with the recessed counterbore at each end of the cylinder, which being unworn remains true.

If, however, only one cylinder cover can be conveniently taken off, the piece of wood will require to fit in the counterbore at the open end, and in the cylinder bore at the closed end of the cylinder; hence we make it large enough for the counterbore, and after having removed the ridge at that end we cut the length of the wood down to fit the cylinder bore, whereas if we made our rest to fit the bore at first we should require to use wedges to make it fit the counterbore. In some cases holes might be bored near the ends of the rest or fulcrum to serve the same purpose as the notches.

The method of using the scraper, Fig. 2516, is shown in Fig. 2514, which latter represents an engine cylinder. At B is shown the wooden rest or fulcrum; and at C the lever scraper operating on the ridge at the closed end of the cylinder. The lever C is worked on the pulling stroke only, and is so held that the edge presents a keen scraping tool which will cut very freely. The fulcrum B should be adjusted as closely as convenient to the work, so as to obtain good leverage for the scraper. It should be moved in its position, so that during the roughing out only the lower notches in the fulcrum are used.

A plan was lately resorted to on the White Star Line of steamships for re-boring a cylinder. The cylinder heads and piston follower were taken off; a groove was cut from the outer end of the cylinder along the bore as far and as deep as the counterboring was required to be done. The counterboring was then accomplished in the manner shown in Fig. 2515. The junk ring was provided with a small tool holder, such as is used upon boring bars. The tool was fastened in the holder while its cutting edge was in the groove referred to, cut as deep and as far up the cylinder as the counterboring was to be. To the junk ring was fastened, by two long bolts, a wooden lever extending above and across the cylinder. Two men walked around pushing the lever, and when the tool at each revolution arrived at the groove, a fresh cut was taken by moving the engine so as to raise the piston the necessary amount. It is obvious that the piston head may be steadied and held true in the bore of the cylinder by means of a few wooden wedges. Thus we see that in this operation the junk ring was made to serve as a boring bar head, the men furnishing the necessary rotative motion, the feed motion to the tool being obtained by advancing the piston toward the end of the cylinder where the work was being done.

The ridges which in time form at the two ends of a cylinder bore are usually removed by the hand-boring bar shown in Fig. 2513, but they may, in cylinders of from 12 to 24 or 30 inches in diameter, be readily cut out by hand as follows:--

Take a bar of steel 9/16 inch square and 3 feet 6 inches long; forge it at one end to the shape shown in Fig. 2516, in which from A to B is the forged end. This end must then be heated along its entire length to a cherry red, and dipped vertically into cold water to harden it; after which it must be ground from A to B on all four faces square across, and as nearly of an even curve as can be ascertained by the eye. Next take a piece of hard wood--oak, for instance--about an inch thick and 3 inches wide; cut it to such a length that when placed upright its ends will wedge tightly into the counterbore of the cylinder. Into the edges of this piece of wood saw out a series of notches, making its finished appearance to be such as shown in Fig. 2517. The object of fitting its length tightly into the counterbore of the cylinder is as follows: If both cylinder covers are off or can be conveniently taken off, the ridge can be operated upon at each end of the cylinder; hence our piece of wood, which is merely an improvised rest to act as a fulcrum for the bar scraper shown at the top of the figure, would require to fit into the counterbore.