Tài liệu Diezel 1410 P11

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General. The operator of any piece of machinery should thoroughly understand the various adjustments that are necessary for perfect operation

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11 JOURNALS, BEARINGS, AND ALIGNMENT A. GENERAL 11A1. General. The operator of any sixty-fourths and thirty-seconds of an piece of machinery should thoroughly inch are not recognized in diesel engine understand the various adjustments that work; the increment of measure for are necessary for perfect operation. It is everything is thousandths of an inch. not enough for him to know merely which valve to open and close or the There should be a regular routine for position of maneuvering levers in order checking the different systems of the to start, stop, and reverse his machine. engine and performing upkeep functions. He must possess knowledge of the At this time all indications of wear, parts functioning of each of its systems when renewed, and adjustments made should he manipulates this gear. He should be be recorded in a systematic log book to alert to note the difference between be used as a history from which efficient and poor performance by the information may be obtained at future sound, smell, and touch of the overhaul periods. This is always done machinery. Instruments, such as gages, during submarine refit periods and at any thermometers, and tachometers, other time when it is found necessary. however, should be the guides that the operator uses in detecting the approach 11A2. Construction of bearings. The of trouble so as to take corrective method used in construction of a bearing measures before anything serious depends upon the type, the bearing occurs. metals to be used, and the type of use required. In the case of precision type The modern diesel engine demands bearings, it is necessary that the two greater skill on the part of the designer halves form a true circle when finished. and builder than any other kind of This requires rather ingenious practice, engine. Likewise in its operation it is and shop procedures will vary. far from being foolproof and requires intelligent attention. The adjustments Other than the shop procedure, there are are precise and to narrow limits. only a few items concerning the Overhaul and fitting of the pistons, construction of bearings that are worthy rings, bearings, valves and fuel pumps of mention. The first of these is the are beyond the capacity of the ordinary question of oil grooves. Bearing machinist and demand the efforts of a lubrication in the 2-stroke cycle engine is skilled mechanic. If it is properly more difficult than in the 4-stroke cycle adjusted, a diesel engine, once started, engine, since in the latter, the point of will run until it is stopped. The extent contact between bearing and journals of of its reliability over a long period of both main and crankpin journals rotates operation depends upon the intelligence around the bearing and assists in the and skill of its operator. distribution of the oil. In the 2-stroke cycle engine, the point of contact swings Care must be used when operating oil back and forth across the lower bearing engines of any make, regardless of shell and hence, in this engine, it is whether the engine is of the 2- or 4- usually necessary to provide oil grooves stroke cycle, vertical or horizontal, air on the unloaded side to carry sufficient or mechanical injection. The working oil to the loaded half of the bearing. principles are the same, and the same Where bronze or other flat bearings are care must be exerted to have everything used as wrist pins, ample grooving must properly adjusted before starting or be provided. Grooves may be cut axially, operating the engine. Otherwise, there circumferentially, diagonally, or helically may be trouble. Every bearing should across the face of the bearing, but should
be adjusted as tightly as possible. This never extend to the edge since this would is a task for the real mechanic and allow the oil to spill from the bearing. All should not be entrusted to unskilled grooves should have rounded personnel. The upkeep of the engine is an important duty, and one in which the real engineer shows his value. It should be kept in mind that measurements of 216 edges, as the sharp edge of a groove has surfaces may make physical contact and a tendency to act as a scraper and may rupture the oil film. impair the oil film. From the above, it is obvious that an oil In order that the flow of oil between the film must be maintained at all times in bearing halves may not be restricted, order to carry the load. This condition is bearings are beveled for an arc of about called stable lubrication. When the oil 20 degrees at the joints where the film is destroyed and lubrication of the bearing halves come together, except bearing depends entirely upon the for a narrow strip at the ends, where the oiliness of the lubricant, we have what is full thickness of the metal must be known as unstable lubrication. This latter retained to prevent the loss of oil. The condition exists when the bearing shaft is spaces formed by beveling are called running at too low a speed to build up an oil film or when the bearing is oil cellars. overloaded. 11A3. Bearing loads. The only bearings in a diesel engine that require 11A4. Bearing metals. Compared with careful consideration due to the heavy the journal, the bearing metal should be loads placed upon them are the main, sufficiently soft so that any solid matter crankpin, and wrist pin bearings. Other passing through in the oil stream will bearings are not so limited in size, and wear the bearing instead of the journal. little attention need be given them in so far as their ability to carry the load is Roller and ball bearings are frequently concerned. The following discussion used in diesel engines for smaller shafts, pertains principally to the above three such as camshafts, and in governors, heavily loaded bearings that are usually because they greatly reduce the bearing limited in size by the space available. friction and because their smaller clearances keep the shaft more rigid. In at The study of bearing loading brings least one opposed piston type of diesel two things to mind: 1) the temperature engine of medium power, ball bearings at which the bearing must operate, and are used as main bearings. For wrist pins, 2) the maximum pressure per unit area roller bearings of the needle type are that will be exerted upon the bearing. used extensively in other types of large Too much pressure will squeeze out the engines. With these bearings, lubrication oil film and ruin the bearing, and too is made simpler, and the amount of much heat will reduce the viscosity of freedom of motion and friction is the oil until the film can no longer be reduced. maintained. Both of these are factors of loading, although the latter is a product Wood is used in the tail shaft bearings of of loading and speed of rotation. naval vessels that are submerged in water and constantly lubricated and cooled. In a diesel engine operating at variable Lignum vitae is the wood commonly loads, the successful bearing design is used for this purpose since it is of a generally the result of experimentation greasy character and extremely hard and directed toward the discovery of a dense. Other types of materials used for
satisfactory bearing for all loads. The this purpose include hard rubber strips loads that a bearing can withstand are and phenolic resinous materials. based upon the assumption that the surfaces of the journal and bearing are Bronze bearings are used where the smooth and parallel, that proper pressures are very high such as at the clearances are provided, and that wrist pin. Here the load on the bearing is sufficient lubrication is provided. Too the total gas pressure less the inertia of much oil clearance at the ends of a the piston. In most modern diesel bearing will cause excessive oil leakage engines, bronze is used as the bearing and subsequent reduction in load- metal for the wrist pin bearing. carrying ability. If the bearing were closed at the ends, the pressure would There is no material known that is be uniform over its entire length, and suitable for all types of bearings. There much greater loads could be carried. If are four general types of alloys used the shafting is of in alignment, or today but each has its own particular uses vibrates severely, as when running at a determined by the maximum unit critical speed, the faces of the journal pressure and temperature at which the and bearing will not be parallel, and the metallic 217 bearing will operate, and by the shells are either forged or cast, and the hardness of the journal. linings are made of lead-base babbitt metal. Bearing metals should be of such composition that the coefficient of In the naval service the most frequently friction is low. They should be encountered bearing metal used in sufficiently hard and strong to carry the precision bearings is that known by the load, but must not be brittle. If they are trade name of Satco. The composition of too soft, they will wipe or be pounded this metal is as follows: out, destroying the clearance and reducing the bearing area. In grooved Percent bearings the grooves will become filled Calcium .30- .70 with wiped metal. When this trouble Mercury .40- .90 arises the oil film is squeezed out, the Tin 1.00-2.00 metal is burned, and failure results. Aluminum .15- .17 The four commonly used types of Magnesium 0.00- .05 bearing linings are: high-lead babbitts, Lead Remainder tin-base babbitts, cadmium alloys, and copper-lead mixtures. 11A5. Bearing installation and adjustment. In order to insure its The backs for bearings are made either successful operation, the bearing must fit of steel or bronze in the case of the the journal perfectly; the bearing and babbitts, while only steel backs are journal surfaces must be smooth and used for cadmium alloy and copper- parallel, and the bearing clearance must lead bearings. In some bearings, an be correct. Too great a clearance will intermediate layer of metal is used allow the oil to spill out at the ends of the between the backs and the bearing bearing, while too small a clearance will metals. cause the bearing to run hot. In general, the least clearance that will allow the The hardness of the above bearing successful operation of the bearing is metals naturally varies with the desirable. percentage of alloying employed. In
general, however, the copper-lead and In the modern high-speed engine the cadmium alloys are the hardest, while precision type of bearing is generally the high-lead and tin-base babbitts are used. No scraping-in is done, and no the softest. The temperature at which shims are used between the faces of the the bearing metals melt is a rough two halves. The bearing is accurately measure of their degree of hardness, the machined to the correct diameter and the softer metals melting at the lower only fitting necessary is an occasional temperatures. The softness of the filing down of the faces of the two halves bearing metal is also a measure of the in order to obtain a close and even fit maximum allowable unit pressure. The when the bearing caps are brought harder the bearing metal, the greater is together. In connection with the fitting of the load that a given size bearing will precision type bearings, too much emphasis cannot be placed upon the carry without failure. importance of having the backs of the bearing shells fit evenly against the Where two metallic surfaces are moving in contact with each other, such bearing support. Recent experience with bearing failures due to this improper as a journal rotating within a bearing, wear will inevitably take place. Since it fitting has shown its importance. The areas not in contact fill with oil or air, is easier and cheaper to renew the both of which are relatively poor bearing, the journal should "be harder than the bearing. Therefore, when using conductors of heat, and the transfer of relatively hard bearing metals, such as heat from the bearing is reduced, causing the bearing temperature to increase. In cadmium alloy and copper-lead, it is addition, if an even fit is not obtained, a necessary to use a hard alloy steel journal or else to harden the surface of flexing of the bearing shell may result, causing the bearing metal to crack and the journal. flake off. The precision type of bearing is rapidly coming into universal use for crankpin and main bearings. There is an increasing use of very thin bearing linings on steel shells. The 218 To assure an even fit the backs of the bearing should be examined at once. bearings should be fitted to their Also the lubricating oil gage pressure to supports in the same manner that the the system and the passage of cooling bearings are fitted to the journal. Since water through the oil cooler should be the back usually is made of steel, it is checked. Sometimes the overheating may necessary to file down the high spots be due to foreign matter in the lubricating rather than scrape them down as is oil. The oil should be rubbed between the possible with softer bearing metals. fingers to detect the presence of grit or dirt. An inspection of the filters will also reveal any abnormal amount of foreign 11A6. Bearing failures. When an matter deposited there. Since used oil engine bearing fails in service it can generally is slightly acid, the presence of generally be attributed to one or more salt water may be detected by inserting a of the following causes: strip of red litmus paper in a sample of the oil. If salt is present to any degree, 1. Poor operating conditions and the litmus paper will turn blue. If salt improper maintenance such as: water is detected in the oil, the crankcase and sump tank should be drained and a. Improper or insufficient lubrication. refilled with new oil after flushing the system thoroughly. If possible, the cause
of the salt water in the system should be b. Insufficient cooling water. determined. At the first opportunity the system should be well cleaned to remove c. Grit or dirt in oil. any particles of salt that may have been deposited there. d. Water in oil. As a rule, hot bearings may be traced to e. Bearings out of alignment. one or more of the following causes: f. Installing the bearing with improper 1. Improper or insufficient lubrication. clearances or uneven bearing surface. 2. Grit or dirt in the oil. g. Excessive load on the bearing. 2. Faulty design of the bearing or of the 3. Bearings out of line. engine itself. 4. Bearings set up too tightly. a. Improper dimensions of length and 5. Uneven surface of bearing or journal. diameter. 6. Bearing overloaded. b. Improper bearing material. If the temperature of the bearing c. Improper lubrication. The lubricant, continues to rise after the oil supply has free from all foreign matter, must be been increased, the condition known as a supplied in ample amounts. hot bearing arises. The danger of a hot bearing lies in the fact that the babbitt d. Improperly cooled. expands until it grips the journal, thus causing a constant increase in friction e. Improperly grooved. and heat. When the temperature reaches the melting point of the bearing metal, f. Improperly baffled. Proper baffles the metal will run or wipe. must be fitted to prevent loss of oil, or its passage to adjacent parts of The treatment of heated bearings machinery, such as generator armature, involves two main items: the removal of where damage would result to the the cause, and the restoration of the commutator. Also in some cases baffles bearing to its normal condition. If the are used to prevent the mixing of water trouble is due to improper or insufficient with the lubricating oil. lubrication and is discovered before the 3. The use of inferior lubricants, or the metal has wiped, an abundant supply of use of a good lubricant which does not oil usually will be sufficient to control the situation and gradually bring the meet the requirements of the piece of bearing back to its normal temperature. machinery. Should the trouble be caused by an accumulation of dirt on the bearing, the a. Corrosion of bearings. abundant supply of oil will generally 4. Inferior workmanship and material in flush out the manufacture of the bearings and engine parts. A bearing that is not operating properly will overheat. When this occurs, and the reason is not immediately known, the oil supply to 219
condition can become serious enough to the impurities sufficiently to permit cause bearing failures, and the only operation. remedy is to machine or grind down the journal until it is again cylindrical. This, If the trouble is caused by foreign of course, will reduce the diameter and matter in the oil, the oil will have to be necessitate using a bearing of a different renovated or renewed. If the bearings bore in order to effect the proper bearing are out of alignment, if they are set up clearances. too tightly, or if they have been improperly fitted, the fault cannot be fully remedied until the improper Journals should be kept smooth, even, adjustments have been rectified. This and free of rust at all times. To remove spots of rust or ridges, the journal should usually involves stopping the engine. be dressed with a fine file and then lapped with an oilstone or with an In all cases the temperature of the oilstone powder. Carborundum may also bearing can be lowered by slowing be used. If Carborundum is used, great down and thus decreasing the amount care must be taken to remove all of load on the bearing. If the trouble particles, as these, if allowed to remain, has reached an advanced stage, it may will cause cutting and grinding of be found necessary to stop the engine. bearings. When stopped, the bearing cap can be eased up a slight amount, thus increasing the clearance between the When bearings have been removed for bearing and journal. However, the long periods, such as during a major greatest care must be exercised in overhaul, it is customary to wrap the easing up on the bearing cap, for if too journals with canvas in order to protect great a clearance is given, trouble will them from accidental damage. When this is done, only new canvas should be used. be experienced from pounding. There have been cases where journals were wrapped with old rags or burlap When the trouble is inherent in the that contained some acid. The action of bearing -as for example, if the this acid corroded and pitted the journals machinery is not properly lined up, or and it was found necessary to renew the the bearings are of insufficient area, or entire shaft. not in proper condition-only temporary relief can be secured from using the various means suggested above. The Each time a bearing is removed for any most effective treatment of a hot reason the journal should be carefully bearing is probably the operation of the inspected. Any evidence of pitting or machinery at a low or moderate power general corrosion indicates the presence until such time as the needed of acid or water, and the lubricating oil readjustments, changes, or repairs can should be analyzed immediately. When a bearing clearance exceeds the allowable be effected. tolerance, or when the bearing fails due to scoring, wiping, spalling, or cracking, To summarize the treatment for a hot looseness of the bearing metal, or for any bearing, the measures to be taken may other reason, it must be renewed. be selected according to the special circumstances, from the following: To renew a precision type bearing it is first necessary to have available a spare 1. Lubrication. bearing. These are manufactured to size and are available from the manufacturer. 2. Slowing down, and consequent They are bored to correct dimensions, so reduction of load, or stopping. that only a slight amount of scraping in and filing of the edges of the shell faces 3. Cooling water to oil cooler. is required to produce an accurate fit.
There seems to be a tendency to renew 4. Easing up bearing caps. Satco bearings before it is necessary. A slight amount of spalling is not Even though relief is obtained by the necessarily an indication that the bearing above measures, it should be borne in properties of the metal are destroyed. mind that once a precision bearing has wiped, it is necessary to renew the bearing as soon as possible. The wear on journals rotating in bearings is seldom, if ever, evenly distributed over the entire surface. Consequently the journal wears until it becomes eccentric or egg-shaped. This 220 B. COUPLINGS 11B1. GM elastic coupling. The the inner driving disk. This helical crankshaft of the GM 16-278A engine internal gear fits on the outer part of the is connected to the generator shaft by crankshaft gear and forms an elastic drive means of an elastic coupling. The through the crankshaft gear which rides elastic coupling connects the engine to on the crankshaft. The splined ring gear the generator flexibly by means of is split and the two parts bolted together radial spring packs. The power from the with a spacer block at each split joint. engine is transmitted from the inner This makes it possible to engage ring, or spring holder of the coupling, separately the two parts of the splined through a number of spring packs to the ring with the crankshaft gear teeth, and to outer spring holder, or driven member. slide them into position with the idler A large driving disk connects the outer gear in place. spring holder to The parts of the elastic coupling are lubricated with oil flowing from the bearing bore of the crankshaft gear through the pilot bearing. 11B2. F-M flexible coupling. The crankshaft coupling on an F-M installation consists of three parts: the engine coupling driving half, the laminated rings, and the generator coupling driven half. The coupling driving half is fastened to the lower crankshaft with fitted bolts, and the coupling driven half is likewise fastened to the generator shaft. Power from the engine is transmitted through the laminated rings by means of a third set of fitted bolts held in place by ring bolt spacers. Figure 11-1. Elastic coupling cross section, GM. Pilot rings between the ends of the generator shaft and the crankshaft form a the flange on the driven shaft. The pilot safety guide in the event of failure of on the end of the crankshaft fits into a
bronze bushed bearing on the outer other parts. Tapped holes for jackscrews driving disk to center the driven shaft. and drilled holes for body fitted bolts are The turning gear ring gear is pressed provided in the lower flanges of the cylinder blocks. To permit fitting of the onto the rim of the outer spring holder. coupling bolts to the generator shaft, it is necessary to remove the lower and upper The inner driving disk through which halves of the end cover back of the the camshaft gear is driven is fastened coupling driver half, the lower bearing to the outer spring holder. A splined cap, and the lower crankcase side cover ring gear is bolted to at the vertical drive compartment. Guards and two jackscrews of different lengths are furnished with the tools by the engine manufacturer for use in removing and installing the coupling bolts. The guards protect the bolt threads and are tapered to facilitate entry of the bolts when fitting. When installing coupling bolts in either set, the shorter jackscrew should be used for starting the installation and the longer jackscrew for completing it. 221 Figure 11-2. Crankshaft coupling, F-M. C. ALIGNMENT 11C1. General. Good engine and good idea as to the status of the generator performance can be obtained alignment of the equipment. The most only if the original coupling installation important and most difficult job of is made with the components in correct alignment is the complete installation, of alignment and with correct clearances. a generator set. The salient points of The problem of originally aligning a these installations will be covered in the generator set and subsequent checking following paragraphs. When the arise quite frequently during submarine principles involved in a complete wartime operations. The original alignment job are understood, smaller alignment, of course, is extremely alignment problems become relatively
important as it greatly influences future simple. operation and adjustment of the engine. During navy yard overhauls it is NOTE. Alignment tests and corrective common practice to take motors and measures should never be undertaken generators out of the ship for overhaul, when a vessel is in drydock because the and the young engineer officer or new alignment of the shafting is not the same leading chief motor machinist's mate is when the vessel is waterborne as when it frequently called upon to check an is in dock. alignment job being done by naval shipyard personnel. It as also become 11C2. Strain gage readings. The strain routine to check crankshaft alignment gage is basically a micrometer for to some degree after an engine overhaul measuring the differences in distance in which many of the engine parts have between the two webs or cheeks of a been renewed. This may be only a crankshaft during a revolution of the checking of the crank cheek deflections shaft. As previously stated, one of the with the use of a strain gage, but even basic alignment procedures is the taking this will give the operating personnel a of strain gage readings. This is a relatively simple 222 Figure 11-3. Position of crankshaft for strain gage readings. Figure 11-4. Measuring crank check deflection with a strain gage. 223
undertaking but it is important that the procedure be followed exactly for best results. A series of strain gage readings of a crankshaft gives a measurement of the crank cheek deflection for various angular positions of the shaft. The measurement is accomplished by placing the gage between the engine crankshaft cheeks. The gage should be installed with its two endpoints in the crankshaft prick-punch marks. The crankshaft should be turned to its initial position so that the gage will be as close to the top position as possible without touching the connecting rod. The dial of the strain gage is then set on Figure 11-5. Using hydraulic jack to zero, and the crankshaft is slowly adjust height of generator body for jacked over to subsequent positions as proper vertical alignment. shown in Figure 11-3 and the readings taken. When taking the readings, the In all modern submarines the engines are gage should not be allowed to rotate attached to a generator rather than about its end-points. directly to propeller shafts. When a After the readings have been taken for generator is being installed, it should be originally placed as nearly as possible in one revolution of the crankshaft, they should be compared, and the maximum final alignment. Subsequent procedure is as follows: crank deflection obtained. Large variations in the individual readings indicate some type of misalignment in 1. Attach the driven half of the crankshaft coupling to the driver half by installing the installation. the outer row of bolts around the coupling. Tighten the bolts evenly. 11C3. Alignment of engine crankshaft with one bearing 2. Secure the generator shaft to the generator. This type of installation is that normally found on F-M generator flexible coupling by installing coupling bolts through the flange on the end of the sets. There are many recognized generator shaft into the driven flange of methods of accomplishing alignment of the coupling. engine and generator. The following procedure is one method and is discussed more from the standpoint of 3. Check the strain gage measurements to determine whether or not the coupling alignment principles than of a operation has affected the original standardized alignment procedure. reading. If a large change is noted at a particular position of the crankshft, it Generators and crankshafts that are indicates that the coupling has placed a being coupled together must be in alignment. This condition is attained by strain on the crankshaft. moving the shaft bearing supports vertically and horizontally until the two 4. Check the thickness of the flexible halves of the coupling are true to each coupling with a micrometer. The other or until the axes of the two shafts measurements should be made at the top and bottom, inboard and outboard. coincide at the point where they are coupled. The operation usually involves Compare the measurements with movement of the entire generator casing.
In the following alignment it is assumed that the engine is already located. Before starting alignment, the amount of crankshaft cheek deflection should be known and recorded in order to be able to make a comparative check during and after the alignment has been completed. The crankshaft cheek deflection readings should agree within approximately 0.002 inches. 224 Figure 11-6. Using portable block and Figure 11-7. Measuring generator thrust jack screw to adjust generator body for bearing clearances. proper lateral alignment. Figure 11-9. Measuring crankshaft thrust Figure 11-8. Using portable block and bearing clearance toward control end of jack screw to adjust generator for F-M engine. proper thrust clearance. 225
the established dimension stamped on the flange by the manufacturer. For example, the manufacturer's dimension is 5.225 inches. The outboard measurement as made with the micrometer is 5.250 inches. The inboard measurement is 5.200 inches. This indicates that the generator shaft is placing a strain on the inboard side of the coupling and is probably also affecting the strain gage reading on the crankshaft. Therefore, the generator casing and shaft must be moved outboard 0.025 inches to balance the readings on the coupling and to remove the strain from the crankshaft. Figure 11-10. Measuring crankshaft Normally, this should bring the strain thrust bearing clearance toward gage readings back to the original generator end of F-M engine. readings. and generator thrust bearing clearances. If a difference in the measurement of the coupling, against the stamped 6. Measure the crankshaft thrust bearing dimension, occurs at the top or bottom clearances by inserting a feeler gage of the coupling, the generator casing between the crank cheek and the face of and shaft will necessarily have to be the bearing (Figure 11-9), and between raised or lowered to effect a balanced the vertical drive gear and the generator condition. The height of the generator end of the bearing face (Figure 11-10). casing and shaft may be adjusted by The total clearance should measure means of hydraulic jacks placed under between 0.004 and 0.010 inch evenly the casing as shown in Figure 11-5. distributed on both sides. If the clearance When the proper height is attained, on one side is greater than on the other, it block up the casing, remove the jacks, will be necessary to move the generator and install shims between the feet and shaft in one direction or the other to the permanent pedestals on the deck. balance the measurements. The generator shaft and casing may be Any movement of the shaft will affect moved inboard or outboard by the clearances at the generator thrust installing a portable block and jack bearing. It may also affect the strain gage screw against the edge of the side foot readings and the setting of the flexible mountings of the casing as shown in coupling. Additional movement, Figure 11-6. To check the distance of therefore, of the shaft, or the casing may the movement, attach a dial indicator be necessary to bring about a balanced on the opposite pedestal with the condition. A check should be made after indicator pointer touching the edge of every move and steps taken to correct the opposite foot of the casing. any offset condition which may have been brought about by a previous move. 5. Remove the generator thrust bearing cap and measure the generator shaft thrust bearing clearances (Figure 11-7). 7. Movement of the generator casing, or The clearances should measure 0.0075 inch (approximately) at each end and on each side of the bearing in an F-M installation. If it is found, for example, that there is no clearance at the thrust face away from the engine, the
generator casing must be moved toward the engine 0.0075 inch with a portable block and jack screw (Figure 11-8). This operation, however, should not be accomplished until the crankshaft thrust bearing clearances have been measured, since it is possible that only one movement of the casing will be needed to correct both crankshaft 226 the shaft, will probably have some than on the other, the crankshaft must be effect on the generator air gap (the moved in whichever direction will space between the armature windings balance the clearances. This may be and the pole pieces). The air gap must accomplished with a pinch bar placed be uniform around the diameter of the between the crank cheeks and the engine armature. The clearance should be kept framework. After clearances have been within the limits specified by the balanced, the crankshaft must be blocked manufacturer of the generator. Air gap with hardwood wedges placed between measurements are taken with long the crank cheeks and the framework, to thickness gages furnished for this prevent movement of the crankshaft purpose. The gages are inserted during the coupling operation. between the armature winding and each pole. When the air gap is found to be 3. Determine the amount of fore-and-aft greater at the top than on the bottom, movement of the elastic coupling. This the generator casing will have to be measurement is made by placing the lowered by loosening the jacking pointer of a dial indicator against the face screws located on the side feet of the of the outer driving disk of the coupling. casing. If the gap is greater at the The indicator may be secured to the bottom, the casing must be raised with upper half of the coupling housing and the jacking screws, and shims inserted the pointer should touch the driving disk between the side feet and the pedestals. near the center. The coupling is then forced as far forward or aft as possible, Assuming that the shaft alignment has with a pinch bar, and the dial indicator is been completed and is true, it will be set on zero. Make a prick-punch mark on necessary to secure the rear foot of the the face of the outer spring holder in line generator casing to the rear pedestal with the jacking gear pointer. Then force with a C-clamp. This will hold the the coupling as far as possible in the alignment of the shaft while the casing opposite direction and make another mark. The dial indicator reading denotes is moved for adjustment of the air gap. the full fore-and-aft movement of the coupling, which normally is about 0.0125 After attaining a balanced air gap, inch. In order to divide the coupling correct shims should be installed. A thrust evenly between the engine and the complete recheck of all clearances generator, the coupling must now be should be made to verify the alignment moved to the center of its thrust or installation. This check must include 0.0625 inch using the dial indicator as a another set of strain gage readings. guide. Make a third prick-punch mark Before this final check, the generator between the two previously made. This casing should be rigidly secured in mark is the reference mark used to check position with a C-clamp to prevent any the center of the coupling thrust after possible movement of the casing. alignment has been completed. 11C4. Alignment of engine 4. Remove the outer driving disk from crankshaft with two-bearing
generator. This type of installation is the coupling and bolt it to the flange on typified by the GM generator set. The the generator shaft. Check the amount of GM engine is connected to the deflection of the face of the disk with a generator by means of an elastic dial indicator by turning the generator coupling. A procedure to follow in armature one complete revolution. The aligning a generator to the coupling is deflection should not exceed 0.001 inch. Next, place the indicator pointer against as follows: the rim of the disk, rotate the shaft one revolution, and check the amount of 1. Take strain gage readings to deflection. This measurement should also determine the amount of crank cheek be within 0.001 inch. If the amount of deflection. The maximum permissible deflection, on either the face or the rim of deflection in a GM engine is 0.0035 the disk, is greater than 0.001 inch, the inch. The measurement should be re- condition may be corrected by loosening recorded for reference after completing the bolts and recentering the disk or by the alignment. cleaning the inner surfaces of both disks. 2. Check the engine crankshaft thrust bearing clearances with feeler gages. Clearance should total approximately 0.030 inch, equally divided on both sides of the bearing. If the clearance is greater on one side of the bearing 227 Figure 11-11. Elastic coupling, outer Figure 11-12. Elastic coupling, inner driving disk removed, GM. spring holder removed, GM.
Figure 11-14. Elastic coupling, outer Figure 11-13. Mastic coupling, outer driving disk mounted on generator, GM driving disk mounted, GM. 228 After obtaining deflection readings with feeler gages. The thrust should be within 0.001 inch, the bolts, the driving evenly divided between the two sides. If disk, and the generator shaft flanges the thrust clearance is greater on one side must be marked so that they may be than on the other, the generator housing replaced in their respective positions must be moved until a balanced condition when the generator is coupled to the is attained. elastic coupling. Before removing the flange, the dowel holes must be reamed 8. Remove the hardwood blocks securing for the body-bound dowels. Dowels the crankshaft. Recheck the engine and dowel holes must also be marked crankshaft thrust bearing clearances and so that they will be replaced in their the setting of the elastic coupling in respective positions. relation to the center prickpunch mark. If either the bearing or the coupling has moved, the condition must be corrected 5. Remove the driving disk from the generator shaft and reinstall it on the by moving the crankshaft, the coupling, or the generator. If any move is made, it elastic coupling. will be necessary to recheck the engine crankshaft thrust, the coupling, and the 6. Install the upper half of the elastic generator thrust bearing. coupling housing. Move the generator toward the engine. Approximate axial alignment may be attained with the When all clearances are correct, a strain jacking screws on the generator feet. gage reading must be taken and checked Inboard and outboard alignment may be against the recorded original reading. A attained by use of portable blocks and change in the strain gage reading indicates misalignment, a condition jack screws working against the edges which, at this point, can be corrected of the generator feet. When an alignment as nearly perfect as possible only by moving the generator. has been attained, the generator is moved farther toward the engine and After perfect alignment has been the generator shaft carefully inserted attained, measure the space between the into the bore of the driving disk. generator feet and the pedestals and install suitable shims. Back off the generator feet jack screws so that the full Align the marked dowels with their
corresponding dowel holes. If the weight of the generator will be on the generator is properly aligned, the shims. Another strain gage reading must dowels will slide into their dowel holes. then be taken to check whether or not the No attempt should be made to force the shims have affected the setting of the dowels. If they cannot be inserted by generator. If a change is noted, it can be hand, the generator must be moved corrected by cutting down or adding to the thickness of the shims. If no change until perfectly aligned. is noted, drill the dowel holes and install the dowels; then drill the bolt holes and After installing the dowels, secure the install the bolts. coupling to the generator shaft flange by installing the tap bolts. A final check is made by rotating the 7. Remove the generator thrust bearing engine with the jacking gear several cap, then remove the bearing. Carefully revolutions in the direction of rotation inspect and clean the bearing. Replace and then rechecking all clearances. A the lower half of the bearing and check slight variation in clearances, if found at this time, is permissible. the thrust clearances 229